Field of Science

The Athyrididae: Spiralia and Lamellae

A specimen of the Devonian Athyris fultonensis photographed by Kentuckiana Mike. This specimen has part of the shell broken away to expose the calcified spiralium underneath.


The Athyrididae were a family of brachiopods that lived from the Silurian to the Permian, or until the end of the Triassic if the Diplospirellidae and Retzioidea are derived from the athyridids (Alvarez et al. 1998). Many athyridids possessed concentric lamellae on the outside of the shell; in the Upper Devonian to Permian Cleiothyridina, these lamellae were developed into a dense forest of flat spines. Specimens of the Devonian species Athyris vittata with preserved colour patterns indicate that the presence of radial stripes (Blodgett et al. 1988).

The Athyrididae are members of the order Athyridida, one of a number of brachiopod groups to possess a calcified spiral support (called, funnily enough, a spiralium) for the lophophore (see the link above for an explanation of the brachiopod lophophore). In the 1965 Treatise on Invertebrate Paleontology volume for brachiopods (Moore 1965), all the spiralia-possessing brachiopods were combined as the Spiriferida; however, other features of the shell are not consistent with a single origin for the spiralium, and they are now divided between the Spiriferida, Atrypida and Athyridida.

The Lower Carboniferous lamellate athyridid Cleiothyridina sublamellosa, photographed by Dwergenpaartje. The fine spines projecting from the lamellae in this genus have been mostly worn off in this specimen.


Many spiralium-bearing species appear to have lived on soft sediments, and it is possible that the spiralium was developed primarily as an adaptation for such habitats (Alvarez & Brunton 1990). For filter-feeders living in such habitats, the greatest challenge for feeding is not so much taking in food particles, but keeping the filter (in this case, the lophophore) from becoming clogged by indigestible particles such as sand. Reversing the direction of beat of the lophophore cilia moves such particles back towards the shell opening, where rapidly closing the valves will give the final impetus to 'spit out' the offending particles. In those species with lamellae, the slow-down of water currents as they hit the lamellae before the water enters between the valves may have also reduced the amount of particulate matter getting in. The lamellae may have also helped to support the shell opening above the sediment surface, though more significant in this regard would have been the pedicle, the fleshy stalk emerging from an opening in the back of the shell that anchored the athyridid in the sediment.

REFERENCES

Alvarez, F., & C. H. C. Brunton. 1990. The shell-structure, growth and functional morphology of some Lower Devonian athyrids from northwest Spain. Lethaia 23: 117-131.

Alvarez, F., Rong J.-Y. & A. J. Boucot. 1998. The classification of athyridid brachiopods. Journal of Paleontology 72 (5): 827-855.

Blodgett, R. B., A. J. Boucot & W. F. Koch II. 1988. New occurrences of color patterns in Devonian articulate brachiopods. Journal of Paleontology 62 (1): 46-51.

Moore, R. C. (ed.) 1965. Treatise on Invertebrate Paleontology pt H. Brachiopoda, vol. 2. The Geological Society of America, Inc., and the University of Kansas Press.

The Saga of Forsteropsalis fabulosa

Male of Forsteropsalis fabulosa, photographed by Neil Fitzgerald.


Technically, I had a paper last week. I say 'technically' because, at only one page long (excluding bibliography), I don't that it counts much in the grand scheme of things. This commentary might be longer than the paper itself. Still, in its own way, this is a resolution for something that's been hanging over me for the last ten years.

The article, published in Zootaxa, is titled Clarification of the type status of Macropsalis fabulosa Phillipps & Grimmett 1932. Macropsalis fabulosa is the harvestman species that currently goes by the name of Forsteropsalis fabulosa. It is one of the largest of New Zealand's harvestmen, with a body length (excluding legs and chelicerae) a little shy of a centimetre (Phillipps & Grimmett 1932). As you can see in the photo at the top of this post, the male has chelicerae that are massively enlarged even by the standards of the group that it belongs to. The second inflated segment of the chelicera is about as large as the main body of the animal!

When I looked at all the (available) type specimens of New Zealand Enantiobuninae for my Master of Science thesis back in 2001, I discovered a problem with the type specimen of M. fabulosa. When a new species is described, the specimen(s) on which the description is based becomes the holotype (if a single specimen is used or designated) or the syntypes (if there is more than one specimen). However, sometimes the original type material of a species may become unavailable: it may be lost, destroyed, or subsequent researchers may not be able to identify what specimens the original author was using. In these cases, it may be necessary for an author to designate a neotype, a replacement type specimen. This is what had happened for M. fabulosa: Ray Forster had designated a neotype for it in 1944 because the original holotype had been destroyed. However, when I looked at Forster's neotype and compared it with the illustration of the holotype in Phillipps & Grimmett's original description, I realised that the two were not the same species! Here is the neotype, taken from the Te Papa online collection:


Compare the size and shape of the cheliceral fingers in that photo to the one at the top of this post. Also, while it is not clear in the photo, the neotype has a heavy covering of small spines over the top of the prosoma (cephalothorax), but Phillipps & Grimmett had specifically noted that, despite its size, M. fabulosa had a prosoma devoid of spines.

This raised a problem: should the name 'Macropsalis fabulosa' be applied to the species represented in the original description, or to the species represented by the neotype? My own preference was towards the former option:

(1) Despite his choice of neotype, Forster (1944) had still maintained the characters of the original holotype in his verbal description of M. fabulosa. It is quite possible that his choice of neotype was a mistake.

(2) The neotype belonged to a named species, currently known as Forsteropsalis inconstans. Because fabulosa is an older name than inconstans, associating fabulosa with the neotype would mean that F. inconstans would have to be called F. fabulosa, while F. fabulosa would be unnamed.

However, to keep the name fabulosa with the original species would require replacing the neotype, and that is something that only the ICZN can do. So last year, myself and my supervisor at the Western Australian Museum, Mark Harvey, drafted an application to the ICZN asking that the neotype of M. fabulosa be replaced with one of the specimens I had attributed to that species in last year's paper on Forsteropsalis (Taylor 2011). The application was duly submitted, but returned a few weeks later with explanations from the commissioners who had reviewed it that the ICZN would not be considering this case. Because they didn't need to.

The ICZN, in its current form, has rather stringent requirements for establishing a neotype. Basically, you cannot designate a neotype for a species solely because it doesn't have a holotype. There has to be an actual need for one, i.e. the species would not be properly identifiable without one. You also have to demonstrate that you took all the steps you could to make sure that the original holotype is honestly, truly lost (many specimens, for instance, may end up in a different museum from the one that the original author said they were in). Forster hadn't done that, and he had also violated the requirements by selecting a specimen that didn't match the diagnostic features of the species. So, according to the commissioners, there was no need to ask the ICZN to replace Forster's neotype because it wasn't valid in the first place.

But without the 'neotype' to confuse matters, there was no need for me to designate a new neotype either. Phillips & Grimmett's original description is quite adequate to identify M. fabulosa (that was how I had identified specimens of it myself). So, after that long process, I end up writing an article explaining why I have nothing to explain. One interesting potential side-effect is that (as one of the commissioners explicitly noted) this case is not unusual: so stringent are the current requirements for neotypification, without any protection for past practices, that probably a great many past neotype designations are technically invalid. However, they remain unchallenged because, in the vast majority of cases, there is no actual need for a neotype.

REFERENCES

Forster, R. R. 1944. The genus Megalopsalis Roewer in New Zealand with keys to the New Zealand genera of Opiliones. Records of the Dominion Museum 1 (1): 183–192.

Phillipps, W. J., & R. E. R. Grimmett. 1932. Some new Opiliones from New Zealand. Proceedings of the Zoological Society of London 1932: 731–740.

Taylor, C. K. 2011. Revision of the genus Megalopsalis (Arachnida: Opiliones: Phalangioidea) in Australia and New Zealand and implications for phalangioid classification. Zootaxa 2773: 1–65.

Life Among a Shrimp's Gills

Female of Schizobopyrina bombyliaster from Williams & Boyko (2004), with red box added on ventral view to indicate position of small male.


For today's random subject, I drew the marine isopod genus Schizobopyrina. Schizobopyrina is a genus in the family Bopyridae, and females of this genus were distinguished by Markham (1985) from those of the related genus Bopyrina by the presence of palp on the maxilliped (part of the mouthparts), by its more elongate oostegites (the lamellae forming the brood pouch in which eggs and larvae are incubated), and by the fusion of the pleomeres (posterior segments) on one side of the body. About ten or so species have been assigned to this genus from warmer waters around the world.

Mature bopyrids are parasites of shrimps and other crustaceans (Schizobopyrina has been found on hosts of the families Palaemonidae, Gnathophyllidae and Hippolytidae). Schizobopyrina and related genera are found in the branchial (gill) cavities of their host. Shrimp gills are developed from side-branches of the base of the legs, and are covered by an overhanging shelf of the carapace (if anyone is familiar with the process of preparing a crayfish or lobster, the gills are the 'dead man's fingers' that you have to remove before serving the crayfish). In a shrimp that is host to Schizobopyrina, the branchial cavity will become greatly protruding, as can be seen in this photo of a bumblebee shrimp Gnathophyllum americanum parasitised by Schizobopyrina bombyliaster (from Williams & Boyko 2004; scale bar equals 1.0 mm):


Bopyrids are released from the parent host as larvae that initially attach themselves to copepods. When they are approaching maturity, they leave the copepod and find an appropriate adult host. The first larva to attach itself to an appropriate shrimp will develop into a female, while any subsequent larva to attach itself will develop into a male (Cash & Bauer 1993). As can be seen in the figure at the top of this post, the female is considerably larger than the male. She is also noticeably asymmetrical in her body form, though a single species may include individuals bent to either the left or the right (Markham 1985). The female bopyrid attaches herself to her host before it reaches maturity: this puts her at risk of losing her place as the host moults, but studies of another branchial parasite bopyrid, Probopyrus pandalicola, indicate that as the host cuticle tears away during the process of moulting, the female is able to reattach herself to the new cuticle underneath and keep her place (Cash & Bauer 1993). The smaller male looks very different to the female, and is much more symmetrical. He attaches himself to the female, but whether or how he feeds is unknown. In Probopyrus pandalicola, the female moults, then produces eggs, after each moult of her host; the male has been observed crawling at this point into the brood pouch of the female, where he presumably fertilises her eggs.

Just as a further aside, the recent description of the species featured in the figures used in this post, Schizobopyrina bombyliaster Williams & Boyko 2004, was of further interest because the type specimen of this parasitic isopod was itself host to a hyperparasitic isopod, the cabiropid Cabirops bombyliophila. Which gives me an idea for a matryoshka design...

REFERENCES

Cash, C. E., & R. T. Bauer. 1993. Adaptations of the branchial parasite Probopyrus pandalicola (Isopoda: Bopyridae) for survival and reproduction related to ecdysis of the host, Palaemonetes pugio (Caridea: Palaemonidae). Journal of Crustacean Biology 13 (1): 111-124.

Markham, J. C. 1985. A review of the bopyrid isopods infesting caridean shrimps in the northwestern Atlantic Ocean, with special reference to those collected during the Hourglass cruises in the Gulf of Mexico. Memoirs of the Hourglass Cruises 7 (3): 1-156.

Williams, J. D., & C. B. Boyko. 2004. A new species of Schizobopyrina Markham, 1985 (Crustacea: Isopoda: Bopyridae: Bopyrinae) parasitic on a Gnathophyllum shrimp from Polynesia, with description of an associated hyperparasitic isopoda (Crustacea: Isopoda: Cabiropidae). Proceedings of the California Academy of Sciences 55 (24): 439-450.

A Bunch of Apocrites

An unidentified male of Megalyridae, a family of 'evaniomorphs' parasitic on wood-boring beetles, from here.


During the late nineteenth century, many women attempted to achieve a 'wasp waist', using corsets to tighten their waist to as narrow a diameter as possible. The style was so-called, of course, because of its resemblance to the body of a wasp, with a sharp constriction dividing the body. However, this feature is not universal among wasps: rather, it characterises a distinct clade within the wasps, the Apocrita.

Basal members of the Hymenoptera possess a broad junction between thorax and abdomen like that seen in other insects. In apocritan wasps, the first segment of the abdomen became incorporated into the body of the thorax (where it is referred to as the propodeum) and the characteristic wasp waist developed at the front of the second abdominal segment. Because the major divisions of the body in Apocrita therefore do not correspond directly to the thorax and abdomen of other insects, workers on Apocrita instead refer to the mesosoma and metasoma (or 'altitrunk' and 'gaster'). So narrow is the connection between mesosoma and metasoma, in fact, that members of the Apocrita are incapable of taking solid food: only liquids can pass through the waist. This limitation is believed to have later been significant in the development of the social wasps and ants: because mature ants cannot themselves eat solids, they must feed any solid food they collect to their larvae. The larvae then regurgitate the semi-digested food in a liquid form that the adults can handle. This dependance on their larvae induced the formation of stable colonies. Mature wasps that do not form colonies feed on naturally-occurring liquids such as nectar.

An unidentified wasp of the Stephanidae ovipositing, from Singapore Nature.


Ancestrally, the Apocrita are a lineage of larval parasites, and the majority of species remain so today. The wide distribution of parasites of wood-boring beetles among basal apocritans, and in their sister group the Orussidae among the non-waisted wasps, suggests that this was probably the original lifestyle for the apocritans (Grimaldi & Engel 2005). Living Apocrita can be divided between five main groups: the Stephanidae, the Aculeata (stinging wasps, including all the social forms such as ants and bees), the Ichneumonoidea (ichneumons and braconids), the Proctotrupomorpha, and the Evaniomorpha (though the monophyly of the latter group is debatable). The Stephanidae are a family of long slender beetle parasites that are most diverse in tropical parts of the world.

An evaniid of the genus Hyptia, from Kurt Schaefer.


The evaniomorphs have been suggested to form a group on the basis of the form of the inner articulation of the coxa (the basal segment) of the middle pair of legs, but the polarity of this feature is debatable (Ronquist 1999). The type superfamily, the Evanioidea, includes a group of families characterised by having the articulation of the metasoma to the mesosoma positioned high up on the propodeum rather than low down as in most other wasps. The hatchet wasps of the Evaniidae have a particularly distinctive body form: the mesosoma is boxy, often almost square in side view; the first segment of the metasoma is developed into a long and narrow petiole; and the remainder of the metasoma is relatively small and hangs off the petiole like the head of the eponymous hatchet. Evaniids are parasites of cockroaches, laying their eggs on the cockroaches' egg cases.

Female trigonalyid of the genus Trigonalys, photographed by Simon van Noort. Note the hooked end to the metasoma; when ovipositing, the female will stand on one side of a leaf and hook her metasoma around to lay her eggs on the other side of the leaf.


Females of another evaniomorph family, the Trigonalyidae, lay large numbers of eggs inserted into incisions on a plant leaf. When a piece of leaf containing a trigonalyid egg is eaten by a caterpillar, the egg hatches out and the trigonalyid larva emerges, then burrows into the body of the caterpillar. However, the larva's target is not the caterpillar itself. Instead, the trigonalyid is looking for the parasitic larva of another wasp that may be inside the caterpillar: it is what is called a hyperparasite (that is, a parasite of a parasite). Trigonalyids are also known as parasites of the larvae of social wasps: when the social wasp feeds its larvae on a caterpillar containing a trigonalyid, the trigonalyid may infect the larva to which it is fed (Grimaldi & Engel 2005).

REFERENCES

Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press.

Ronquist, F. 1999. Evolution of the Hymenoptera (Insecta): the state of the art. Zoologica Scripta 28: 3-11.

Brown Ticks

Brown dog tick Rhipicephalus sanguineus, from here.


In an earlier post on this site, I gave a brief overview of the hard ticks, those lovable suckers of blood and (often) vectors of disease. Today, I'll take one particular subgroup of the hard ticks to look at: the genus Rhipicephalus.

Rhipicephalus species are generally referred to as 'brown ticks' as, for the most part, they lack any prominent spots or other markings. Rhipicephalus species are found worldwide, though the highest diversity is in Africa, home to about three-quarters of the known species (Walker et al. 2000). They are mostly parasites of mammals, but individual species may be found on a range of host species. A few species are economically significant as vectors of such pathogenic organisms as rickettsias and various Sporozoa, notably the brown dog tick R. sanguineus and the cattle tick R. microplus. The former species has been estimated to cause about US$168 million of losses per year in Africa, while the latter costs Australia about US$100 million a year (Murrell & Barker 2003). A brief drive north of Perth is enough for me to see the impact of the cattle tick on Australian agriculture: as one passes the southernmost limit of the tick's range, there is a noticeable shift between the Europe-derived cattle breeds (such as shorthorns and Herefords) kept in the south of the country, and the tick-resistant India-derived breeds (such as Brahmans) kept in the north.

Cattle ticks Rhipicephalus microplus on a host, from here.


Distinguishing features of Rhipicephalus from other tick genera include the presence of adanal shields in the males, and a short hypostome and palps. Until recently, R. microplus and four other species were separated into their own genus, Boophilus, but a number of analyses, particularly molecular ones, have indicated that Boophilus is nested within Rhipicephalus (e.g. Beati & Keirans 2001) and the genera were synonymised by Murrell & Barker (2003). Members of the now-subgenus Boophilus differ from the remaining Rhipicephalus species in lacking festoons, a series of crimped grooves running around the posterior body margin (visible in the photo at the top of this post). They are also one-host parasites (that is, they remain on a single host through their lifespan and do not leave the host when moulting) while most other Rhipicephalus (such as R. sanguineus) are three-host ticks (they leave their host when moulting and then find a new host). However, close relatives of Boophilus in the subgenus Digineus are two-host ticks, only changing host when moulting from nymph to adult (Murrell & Barker 2003). However, it is worth noting that none of the analyses that led to the subsuming of Boophilus within Rhipicephalus included any representatives of the genus Margaropus, similar to Rhipicephalus but distinguished by possessing broad heavily-segmented legs. A close relationship between Boophilus and Margaropus was indicated by the morphological analysis of Klompen et al. (1997). If Boophilus is nested within Rhipicephalus, it seems quite possible that Margaropus is as well.

REFERENCES

Beati, L., & J. E. Keirans. 2001. Analysis of the systematic relationships among ticks of the genera Rhipicephalus and Boophilus (Acari: Ixodidae) based on mitochondrial 12S ribosomal DNA gene sequences and morphological characters. Journal of Parasitology 87 (1): 32-48.

Klompen, J. S. H., J. H. Oliver Jr, J. E. Keirans & P. J. Homsher. 1997. A re-evaluation of relationships in the Metastriata (Acari: Parasitiformes: Ixodidae). Systematic Parasitology 38: 1-24.

Murrell, A., & S. C. Barker. 2003. Synonymy of Boophilus Curtice, 1891 with Rhipicephalus Koch, 1844 (Acari: Ixodidae). Systematic Parasitology 56: 169-172.

Walker, J. B., J. E. Keirans & I. G. Horak. 2000. The Genus Rhipicephalus (Acari, Ixodidae): a guide to the brown ticks of the world. Cambridge University Press.