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.

Tillinae

Tillus elongatus, copyright Gilles San Martin.

The above individual is a representative of a species of the subfamily Tillinae of the beetle family Cleridae. Clerids are a widespread group of moderate-sized beetles, larger individuals being about a centimetre in length, but most species tend to attract little attention from humans. They are mostly predators in confined spaces (Gunter et al. 2013): larvae hunt down wood-boring insects in their burrows, or the young of bees and wasps in their nests, whereas adults hunt for other insects under bark. Adults are more or less elongate in shape and commonly have an even covering of setae and a prominently punctate dorsum. The legs have five-segmented tarsi, each tarsus often with multiple segments lobed. Clerids are commonly referred to as 'checkered beetles' in reference to the contrasting colour patterns of many species but, as you can clearly see, not all clerids have such checkered patterns.

The subfamilial classification of clerids has shifted around a lot in the past but the Tillinae have been one of the more consistently recognised subfamilies. The feature most consistently separating tillines from other clerids is that the fore coxal cavities are both externally and internally closed: that is, the external rim and internal collar around the fore coxae are both complete rather than being interrupted posteriorly. Other distinctive features of the tillines are that all five tarsal segments are well developed and distinct, the pronotum is campanulate (bell-shaped) or bisinuate, and the eyes usually have coarse ommatidia (Burke & Zolnerowich 2017).

Cylidrus megacephalus, copyright Udo Schmidt.

The taxonomy of tillines is (as always) in great need of study. Around 550 or more species have been assigned to the subfamily worldwide, with the highest diversity in the Afrotropical and Oriental regions. However, many species can be quite variable in appearance and it is suspected that many previously described species may turn out to be synonyms. The situation is not helped by many species being rarely collected. For instance, Bostrichoclerus bicornis is a remarkable species distinguished by the presence of a pair of prominent, apically bifurcate horns arising alongside the antennal insertions. To date, this species is known from just two specimens, collected at separate locations in Baja California and southern California (Burke & Zolnerowich 2017).

A molecular phylogenetic analysis of the Cleridae by Gunter et al. (2013) suggested that the Tillinae represent the sister group of all other clerids. While unexpected from a morphological perspective, this result does tally with the long recognition of the tillines as a distinctive group. They may prove to have interesting things to tell us about the evolution of the clerids as a whole.

REFERENCES

Burke, A., & G. Zolnerowich. 2017. A taxonomic revision of the subfamily Tillinae Leach sensu lato (Coleoptera, Cleridae) in the New World. ZooKeys 179: 75–157.

Gunter, N. L., J. M. Leavengood, J. S. Bartlett, E. G. Chapman & S. L. Cameron. 2013. A molecular phylogeny of the checkered beetles and a description of Epiclininae a new subfamily (Coleoptera: Cleroidea: Cleridae). Systematic Entomology 38 (3): 626–636.

Where There's a Whip, There's a Scorpion

As our understanding of the higher relationships between organisms has improved vastly in recent decades, the arachnids have remained an intransigent bunch. Proposed connections between the various historically recognised orders have remained poorly supported and, even now, there are few that do not continue to jump about with gleeful abandon with each successive analysis. One small bastion of reliable support, however, has been been the tropical clade known as the Pedipalpi.

Whip spider Phrynus exsul, copyright Michel Candel.

Members of the Pedipalpi have traditionally been divided between two or three distinct orders: the whip spiders or tailless whip scorpions of the Amblypygi, the whip scorpions of the Uropygi, and the micro-whip scorpions of the Schizomida (alternative classifications have combined the last two in a single order Uropygi or Thelyphonida). All have a broad distribution in tropical and subtropical regions of the world. Representatives of the Pedipalpi are active hunters, united by the possession of large, raptorial pedipalps used in the capture of prey. All three groups also have the first pair of legs modified to become elongate and whip-like (Shultz 2007). These legs are not used in walking but are held forwards to function like antennae. The Uropygi and Schizomida are further united by the possession of a terminal appendage on the body, the 'whip' of a 'whip scorpion'. There is also a general agreement in recent years that the Pedipalpi are in turn the sister lineage to the spiders. Some researchers have argued for a closer relationship of the Amblypygi to the spiders rather than the whip scorpions, reflecting their (among other things) similar habitus, but this remains a minority view.

Syntype (one of the original described specimens) of Paracaron caecus, from Garwood et al. (2017). Scale bar = 5 mm.

Globally, the Pedipalpi are not a hugely diverse lineage, with a bit more than 600 known species overall. About 190 species belong to the Amblypygi, the whip spiders. As noted above, these arachnids are quite spider-like in appearance owing the lack of a terminal flagellum and the presence of a well-defined waist between cephalothorax and abdomen, but they lack the poison fangs and spinnerets of a spider. Most whip spiders have a distinctly flattened habitus, allowing them to enter narrow spaces under bark or between rocks. They also have the most remarkably elongate first legs among the Pedipalpi. Living whip spiders can be divided between two lineages, referred to as the Paleoamblypygi and Euamblypygi (Garwood et al. 2017). The Paleoamblypygi are represented in the modern fauna by only a single known (but little known) species, Paracharon caecus, a blind inhabitant of termite nests in western Africa. Paracharon caecus differs from other living whip spiders in retaining a vertical plane of motion of the pedipalps, like those of whip scorpions. In the Euamblypygi, the orientation of the pedipalps has shifted so they move in a horizontal plane only. In some whip spiders, the pedipalps have become remarkably long, perfect for clasping prey in a fatal hug.

Giant whip scorpion Mastigoproctus giganteus, copyright David Bygott.

The whip scorpions of the Uropygi are the least diverse of the three lineages of Pedipalpi, with about 110 known species. They are large, robust arachnids characterised by their long, filamentous terminal flagellum. Glands at the base of the flagellum produce noxious chemicals used in defense, giving some species the alternative name of 'vinegaroons'. The Schizomida are the most diverse subgroup of the Pedipalpi, including about half the known species. Some species have become widespread as a result of human transportation in association with greenhouses whereas others have even been collected among ice and snow in California (Harvey 2003). Schizomids are smaller and softer-bodied than the Uropygi and the terminal flagellum is shorter (as in Uropygi, the flagellum is flanked by repugnatorial glands). In male schizomids, the flagellum is often distinct in shape from that of the females, becoming bulbous. Schizomids also differ from most other arachnids in the presence of visible dorsal divisions between the segments of the cephalothorax.

Female schizomid Hubbardia briggsi, copyright Marshal Hedin.

In all subgroups of the Pedipalpi, reproduction involves mating displays in which the male deposits a spermatophore on the ground and then guides the female over it (Harvey 2003). The exact manner in which the male guides the female differs between subgroups. In schizomids, the female grasps onto the male's flagellum and he leads her. In Uropygi, the male grasps the female's fore legs with his pedipalps before turning to face the same direction as her with himself in front, and pulls her over the spermatophore. He then turns, embraces her abdomen with his pedipalps, and manually inserts the spermatophore into her genital operculum. Amblypygi have perhaps the most graceful option of the three: the male stands facing the female then gently beckons her forward, allowing her to approach and collect the spermatophore of her own volition.

REFERENCES

Garwood, R. J., J. A. Dunlop, B. J. Knecht & T. A. Hegna. 2017. The phylogeny of fossil whip spiders. BMC Evolutionary Biology 17: 105.

Harvey, M. S. 2003. Catalogue of the Smaller Arachnid Orders of the World: Amblypygi, Uropygi, Schizomida, Palpigradi, Ricinulei and Solifugae. CSIRO Publishing.

Shultz, J. W. 2007. A phylogenetic analysis of the arachnid orders based on morphological characters. Zoological Journal of the Linnean Society 150 (2): 221–265.