Amaurobioidea: Rummaging through a Wastebasket

A representative of the strikingly-coloured Nicodamidae from Australia. Photo by Nick Monaghan. While such spiders were previously identified as Nicodamus bicolor, there are no less than 23 species in seven genera that have previously been included under that name.

One term that you may come across in discussions of phylogeny is the concept of a "wastebasket" taxon. As the name suggests, a wastebasket taxon is one into which authors tend to throw everything that they can't really deal with. Often, a wastebasket will include the members of a group that are relatively unspecialised, often primitive, and united less by their shared characters than their lack of distinct features to connect them to one or another of the specialised subgroups that the author may recognise within the parent group. Phalangodidae among short-legged harvestmen, Sylviidae among passerine birds and Perciformes among spiny-finned fishes are all examples of taxa that have become wastebaskets in the past. Some wastebasket taxa are explicitly established as such, like the 'Deuteromycota' that included asexual fungi before techniques were developed that made it significantly easier to relate asexual and sexual fungal taxa. More often, though, a taxon originally based on a certain combination of features will develop into a wastebasket over time as phylogenetic studies show that the original basis characters for that taxon represent plesiomorphies (ancestral characters). This week's highlight taxon, the spider superfamily Amaurobioidea, perhaps belongs to the latter group.


Tegenaria gigantea (Agelenidae). Photo from Wikipedia. Agelenids build funnel-shaped webs and are apparently often called some variant of "funnel spiders" in North America, but such names are likely to cause confusion here in Australia with a certain notorious mygalomorphs. Some species of Tegenaria such as the hobo spider are also known for being toxic, but nowhere near as toxic as the Australian funnel-web.

In an earlier post, I included a quick overview of basal spider phylogeny, going as far down as the clade Araneoclada that unites those spiders that have only a single pair of book lungs (ancestrally, at least - many families of Araneoclada have lost the book lungs entirely, or evolved tracheae in their place). Members of the Araneoclada are further divided between the Haplogynae and the Entelegynae, originally based on the presence (Entelegynae) or absence (Haplogynae) in females of paired copulatory ducts opening on a sclerotised plate called the epigyne. While the absence of such ducts in the Haplogynae is obviously a primitive character and no longer regarded as uniting them, the group has funnily enough been supported as monophyletic based on a number of other characters (except for a small number of 'haplogyne' taxa that are phylogenetically entelegynes) (Coddington & Levi, 1991). However, the Amaurobioidea belong to the Entelegynae, which is by far the larger of the two clades. Within the Entelegynae, the primary division was long based on whether or not a species possessed a cribellum, a plate-like structure among the spinnerets that bears hundreds of tiny silk-producing spigots. As these spigots exude silk simultaneously, the spider uses a specialised arrangement of bristles on the fourth pair of legs to weave them together to form a woolly thread (see here for a more detailed description). Because this woolly thread is composed of multiple tangled strands, it can effectively entangle prey such as small insects that get caught among the strands. Unfortunately, as knowledge of entelegyne spiders improved it became clear that possession of a cribellum did not define a phylogenetically coherent group. A number of cases were identified of pairs of taxa clearly related by other characters in which one taxon possessed a cribellum and the other did not. The eventual conclusion was that the cribellum was an ancestral character for the Entelegynae (as also supported by its presence in one haplogyne family, the Filistatidae) that had been lost on numerous occassions.


Ctenus floweri (Ctenidae), from Singapore. Photo by David Court. Ctenids are active hunters.

In general, the Amaurobioidea included cribellate spiders with unbranched abdominal median tracheae, as opposed to Dictynoidea with branched abdominal median tracheae (Coddington & Levi, 1991). Families that have been assigned to Amaurobioidea include (among others) Amaurobiidae, Agelenidae, Ctenidae, Amphinectidae and Nicodamidae, but relatively little unites these families. Most of them are generally ground-dwellers (which may explain the common name of one of the best-known members, the hobo spider Tegenaria agrestis). Many members build small sheet-webs, but others are active hunters. Both the characters referred to above have since been shown to represent plesiomorphies of larger clades, with the alternative conditions arising multiple times. The phylogenetic analysis of entelegyne spiders by Griswold et al. (1999) found the 'Amaurobioidea' to fall within a clade that was sister to the clade including the orb-weavers, but the same clade included the Dictynoidea and Lycosoidea (wolf spiders and such) nested within 'amaurobioids'. Indeed, not even the type family of Amaurobiidae was monophyletic, with some members closer to the lycosoids while others were closer to the agelenoids. The Amaurobioidea, it seems, was a bust.

Coming up - science and art, whether taxonomy is science, why family names are so awful, micro-spiders, and Parapseudoleptomesochrella almoravidensis.

REFERENCES

Coddington, J. A., & H. W. Levi. 1991. Systematics and evolution of spiders (Araneae). Annual Review of Ecology and Systematics 22: 565-592.

Griswold, C. E., J. A. Coddington, N. I. Platnick & R. R. Forster. 1999. Towards a phylogeny of entelegyne spiders (Araneae, Araneomorphae, Entelegynae). Journal of Arachnology 27: 53-63.

In Which I Reveal Just How Much of a Freak I Am

It's all there in the subtitle to this site. In the last few days I've decided to set myself a task that will probably be ridiculously time-confusing, gut-wrenchingly futile and will doubtless cause me to become even older before my time than I already am. But it's something that hasn't been done since 1923, and I think the time is ripe for it to be done again. I'm thinking of compiling an index for all described taxa of long-legged harvestmen. With a few thousand species involved, this is no small task.

But the thing is, and this is the freakish part, I actually really like nomenclature. Nomenclature is the specific part of the taxonomic process where the researcher sifts through the assortment of available names and works out which is the correct name to use for the organism sitting before them. It is important to distinguish the identification of the correct nomenclature from the identification of the organism itself - the nature of the specimen won't somehow magically change if the name attached to it does. Nomenclature is simply the system of labels that researchers have agreed to use in order to allow communication. As such, many people seem to regard the identification of the appropriate label as a somewhat arduous and uninspiring task, but personally I find it can be quite a lot of fun. As frustrating as past confusions can be, there is also something appealing in the challenge of sorting them out.

As a group, harvestmen have their share of nomenclatural challenges. I've just linked to my post on the mess that is Gagrella in which I just scratched the surface. There are no less than five taxa laying claim to the name Gagrella bispinosa as a result of its repeated use as a subspecific name. The oldest harvestman genus, Phalangium, was originally used by Linnaeus for pretty much any arachnid that wasn't a spider or a scorpion, leading to a fair number of homonyms spread between a number of orders. These are the sort of things I'd like to delve into for the next few years. Sure it's a big call, but if you can't be a little hubristic as a grad student, when can you be?

Of Lions and Lace

The "non-green, green lacewing" (Catanach, 2007) Abachrysa eureka. Photo by M. C. Thomas.

There is a term that bird-spotters use to describe the ability to recognise what species a bird belongs to even if one cannot see the details of its features - they refer to the "jizz" of a bird, derived from the acronym GIS for "general impression and shape". The jizz of a bird species is not something that can be described easily, if at all - it is something that can really only be appreciated with experience. It should hardly come as a surprise that the same concept applies with identifying other organisms just as much as birds. Lacewings (Neuroptera) are a smallish order of insects (only about 5000 species) that include a diversity of forms, but many look at first glance not unlike small dragonflies. Still, a closer look will reveal significant differences to a dragonfly. For a start, lacewings have longer antennae and are able to fold their wings back over their abdomen in a way that no dragonfly can. There is also the feature that gives them their name - the wings of lacewings are particularly densely covered with veins, the little criss-crossing fluid-carrying lines that you can see on any insect wing. While you might need to look very closely indeed to see the individual veins, the cumulative effect of the dense veins is to give lacewing wings a distinctive shimmer, like light off satin, or the glimmer of colour across oil. This week's highlight taxon is a specific group of lacewings - the tribe Belonopterygini.

Lacewings have a complete metamorphosis, meaning they have a distinct larval stage separated by a dormant pupal stage from a very different-looking adult. Most lacewings start out life as formidable predators, and are quite recognisable by their large, protruding jaws. The most famous are the antlions of the family Myrmeleontidae, which dig themselves conical pits at the bottom of which they lie dug into the soil, waiting for any small insects unlucky enough to fall into the pit. While the large jaws are used for capturing and macerating prey, lacewing larvae are actually liquid feeders, injecting digestive saliva into their prey then sucking out the dissolved juices (Canard, 2007). One intriguing (yet kind of disgusting) feature of the order is that the midgut is not actually connected to the hindgut until pupation, meaning that the larva is not capable of defecation. Any indigestible waste products are stored in the gut until the lacewing reaches adulthood and passed after emerging from the pupa. Can you imagine the relief?


The belonopterygin Italochrysa insignis. This photo illustrates very well the distinctive shimmer that neuropteran wings possess in the right light and which I've found is actually one of the quickest ways to recognise an adult lacewing. Photo by Sheila.

Belonopterygini are a cosmopolitan tribe of a different family, the Chrysopidae (green lacewings), whose larvae are active hunters, many of them of economic significance as predators of plant pests such as aphids and thrips. Belonopterygin larvae are specialist associates of ant nests (Freitas & Penny, 2001), feeding on the ants therein. Unfortunately, such specialist habits make Belonopterygini one of the less-studied chrysopid groups, and I have been unable to find how the larvae evade detection by the ants. Like other chrysopids, belonopterygin larvae use small bits of soil and debris to disguise themselves, starting with the shell of the egg they hatched from (Catanach, 2007). Larvae of other chrysopids have been observed to incorporate the husks of drained prey into their trashy disguises so I would be interested to know if belonopterygins do the same, as has been described recently for assassin bugs.

Adult chrysopids may be predacious like the larvae, or they may feed on non-live food such as honeydew. Honeydew-feeding species possess diverticula in the gut that house symbiotic yeasts aiding the lacewing in digestion. Sounds produced by tapping the abdomen on the substrate are used by chrysopids in courtship, and the pattern of sounds produced may differ significantly between closely related species (New, 1991). Eggs are laid perched on the end of long silk threads.

REFERENCES

Canard, M. 2007. Natural food and feeding habits of lacewings. In Lacewings in the Crop Environment (P. McEwen, T. R. New & A. Whittington, eds.) pp. 116-129. Cambridge University Press.

Catanach, T. A. 2007. Abachrysa eureka (Banks) (Neuroptera: Chrysopidae): egg, first instar larva and biological notes. Unpublished thesis, Texas A & M University.

Freitas, S. de, & N. D. Penny. 2001. The green lacewings (Neuroptera: Chrysopidae) of Brazilian agro-ecosystems. Proceedings of the California Academy of Sciences 52: 245-395.

New, T. R. 1991. Neuroptera. In The Insects of Australia (CSIRO, ed.) pp. 525-542. Melbourne University Press.

Araneidae - With Web and With Scent

The St. Andrew's Cross (Argiope keyserlingi). Photo by Louise Docker.

The orb-weavers are undoubtedly the best-known of all spiders. Ask anyone to imagine a spider and they will probably picture an orb-weaver (they may also have transcribed the words "some pig" in the web). This is something of an unfair characterisation - of the more than 100 recognised families of spiders, less than ten are orb-weavers. Still, it is one of the orb-weaving genera that holds the name of "spider", Araneus, which, as the only generic name used in Clerck's (1757) Aranei Svecici, the only taxonomic work recognised by the ICZN that predates the 1758 tenth edition of Linnaeus' Systema Naturae, is officially the oldest generic name in zoological nomenclature*. That's right - spiders came before humans. Nyeh nyeh nyeh.

*Admittedly Clerck did use the name Araneus for all spiders, not just species included in the modern Araneus.

The Araneidae are the largest family of orb-weaving spiders, with a little less than 3000 described species. They are actually a lot more numerous than you might realise - many species build their webs only at night, taking them down in the morning before hiding during the day and rebuilding the web every evening. The family is decidedly diverse in appearance - from the gaudy colours and spines of the Christmas spiders to the idiosyncratic figures of the tailed spiders to one group whose common name describes their appearance perfectly - the bird-dropping spiders.



The classic orb-web is made by first floating a line of sticky silk horizontally across a space between two anhoring points (such as a pair of branches), then running a second looser non-sticky strand along the initial strand. The spider then drops herself* from the centre-point of the second strand, trailing a third strand behind her, so that the second and third strands form a Y-shape. The vertex of the Y will be the centre of the web. The spider next constructs an outer frame, as shown above in a diagram by Ed Nieuwenhuys (the page linked to has diagrams of each of the stages in orb-web construction), then runs a series of spokes from the centre of the web to the outside. She then runs a broad spiral of non-sticky thread from the centre of the web until she reaches the outer edge. After that, it travels back to the centre laying a much tighter spiral of sticky thread, removing the non-sticky scaffold as she goes. As the sticky thread is stretched, the sticky coating breaks into a series of globules of coiled thread, which is how the web is able to be so elastic and stand up to the thrashings of captured prey. The spider herself is able to move about without being trapped by means of secretions produced by glands near the mouth with which she coats her legs. Forster & Forster (1999) refer to an experiment where the tips of a spider's legs were dipped in solvent before the spider was returned to its web. The spider initially showed great difficulty in moving due to the removal of its protective coating, though it was able to renew the covering and regain mobility. After the web has been completed, the spider will take up residence at the central hub, legs resting on the radiating spokes in order to feel for any vibrations. Araneid eyesight is almost non-existent, and orb-weavers are incapable of hunting without a web. They are perhaps the closest thing to a terrestrial filter-feeder, filtering the air for small animals.

*All spiders are referred to as female unless proven otherwise, like ships and birds of prey. It's another one of those things that make the English language so damn confusing.


An unidentified member of the genus Gasteracantha. These spiders come in a dazzling array of colours and ornamentations, and unlike many other araneids are often visible during the day, earning them such names as "jewel spider" or "Christmas spider". Colour patterns can vary significantly even between members of the same species. Photo from here.

Many araneids may vary the basic orb-web design further. Ladder-web spiders, for instance, have a long narrow web instead of the usual circle. The function of these is not really understood, though it has been suggested as a specialisation for catching moths - moths have a covering of loose scales on their wings which would normally allow them to shake off a web and escape, but it is suggested that the elongate shape of a ladder-web means that as the moth shakes off its scales, it falls onto a lower part of the web until eventually it is no longer able to escape. Many orb-weavers construct a stabilimentum, a zig-zag ladder-shaped structure that extends upwards from the central hub. Again, despite being such a distinctive structure, the function of the stabilimentum remains largely unknown, though subject to intense debate - suggested roles include strengthening the web (the original source of the name), disguising the position of the spider from predators or making the spider look bigger, attracting prey or even making the web more visible for larger animals and so reducing the risk of them walking or flying through it. One large and striking araneid found here in Australia, the St. Andrew's cross (Argiope keyserlingi), shown at the top of this post, gets its name because it builds four stabilimenta radiating from the central hub, while the spider itself sits with the front two and rear two pairs of legs held alongside each other, so the spider itself forms the eponymous cross shape.

Perhaps the most remarkable thing about araneids, however, is that despite the total dependence of most species on their webs for survival, some species no longer make them. The aforementioned bird-dropping spider (Celaenia) is so-called because its lumpy brown-and-white-splotched abdomen really does look like a lump of bird poo, offering excellent camouflage from discerning predators. Instead of constructing a full web, Celaenia simply hang from a leaf or a thread with their legs outstreched. There they catch and feed on moths (excellent pictures of hunting Celaenia can be seen at Esperance Blog). It used to be a mystery how this seemingly limited and haphazard means of capture could possibly feed the spider (after all, how many moths could reasonably be expected to pass by one point over the course of a night) until it was observed that a surprising proportion of the moths being caught (that is, all of them) were males, and that, far from passing by the spider accidentally, male moths will actually approach the spider and remain close by it until caught. It seems that the spider actually emits pheromones that mimic those of a female moth, luring their prey in with the false promise of sexual gratification (like a Trojan virus attached to a spam e-mail). The bolas spiders of the tribe Mastophoreae have refined this process further - as well as producing attractive pheromones, they also dangle a single sticky thread below themselves. When a moth approaches close enough, the spider spins the sticky thread around in the air until it sticks to the moth and they are able to draw it in. How bird-dropping and bolas spiders make their living until they become large enough to handle moths seems a little confused - Brunet (1996) claims that Celaenia construct standard orb-webs until they reach maturity, while bolas spiders produce different pheromones for attracting different-sized moths when at different ages. Forster & Forster (1999) and Yeargan (1994), in contrast, both claim that Celaenia spiderlings produce pheromones to attract psychodid midges. Interestingly, while bird-dropping and bolas spiders are both members of the subfamily Araneinae, it is debatable whether they are each other's closest relatives within the subfamily (Yeargan, 1994), so it is possible that their amazing pheromone-capture techniques could have arisen separately of each other!

REFERENCES

Brunet, B. 1996. Spiderwatch: A Guide to Australian Spiders. Reed New Holland: Sydney.

Forster, R. R., L. M. Forster. 1999. Spiders of New Zealand and their Worldwide Kin. University of Otago Press: Dunedin (New Zealand), and Otago Museum: Dunedin.

Yeargan, K. V. 1994. Biology of bolas spiders. Annual Review of Entomology 39: 81-99.

Gnah! Gagrella! Headdesk!

'Gagrella' splendens - is this the face of Evil? Photo by sswroom.

Please permit me to vent some frustration. I've written before about the ghastly legacy left to many areas of harvestman taxonomy by the work in the first half of the 1900s of Carl-Friedrich Roewer, henceforth referred to as the Antichrist of Arachnology, through his use of artificial classification systems and slipshod taxonomy. In the past, I personally have managed to remain relatively unscathed by the dark influence of Roewer, who did not deal much with the Australian opilionidan fauna. In the last few days, this has sadly changed dramatically. I have found myself wandering into the toxic wasteland that is Gagrella.

The Gagrellinae are a sizable subfamily found in tropical and subtropical Asia and the Americas. The centre of diversity for the subfamily is in Asia, whence about 700 species have been described. Many of these species are exceedingly colourful, strikingly ornamented and just downright remarkable. The problem is that most of the Gagrellinae, including Gagrella itself, have not really been revised since Roewer's massive investigation of the group, culminating in a monograph of the Asian Gagrellinae published in four parts over 1954 and 1955. As with other groups of harvestmen, Roewer used an artificial classification system based on characters such as the numbers of nodules in the legs or spines on the carapace - characters which have sometimes since been shown to not even be consistent between members of the same species, let alone the same genus (there are specimens of other taxa that, if one was to use Roewer's identification system, the left side of the animal would key out as one genus while the right side would key out as another). It is therefore quite likely that, were a full revision to be conducted, many species would have to be placed in different genera from their current position. With, as I said, about 700 species involved, this would be a mammoth task.

And yet there is a second layer of ghastliness, to make the problem even more difficult. Of the species assigned to Gagrellinae, a little less than 200 have been assigned to the largest genus, Gagrella. The type species of this genus is one Gagrella signata. However, when Roewer worked on the genus, he moved G. signata out of Gagrella and into another genus, Crassicippus, leaving the remaining species as Gagrella. Because the genus name is required to always stay with the type species, this actually meant that what Roewer called Crassicippus should have been called Gagrella, while what he called Gagrella should have been something else! Unfortunately, almost all authors following Roewer used his inaccurate sense of Gagrella, meaning that of those nearly 200 species, none of them actually belong to Gagrella unless they happen by coincidence to have been placed in the wrong genus and are actually closer to G. signata.


Unidentified South American Gagrellinae, congregating suspiciously. Photo by Bruno Buzatto.

Under strict application of the rules of nomenclature, what is now 'Gagrella' should actually be called Hexomma, that being the oldest genus name synonymised with Gagrella sensu Roewer in the past (Crawford, 1992). Unfortunately, the name Hexomma has been used as a valid genus in all of about three publications since it was first published back in 1876. Also, there are serious doubts about whether the type species, Hexomma vulcanicum, is actually identifiable - Roewer (1954), who may or may not have seen the type specimens*, claimed it to be based on unidentifiable juveniles, and the type specimen(s) seems to have since gone AWOL (Crawford, 1992).

*Roewer (1954) claims to have examined type specimens that he had borrowed from Vienna, but then eight lines later lists "Holotypus (Thorell) (Mus. Stockholm, Genua?)". As the Vienna specimens were correctly attributed to Doleschall rather than the later Thorell (albeit from the wrong publication), the Vienna record seems more likely to be accurate. Thorell later redescribed Hexomma vulcanicum as Gagrella vulcanica, and the Stockholm/Genoa specimen listing probably refers to the specimen used by Thorell for the redescription (and so not actually a holotype).

Why does all this matter to me? I am currently trying to write a description of a new species of Gagrellinae. Seeing as I am not in a position to conduct the full revision of the Asian Gagrellinae, my best option for now would be to follow the Roewer classification, despite its faults. Unfortunately, the species keys out to 'Gagrella'... What am I (or other workers on Asian Gagrellinae) to do about this huge ugly pile of taxonomic blancmange? Among the options:

1. Move everything currently in Gagrella to Hexomma: Probably not that good an idea, considering that Hexomma is not a well-defined genus and many (if not most) of the species will end up having to be moved out anyway.


2. Conserve the definition of Gagrella as used by Roewer: One option might be ask the ICZN to conserve Roewer's usage of Gagrella. Under normal conditions, this would be ideal, but in this case much the same issues apply as with the first option - what's the point with conserving Gagrella in its current condition if most of the species are probably going to end up having to move anyway?


3. Run screaming in horror from the entire concept of Asian Gagrellinae and end up crouched into foetal position and whimpering in the darkest recesses of the wet collection: At the moment, this option is looking increasingly attractive...

REFERENCES

Crawford, R. L. 1992. Catalogue of the genera and type species of the harvestman superfamily Phalangioidea (Arachnida). Burke Museum Contributions in Anthropology and Natural History 8: 1-60.

Roewer, C. F. 1954. Indoaustralische Gagrellinae (Opiliones, Arachnidae). (Weitere Weberknechte XVIII). 1. Teil. Senckenbergiana Biologica 35 (3-4): 181-236.

Forcing Out the Secret

SEM of a y-cypris (Hansenocaris, Facetotecta), from Høeg & Kolbasov (2002).

A few months ago, I wrote a post on the mysterious y-larvae or Hansenocaris (Facetotecta), distinctive crustaceans known only from their larval form and of unknown adult morphology. I've just been informed of a significant step that has been taken towards solving this mystery (Glenner et al., 2008).

One way to discover the adult form of Hansenocaris would be to rear larvae through to adulthood. However, so far it has not been possible to rear y-larvae past the cypris stage (y-larvae belong to a group of crustaceans called Thecostraca, also including barnacles, that hatch out as a nauplius larva, which eventually transforms into a cypris larva, followed by other larval stages or adulthood). Glenner et al. have broken that barrier by exposing cypris y-larvae to the moulting hormone 20-hydroxyecdysone (20-HE). Exposure to this hormone induced the cyprids to moult through to the next stage in the life cycle.

The appearance of this next stage certainly goes some way to explaining why adult facetotectans have not yet been recognised. Gone are the swimming appendages and arthropod segmentation of the cypris. Instead, the y-larvae moults into a limbless, worm-like organism that wriggles vigorously. This worm-like creature is without a properly developed digestive system or other such extravagances, and about the only feature suggestive of its arthropodan nature are the disorganised and degenerate remnants of a pair of compound eyes. Overall, the emerged organism (dubbed an "ypsigon" by Glenner et al.) bears a significant resemblance to the vermigon larva described for some members of another group of the Thecostraca, the parasitic Rhizocephala. Ypsigons kept in culture for 24 hours underwent another moult (remaining as an ypsigon), but no specimens were kept alive beyond that stage. I am inclined to wonder whether the laboratory-induced form is truly the same as what would emerge in the wild or whether the growth hormone adversely affected the larvae's development, but Glenner et al. do indicate that rhizocephalan vermigons induced in the lab are comparable to those occurring naturally.


Emerged ypsigon next to its moulted cypris cuticle. From Glenner et al. (2008).

Loss of derived arthropod characters is not uncommon among endoparasitic crustaceans - the Rhizocephala and Pentastomida are two particularly extreme examples, and certain features of the y-larvae cypris had already lead researchers to suspect that the adult might be parasitic. Unfortunately, it is still unknown what the host of that parasitic adult might be. It is also worth stressing that, contrary to what has been implied on news releases, the ypsigon is not the adult, but an additional larval stage, probably (by analogy with the rhizocephalan vermigon) representing the stage at which the y-larva enters its host. Identification of the full adult form (which may or may not resemble the vermigon) will probably require the identification of that host. Despite the similarities between the facetotectan ypsigon and the rhizocephalan vermigon, the two groups are not believed to be each other's closest relatives within the Thecostraca (Facetotecta are a basal branch, while Rhizocephala are closer to barnacles - Høeg & Kolbasov, 2002), suggesting that this derived parasitic form has developed independently in the two groups. We eagerly await any discovery that will reveal the final clue to this mystery and present with a fully adult facetotectan in all its slimy glory.

REFERENCES

Glenner, H., J. T. Hoeg, M. J. Grygier & Y. Fujita. 2008. Induced metamorphosis in crustacean y-larvae: Towards a solution to a 100-year-old riddle. BMC Biology 6: 21.

Høeg, J. T., & G. A. Kolbasov. 2002. Lattice organs in y-cyprids of the Facetotecta and their significance in the phylogeny of the Crustacea Thecostraca. Acta Zoologica 83: 67-79.

Southern Crustacean Relicts

Eophreatoicus from Kakadu in the Northern Territory of Australia. Image from here.

This week's highlight taxon is the Phreatoicidea, a suborder of isopods restricted to freshwater habitats in ex-Gondwanan continents. This is not a particularly large group - only about a hundred species have been described, though it is estimated that at least that number again remain undescribed. A reasonably high proportion of the species are known from subterranean habitats*, including the first species to be described, Phreatoicus typicus. Knott (1986) listed eleven subterranean species, which at the time was about a quarter of the total known diversity (over half the known species have been described since then). The diversity of the suborder is also heavily centred in Australasia - 94 species have been described from there, in contrast to four species from South Africa and only two from India (Wilson, 2008), but again this is probably heavily biased by the fact that almost all taxonomic work on this group has been conducted in Australia. For instance, Knott (1986) refers to possible undescribed species from India - these species seemingly still have not appeared in print twelve years later. The supposed Gondwanan distribution of phreatoicids also makes their apparent absence from South America very interesting, but how confident can we be that they are truly absent from that continent?

*I should make it clear that "subterranean" does not necessarily mean "cave-dwelling". Caves actually only make up a small proportion of the subterranean habitat, and only one cave-dwelling phreatoicid species is known (Knott, 1986). The majority of subterreanean species are sediment-dwelling forms whose habitats can extend right down into groundwater aquifers. Phreatoicus typicus, for instance, was originally described from a well near Christchurch in New Zealand, into which it would have emerged from the surrounding bedrock.

Most people imagine isopods as dorsoventrally flattened animals, like their most familiar representatives the woodlice and slaters. Phreatoicids, however, represent an exception to this rule, being fairly high-vaulted, narrow animals. Stygobiotic forms tend to be more elongated. Phylogenetically, phreatoicids are one of the most basal groups of isopods, and have one of the earliest fossil records. The Palaeozoic phreatoicids (or, technically, stem-phreatoicids) Palaeophreatoicidae are known from marine sediments, but since the Triassic all known representatives have been freshwater. Phreatoicids are detritivores feeding primarily on decaying vegetation or on the micro-organisms associated with the former, but may occassionally be carnivorous (Wilson, 2008). Phreatoicids are a significant part of the pholeteros - the specific faunal assemblage of organisms associated with the burrows of larger animals such as freshwater crayfish.


Pilbarophreatoicus platyarthricus, a potentially subterranean form from the Pilbara in Western Australia. Pilbarophreatoicus was described from an intermittent stream (i.e. one that dries up outside the rainy season), but shows features usually associated with subterranean habitats such as blindness and elongated body form. Like many subterranean phreatoicids in arid regions, it probably emerges from the ground when standing water is available and retreats back into the groundwater during the dry season. Figure from Knott & Halse (1999). shale bar = 1 mm.

Taxonomically, the Phreatoicidea have been a difficult group. For many years the classificatory sytem used was that established by G. E. Nicholls in the early 1940s, which divided phreatoicids between two families, each divided into a number of subfamilies. Unfortunately, the features used to separate these taxa have been shown to be largely artificial, and a high degree of variation can occur between closely-related species or even within examples of the one species. Wilson & Keable (2002)revised the classification somewhat through phylogenetic analysis, recognising three families and abandoning Nicholls' subfamilies. The suborder as a whole seems to be characterised by fairly slow morphological evolution. Gouws et al. (2004) showed that at least one supposed species, the South African Mesamphisopus capensis, is divisible on genetic and morphometric grounds into a number of potential cryptic species.

Like many freshwater and subterranean organisms, many phreatoicids have very restricted distributions and are placed at significant risk of human activities. Genetic studies show that each separate aquifer may have its own isolated population (Wilson, 2008). Indeed, a number of species are believed to have already gone extinct, due to factors such as increasing groundwater salinity as a result of deforestation (Knott, 1986) or alteration and exhaustion of water supplies and aquifers (Wilson, 2008). Unfortunately, the lack of taxonomic resolution within the group, as well as the difficulty of surveying the habitats of subterranean species in particular, make it very difficult to assess the risk to individual species.

REFERENCES

Gouws, G., B. A. Stewart & S. R. Daniels. 2004. Cryptic species within the freshwater isopod Mesamphisopus capensis (Phreatoicidea: Amphisopodidae) in the Western Cape, South Africa: allozyme and 12S rRNA sequence data and morphometric evidence. Biological Journal of the Linnean Society 81: 235-253.

Knott, B. 1986. Isopoda: Phreatoicidea. In Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) (L. Botosaneanu, ed.) pp. 486-492. E. J. Brill / Dr. W. Backhuys: Leiden.

Knott, B., & S. A. Halse. 1999. Pilbarophreatoicus platyarthricus n.gen., n.sp. (Isopoda: Phreatoicidea: Amphisopodidae) from the Pilbara Region of Western Australia. Records of the Australian Museum 51: 33-42.

Wilson, G. D. F. 2008. Global diversity of Isopod crustaceans (Crustacea; Isopoda) in freshwater. Hydrobiologia 595: 231–240.

Wilson, G. D. F., & S. J. Keable. 2002. New Phreatoicidea (Crustacea: Isopoda) from Grampians National Park, with revisions of Synamphisopus and Phreatoicopsis. Memoirs of the Museum of Victoria 59 (2): 457-529.

Soft Waxy Scales

Nettle ensign scale (Orthezia urticae). Photo by Pavel Krásenský.

The Hemiptera (true bugs) are one of the definite contenders for the insect order containing the most oddballs (Coleoptera and Hymenoptera are probably their competitors). Hemiptera are well marked as a group by their specialised sucking mouthparts, but within the Hemiptera a wide range of body plans have arisen. The scale insects (Coccinea) are perhaps one of the oddest groups of all, and it is one of the scale families, the Ortheziidae, that is our current Taxon of the Week.

Scale insects get their name from the adult females, which have completely abandoned the joys of mobility and live their lives on a single spot, sucking the sap from a host plant. To protect themselves they secrete a covering of sticky wax or a hardened scale. Because of their sedentary lifestyle, indulgences such as legs or eyes are unnecessary, and have become reduced or lost. Only close inspection of the adult, or of the males or nymphs, would identify these creatures as even being insects. Those scales that are significant to humans are mostly plant pests, though some species are used to produce lacquer or the red dye known as cochineal (yep, gramophone records were once made from crushed insects).


Orthezia insignis female with crawlers emerging from the ovisac. Photo from here.

Scales of both sexes first hatch out of their eggs as highly mobile nymphs called 'crawlers', with fully developed legs and antennae (Williams, 1991). This is the dispersal phase of their life cycle - not only can they crawl around, but they are also small enough to be easily blown by the wind. Once they find a suitable host plant and moult to the next instar, scale nymphs become pretty much immobile, and lose all the paraphernalia of their youth. While females pretty much remain in this state for the rest of their life, males do things quite differently. They feed for the second and third instars, then enter a non-feeding pupal stage before emerging as the winged adult (the adult males of a few species lack wings). Adult male scales also don't feed and lack mouthparts - they will only live for a short time while they find a mate. Male scales are also one of the few groups of winged insects, in addition to Diptera (flies) and Strepsiptera, to have lost one of the pairs of wings (the first time I ever saw one, I was not yet aware of this and it confused me immensely). Because of their brief lifespan, male scales are relatively rare overall, though I get the impression that they can appear in large numbers in the right season. However, they are also of microscopic size, so are not likely to be noticed.


Male Orthezia insignis. Photo from here.

Scale insects are divided between a number of families. They are often divided into two superfamilies, the Orthezioidea (archaeococcids) and Coccoidea (neococcids) (Koteja, 2000), though other authors combine them all into the Coccoidea. However, the archaeococcids are united only by primitive characters and are assumed to be paraphyletic and ancestral to neococcids. The Ortheziidae (ensign scales) is one of the most basal of the families of Coccinea, and one of the earliest families known from the fossil record, in the Lower Cretaceous (Koteja, 2000) - however, the Coccinea fossil record is extremely poor and should be treated with caution (most female scales are distinguished by microscopic characters not usually preserved in fossils, and the great difference between males and females makes them impossible to identify with each other unless specimens are preserved in the process of mating). Characters giving away the basal position of ortheziids include the presence of abdominal spiracles in the female (lost in neococcids), and compound eyes in the male (in neococcids the compound eye has disintegrated into a row of separate simple eyes). Nymphs and adult females secrete symmetrical plates of wax on their backs, while the female also secretes a wax ovisac at the end of the abdomen in which she incubates her eggs. This is the 'ensign' referred to in the common name.

The Ortheziidae are not a particularly large family by insect standards - about 200 species are known. As with other scales, a number of species have been spread around the world along with infected host plants, and some can cause trouble as pest species.

REFERENCES

Koteja, J. 2000. Advances in the study of fossil coccids (Hemiptera: Coccinea). Polskie Pismo Entomologiczne 69: 187-218.

Williams, D. J. 1991. Superfamily Coccoidea. In The Insects of Australia, 2nd ed. vol. I pp. 457-464. Melbourne University Press.

Spiders Losing their Lungs

Hypochilus petrunkevitchi - photo by Marshal Hedin from Wikipedia.

The current Taxon of the Week arguably has a pretty poor claim on the title, because it is no longer recognised as a valid taxonomic grouping. As I have explained before, modern spiders can be divided into three suborders or infraorders or what-have-you. The Mesothelae or Liphistiomorphae (segmented spiders) are a small group distinguishable from all other spiders by their obviously segmented abdomens. The Mygalomorphae (vertical-fanged spiders) have fangs that move straight up and down, and include the trapdoor and funnel-web spiders and American tarantulas. The largest group of spiders by far is the Araneomorphae (cross-fanged spiders), with fangs angled towards each other, including orb-weavers, cobweb spiders, jumping spiders, wolf spiders, and pretty much any other spider family you're likely to be familiar with. However, some older references may list a fourth group, the Hypochilomorphae, and it's with the latter that we're dealing today.


The Tasmanian cave-dwelling austrochilid Hickmania troglodytes. The four yellow spots visible on the underside correspond to the positions of the book lungs. Photo by Niall Doran from here.

The 'hypochilomorphs' include three small families, the Hypochilidae, Austrochilidae and Gradungulidae, that are now regarded as basal members of the Araneomorphae. Like other araneomorphs, they possess fangs that are angled towards each other rather than parallel. Where they differ from other araneomorphs is in the number of book lungs they possess. Book lungs are the ancestral respiratory structure for all arachnids, and evolved from the gills of their aquatic ancestors as they adapted to life on land. They are little more than gills recessed into the underside of the animal and covered over to prevent moisture loss, and the name "book lung" refers to their appearance in cross-section like leaves of a book. The ancestral number of book lungs in arachnids is four, though many arachnids (particularly the smaller forms, and including some spiders) have independently replaced the book lungs with tracheae, or lack any specialised respiratory structures entirely. Most araneomorphs with book lungs have lost the posterior pair and only have two book lungs. Hypochilomorphs retain the posterior pair, demonstrating their basal position to other araneomorphs and causing them to all too often be damned with the execrable title of "living fossil". However, because this is an ancestral feature rather than a derived one, it does not indicate that hypochilomorphs form a group exclusive of other araneomorphs, and other features make it clear that Austrochiloidea (Grandungulidae and Austrochilidae) are more closely related to the other araneomorphs than they are to Hypochilidae (Griswold et al., 1999). The remaining araneomorphs have usually been presented as a single clade (the Araneoclada), though at least one species of Filistatidae, Kukulcania hibernalis, possesses posterior book lungs as a juvenile, suggesting that family lost the posterior book lungs independently of other araneomorphs, and Lopardo et al. (2004) suggested that Filistatidae may be outside the Austrochiloidea + Araneoclada clade.

The Hypochilidae are large spiders found in Asia and North America. They construct a unique web for snaring prey, often referred to as a "lampshade web" in reference to its shape, though if the description in Forster & Forster (1999) holds for all hypochilids, then the photo on the Wikipedia page for this family is quite possibly upside down. According to Forster & Forster, Hypochilus builds its web on the underside of an overhanging rock, with a tightly woven upper section flaring out around the lower circular edge. Hypochilids are mostly montane species.



The Austrochiloidea are restricted to Southern Hemisphere continents - the Austrochilidae are found in southern South America and Tasmania, while the Gradungulidae are found in eastern Australia and the South Island of New Zealand (Forster & Forster, 1999). The Austrochilidae build large horizontal webs, but many Grandungulidae have abandoned web-building and become active hunters. The Gradungulidae are characterised by the significant increase in size of one of the claws on the legs, which is used to great effect in seizing prey. In one of the Australian web-building species, the cave-dwelling Progradungula carraiensis, a long, sparse web is built between the ground and an overhang, up to and exceeding a metre in height. The spider itself sits head downwards at the base of the web, low enough that the front legs are near the ground. Any suitable prey that walks by the spider is grabbed with the front legs and bitten. The prey may be eaten where it is caught, or carried up to the top part of the web that also serves as a retreat for the spider. One of the New Zealand species, Pianoa isolata, has abandoned the web but hangs down among strands of dense moss, catching its prey in a similar manner to Progradungula. A New Zealand cave-dwelling species, Spelungula cavernicola, shown above in a photo by Paddy Ryan, is an active hunter but often feeds on its prey suspended in mid-air from a silk dragline. The round egg-sacs are also hung from draglines, probably as protection from potential predators.

REFERENCES

Forster, R. R., & L. M. Forster. 1999. Spiders of New Zealand and their Worldwide Kin. University of Otago Press: Dunedin (New Zealand), and Otago Museum: Dunedin.

Griswold, C. E., J. A. Coddington, N. I. Platnick & R. R. Forster. 1999. Towards a phylogeny of entelegyne spiders (Araneae, Araneomorphae, Entelegynae). Journal of Arachnology 27: 53-63.

Lopardo, L., M. J. Ramírez, C. Grismado & L. A. Compagnucci. 2004. Web building behavior and the phylogeny of austrochiline spiders. Journal of Arachnology 32: 42-54.

Your Little Friends that are With You Always

Demodex folliculorum, male above and female below, from Desch and Nutting (1972).

At all times, you are surrounded by life. Micro-organisms swarm on your skin, swim in your gut, and set up shop in your organs. Indeed, at any one time, there are considerably more microbial cells around your person than there even are of your own cells. The micro-organisms are not living on you - you are living among the micro-organisms.

They're not all bacteria, either. I just thought that I'd briefly introduce you to one of the more distinctive micro-organisms that you are almost certainly carrying about with you - the follicle mite. I also challenge you to keep from scratching yourself while reading this.


Demodex brevis, male on left and female on right, from Desch and Nutting (1972)..

Demodex, the follicle mite, is a specialised inhabitant of the follicles and pores of mammalian skin. A significant number of species appear to have been described from different hosts, ranging from humans to dogs to cattle to marsupial mice to honest-to-goodness mice. The most distinctive feature of Demodex is its elongate body shape, which allows it to live head-first inside the follicles of its host, feeding on cells within the follicle. Humans are actually inhabited by two species, Demodex folliculorum and D. brevis (Desch & Nutting, 1972). The more elongate D. folliculorum lives in the follicles themselves, and feeds on the epithelial lining. The rarer D. brevis is shorter, and is found within the sebaceous gland on which it feeds. Demodex brevis is found on less people, and also at lower numbers - multiple D. folliculorum may be found in a single follicle (as shown below in an image from here), but usually only one D. brevis.




The question of whether Demodex causes any harm to its human host is a difficult one. The sheer universality of Demodex within the human population implies that its presence is usually of no concern to the host. However, another species, D. canis, is widely connected with mange in dogs, and Demodex has been connected with skin disorders (demodicidosis) in a number of humans. The difficult question is whether Demodex is a direct causative agent or not. As one might reasonably expect Demodex to be present anyway, it's mere presence at an infection site does not automatically indicate its responsibility for the infection. It seems likely that Demodex may be a facultative agitator of problems arising from other ultimate causes, such as a suppressed immune system (Jansen et al., 2001) or an already-damaged follicle (Pena & Andrade Filho, 2000). It is noteworthy in this light that prevalence of demodicidosis varies seasonally (it is most common in spring), but the prevalence of Demodex itself does not (Desch & Nutting, 1972). Demodex folliculorum may cause damage when more than six individuals are present in the same follicle (Desch & Nutting, 1972).

REFERENCES

Desch, C., & W. B. Nutting. 1972. Demodex folliculorum (Simon) and D. brevis Akbulatova of man: redescription and reevaluation. Journal of Parasitology 58 (1): 169-177.

Jansen, T., U. Kastner, A. Kreuter & P. Altmeyer. 2001. Rosacea-like demodicidosis associated with acquired immunodeficiency syndrome. British Journal of Dermatology 144 (1): 139–142.

Pena, G. P., & J. de S. Andrade Filho. 2000. Is Demodex really non-pathogenic? Revista do Instituto de Medicina Tropical de São Paulo 42 (3): 171-173.

Barklice and Booklice and Such

Psocoptera is arguably the least deservedly obscure of the obscure insect orders. They're not uncommon - there's a reasonable chance that you'll have seen one in your life. You probably squashed it without giving much thought to what it was. And yet, so obscure is this order of insects that there isn't even a good vernacular name for the group. Psocoptera are minute insects (usually only a couple of millimetres long) that generally live among bark and litter, feeding on fungi. Some wingless species can be found in houses (where you might have seen one) and feed on such delicacies as dust or the glue used in book bindings, leading to their being known as booklice. The tree-living forms are sometimes referred to as barklice in comparison to booklice. Most entomologists that I know simply refer to the group as psocids, and that's exactly what I'm going to do.

Technically speaking, 'Psocoptera' is a paraphyletic group. The Phthiraptera, the true lice*, are derived from within the psocids. At the moment, things seem to be going through a transitional phase, with many authors dropping the paraphyletic 'Psocoptera' for the name Psocodea, which refers to the total group of psocids and lice. The 'Psocoptera' are divided into three suborders, the Trogiomorpha, Psocomorpha and Troctomorpha, the Phthiraptera being properly speaking a subgroup of the last. A representative of the second group, the psocomorph Blaste (photo from TOLWeb), can be seen at the top of this post, and it's the Psocomorpha that I'm looking at today.

*And holders of what is probably the worst insect order name of all to pronounce.



With over 3500 species, the Psocomorpha are generally regarded as the largest of the psocid suborders, though the Troctomorpha could give them a run for their money once the Phthiraptera are taken into account. We should probably be careful about making definite statements about this - because of their neglected nature, new species and sometimes even families of psocids continue to appear in the literature at a respectable rate. At the moment, though, it is a psocomorph that holds the honour of being probably the only invertebrate to get its picture plastered over Tetrapod Zoology, due to the nomenclatural issues that have arisen from the similarity in names of the psocid Caecilius and the amphibian Caecilia. The photo above is the one featured in Tet Zoo, and shows an identified member of the Caeciliusidae.



Most Psocomorpha are dwellers on bark or rocks. One group, the Caeciliusoidea, inhabits living foliage. Adults may be winged or wingless - many species have both forms. Many psocids cluster as nymphs - the photo above (from here*) shows one such congregation - and spin protective webs, but this is taken to the extreme in the genus Archipsocus. Archipsocus species form large colonies, and may build webs large enough to obscure tree-trunks, as can be seen in the picture below (from here). As with Embioptera, these colonies appear to be conglomerations of convenience, and there is no real social behaviour. Like aphids, Archipsocus may go through multiple generations in a summer, and the colony will contain individuals at all stages of development, both winged and wingless forms (Mockford, 1957). Once winter arrives, the colony breaks down and disperses, the survivors diapausing until the spring when they will start new colonies.

*This page also records a fantastic common name for psocids - "bark cattle", apparently because the nymphs move like a herd when disturbed.



Molecular and morphological data are mostly in agreement that the Psocomorpha can mostly be divided between four infraorders, the Psocetae, Homilopsocidea, Epipsocetae and Caeciliusetae (Johnson & Mockford, 2003; Yoshizawa, 2002). Both studies also agreed in placing Archipsocus outside these groups, as the basalmost member of the Psocomorpha. Unfortunately, beyond the bare morphology, information about most psocid groups seems to be few and far between, and there is a great deal about the order that we have yet to know.

REFERENCES

Johnson, K. P., & E. L. Mockford. 2003. Molecular systematics of Psocomorpha (Psocoptera). Systematic Entomology 28: 409-416.

Mockford, E. L. 1957. Life history studies on some Florida insects of the genus Archipsocus (Psocoptera). Bulletin of the Florida State Museum - Biological Sciences 1 (5): 254-274.

Yoshizawa, K. 2002. Phylogeny and higher classification of suborder Psocomorpha (Insecta: Psocodea: ‘Psocoptera’). Zoological Journal of the Linnean Society 136: 371-400.

The Secret of Y-Larvae

Deep Sea News has some neat pictures of a rhizocephalan for you to look at. Rhizocephalans are definitely one of the stranger parasitic crustaceans, with an almost fungal-looking structure that spreads through their crustacean host, and its machiavellian hijacking of the host's reproductive system for its own ends. Seriously, take a look, though you may want to wait a little if you've just had breakfast.



Rhizocephalans are actually fairly close relatives of barnacles, both of them belonging to a group of crustaceans called Thecostraca. Though the different thecostracan subgroups are very different in adult morphology, they are united by their similar larval morphology. As well as the standard crustacean nauplius larva, thecostracans have an additional larval stage known as a cypris larva, a motile stage with specialised sensory structures that the larva uses to seek out a suitable host or substrate to attach to and develop into the adult. As well as barnacles and rhizocephalans, the Thecostraca includes another few small crustacean groups, the Ascothoracida, the Acrothoracica, and the Facetotecta. Acrothoracica or burrowing barnacles burrow into hard substrates such as mollusc shells, other free-living barnacles, corals or limestone. Ascothoracida are minute parasites of molluscs and other marine animals. But I thought I'd reply to Deep Sea News' post by writing something on the last group, the Facetotecta.

The infraclass (or subclass, or whatever you want to call it) Facetotecta contains a single genus, Hansenocaris. Despite being discovered well over a hundred years ago, Hansenocaris remains, in many regards, very little known. The main thing we don't know about Hansenocaris is what it actually looks like. So far, this group of thecostracans is known only from distinctive larvae referred to as "y-larvae"* - the adult form is a complete mystery. The most distinctive feature of the y-larva is its large univalved head shield, whose faceted nature is the source of the name "Facetotecta". Both nauplius and cypris stages have been collected and well-studied, but that's as far as it goes (the photo above, from Høeg & Kolbasov, 2002, shows an SEM of a y-cypris). Certain features of the cypris larva's morphology suggest that, like most other thecostracan subgroups, Hansenocaris becomes parasitic at maturity (as I noted in a comment at Deep Sea News, the non-parasitic barnacles are actually the odd ones out here), but no-one knows on what.

*Why "y-larvae"? That I couldn't tell you, but according to Ponomarenko (2006) the name dates back to their original description by Hansen in 1899.

One suggestion that has been made is that y-larvae may fit into the little-known sexual phase of the life cycle of the Tantulocarida (Ponomarenko, 2006). Tantulocarids are another group of ectoparasitic crustaceans (living on other crustaceans) that are believed to be the sister group of the thecostracans, and are another group of animals that contend for the title of "almost too stupidly bizarre to be believable". The tantulocarid life cycle is unique in lacking the usual moulting stages of all other crustaceans - instead, the mature adult actually develops within the attached parasitic tantulus larva (Boxshall & Lincoln, 1997). Check out the diagram below from Boxshall & Lincoln (1997) showing this process. Personally, I have a hard time thinking of this as development from larva to adult (despite all the papers describing it as such) - it looks more like a reproductive process where the adult develops asexually by a sort of internal budding from the tantulus. Reproduction in tantulocarids is either asexual or sexual (Huys et al., 1993) - in the asexual phase, the tantulus larva swells into a sac filled with developing eggs that are believed to be retained to hatch out into fully-developed tantulus larvae. In the sexual phase, as shown, the larva gives rise to a single mature adult. What happens once the mature male is released into the world is unknown, but as the male lacks functional mouthparts it undoubtedly dies after finding a mate. The sexual female described by Huys et al. (1993) was still attached to the host via the umbilicus, the nutrient-delivering tube you can see in fig. 26 below, and it seems possible that it remains so attached for all or most of its life, continuing to draw nutrients from the host to nurse its developing eggs. Huys et al.'s female, unfortunately, was carrying only immature eggs, so whether the eggs are retained to the tantulus stage as in the parthenogenetic phase, or hatch into more standard nauplius larvae, remains unknown.



This period of ignorance does give a window for identifying y-larvae with tantulocaridans. The idea is also not without phylogenetic merit - tantulocaridans are regarded as the sister group to Thecostraca, while most phylogenetic analyses place Facetotecta as fairly basal thecostracans. However, the identification does not seem to be well-accepted*. Most significantly, the tantulus larva of Tantulocarida has no sign of lattice organs. Lattice organs are specialised sensory organs on the carapaces of thecostracan cypris larvae, including y-larvae, that are believed to function in helping the cypris find a suitable substrate for attachment** (Høeg & Kolbasov, 2002). It would be surprising if sexually-produced dispersing larvae of tantulocaridans were to possess lattice organs but asexually-produced dispersing larvae (that surely would have just as much use for them) did not.

*Google Books can be very frustrating. The Google Book preview for Scholtz (2004) allows me to read that "there are strong arguments against a tantulocaridan-facetotectan relation" at the end of page 209, but then page 210, where I would have undoubtedly been told about said arguments, is not part of the preview. Gah!

**However, Lange & Schram (2002) identified apparent sensory structures on the carapace of fossil thylacocephalans as possibly homologous to lattice organs, despite the believed free-living nature of thylacocephalans. Mind you, the strange morphology of Thylacocephala was so highly derived that it's pretty much anyone's guess just what they were up to.

Which brings us firmly back to square one. The adult form of Hansenocaris remains one more example of just how little we know of the marine environment. It's out there somewhere - the question is where.

REFERENCES

Boxshall, G. A., & R. J. Lincoln. 1987. The life cycle of the Tantulocarida (Crustacea). Philosophical Transactions of the Royal Society of London Series B - Biological Sciences 315 (1173): 267-303.

Høeg, J. T., & G. A. Kolbasov. 2002. Lattice organs in y-cyprids of the Facetotecta and their significance in the phylogeny of the Crustacea Thecostraca. Acta Zoologica 83: 67-79.

Huys, R., G. A. Boxshall & R. J. Lincoln. 1993. The tantulocaridan life cycle: the circle closed? Journal of Crustacean Biology 13 (3): 432-442.

Lange, S., & F. R. Schram. 2002. Possible lattice organs in Cretaceous Thylacocephala. Contributions to Zoology 71 (4): 159-169.

Ponomarenko, E. A. 2006. Facetotecta - unsolved mystery of marine biology. Russian Journal of Marine Biology 32 (Suppl 1): S1-S10.

Scholtz, G. 2004. Evolutionary Developmental Biology of Crustacea. CRC Press.

What is the Sound of One Mayfly Fossilising?

Actually, two mayflies. That is, unless they're not mayflies.

Krzeminski, W. & C. Lombardo. 2001. New fossil Ephemeroptera and Coleoptera from the Ladinian (Middle Triassic) of Canton Ticino (Switzerland). Rivista Italiana de Paleontologia e Stratigrafia 107 (1): 69-78.

The Triassic is apparently not a fantastic time, insect-wise. Fossil insects from the Triassic are fairly few and far between. Needless to say, this is really annoying, because it was probably a fairly significant time in insect evolution. The giant insects of the Palaeozoic were no more - instead, it was about this time that many of the modern insect orders stepped in to take their place (Grimaldi & Engel, 2005). This unfortunately brief paper by Krzeminski & Lombardo (2001) gives us just a couple of pieces of the puzzle, but it's debatable just what we can do with them.

First, the maybe-mayfly. Krzeminski & Lombardo described Tintorina from two specimens (unfortunately, while the name Tintorina triassica appears in the abstract, the name used in the body of the article is Tintorina meridensis - I'm not sure, but I think the latter would be the correct name). The holotype retains most of the body (the head is missing), two of the wings and a few bits of leg. The paratype is just a pair of wings and a fragment of body. Though fragmentary, this collection does not put us too badly off. A large percen