Field of Science

The Cephalodiscids

Among the more obscure inhabitants of the world's oceans are the Cephalodiscidae, a family of small (only a few millimetres in length), largely sessile animals that mostly live in colonies within a shared domicile. Though rarely observed, cephalodiscids have received their fair share of attention due to being among the closest living relatives of the graptolites that once dominated the world's oceans during the early Palaeozoic era.

Preserved Cephalodiscus colony, copyright E. A. Lazo-Wasem.


Cephalodiscids are one of the two living branches of the pterobranchs (the other being the Rhabdopleuridae), which together with the acorn worms make up the phylum Hemichordata. Hemichordates are in turn one of the three living phyla of the deuterostomes, together with the echinoderms and chordates (to which, of course, we ourselves belong). Pterobranchs are filter feeders, using an arrangement of tentaculated arms arising just behind the head to collect particles from the water. In cephalodiscids, each individual usually possesses multiple pairs of arms in contrast to the single pair in rhabdopleurids (though at least one species of Cephalodiscus has small males with a single pair). The head carries a large glandular disc (hence the name of the family) that is used to secrete the horny tissue making up the external dwelling (referred to as the tubarium) in which a colony of Cephalodiscus lives. Both cephalodiscids and rhabdopleurids have a contractile stalk at the end of the body from which new individuals (zooids) are budded. However, whereas the zooids of rhabdopleurids (and presumably their extinct graptolite relatives) remain attached to each other throughout their life, cephalodiscid zooids split away from their parent by the time they mature. The majority of cephalodiscid species have distinct males and females though a small number may be hermaphrodites. Some species exhibit sexual dimorphism; males may be considerably smaller than females.

Individual zooid of Cephalodiscus dodecalophus, from Sedgwick et al. (1898).


About twenty species of living cephalodiscids are currently recognised. The majority of these have been included in a single genus Cephalodiscus, albeit divided between a number of subgenera. The single outlier, Atubaria heterolopha, was described in 1936 from a single dredge haul near Japan (Mitchell et al. 2013). No dwelling material was found in the haul so it was presumed this species does not construct a tubarium like other cephalodiscids. However, its zooids were otherwise little different from those of Cephalodiscus. The subgenera of Cephalodiscus are mostly distinguished by tubarium structure. In some species, each individual in the colony will have its own separate tube closed off at the base. In other species, tubes will open into a central chamber shared between multiple zooids (Maletz 2014). Openings of the tubarium may be surrounded by spines and the like, secreted by the zooids as they creep out from their domicile.

Recent studies have indicated that cephalodiscids represent the sister group to all other pterobranchs/graptolites, implying an history that may extend back to the Cambrian. However, the fossil record of cephalodiscids themselves is minimal. This is largely due to practical difficulties: because the soft-bodied zooids are not preserved, fossils can only be identified from the external tubarium structure alone. Unless the origin point of the tubarium is preserved and identifiable, there is little to distinguish a cephalodiscid tubarium from a benthic graptolite (graptolite colonies begin with a differentiated larval chamber called a sicula, cephalodiscids produce no such structure). A handful of fossil cephalodiscids have been identified, notably the early Devonian Eocephalodiscus, but as yet they tell us little about the evolution of this ancient lineage.

REFERENCES

Maletz, J. 2014. The classification of the Pterobranchia (Cephalodiscida and Graptolithina). Bulletin of Geosciences 89 (3): 477–540.

Mitchell, C. E., M. J. Melchin, C. B. Cameron & J. Maletz. 2013. Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite. Lethaia 46: 34–56.

Lilies of Blood

The flora of southern Africa is renowned for being remarkably diverse and, in many cases, remarkably eye-catching. The region is home to more than its fair share of ornamental plants, many of which have become popular garden subjects. Among the remarkable members of the southern African flora are the blood lilies of the genus Haemanthus.

Haemanthus coccineus, copyright Peter Coxhead.


Haemanthus is a genus of 22 known species found in the very southern part of the continent, in the countries of South Africa and Namibia (species from further north that have historically been included in Haemanthus are now treated as a separate genus Scadoxus). It is a member of the belladonna family Amaryllidaceae and, like many other members of that family, grows as a herb from a fleshy bulb that is partially or entirely concealed underground. The plant above ground may be annual or persistent, depending on species. Each individual Haemanthus plant produces very few leaves at a time: two is the most common number (Van Jaarsveld 2020). The leaves are more or less fleshy, often hairy, and may be directed upwards or spread outwards.

In those species that shed their leaves, flower stalks are produced before the next season's leaves appear, in a similar matter to the related naked ladies Amaryllis belladonna. Flowers are produced in dense umbels, subtended by bracts that are often brightly coloured, so at a glance the inflorescence of some species might be taken for a single large flower up to ten centimetres in diameter. Depending on the species, the supporting stalk may vary from over a foot in height to only a few centimetres. The first species to be described bear flowers of a bright red colour, explaining both the genus and vernacular names, but flowers may also be pale pink or white. Species that lack the red colour may be referred to as 'paintbrush lilies' rather than 'blood lilies'. Fruits are soft fleshy berries.

Haemanthus albiflos, copyright Krzysztof Ziarnek, Kenraiz.


Phylogenetic analyses of the genus have identified two major clades, a mostly eastern clade found in regions with summer rainfall and a mostly western clade associated with winter rainfall. A notable outlier is the eastern summer-rainfall species H. montanus which is the sister taxon to the winter rainfall clade. Members of the summer-rainfall clade have white or pale pink flowers; members of the winter-rainfall clade have pale pink to dark red flowers. Members of both clades have been grown as pot plants for their unusual appearance though the scent of the flowers is not regarded as pleasant. Perhaps the most widely grown species is H. albiflos, a species native to both the western and eastern parts of South Africa that bears flowers in umbels up to seven centimetres wide. This species is evergreen, carrying its leaves year-round.

REFERENCE

Van Jaarsveld, E. 2020. Haemanthus. In: Eggli, U., & R. Nyffeler (eds) Illustrated Handbook of Succulent Plants: Monocotyledons 2nd ed. pp. 441–443. Springer.

The Oligorhynchiidae

Dorsal view of Oligorhynchia subplana gibbosa, from Cooper (1935).


From Oligochiton, we move onto Oligorhynchia. The Oligorhynchiidae are a family of very small brachiopods known from the Middle and Late Ordovician. They were among the earliest representatives of the Rhynchonellida, a major group of brachiopods that survives to the present day. Rhynchonellidan shells are usually characterised by a strong beak associated in life with a well-developed pedicel. In oligorhynchiids, this beak is suberect and the shell as a whole is an elongate subtriangular shape. The valves of the shell are folded into coarse plicae (ridges). At least towards the base of the shells, the major folds are in what is called an inverted arrangement, with a ridge in the dorsal valve matched by a valley in the ventral valve (Schmidt & McLaren 1965). Other structural features defining the group include small plates projecting into the pedicel opening, distinct vertical dental plates and divided hinge plates in the valve articulation, and the usual absence of a median septum or cardinal process inside the shell (Savage 1996).

The oligorhynchiids first arose in the east of what was then the continent of Laurentia (corresponding to modern North America). They subsequently spread across the Iapetus Ocean to the continents of Baltica and Kazakhstan (Jin 1996). The end of the Ordovician saw their replacement by other rhynchonellid families. Nevertheless, their genetic lineage would continue for some time yet as they have been identified as ancestors of later families: the Trigonirhynchiidae and Camarotoechiidae (Jin 1989). The brief oligorhynchiid spark would blossom into later rhynchonellid success.

REFERENCES


Jin, J. 1989. Late Ordovician–Early Silurian rhynchonellid brachiopods from Anticosti Island, Quebec. Biostratigraphie du Paléozoïque 10: 1–127, 130 pls.

Jin, J. 1996. Ordovician (Llanvirn–Ashgill) rhynchonellid brachiopod biogeography. In: Copper, P., & J. Jin (eds) Brachiopods pp. 123–132. CRC Press.

Savage, N. M. 1996. Classification of Paleozoic rhynchonellid brachiopods. In: P. Copper, & J. Jin (eds) Brachiopods pp. 249–260. CRC Press.

The Fate of Oligochiton

Chitons are one of the most distinctive and evolutionarily divergent groups of molluscs alive today. But compared to other groups of molluscs, the fossil record of chitons is rather sparse—or at least sparsely studied. It's not hard to see why. The multi-plated nature of the chiton shell means that it tends to fall apart after death, and the structure of the plates is such that critical features are easily abraded.

(Clockwise from top left) head, intermediate and tail valves of Lepidochitona lioplax, from Dell'Angelo et al. (2011).


Lepidochitona lioplax is one example of a fossil chiton. It was originally described from Oligocene rocks belonging to the Sooke Formation of southern Vancouver Island in British Columbia. Only four moderate-sized valves were initially identified: one head valve, one intermediate, and two tails (so at least two individuals were involved). The valves had a smooth outer surface without a strong distinction in appearance between the central and lateral areas. The insertion plates (lateral projections of the lower surface of the valves that in life anchor them into the surrounding girdle) were very short. The sutural laminae (anterior projections of the lower surface of the intermediate and tail valves that articulate with the valve in front) were low, wide, and divided in the middle by a broad shallow surface. Slits in the lateral insertion plates were numerous, with several in the tail valves and probably two or three on each side in the intermediate valves (Smith 1960). When first described, this species was thought distinct enough to belong in its own genus Oligochiton.

Oligochiton lioplax would then go little reported on until 2011 when Dell'Angelo et al. described an assemblage of chiton fossil from the latest Eocene or early Oligocene of the Lincoln Creek Formation in Washington State. Specimens of lioplax were relatively numerous in this collection and Dell'Angelo et al. were able to examine close to a hundred valves. Their observations would lead to something of a downgrade in the species status. Rather than deserving its own extinct genus, Dell'Angelo et al. felt that lioplax could be comfortably accommodated in the living genus Lepidochitona. Its smooth valves are unusual within Lepidochitona but not unique. The supposed multiple slits in the sides of the valves did not stand up to scrutiny. Instead, intermediate valves of L. lioplax bore only a single slit on each side, in line with other Lepidochitona species. The original inference of multiple slits was an error due to the original specimen being still partially embedded in the surrounding matrix.

Lepidochitona lioplax is one of the earliest known representatives of its genus but its exact significance is obscure. It has been suggested as a direct ancestor of the modern subgenus Spongioradsia but this, again, was based on the supposed slits in the intermediate valves that Dell'Angelo et al. refuted. To know how L. lioplax connects to the big picture of Lepidochitona evolution, we would probably need a better picture of Lepidochitona evolution overall.

REFERENCES

Dell'Angelo, B., A. Bonfitto & M. Taviani. 2011. Chitons (Polyplacophora) from Paleogene strata in western Washington State, U.S.A. Journal of Paleontology 85 (5): 936–954.

Smith, A. G. 1960. Amphineura. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I41–I76. Geological Society of America, and University of Kansas Press.

The Feared Mosquito

It's one of those standard pub-quiz "trick" questions. What animal kills the most people? The hope is that contestants will nominate the 'obvious'—snakes, sharks, bears, whatever—before being blind-sided by the revelation that mosquitoes kill over a million people. They don't kill them directly, of course; their victims die from the diseases they spread*. The statistic also glosses over the point that there are many hundreds of species of mosquito that vary significantly in the nature and severity of their role as disease vectors. Nevertheless, for this post I'm considering the group that includes some of the most notorious vectors: the genus Anopheles.

*For the record, if the question was confined to active killings, the most dangerous animal to humans is other humans. Dogs come a distant second.

Anopheles punctipennis feeding, with the long palps extended in front of the head, copyright Nathan D. Burkett-Cadena/University of Florida.


Anopheles is one of the most divergent genera of mosquitoes, being placed in a distinct subfamily Anophelinae (along with a couple of small related genera) from the bulk of mosquitoes in the subfamily Culicinae. Adult Anopheles can be readily distinguished from culicine mosquitoes by their palps which are about as long as the proboscis (in other mosquitoes, the palps are distinctly shorter). Larvae of Anopheles lack the long respiratory siphons at the end of the abdomen found in other mosquito larvae so they rest parallel with the water surface rather than hanging below it. The genus is found around the world; over 450 named species are currently known (Harbach 2013) with many more waiting to be described. The genus is currently divided between seven subgenera though one of the largest of these, the cosmopolitan subgenus Anopheles, is not monophyletic. The remaining subgenera are better supported with the largest of these, Cellia, being found in the Old World. Between them, the subgenera Anopheles and Cellia account for over 400 of the known Anopheles species. The remaining small subgenera are mostly Neotropical with a single Oriental species being awarded its own subgenus.

Anopheles maculipennis, copyright Ryszard.


Anopheles is of most concern to humans, of course, for its role as a disease vector. As with other mosquitoes, the transmission of disease is done entirely by females taking blood meals to provide nutrients for their developing eggs. Males are not blood feeders, instead feeding entirely on sugar sources such as nectar (females also feed on nectar for their own nutrition). The main disease spread by Anopheles is malaria, but they may also spread malaises such as filariasis and arboviruses (Krzywinski & Besansky 2003). As noted above, species may vary significantly in their importance as disease vectors, even between quite closely related taxa. Many historically recognised vector "species" have proved, on close inspection, to represent species complexes of which some may be vectors and others not. For instance, one of the most important transmitters of malaria, the African A. gambiae, has been divided between at least eight different species (Coetzee et al. 2013). Misidentification of vectors can be a significant issue. For instance, mosquito control regimes in central Vietnam during the 1990s focused on two species, A. dirus and A. minimus, that were each active at different times of year. However, Van Bortel et al. (2001) found that A. minimus was in fact very rare in this area, with specimens previously thought to be A. minimus proving to be another species, A. varuna. Anopheles varuna is not a significant malaria vector, feeding almost entirely on animals such as cattle rather than on humans. Large amounts of resources would have been wasted trying to control a mosquito that was of little concern. What is more, the fact that malaria was not being transmitted by A. minimus raises the possibility that it was being spread by yet another species, one that had managed to escape attention. Remember, kids: bad taxonomy kills.

REFERENCES

Coetzee, M., R. H. Hunt, R. Wilkerson, A. Della Torre, M. B. Coulibaly & N. J. Besansky. 2013. Anopheles coluzzii and Anopheles amharicus, new members of the Anopheles gambiae complex. Zootaxa 3619 (3): 246–274.

Harbach, R. E. 2013. The phylogeny and classification of Anopheles. In: S. Manguin (ed.) Anopheles Mosquitoes: New insights into malaria vectors. InTechOpen.

Krzywinski, J., & N. J. Besansky. 2003. Molecular systematics of Anopheles: from subgenera to subpopulations. Annual Review of Entomology 48: 111–139.

Van Bortel, W., R. E. Harbach, H. D. Trung, P. Roelants, T. Backeljau & M. Coosemans. 2001. Confirmation of Anopheles varuna in Vietnam, previously misidentified and mistargeted as the malaria vector Anopheles minimus. American Journal of Tropical Medicine and Hygiene 65 (6): 729–732.

The Running of the Termites

I don't know how many people would profess to have a favourite genus of termites. Which is a shame, because there are some real stand-out examples. Snapping termites, magnetic termites, glue-spraying termites... For my own part, though, I have a particular fondness for the Australian harvester termites of the genus Drepanotermes.

Soldiers and workers of Drepanotermes perniger, copyright Jean Hort.


Nearly two dozen species of Drepanotermes are found on the Australian continent to which they are unique (Watson & Perry 1981). They are arid-environment specialists, being most diverse in the northern part of Australia. My reasons for being so fond of them are, I'll admit, decidedly prosaic. The worker caste of most termite species is very difficult if not impossible to identify taxonomically; one termite worker usually looks very much like another. Drepanotermes workers, however, are different. The name Drepanotermes can be translated as "running termite" and, as befits their name, Drepanotermes of all castes stand out for their distinctly long legs. Soldiers of Drepanotermes also have distinctively shaped mandibles which are sickle-shaped and have a single projecting tooth on the inner margin. They are similar to soldiers of the related genus Amitermes (of which Drepanotermes may represent a derived subclade) but the mandibles of Amitermes tend to be straighter and more robust.

The long legs of Drepanotermes reflect their active harvester lifestyles. Workers will emerge from the nest at night in search of food to carry back home. In the red centre of Australia they will primarily collect spinifex; they will also take fallen leaves, tree bark and the like. Soldiers keep guard while the workers forage. I've found them clustered around a nest entrance of an evening, just their heads poking out to snap at passers-by. Workers may wander up to about half a metre from the nest entrance as they forage. The concentrations of vegetable matter produced by Drepanotermes storing food sources in their nest may form a significant factor in the nutrient profile of areas where they are found.

Alate and soldiers of Drepanotermes rubriceps, copyright Jean Hort.


Depending on species and circumstance, the nests of Drepanotermes may be mounds or entirely subterranean with the latter being the majority option. They prefer compact soils such as clay though they may burrow through looser soils where there is a denser subsoil. Drepanotermes may construct their own nest or move into nests constructed by other termites. One aptly named species, D. invasor, seems to take over pre-existing nests more often than not. Subterranean nests are arranged as a series of chambers about five to ten centimetres in diameter connected by tunnels. These chambers may be arranged vertically, one below another, or they may form a rambling transverse network. Above ground, subterranean nests may be visible as an open circle devoid of vegetation. The ground in these circles is hard as concrete and may remain clear for decades after the actual nest has gone. Walsh et al. (2016) refer to the remains of nests protruding above ground along vehicle tracks after the soil around them has worn down. Local people have a long history of taking advantage of the open space offered by termite nests, such as to move more easily through scrub or as resting or working places.

The alate castes of Drepanotermes tend to be poorly known. Indications are that mature reproductives spend little time in the parent nest before leaving to breed. For most species, breeding flights take place in late summer. Alates may emerge either by day or night. The time of emergence seems to depend on the species; night-flying alates have distinctly larger eyes than day-fliers. Unfortunately, because alates have rarely been collected in association with a nest, we are largely still unable to tell which alates belong to which species.

REFERENCES

Walsh, F. J., A. D. Sparrow, P. Kendrick & J. Schofield. 2016. Fairy circles or ghosts of termitaria? Pavement termites as alternative causes of circular patterns in vegetation of desert Australia. Proceedings of the National Academy of Sciences of the USA 113 (37): E5365–E5367.

Watson, J. A. L., & D. H. Perry. 1981. The Australian harvester termites of the genus Drepanotermes (Isoptera: Termitinae). Australian Journal of Zoology, Supplementary Series 78: 1–153.

Sparrows of the West

Recent decades have seen significant shifts in the classification of birds, particularly among the Passeriformes, the perching birds. These shifts have lead to the recognition of a number of major groups that were previously obscured. Among these recent elevations are the New World sparrows of the Passerellidae.

Gambel's white-crowned sparrow Zonotrichia leucophrys gambeli, copyright Gregory Smith.


The New World sparrows are part of a broader radiation known as the nine-primaried songbirds, along with such luminaries as finches, tanagers, and their Old World namesakes. The name 'nine-primaried' refers to the number of well-developed primary feathers (the long outer ones) in the wings; most other perching birds have ten distinct primaries. Though the nine-primaried songbirds have long been recognised as a coherent group, there has been a lot of disagreement over their subdivision. Historically, these subdivisions were strongly influenced by different bill shapes representing different diet specialisations, but recent molecular phylogenies have demonstrated that bill shape is more labile than previously recognised. The New World sparrows were usually regarded previously as a subgroup of the generalist seed-eating family Emberizidae, along with the buntings of the Old World, but molecular phylogenies have asserted the division between the hemispheres. Not all New World representatives of the old Emberizidae have shifted to the Passerellidae: a significant component of the Neotropical fauna (including the finches of the Galapagos islands) have instead proven to be closer to the fruit-eating tanagers of the Thraupidae. As currently recognised, the passerellids are a fairly coherent group of about 140 species distributed around North and South America.

Goldwn-winged sparrow Arremon schlegeli schlegeli, copyright Nick Athanas.


In general, the passerellids are small birds with simple, conical bills. Most are dull brownish in coloration though many are strikingly patterned, particularly around the head. Some are more distinctive: the South American sparrows of the genus Arremon often stand out as particularly colourful. Most passerellids are fairly retiring in their usual habits, foraging at or close to ground level. As noted before, they are mostly generalist feeders. Their short bills are excellently suited for milling the small seeds which make up a large part of their diet. However, they will also take insects and other small invertebrates. One widespread North American species, Ammodramus savannarum, has earned the vernacular name of "grasshopper sparrow" as a result. Notable outliers dietwise are the Neotropical bush-tanagers of the genus Chlorospingus which are primarily berry feeders. These largely greenish birds were previously classified with the Thraupidae as a result before molecular data led to their reassignment.

Common bush-tanager Chlorospingus flavopectus, copyright Becky Matsubara.


Whereas Neotropical members of the Passerellidae are mostly sedentary, North American species are often migratory, moving north with the approach of summer. However, migration is commonly related to environmental conditions. A number of species are migratory in the northern parts of their range but may be found in their southern territories year-round. In some species, migrating populations will leap-frog over resident populations, moving further south than any resident individuals during the winter months. Many passerellid species are strong singers and courting males will often select an exposed branch to sing from in contrast to their usual skulking habits. Other species, particularly those inhabiting open habitats where trees and shrubs are in short supply, may have prominent aerial displays. Males of one of these latter species, the lark bunting Calamospiza melanocorys, moult during the breeding season into black plumage with contrasting white patches on the wings and tail. During the remainder of the year, they are dull in coloration like their females. Nesting is conducted close to ground level like feeding with the nest often being a small cup in the ground concealed under vegetation. Where breeding has been studied in detail, passerellids are commonly what has been called "socially monogamous". Males and females will form what appear to be monogamous pairs with one male remaining close to one female (though construction of the nest and incubation are done by the female alone). However, genetic studies on nestlings have found that chicks are not uncommonly not the child of their apparent 'father', indicating that females have not remained faithful to their mate.

Yellow-striped brush-finch Atlapetes citrinellus, copyright Ron Knight.


Prior to molecular studies, authors had suggested a possible division of North American passerellids between two evolutionary lineages based on ecology and behaviour, the grassland and brushland sparrows. A molecular study of passerellids by Klicka et al. (2014) identified eight well-supported clades within the family. Two further species, the large-footed finch Pezopetes capitalis of Central America and the Zapata sparrow Torreornis inexpectata of Cuba, were not robustly assigned to a clade. Identified relationships were comparable to but not entirely congruent with prior hypotheses. For instance, most 'brushland sparrows' (of the genera Passerella, Zonotrichia and Junco) belonged to a single clade but the remaining 'brushland' genus Melospiza was placed in a clade mostly made up of 'grassland' species. The diverse South American genus Arremon was supported as monophyletic but others were not. In particular, the North American Ammodramus was divided between two widely separated clades. This lead to the resurrection of the genus Ammospiza for a group of saltmarsh-breeding species. Deeper relationships within the family deserve further investigation.

REFERENCES

Hoyo, J. del, A. Elliott & D. A. Christie (eds) 2011. Handbook of the Birds of the World vol. 16. Tanagers to New World Blackbirds. Lynx Edicions: Barcelona.

Klicka, J., F. K. Barker, K. J. Burns, S. M. Lanyon, I. J. Lovette, J. A. Chaves & R. W. Bryson, Jr. 2014. A comprehensive multilocus assessment of sparrow (Aves: Passerellidae) relationships. Molecular Phylogenetics and Evolution 77: 177–182.

Steatocranus gibbiceps, the Rapid River Bumphead

The cichlid fishes of the Great Lakes of Africa are rightly renowned as one of the world's most spectacular species radiations. Hundreds of species, occupying a wide range of ecological niches, have evolved in what is, geologically speaking, a short period of time. However, cichlids in Africa are not a phenomenon of the Great Lakes alone and many interesting species may be found in other parts of the continent, some of them belonging to local radiations of their own. Consider, for instance, the Congo River rapids endemic Steatocranus gibbiceps.

Male Steatocranus gibbiceps, copyright Polypterus.


The Congo is one of the largest African rivers with a drainage basin covering one-eighth of the continent (Schwarzer et al. 2011). Downstream of Kinshasa, the river gets funneled into an intermittently deep, narrow channel for a distance of some 300 km before broadening as it approaches the sea. The result is the world's longest stretch of river rapids. Many fish species are found only in this unique region of fast-flowing waters, among them multiple species of the cichlid genus Steatocranus including S. gibbiceps. The genus as a whole is restricted to the Congo basin; a single species previously recognised from the Volta River has since been transferred to its own genus (Weiss et al. 2019). The names Steatocranus and gibbiceps both basically mean the same thing: 'fat head', in reference to a fleshy swelling atop the fish's noggin. The exact size of this swelling varies between individuals, being most prominent in large males. Vernacular names given to Steatocranus species generally reflect this feature, such as bumphead cichlid or buffalo-head cichlid. Half a dozen species have been named within Steatocranus with several more being recognised but not yet formally described, most of them belonging to the radiation within the rapids. Schwarzer et al. (2012) found evidence for extensive historical cross-breeding between species and suggested that hybridisation may have been a significant factor in the genus' diversification.

Steatocranus gibbiceps is the largest species in this genus of moderately-sized fishes, growing up to about nine centimetres in length (Roberts & Stewart 1976). Its fast-current habitat is reflected in its slender body form. It is olive brown in coloration with the scales being light in colour at the centre and darker around the margins. Steatocranus gibbiceps is most clearly distinguished from other described species in its genus by its teeth: the front teeth of both the upper and lower jaws are conspicuously large and truncate. It also has a shorter gut than its congeners. This species appears to be specialised in feeding on freshwater snails which it scoops up and swallows whole, though it will take a broader range of food in captivity. Other species of Steatocranus mostly feed on algae.

Steatocranus species are not buoyant and tend to sit at the bottom of the water (Chase Klinesteker describes their behaviour as 'hopping around the bottom like a goby'). They escape the current by spending time in the hollows and crevices among rocks. Breeding happens within such hollows with dedicated pairs forming and females affixing their eggs to the rocks. Like many other cichlids, Steatocranus gibbiceps are dedicated parents after the eggs hatch. Tending of the fry is mostly the responsibility of the female while the male patrols the territory on the watch for danger. In this way, the baby bumpheads are given the best possible start at life.

REFERENCES

Roberts, T. R., & D. J. Stewart. 1976. An ecological and systematic survey of fishes in the rapids of the lower Zaïre or Congo River. Bulletin of the Museum of Comparative Zoology 147 (6): 239–317.

Schwarzer, J., B. Misof, S. N. Ifuta & U. K. Schliewen. 2011. Time and origin of cichlid colonization of the lower Congo rapids. PLoS One 6 (7): e22380.

Schwarzer, J., B. Misof & U. K. Schliewen. 2012. Speciation within genomic networks: a case study based on Steatocranus cichlids of the lower Congo rapids. Journal of Evolutionary Biology 25: 138–148.

Weiss, J. D., F. D. B. Schedel, A. I. Zamba, E. J. W. M. N. Vreven & U. K. Schliewen. 2019. Paragobiocichla, a new genus name for Gobiochromis irvinei Trewavas, 1943 (Teleostei, Cichlidae). Spixiana 42 (1): 133–139.

The Cordia Clade

The tropics are home to a wide diversity of plant species, many of them belonging to groups less familiar in cooler regions of the world. Prominent among these are members of the family Cordiaceae, a group of about 350 known species of mostly trees and shrubs. The Cordiaceae (alternatively treated as the subfamily Cordioideae of the family Boraginaceae) are a well distinguished clade both molecularly and morphologically. Most members of the clade have flowers with the stigma divided between four lobes, fruits with an undivided endocarp, and plicate cotyledons (Miller & Gottschling 2007).

Beach cordia Cordia subcordata, copyright Tauʻolunga.


Historically, most members of the clade have been assigned to a single genus, Cordia. This arrangement was revised by Miller & Gottschling (2007) who recognised the separate genus Varronia for about 100 species of multi-stemmed shrubs native to the New World. The remaining 250 or so species, most of them single-trunked trees, remained in the pantropical Cordia. The two genera also generally differ in their leaves (most Varronia have leaves with serrate margins whereas Cordia have entire margins) and inflorescences (most Cordia have broad cymose inflorescences whereas Varronia have smaller, more compact inflorescences). Few species of Cordiaceae are not assigned to either Cordia or Varronia. Three previously recognised small genera, Auxemma, Patagonula and Saccellium, are now synonymised with Cordia. The small African genus Hoplestigma and the prostrate annual herb Coldenia procumbens are placed in Cordiaceae primarily on the basis of molecular data (Miller & Gottschling 2007; Weigend et al. 2014).

Black sage Varronia curassavica, copyright Mauricio Mercadante.


A number of Cordia species are grown for their wood, with South American species providing timbers known as bocote, freijo (C. alliodora), and ziricote (C. dodecandra). These are only moderately strong woods but strikingly patterned and are more often used for aesthetic rather than structural purposes (such as cabinet veneers and musical instruments). Cordia alliodora has become an invasive in regions where it has been planted outside its native range such as Africa and Vanuatu. Various species are also grown for their edible fruits, such as the Assyrian plum C. myxa and the fragrant manjack C. dichotoma. These fruits are decidedly gooey when ripe and are often given names reflecting this fact such as glue berries, clammy cherries or, here in Australia, snotty gobbles (though this name is more widely used for fruits of the unrelated genus Persoonia). Pulp from unripe fruits of C. myxa can supposedly also be used as a type of glue. Your office reports may not be informative but they will at least be tasty!

REFERENCES

Miller, J. S., & M. Gottschling. 2007. Generic classification in the Cordiaceae (Boraginales): resurrection of the genus Varronia P. Br. Taxon 56 (1): 163–169.

Weigend, M., F. Luebert, M. Gottschling, T. L. P. Couvreur, H. H. Hilger & J. S. Miller. 2014. From capsules to nutlets—phylogenetic relationships in the Boraginales. Cladistics 30: 508–518.

Dictyotales

Most of the various 'seaweeds' found around the world can be assigned to one of three major groups, each named for their most characteristic pigments: green algae, red algae and brown algae. Of these, green algae are the closest relatives of land plants, and red algae are the most taxonomically diverse. But for many people, the most familiar of the three will be brown algae. Owing to their often relatively large size and predilection for growing in visible locations, brown algae are likely to be the first examples to come to mind when one thinks of seaweed. For this post, I'm examining a particular subgroup of the brown algae, the family Dictyotaceae.

Forkweed Dictyota dichotoma, copyright Ria Tan.


Representatives of the Dictyotaceae can be found around the world but are more diverse in warmer tropical and subtropical waters. They seem to be particularly diverse in the Australasian region. Dictyotaceae are moderately sized seaweeds with flattened thalli that may grow as branching ribbons or radiating fans. One fan-shaped species of Dictyotaceae, Padina pavonica, has earned itself the vernacular name of 'peacock's tail'(this species is also notable for being one of the few calcified brown algae). These thalli grow apically from meristematic cells. Dictyotaceae have an isomorphic life cycle with the alternating sexually and asexually reproducing generations being similar in overall appearance. Sporangia in asexual individuals grow as superficial nodules scattered over the surface of the thallus; the resulting spores usually differ from those of other brown algae in lacking flagella. The less abundant sexual individuals are mostly divided between separate males and females (Bittner et al. 2008).

Peacock's tail Padina pavonica, copyright Diego Delso.


Dictyotaceae are distinct enough from other brown algae to have consistently been treated as their own order (indeed, their sporangia are unique enough that some very early authors did not even regard them as brown algae). Two species found around Australasia, Dictyotopsis propagulifera and Scoresbyella profunda, have previously been considered distinct enough to warrant their own separate families within this order Dictyotales. Dictyotopsis propagulifera has a monostromatic thallus (that is, the thallus is only one layer of cells thick). Scoresbyella profunda has an apical growing cell that divides lengthwise to the thallus instead of transversely as in other Dictyotales. However, molecular data have indicated that these two genera are nested within Dictyotaceae and so only the single family is currently recognised. Dictyotaceae has also been divided in the past between tribes Dictyoteae and Zonarieae based on the nature of the apical growing cells (Dictyoteae have a single meristematic cell whereas Zonarieae have a cluster or row of cells) and some authors have even treated them as distinct families. Again, however, molecular data have not corroborated this division (Bittner et al. 2008).

Lobophora variegata, copyright John Turnbull.


For most species of Dictyotaceae, their greatest significance to humans probably comes from the role they play in providing habitats to fish and other marine animals. As with other algae, Dictyotaceae produce a range of secondary metabolites that serve functions such as protecting them from grazers, and some of these may prove to have economic applications. Some species of Dictyotaceae, on the other hand, have become significant invasive species. A dramatic recent example has been provided by the northern Pacific species Rugulopteryx okamurae which was probably first imported to the Mediterranean as a contaminant on farmed oysters (García-Gómez et al. 2020). This species was recorded on the southern coast of France in 2002 and was later recorded on the coast of Ceuta in 2015. Within a year of the latter record, its presence in Ceuta had reached absolute plague proportions. Most of the illuminated rocky sea bottom was covered by R okamurae, up to about 90% coverage at optimal depths about ten to twenty metres. Over 5000 tons of washed-up seaweed was removed from the beaches of Ceuta in 2016. Needless to say, native seaweeds, and other sessile marine organisms such as corals, would have been severely impacted by this spread.

Rugulopteryx okamurae in Morocco, from El Aamri et al. (2018).


What caused this dramatic invasion? It would have certainly been a factor that defensive metabolites produced by Rugulopteryx okamurae had a negative impact on competitors. But perhaps even more significant a factor was climate change. Rising sea temperatures in the Straits of Gibraltar would have made things uncomfortable for native marine life used to cooler conditions. Meanwhile, the subtropical immigrant would have found things increasingly to its liking. With its competition hobbled and nothing to hold it back, R. okamurae was set to take over.

REFERENCES

Bittner, L., C. E. Payri, A. Couloux, C. Cruaud, B. de Reviers & F. Rousseau. 2008. Molecular phylogeny of the Dictyotales and their position within the Phaeophyceae, based on nuclear, plastid and mitochondrial DNA sequence data. Molecular Phylogenetics and Evolution 49: 211–226.

García-Gómez, J. C., J. Sempere-Valverde, A. R. González, M. Martínez-Chacón, L. Olaya-Ponzone, E. Sánchez-Moyano, E. Ostalé-Valriberas & C. Megina. 2020. From exotic to invasive in record time: the extreme impact of Rugulopteryx okamurae (Dictyotales, Ochrophyta) in the strait of Gibraltar. Science of the Total Environment 704: 135408.

Snails of Crystal

In many parts of the world, searching under pots or among other garden rubbish may turn up minute snails with translucent shells. Among the various families which might be found in this way are representatives of the family Pristilomatidae, commonly known as crystal snails.

Common crystal snail Vitrea crystallina, copyright O. Gargominy.


All members of the Pristilomatidae* are tiny: the minute gem snail Hawaiia minuscula, one species which has become widespread, is a giant within the family at close to three millimetres in diameter. The shells have a low spire, growing in more or less a disc shape, and are generally smooth or ornamented with very fine radial lines. In life, they are transparent or a cloudy white, explaining their vernacular name. Internal organs are often visible through the shell. The Pristilomatidae are part of the broader group of mostly tiny snails known as the Gastrodontoidea (which I've covered on this site earlier, albeit in a rather inept fashion). Even among this array, however, they are notably small. Within the gastrodontoids, the pristilomatids are primarily distinguished by the structure of the male genitalia, in which the vas deferens in attached to the proximal end of the penial tunica (a sheath of muscle tissue around the penis; Hausdorf 1998). However, there is a bit of an open question about how well supported they are as a group. Their distinguishing features could all be side effects of their reduced size.

*In older texts, you may find this family referred to as the Vitreidae, after one of the larger genera included. However, the name Pristilomatidae has priority.

Minute gem snail Hawaiia minuscula, copyright Chris Mallory.


Within their native range, crystal snails may mostly be found in western North America and the western Palaearctic. Several species, however, have become further distributed in association with humans. As such, they are mostly found in damp, disturbed habitats, such as gardens, nurseries and parks. They will be found in secluded locations such as under flower pots or buried among moss or leaf litter. Some species prefer to fully bury themselves within the soil. Some other members of the gastrodontoids are known to be predatory, feeding on small arthropods or other snails and their eggs, but I haven't been able to find any direct reference to such habits among pristilomatids. It seems more likely that they prefer to feed on decaying fragments of vegetation. They do not seem to be regarded as presenting a challenge to the gardener; rather, they may provide their own small amount of assistance in keeping things tidy.

REFERENCES

Hausdorf, B. 1998. Phylogeny of the Limacoidea sensu lato (Gastropoda: Stylommatophora). Journal of Molluscan Studies 64 (1): 35-66.

Hausdorf, B. 2000. Biogeography of the Limacoidea sensu lato (Gastropoda: Stylommatophora): vicariance events and long-distance dispersal. Journal of Biogeography 27: 379–390.

The Stizus Sand Wasps

Some years ago, I presented a post on the sand wasps of the tribe Bembicini. Bembicini are just part of the broader range of sand wasps that have been variously classified as the Bembicidae, Bembicinae or Nyssoninae (Bohart & Menke 1976; Sann et al. 2018). Another diverse subgroup of the bembicids is the genus Stizus, of which more than 120 species are found in Eurasia, Africa and North America (but not in Australia or South America). Stizus species are relatively large wasps, getting up to 3.5 cm in length. Like Bembicini, they are often brightly coloured, black banded with yellow and/or red. They are otherwise fairly generalised in appearance: the labrum is exserted but is not remarkably long like that of bembicins, and the ocelli are not reduced (Bohart & Menke 1976).

Stizus pulcherrimus, copyright Phonon B.


The nesting behaviour of Stizus species was reviewed by Evans & O'Neill (2007). All known Stizus nests are constructed in soil and sand, sometimes in relatively damp locations such as salt marshes or near water bodies. Burrows of nests may be a foot or more deep and contain multiple cells; acessory burrows are common. Though females construct their burrows strictly single-handedly, they will often nest in clusters with other females. Polidori et al. (2008) found that this clustering behaviour in the European Stizus continuus was due to females being actively attracted to nests of other females, rather than just a side effect of limited nest sites. The most commonly used prey are various Orthoptera (grasshoppers or katydids); a handful of species instead prey on mantids. Prey are paralysed by repeated stinging before being flown back to the nest carried under the female. After the prey insect has been placed in a nest cell, the female lays an egg on its thorax. In most cases, cells are fully stocked with prey before laying, but females of S. continuus have been observed carrying fresh prey back to nests in which larvae have already hatched and begun eating.

Stizus perrisi female constructing nest, copyright David Genoud.


Mating between males and females generally occurs as the newly matured females emerge from the parent nest. Males often emerge before females and begin patrolling the nesting area, searching for females and chasing away other males. In some cases, they may begin actively digging for females emerging from burrows, and a newly emerged female may find herself surrounded by a pack of competing males. In their eagerness, males may become rather hasty: males of the Japanese S. pulcherrimus have been observed attempting to force themselves on females of the related genus Bembix!

REFERENCES

Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World. University of California Press: Berkeley.

Evans, H. E., & K. M. O'Neill. 2007. The Sand Wasps: Natural History and Behavior. Harvard University Press.

Polidori, C., P. Mendiola, J. D. Asís, J. Tormos, J. Selfa & F. Andrietti. 2008. Female-female attraction influences nest establishment in the digger wasp Stizus continuus (Hymenoptera: Crabronidae). Animal Behaviour 75: 1651–1661.

Sann, M., O. Niehuis, R. S. Peters, C. Mayer, A. Kozlov, L. Podsiadlowski, S. Bank, K. Meusemann, B. Misof, C. Bleidorn & M. Ohl. 2018. Phylogenomic analysis of Apoidea sheds new light on the sister group of bees. BMC Evolutionary Biology 18: 71.

Hydroglyphus pusillus, the Tiny Tiger

Hydroglyphus pusillus, copyright Udo Schmidt.


Let's take another visit to the world of diving beetles. Above is Hydroglyphus pusillus, one of the few representatives in northern Europe of a genus that otherwise includes close to ninety species spread through the Old World, primarily in the tropics. Hydroglyphus species are tiny diving beetles, only about two or three millimetres in length, with an elongate oval body shape. Characteristic features of the genus include basal striae on the pronotum and elytra, sutural striae on the elytra, and no transverse stria on the top of the head (Watts 1978, as Guignotus, a subsequently synonymised name). Species are often marked with distinctive colour patterns of streaks and blotches.

Hydroglyphus pusillus attacking larva of mosquito Culex pipiens, from Bellini et al. (2000).


Despite their small size, Hydroglyphus species are (like other diving beetles) voracious predators of other aquatic insects. Bellini et al. (2000) investigated the possible role of H. pusillus in controlling mosquito larvae in flooded rice fields in Italy. The larvae of H. pusillus mostly kept to the bottom sediment (so might be expected to be hunting prey other than mosquitoes) but adults were the most abundant diving beetle in the water column at the surveyed locations. One might expect that H. pusillus would not be effective predators of mosquito larvae that greatly outsized them. One would be wrong: not only are they indeed capable of taking down mosquitoes, Bellini et al. went so far as to describe their effects as "a real slaughter". A diving beetle latching onto a mosquito larva would soon find itself joined by others seemingly scenting haemolymph in the water. Between them, this mob of beetles could destroy a larva in a matter of seconds. Tiny, but terrifying.

REFERENCES

Bellini, R., F. Pederzani, R. Pilani, R. Veronesi & S. Maini. 2000. Hydroglyphus pusillus (Fabricius) (Coleoptera Dytiscidae): its role as a mosquito larvae predator in rice fields. Boll. Ist. Ent. "G. Grandi" Univ. Bologna 54: 155–163.

Watts, C. H. S. 1978. A revision of the Australian Dytiscidae. Australian Journal of Zoology, Supplementary Series 57: 1-166.

The Microzetid Enigma

The armoured mites of the Oribatida include their fair share of ornately ornamented species but perhaps the most grotesque of all are to be found under members of the family Microzetidae. These typically fairly small oribatids (the average size is about a third of a millimetre) are primarily found in soil and litter deposits around the world. They include a handful of species found in the far north but are primarily found in warmer regions with the greatest known diversity in the Neotropics (Woas 2002).

Dorsal, ventral and lateral views of Acaroceras galapagoensis, from Heinrich Schatz & Jose Palacios-Vargas.


The microzetids are primarily distinguished by elaborate outgrowths of the cuticle around the front of the body. In many oribatids, a pair of thin lamellae run down either side of the prodorsum (the part of a mite that might at first glance be taken for the 'head'). In microzetids, these lamellae have become massively enlarged and detached from the prodorsum over much of their length. As a result, they form a kind of hood over the front of the body. They are flanked on either side by similar lateral extensions called tutoria. The prodorsum as a whole is often remarkably large compared to the rear part of the dorsum, the notogaster. Indeed, the notogaster is often as wide as or wider than it is long. A pair of wing-like extensions, pteromorphs, extend on either side of the front of the notogaster; in microzetids, the pteromorphs are typically sharply pointed. To top all these excrescences off, the insertions of the first pair of legs are also shielded by well-developed flanges called pedotecta.

What, if anything, is the purpose of all these anatomical extravagances is a question I am unable to answer: whether they are related in some way to defense or water retention, for instance. They also make it difficult to understand the position of microzetids relative to other oribatids. The presence of pteromorphs has commonly been thought characteristic of a group of oribatids that have been referred to as the Poronoticae. However, microzetids lack any sign of another distinctive feature of poronotic oribatids: the array of glandular openings on the cuticle known as the octotaxic system. Some oribatids are known to have reduced octotaxic systems, and microzetids do bear a certain resemblance to a definitely poronotic family in the Oribatellidae, so it is possible they represent poronotic mites in which the octotaxic system has been lost. However, other features of microzetids further support affinities outside the Poronoticae. In particular, nymphs of microzetids carry scalps. As they moult from one instar to the next, the shed cuticle of the notogaster is retained in place like a cap. Over successive instars, this cap becomes a stack of scalps that potentially assist in defence (a would-be predator attempting to grab onto the notogaster finds itself holding only an empty scalp). This is generally thought to be a primitive bahaviour that was lost in the ancestor of the poronotics. So are the microzetids primitive relatives of the poronotics, descended from ancestors that had acquired pteromorphs but not yet lost the scalp-carrying habit? Are they derived poronotics that eschewed the octotaxic system and taken up their scalps once more? Further research into oribatid phylogeny is needed to know.

REFERENCE

Woas, S. 2002. Acari: Oribatida. In: Adis, J. (ed.) Amazonian Arachnida and Myriapoda: Identification keys to all classes, orders, families, some genera, and lists of known terrestrial species pp. 21–291. Pensoft: Sofia.

The Long-eared Bats of Australasia

When most people think of Australian mammals, they imagine the fauna as dominated by marsupials and monotremes, representatives of lineages long isolated from those found elsewhere. But Australia is also home to a remarkable diversity of native placentals. Immigrating from the north as Australia drifted closer to Asia, the rodents and bats underwent their own radiations on the Australian continent and its neighbouring islands. Among these distinctly Australasian assemblages of placentals are the long-eared bats or big-eared bats of the tribe Nyctophilini.

Lesser long-eared bat Nyctophilus geoffroyi, copyright Michael Pennay.


The long-eared bats comprise fifteen or so species found over a range between eastern Indonesia and Australia with outlying species in New Caledonia and Fiji. They are members of the Vespertilionidae, the most diverse recognised family of bats, and share with most other vespertilionids a fairly generalised appearance with dull coloration. They differ from other vespertilionids in having a relatively short muzzle (with a correspondingly reduced number of teeth) with a small nose-leaf at its end (Miller 1907). They also (as the vernacular name indicates) have particularly large ears, as long as or longer than the rest of the head, that are commonly connected medially by a distinct membrane. At rest, the ears may be folded like a concertina along the hind margin to protect them from damage (Hall & Woodside 1989). Historically, the long-eared bats were treated as their own subfamily within the Vespertilionidae that also included a similar North American genus Antrozous. However, the nyctophilins are now regarded as a derived tribe within the larger subfamily Vespertilioninae (albeit one whose exact relationships remain uncertain) and similarities between Nyctophilini and Antrozous are thought to be convergent rather than reflecing a close relationship. The majority of nyctophilins are placed in a single genus Nyctophilus with the exception of the New Guinea big-eared bat Pharotis imogene. This species differs from Nyctophilus in lacking hair at the end of the muzzle.

Nyctophilins are found in a range of habitats but seem to prefer dry woodlands. Vespertilionids as a whole are differentiated from other bats by modifications of the fore arms including a highly developed double joint between scapula and humerus and reduction of the ulna. As a result, they may be less powerful fliers than other bats but they would be more agile. This trend would be particularly pronounced in nyctophilins which have relatively short wings compared to other vespertilionids (Hall & Woodside 1989). The development of a nose-leaf in nyctophilins is associated with their use of signals emitted at a constant frequency through the nose for echolocation whereas other vespertilionids use signals of varying frequency emitted through the mouth. As well as catching insect prey in flight, long-eared bats are able to recognise prey at rest and so glean insects off vegetation or on the ground. This gleaning habit is presumably also associated with long-eared bats having relatively larger eyes than other vespertilionids.

Gould's long-eared bat Nyctophilus gouldi with ears partially reclined, copyright Department of Environment and Primary Industries, Victoria.


Caves in Australia are mostly not very extensive so the formation of colonies by Australian vespertilionids is constrained by the availability of suitable roosting sites such as hollows in trees or crevices in rocks. At least some long-eared bats may be solitary (Hall & Woodside 1989). Their distribution in Australia (as with pretty much all Australian animals) is also largely contingent on the availability of water. Mating happens in autumn but gestation is generally delayed, whether by delaying fertilisation or development of the embryo, and does not kick off until spring. Pregnancy then lasts about six weeks though it may again be slowed down if conditions turn bad. Long-eared bats are unusual among bats in that twins are not uncommon.

Whereas at least some nyctophilin species remain common (the lesser long-eared bat Nyctophilus geoffroyi is found over most of Australia), others are rare or little-known. A species described from Lord Howe Island, N. howensis, is believed to be extinct. The most remarkable case of obscurity is Pharotis imogene which was not recorded between 1890 and 2012, over 120 years. Evidence of extreme rarity? Quite probably, but also possibly evidence of just how few people are paying attention to bats.

REFERENCES

Hall, L. S., & D. P. Woodside. 1989. Vespertilionidae. In: D. W. Walton, & B. J. Richardson (eds) Fauna of Australia vol. 1B. Mammalia pp. 871–886. Australian Government Publishing Service: Canberra.

Miller, G. S., Jr. 1907. The families and genera of bats. Smithsonian Institution, United States National Museum, Bulletin 57: i–xvii, 1–282, pls 281–214.

Sweet Moulds

For reasons that shouldn't be too hard to work out, much of microbial diversity has only been identified within the last few decades. In 1985, researchers identified a distinctive new species of mycelium-forming bacterium from soil in China that they dubbed Glycomyces harbinensis. This was the first known species of the actinobacterial family Glycomycetaceae which have since been isolated from a wide range of soil microbiomes.

Agar culture of Stackebrandtia nassauensis (scanning electron micrograph), from Goodfellow et al. (2012).


Glycomycetes form pale (white to tan-coloured) branching mycelium a bit less than half a micron in diameter. Under certain conditions, they will form aerial mycelia comprising long chains of spores but these seem to only ever be sparse. The name of the family (which could be translated as 'sweet moulds') refers to the presence of the amino-acid glycine as a significant component of the cell wall. Other diagnostic components of the cell include the sugar ribose and the phospholipid phosphatidylglycerol (Goodfellow et al. 2012).

Since the original description of Glycomyces, half a dozen genera and numerous species have been recognised among the Glycomycetaceae. Some, such as Haloglycomyces and Natronoglycomyces, were described from high salinity soils (Sorokin et al. 2021). Other glycomycetes, such as Glycomyces sambucus, are endophytic, living inside the roots of plants. Doubtless (as always) many more remain to be discovered.

I haven't found any references to direct usage of glycomycetes by humans as yet. It has been suggested that endophytic bacteria may play a role in their hosts' uptake of nutrients from the soil. And I wonder if those species found in salty soils may have a contribution to make to the rehabilitation of such environments. In parts of the world such as here in southern Western Australia, where rising soil salinity is a concerning issue, any help would be more than welcome!

REFERENCES

Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) 2012. Bergey's Manual of Systematic Bacteriology 2nd ed. vol. 5. The Actinobacteria, Part A and B. Springer.

Sorokin, D. Y., T. V. Khijniak, A. P. Zakharycheva, A. G. Elcheninov, R. L. Hahnke, O. V. Boueva, E. V. Ariskina, B. Bunk, I. V. Kublanov & L. I. Evtushenko. 2021. Natronoglycomyces albus gen. nov., sp. nov., a haloalkaliphilic actinobacterium from a soda solonchak soil. International Journal of Systematic and Evolutionary Microbiology 71: 004804.

Gel Weeds

The red algae of the genus Gigartina are a widespread bunch, most diverse in temperate regions of the southern hemisphere but also found on most coasts of the north. They grow as erect thalli that may come in a variety of forms: foliose or dichotomously branched, cylindrical, compressed or flattened (Hommersand et al. 1993). Like other members of the Gigartinaceae, the family to which they belong, growth is multiaxial (the primary growth axes composed of multiple filaments). The inner cortical and medullary cells are rather loosely arranged and separated by a copious matrix (Hommersand et al. 1999).

Pestle weed Gigartina pistillata, copyright Ignacio Bárbara.


Members of the Gigartinaceae have an isomorphic life history with the alternating haploid gametophyte and diploid tetrasporophyte generations being similar in overall appearance. Historically, Gigartina has included some species that were subsequently found to have a heteromorphic life cycle with very different-looking generations (Guiry & West 1983). Despite the similarities in appearance of the gametophytes to true Gigartina, these species are now thought to belong to a distinct family, the Phyllophoraceae. The specific details of Gigartina reproduction are, as with all red algae, obscenely complicated, but it is on the basis of these details that Gigartina is distinguished from related genera (Hommersand et al. 1993). Gigartina gametophytes may be either monoecious (with male and female gametes formed on a single thallus) or dioecious (with separate male and female individuals). The reproductive structures of the gametophytes are formed near the apex of the thallus on distinct branchlets, pinnules or papillae. Again as is typical for red algae, ova are not released but retained on the gametophyte, and their fertilisation results in the growth of a diploid carposporophyte on the parent gametophyte. The carposporophyte then releases diploid spores (carpospores) that are released to give rise to the tetrasporophyte generation. In Gigartina, the carposporophytes are each surrounded by an envelope of secondary filaments. Filaments of the carposporophyte penetrate between the cells of the envelope and fuse with them to form a placenta composed of heterokaryotic cells (with a mix of haploid and diploid nuclei). Carposporangia are produced in grape-like clusters. In the tetrasporophytes, tetrasporangia develop embedded within the thallus at the boundary between the cortex and the medulla. Tetraspores are released when the tetrasporangium as a whole is released by the breakdown of the containing patch of cortex; the resulting holes can leave the tetrasporophyte thallus with a reticulate appearance.

Mature carposporophyte of Gigartina pistillata, from Hommersand et al. (1993).


Economically, Gigartina species are of most interest to humans as a source of long polysaccharides called carrageenans. Carrageenans are characteristic of the Gigartinaceae; other notable carrageenan producers include the well-known Irish moss Chondrus crispus. Though not digestible by humans (they largely past through the digestive tract unaltered), carrageenans are used in food production to thicken and set liquids in a similar manner to gelatin. According to Wikipedia, the use of Gigartina for food production is known as far back as 600 BC in China. In pre-industrial methods, carrageenan can be obtained by boiling cleaned seaweed and then straining the resulting brew. In modern times, carrageenans are used to provide texture to a wide range of products, including dairy products such as ice cream or yoghurt, processed meats or vegetarian meat substitutes, or cosmetic products such as toothpaste or shampoo. It has even been used in paper production: old-style marbled paper was made by floating ink on a mixture including carrageenan. Truly a versatile little compound!

REFERENCES

Guiry, M. D., & J. A. West. 1983. Life history and hybridization studies on Gigartina stellata and Petrocelis cruenta (Rhodophyta) in the North Atlantic. Journal of Phycology 19: 474–494.

Hommersand, M. H., S. Fredericq, D. W. Freshwater & J. Hughey. 1999. Recent developments in the systematics of the Gigartinaceae (Gigartinales, Rhodophyta) based on rbcL sequence analysis and morphological evidence. Phycological Research 47: 139–151.

Hommersand, M. H., M. D. Guiry, S. Fredericq & G. L. Leister. 1993. New perspectives in the taxonomy of the Gigartinaceae (Gigartinales, Rhodophyta). Hydrobiologia 260–261: 105–120.

Murderous Cones

The cone shells of the family Conidae have long been the subject of extreme interest from collectors. Their architectural form, polished surface and intricate patterning make it hard to argue that they are things of beauty, indeed. Not surprisingly, this long-standing aesthetic interest has also made them the subject of much taxonomic interest—some for the better, some arguably for the worse. For today's post, I've selected a particular subgroup of the cone shells: the species of the subgenus Textilia.

Bubble cone Conus bullatus, copyright H. Zell.


To describe the generic taxonomy of cone shells as 'messy' is something of an understatement. Part of the problem is that cone shells are another one of those groups in which a high level of species diversity contrasts with a low level of morphological disparity. Though species are readily distinguishable on the basis of superficial features such as colour patterning, they generally hew pretty closely to a particular overall morphotype. This can make it difficult to associate particular species into evolutionary groups. For many authors, the problem has been solved (or at least satisfyingly swept under the rug) by treating all cone shells as belonging to a single genus Conus. But with over 800 known species of conid, many showing intriguing variations in biology and natural history, many have yearned for a more informative system. Those who would divide, however, have disagreed significantly on how many divisions there should be. At the most disassociative end on the scale, one recent system divided the cone shells between no less than 113 genera, separated into five families. A more conservative approach was taken by Puillandre et al. (2014) who recognised four genera of cone shells (in a single family) with the larger genera encompassing multiple subgenera. Textilia was treated by PUillandre et al. as a subgenus within Conus, which remains the largest genus in the family by a considerable margin.

Pallisade cone Conus cervus, copyright James St. John.


Ten species of cone shell were included in Textilia by Puillandre et al. (2014). The species are found in the Indo-west Pacific, between south-east Africa and Hawaii. They are medium- to large-sized cone shells with the largest species, the pallisade cone Conus cervus reaching close to 12 cm in length. The smallest, the Timor cone C. timorensis, is at least 13 mm long. Textilia species have smooth, inflated shells and flared lips on the aperture (Old 1973). Only one species of Textilia, the bubble cone C. bullatus, can be considered well known. Not only is it found over almost the subgenus' entire range (other species are more localised), it is the only species found in shallower waters, being most common from slightly subtidally to 50 m (Hu et al. 2011). All other Textilia species are restricted to deeper waters. Just to confuse matters slightly, the textile cone C. textile is not a member of subgenus Textilia but another subgenus Cylinder.

Video of cone shells capturing fish, from here. The first individual is a striated cone Conus striatus (subgenus Pionoconus), the second is a bubble cone Conus bullatus.


Textilia forms part of a clade of cone shells with a diet composed primarily of fish. A slow-moving gastropod is obviously ill-suited to taking down a fast-moving fish by brute strength alone so cone shells make use of a quite different tactic: lethal poisons. The venom of a cone shell can be exceedingly powerful, enough so that multiple species have been known to cause severe injury or fatality to humans unwise enough to handle them live (cone shells may use their venom for defense as well as for attack). The teeth of the cone shell's radula have been modified into elongate, hollow needles. While most of the teeth are retained in a sac at the rear of the buccal cavity, only a single tooth is in use at any one time. When a suitable prey animal comes within reach, the snail's proboscis is stealthily extended towards it. The active tooth is then fired along the proboscis into the target, injecting a complete payload of toxins. Among Textilia, Conus bullatus is the only species whose toxic characteristics and capabilities have been studied as yet, but it is probably representative of the subgenus as a whole. As with other fish-hunting cone shells, the injected venom carries a mixture of toxic peptides that can be divided between two functional groups (Hu et al. 2011). These have been referred to as the "lightning-strike cabal" and the "motor cabal". The peptides of the lightning-strike cabal are the first to take effect, causing a rapid (almost instantaneous) tetanic immobilisation of the prey. After this, the motor cabal of peptides act to block neuromuscular transmission, preventing the prey from recovering from its freeze. And all this in a matter of milliseconds: as of 2011, at least, C. bullatus had the fastest immobilisation capacities of any fish-hunting cone shell. As beautiful as they are, cone shells are a force to be feared.

REFERENCES

Hu, H., P. K. Bandyopadhyay, B. M. Olivera & M. Yandell. 2011. Characterization of the Conus bullatus genome and its venom-duct transcriptome. BMC Genomics 12: 60.

Old, W. E., Jr. 1973. A new species of Conus from Indonesian waters. Veliger 16 (1): 58–60.

Puillandre, N., T. F. Duda, C. Meyer, B. M. Olivera & P. Bouchet. 2014. One, four or 100 genera? A new classification of the cone snails. Journal of Molluscan Studies 81: 1–23.

The Diosaccinae: Worldwide Sediment Dwellers

The harpacticoid copepods have been featured on this site a reasonable number of times now. These tiny crustaceans are among the most numerous animals in the world, both in terms of numbers of individuals and (in certain habitats) numbers of species. And among the most widespread representatives of the harpacticoids are members of the subfamily Diosaccinae.

Diosaccus tenuicornis, from Sars (1906).


The Diosaccinae are currently recognised as members of the family Miraciidae; earlier sources will usually refer to a family Diosaccidae but the recognition of the pelagic Miraciinae as derived members of this group (Willen 2000) requires use of the older name. Distinctive features of the Miraciidae compared to other harpacticoids include the presence of a relatively large, mobile rostrum and a number of distinctive arrangements of setae, including the inner seta on the basal endopodal segment of the first peraeopod (trunk leg) arising distally (Nicholls 1941, Willen 2000). Miraciids are also unusual in that females carry paired egg-sacs laterally; most other harpacticoid families carry only a single median egg-sac. Miraciids are divided between three subfamilies of which the Diosaccinae are the most diverse. Diosaccines are most readily distinguished by their retention of a number of plesiomorphic features such as crawling legs and relatively short caudal rami (Nicholls 1941; this author divided the current diosaccines between two subfamilies, the Diosaccinae sensu stricto and Amphiascinae, based on the presence or absence, respectively, of a clear distinction in breadth between the metasome and urosome, or 'trunk' and 'abdomen', but this division does not appear to have been recognised at this level by any subsequent authors). The great majority of diosaccines are marine, free-living and benthic. A handful of species have been described as associates of lobsters, whether commensals or semi-parasites. A small radiation of species of the genus Schizopera is known from Lake Tanganyika, and Karanovic & Reddy (2004) described a species Neomiscegenus indicus from subterranean fresh water in India. Marine diosaccines are found at all depths from the intertidal zone to the deep abyss. I don't know for sure but, though they are sediment dwellers, I don't get the impression (I could be wrong) that they are strictly meiofaunal. As noted earlier, many do not have the vermiform body shape characteristic of interstitial copepods. Many species also are around the half-millimetre size range, which I think may be relatively large for meiofauna?

Four species of Schizopera collected from Korea, from Karanovic & Cho (2016). Left to right: S. yeonghaensis, S. daejinensis, S. gangneungensis, S. sindoensis.


The other two subfamilies of Miraciidae are the aforementioned Miraciinae and the Stenheliinae, which have the endopod of the first peraeopod adapted for swimming rather than grasping and longer caudal rami. Though potential synapomorphies of the Diosaccinae were identified by Willen (2000), they're a bit weaksauce. There is a distinct possibility that further studies may identify the diosaccines as paraphyletic to the other two subfamilies. In particular, some diosaccines say a very unusual form of nauplius larva with the Stenheliinae, in which the body is strongly foreshortened and crab-like (Dahms et al. 2005). These nauplii also move sideways in a crab-like fashion and do not swim in the water column like the nauplii of other species. Practical considerations have lead most investigators of crustacean phylogeny to emphasis adult over larval morphology but the larval morphology of diosaccines raises some interesting questions.

REFERENCES

Karanovic, T., & Y. R. Reddy. 2004. A new genus and species of the family Diosaccidae (Copepoda: Harpacticoida) from the groundwaters of India. Journal of Crustacean Biology 24 (2): 246–260.

Nicholls, A. G. 1941. A revision of the families Diosaccidae Sars, 1906 and Laophontidae T. Scott, 1905 (Copepoda, Harpacticoida). Records of the South Australian Museum 7 (1): 65–110.

Willen, E. 2000. Phylogeny of the Thalestridimorpha Lang, 1944 (Crustacea, Copepoda). Cuvillier Verlag: Göttingen.