Floating Forams (Taxon of the Week: Globorotaliidae)

The planktic foraminiferan Globorotalia ungulata. Photo by Kenneth Finger.

Foraminifera have previously been covered at Catalogue of Organisms here and here. In those posts, the families covered were benthic forams while the family I'm covering today, Globorotaliidae, contains plaktonic forams.

The benthic vs planktonic division is generally treated as the basic starting point by foram workers. This is not because of any fundamental taxonomic distinction; benthic forams are considerably more diverse than planktonic species and, while past authors have treated planktonic forams as a single order Globigerinida, recent studies are often more consistent with a polyphyletic origin for planktonic lineages (Ujiié et al., 2008). It has even been shown that some individual foram species may alternative between benthic and planktonic stages (Darling et al., 2009). Planktonic forams also have much less history than benthic forams - while the earliest forams deep in the Palaeozoic were benthic, planktonic forms didn't appear until the Triassic (and didn't really become abundant until much later). However, the two groups do have very different ecologies and practical significance. While benthic species may be very localised, planktonic foram species are usually very widespread and abundant. About one-third of the world's ocean floor is covered with "Globigerina ooze", a thick deposit of the shells of dead planktonic forams. This great abundance and distribution, together with a high species turnover rate compared to benthic taxa, has made planktonic forams perhaps the most significant group of organisms of all for marine biostratigraphy.


Live specimen of Globorotalia menardii (Globorotaliidae; left) compared to Globigerinoides sacculifer (Globigerinidae; right). Photos by Colomban de Vargas.

The Globorotaliidae are a family of planktonic forams whose first definite appearance was in the Oligocene (de Vargas et al., 1997) assignations of earlier taxa to the globorotaliids are more contentious). Globorotaliids are distinguished from the other major family of planktonic forams, the Globigerinidae, by their different form (flattened rather than globular) and their smooth shell (globigerinids are spinose and honeycombed). While globigerinids feed on zooplankton as well as phytoplankton, globorotaliids are more specific feeders on phytoplankton. Ochrophyte endosymbionts have also been recorded in globorotaliids though the exact species involved does not appear to have been determined (Gastrich, 1988).

Blow (1979) recognised two subfamilies in the Globorotaliidae, the Globorotaliinae and Pulleniatininae; other authors may recognise them as separate families. In both subfamilies, the initial growth form is trochospiral (chambers arranged like the whorls of a top shell). In Globorotaliinae, it remains so throughout the life span; in Pulleniatininae, the earlier trochospiral stage is followed by a later streptospiral stage (each individual chamber occupies half a whorl and grows over the earlier chambers).


External and X-ray view of Pulleniatina obliquiloculata to show the change in spiral direction during growth. Photos from e-Foram Stock.

REFERENCES

Blow, W. H. 1979. The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and the stratigraphical distribution of some Globigerinida (mostly Globigerinacea). E. J. Brill: Leiden.

Darling, K. F., E. Thomas, S. A. Kasemann, H. A. Seears, C. W. Smart & C. M. Wade. 2009. Surviving mass extinction by bridging the benthic/planktic divide. Proceedings of the National Academy of Sciences of the USA 106 (31): 12629-12633.

Gastrich, M. D. 1988. Ultrastructure of a new intracellular symbiotic alga found within planktonic foraminifera. Journal of Phycology 23 (4): 623-632.

Ujiié, Y., K. Kimoto & J. Pawlowski. 2008. Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors. Marine Micropaleontology 69 (3-4): 334-340.

Vargas, C. de, L. Zaninetti, H. Hilbrecht & J. Pawlowski. 1997. Phylogeny and rates of molecular evolution of planktonic foraminifera: SSU rDNA Sequences compared to the fossil record. Journal of Molecular Evolution 45 (3): 285-294.

Nectocaris: Largely Irrelevant to Cephalopods?

Nectocaris pteryx as reconstructed by Marianne Collins in Smith & Caron (2010).

Today's issue of Nature sees the publication of a paper presenting a radical reinterpretation of the Middle Cambrian nektonic animal Nectocaris pteryx (Smith & Caron, 2010). Previously only known from a single specimen, Smith & Caron increase the hypodigm of Nectocaris by a whopping 91 specimens, an absolutely mindblowing advance. Unfortunately (and, I'm sad to say, not uncommonly for a Nature paper), the authors then take this amazing discovery and use it to make some decidedly unwarranted inferences.

Smith & Caron reconstruct Nectocaris as a small squid-like animal with two anterior tentacles, broad lateral fins and a ventral cylindrical funnel close to the head. Based on the similarity of the funnel to the siphon of living cephalopods, the authors infer a relationship between Nectocaris and cephalopods and suggest that the former is representative of the ancestral morphology of the latter. One problem with that - Nectocaris doesn't have a shell and cephalopods have always been assumed to have evolved from shelled ancestors like other mollusc classes. Smith & Caron suggest that this assumption is incorrect and that each of the living mollusc classes acquired shells independently.

This is the representation given by Smith & Caron (2010) of molluscan evolution and the known fossil record of each of the classes:


Smith & Caron (2010): "Arrows indicate the crown groups of 1, molluscs; 2, conchifera; 3, cephalopods. Stars represent the earliest record of mineralization in each lineage (after ref. 23). Clade divergence times (dotted lines) are unconstrained. Early branches follow previous phylogeny (after ref. 20)."

Simple, straightforward and very misleading. The diagram only shows the living classes of mollusc but omits all lineages not directly relatable to one or another of the recent taxa - a category that includes most Cambrian molluscs, including many that are directly relevant to cephalopod ancestry. The phylogenetic positions of Tryblidiida (including modern 'monoplacophorans') and Polyplacophora (chitons) as sister group or serial* sister groups to other molluscs, together with features of putative stem molluscs such as Wiwaxia and their possible nearest living relatives the annelids, suggest that serially-repeated structures were part of the ancestral ground plan for molluscs. The absence of indications of serial structures in many Cambrian 'monoplacophorans' such as helcionelloids suggests that they were (at least) part of the clade including bivalves, gastropods and cephalopods, and the fossil record for helcionelloids extends back to the very earliest Cambrian (Runnegar & Jell, 1976). The supposed absence of an early fossil record for scaphopods overlooks good support for a derivation of scaphopods from the Rostroconchia, another Palaeozoic mollusc group (Peel, 2006) which may take the scaphopod lineage back to the early Cambrian. Smith & Caron dismiss the possibility that Nectocaris may have secondarily lost an ancestral shell by claiming that it is too early in the fossil record and lacks likely predecessors; however, shells have been lost on a large number of occasions in molluscan history; shelled molluscs appeared in the fossil record some twenty million years or so before the earliest known nectocarids; and the relative rarity and simplicity of early molluscan fossils (early molluscs were generally small and fairly delicate) means that it is quite possible that a direct nectocarid ancestor may not have been preserved, nor is there any guarantee that it would be recognised as such if it had.

*No pun intended.

As described in an earlier post, the earliest known stem cephalopods (from the Late Cambrian) possessed shells with large numbers of very tightly packed septa and were unlikely to have been very buoyant. Their generally short conical shape would have been ill-suited for jet-propelled swimming as in modern cephalopods and they were most likely benthic. As other molluscan classes were also ancestrally benthic, it seems unparsimonious that the actively swimming Nectocaris represents the ancestral cephalopod lifestyle.

If Nectocaris is a stem cephalopod (which essentially depends on how strong the siphon is as a supporting apomorphy), then the most likely scenario is that its shell loss and squid-like form is an independent convergence on modern shell-less cephalopods rather than representing the ancestral form for cephalopods as a whole. Nectocaris would not be an ancestor, but a highly specialised side branch of its own.

REFERENCES

Smith, M. R., & J.-B. Caron. 2010. Primitive soft-bodied cephalopods from the Cambrian. Nature 465: 469-472.

Peel, J. S. 2006. Scaphopodization in Palaeozoic molluscs. Palaeontology 49 (6): 1357-1364.

Runnegar, B., & P. A. Jell. 1976. Australian Middle Cambrian molluscs and their bearing on early molluscan evolution. Alcheringa 1 (2): 109-138.

Stacks of Barley (Taxon of the Week: Hordeum)

Foxtail barley, Hordeum jubatum, a weedy species found in northern North America and northeast Asia. Photo by Colin Stone.

Hordeum is a genus of thirty or so species (Blattner, 2009, lists 33) whose native range mostly covers Eurasia and the Americas though various species have been spread by humans pretty much throughout the world, either willingly or unwillingly. The most significant of these species from a human perspective is Hordeum vulgare, barley, used in the making of refreshing beverages and the manufacture of eyewear. This is the genus that gave us beer.


Six-rowed barley, Hordeum vulgare, the main cultivated variety of barley. Hordeum species bear single-flowered spikes in groups of three but usually only the central spike develops a seed while the lateral two are abortive. Six-rowed barley has been bred so all three develop seeds. Photo from here.

Hordeum is one of the more basally diverging genera in the grass tribe Triticeae, previously discussed here in relation to the genus Elymus. Unlike many other triticean genera, the concept of Hordeum has remained relatively stable with the exception that some authors have restricted Hordeum to the species H. vulgare and H. bulbosum, placing the other species in a genus Critesion. Blattner (2009) divided the genus into five sections, four monophyletic (sensu Ashlock, at least) sections corresponding to the four genome types found in Hordeum (see the Elymus post for an explanation of the concept of genome types) and an explicitly polyphyletic section Nodosa for species derived from hybrids between species of sections Marina and Stenostachys.


Hare barley, Hordeum murinum ssp. leporinum, native to Europe but widely established around the world. Photo from here.

Hordeum is most diverse in the Americas - 24 species are found naturally in the New World (including two, H. brachyantherum and H. jubatum, that are also native to northeast Asia) with 15 of those native to South America. However, phylogenetic studies show that the genus is in fact Eurasian in origin with all of the New World diploid species belonging to a subclade of a single section (Stenostachys) which probably arrived in North America about four to six million years ago (Blattner, 2009). A number of the polyploid New World species (including both the Bering Strait-straddling species) appear to be derived from hybrids between New World Stenostachys and one of the central Asian Stenostachys species, probably H. roshevitzii - my guess is that they form a tribute to the ability of pollen to be carried amazingly long distances. Also biogeographically interesting are the section Nodosa species, the European H. secalinum and the South African H. capense. Hordeum secalinum appears derived from a cross between the mostly Mediterranean section Marina and a Stenostachys species (the ranges of the two sections overlap in central Asia). Hordeum capense is a biogeographical enigma; geographically isolated from all other species, it carries the same genome combination as H. secalinum (Baum & Johnson, 2003; Blattner, 2009) with which it is morphologically almost identical. Indeed, for a long time H. capense was regarded as a human-introduced population of H. secalinum, probably brought over in the earliest days of European colonisation. However, hybrids between H. secalinum and H. capense are infertile (Baum & Johnson, 2003). Petersen & Seberg (2004) calculated that the genetic divergence between H. secalinum and H. capense was too great for it to be a recent derivative of a human introduction; instead, they felt it must be an older relict that had reached South Africa by means unknown.

REFERENCES

Baum, B. R., & D. A. Johnson. 2003. The South African Hordeum capense is more closely related to some American Hordeum species than to the European Hordeum secalinum: a perspective based on the 5S DNA units (Triticeae: Poaceae). Canadian Journal of Botany 81: 1-11.

Blattner, F. R. 2009. Progress in phylogenetic analysis and a new infrageneric classification of the barley genus Hordeum (Poaceae: Triticeae). Breeding Science 59: 471-480.

Petersen, G., & O. Seberg. 2004. On the origin of the tetraploid species Hordeum capense and H. secalinum (Poaceae). Systematic Botany 29 (4): 862-873.

Meet the Shrews (Taxon of the Week: Soricidae)

Juvenile northern short-tailed shrew, Blarina brevicauda. Photo by Jamie McCarthy.

Assuming, of course, that you haven't already met. The Soricidae are a family of small insectivorous mammals found throughout Eurasia, Africa and North America, with a small number of species extending to South America. By mammal standards, this is a fairly large family with about 370 species currently recognised and a small but steady trickle of new species still being published such as Sylvisorex akaibei from the Congo within the past year (Mukinzi et al., 2009).


Caravan of house shrews, Suncus murinus. Photo from Osamu Matsuzaki.

Living shrews are usually divided between two subfamilies, the Soricinae and the Crocidurinae, or the red-toothed shrews and white-toothed shrews respectively (Dubey et al, 2007). Red-toothed shrews, found in Eurasia and the Americas, are named after one of their most unusual features, red crowns to their teeth due to the deposition of iron in their enamel (this feature has been lost in a few soricine genera). White-toothed shrews are found in Africa and tropical Asia and make up for lacking the funky tooth pigment of Soricinae by including such creatures as the insanely over-developed hero shrew Scutisorex somereni and the bewildering diversity of the genus Crocidura with in excess of 150 species. Other notable features of shrews include the production by at least some species of toxic saliva, and the formation by young shrews of 'caravans'. One youngster will grasp its mother's rump in its mouth, its own rump will be grabbed by another, and so on until the entire brood forms a train by which the mother will lead it about. The young shrews will remain determinedly clinging to each other even picked up and dangled above the ground like a living monkey chain (Nowak, 1999).


Close-up of mouth of a common shrew Sorex araneus showing the red teeth. Photo by A. Dale.

Most shrews are terrestrial generalists though a number of species are semi-aquatic, particularly in the soricine tribe Nectogalini. The American and Pacific water shrews, Sorex palustris and S. bendirii, are capable of running short distances across the surface of water due to their small size and hairy feet. The little-known central African Ruwenzorisorex suncoides has large premolars that have been suggested to indicate a diet of molluscs. In contrast, the mole shrews of the genus Anourosorex are (funnily enough) mole-like burrowers feeding on burrowing insects and earthworms.

REFERENCES

Dubey, S., N. Salamin, S. D. Ohdachi, P. Barrière & P. Vogel. 2007. Molecular phylogenetics of shrews (Mammalia: Soricidae) reveal timing of transcontinental colonizations. Molecular Phylogenetics and Evolution 44 (1): 126-137.

Mukinzi, I., R. Hutterer & P. Barriere. 2009. A new species of Sylvisorex (Mammalia: Soricidae) from lowland forests north of Kisangani, Democratic Republic of Congo. Mammalia 73 (2): 130-134.

Nowak, R. M. 1999. Walker's Mammals of the World, 6th ed., vol. 1. JHU Press.

Taxon of the Week: Lacy Lepraliellidae

Celleporaria sibogae, showing the characteristic hollow colony structure of this bryozoan genus. Image by Bob Fenner.

Lepraliellidae are a family of bryozoans (small colonial animals sometimes known as 'lace animals' or 'moss animals' due to the appearance of the colonies) found around the world with the highest diversity in warmer waters. Different species may grow as encrusting forms or as upright branching colonies and even lunulitiform varieties have been recorded from the Eocene of Australia (Schmidt & Bone, 2002).

Distinction of the various types of bryozoan requires close microscopic examination of the individual zooids (the units of the colony). Lepraliellidae belong to one of the more successful branches of the bryozoans, the Cheilostomata, which have each individual animal in a separate calcified box-shaped chamber. Within the Cheilostomata, they belong to the Ascophora which have an entirely calcified frontal wall on each chamber. Characters used in distinguishing Lepraliellidae from other ascophorans include umbonuloid growth of the relatively smooth frontal wall (i. e. primary calcification of the wall is internal rather than external), widely open ovicells (embryo brooding chambers) and a small spine-encircled ancestrula (the first zooid of a new colony to develop from a metamorphosed larva). In most species, an avicularium is present on the lower edge of the main opening of each feeding zooid though this feature is absent in Kladapheles gammadeka (Gordon, 1993).


SEM image of Buchneria dofleini colony showing individual zooids. The larger openings are those of feeding zooids, with a smaller avicularium opening against each one. Image by Dennis Gordon.

Lepraliellids of the genus Celleporaria include some of the largest of all bryozoan colonies, with individual heads up to a foot in height and nearly a metre in diameter, that may form predominantly bryozoan reefs (Hageman et al., 2003). Branches of upright Celleporaria colonies have a characteristic nodular appearance and are generally thick but hollow as they originally grow around an organic substrate such as a sponge that later dies off after being overgrown. Some species of Celleporaria are significant fouling agents on the bottoms of boats, and have been spread around the world by shipping.

REFERENCES

Gordon, D. P. 1993. Bryozoan frontal shields: studies on umbonulomorphs and impacts on classification. Zoologica Scripta 22 (2): 203-221.

Hageman, S. J., J. Lukasik, B. McGowran & Y. Bone. 2003. Paleoenvironmental significance of Celleporaria (Bryozoa) from modern and Tertiary cool-water carbonates of southern Australia. Palaios 18 (6): 510-527.

Schmidt, R., & Y. Bone. 2002. Eocene bryozoan assemblages of the St Vincent Basin, South Australia. In Bryozoan Studies 2001 (P. N. Wyse Jackson, C. J. Buttler & M. E. Spencer Jones, eds) pp. 293-298. A. A. Balkema.

Name the Bug: Yochelcionella daleki

Yochelcionella daleki, from Runnegar & Jell (1976).

As I kind of expected, the identity of this animal was revealed very quickly. This is the Cambrian mollusk Yochelcionella daleki, named after the most popular science fiction villains ever to be constructed from an upturned dustbin and a toilet plunger. And to be honest, anyone that knew me and knew that there was such an animal could have probably expected it to make an appearance here sooner or later. The high conical shell and the lateral 'snorkel' (which would have functioned in the living animal to expel water drawn in over the gills) distinguish it as Yochelcionella while Y. daleki is distinguished from other Yochelcionella species by its closely spaced rings and overall profile.

Yochelcionella is classified in the Helcionelloida, an assemblage of small mollusks that were found in the Cambrian and Ordovician. Helcionelloids are in turn one of the groups of mollusks referred to as 'monoplacophorans'. 'Monoplacophorans' have a small, undivided, generally cap-shaped shell and are essentially defined by their lack of the derived features of other molluscan 'classes'. As a classic negative grouping, 'monoplacophorans' have never been regarded as holophyletic. The uniting features of helcionelloids, such as a certain degree of lateral compression and an endogastric (directed backwards) shell, are also fairly plesiomorphic and the monophyly of helcionelloids is also suspect. The term 'monoplacophoran' is most commonly used in relation to the living species such as Neopilina galatheae; however, these species belong to a group called Tryblidiida characterised by serially-repeated organs and an exogastric (forward-directed) shell that is probably not closely related to helcionelloids.

Recent studies of mollusc phylogeny have recognised a clade uniting gastropods, scaphopods and cephalopods with the latter two more closely related (e.g. Wilson et al., 2010; the inclusion by that study of the shell-less caudofoveates in this clade has not been proposed elsewhere on morphological grounds but the remaining relationships have been). Many authors have regarded the 'helcionelloids' as representing the ancestral morphology of this clade. Yochelcionella and the related Eotebenna in particular have been suggested to be potentially connected to the origins of scaphopods and cephalopods (Peel, 2006); in contrast, Parkhaev (2002) classifies all 'helcionelloids' as early gastropods (albeit mostly stem taxa, so it kind of comes down to your definition of a 'gastropod'). Unfortunately, suggested relationships of helcionelloids to other molluscs are largely based on comparison of overall morphology and stratigraphy; because helcionelloid shells are generally small and fairly undistinguished, they preserve few characters for more detailed formal analyses.

REFERENCES

Parkhaev, P. Y. 2002. Phylogenesis and the system of the Cambrian univalved molluscs. Paleontologicheskii Zhurnal 2002 (1): 27-39.

Peel, J. S. 2006. Scaphopodization in Palaeozoic molluscs. Palaeontology 49 (6): 1357-1364.

Runnegar, B., & P. A. Jell. 1976. Australian Middle Cambrian molluscs and their bearing on early molluscan evolution. Alcheringa 1 (2): 109-138.

Wilson, N. G., G. W. Rouse & G. Giribet. 2010. Assessing the molluscan hypothesis Serialia (Monoplacophora + Polyplacophora) using novel molecular data. Molecular Phylogenetics and Evolution 54 (1): 187-193.

Weevil Ball (Taxon of the Week: Diorymerina)

Diorymerus lancifer, from Davis (2009).

The Diorymerina are a South American subtribe of the weevil subfamily Baridinae. Alonso-Zarazaga & Lyal (1999) include ten genera in the Diorymerina according to the International Weevil Community Website* (though this listing differs slightly from that given by Casey, 1922) but available info on members of the group appears to be rather sparse to almost non-existent. Which is a pity because they are certainly eye-catching animals.

*I do think it rather neat that there's an "International Weevil Community".

Baridinae as a whole are characterised by a rounded body shape but in the Diorymerina this is taken to an extreme. The dorsal profile of diorymerins is highly arched, almost circular, and at least some diorymerins have bodies nearly as deep as they are long (Casey, 1922; Davis, 2009). All members of the Diorymerina are glossy in appearance and usually such colours as black or mahogany brown though Bonomius aeneoviridis is a bright metallic green. The beak of diorymerins is usually relatively short and stout compared to other weevils.


Hiotus inflatus, from Davis (2009) again.

Lima (1956) recorded species of Diorymerina feeding on shoots and seeds of Malpighiaceae trees but other than that most species seem not to have been touched on since their original morphological descriptions, and even those are scattered and difficult to locate. Significant landmarks appear to be Casey (1922) and Hustache (1950), the latter being the first part of the rather unpleasant 'Nouveaux Barinae Sud Américains'. Most of this publication's eccentricities may perhaps be excused by its unusual publication history (Kuschel, 1983): while the original manuscript was prepared in 1929, it languished for twenty years due to lack of funding and was not published until after the author's death. Nevertheless, the four parts together add up to over three hundred pages of bare species descriptions with absolutely no illustrations, usually no explicit comparisons with previously described taxa and a whole universe of typological errors.

REFERENCES

Alonso-Zarazaga, M. A., & C. H. C. Lyal. 1999. A world catalogue of families and genera of Curculionoidea (Insecta: Coleoptera) (excepting Scolytidae and Platypodidae). Barcelona.

Casey, T. L. 1922. Studies in the rhyncophorous subfamily Barinae of the Brazilian fauna. Memoirs on the Coleoptera 10: 1-520.

Davis, S. R. 2009. Morphology of Baridinae and related groups (Coleoptera, Curculionidae). ZooKeys 10: 1-136.

Kuschel, G. 1983. New synonymies and combinations of Baridinae from the Neotropic and Nearctic regions (Coleoptera: Curculionidae). Coleopterists Bulletin 37 (1): 34-44.

Lima, A. M. da C. 1956. Insetos do Brasil vol. 10. Coleópteros. Esc. Nac. Agronomia: Rio de Janeiro.