Field of Science

Trap-jaw Ants of Australia (and a couple from Africa)

Foraging worker of Epopostruma frosti, copyright Alex Wild.


Anyone who finds themselves travelling through regional Australia will soon find themselves convinced that this is a continent ruled by ants. During the course of the day, while the hot Australian sun drives other animals to seek shelter and seclusion, ants are often the only living things (other than plants) to be seen. To match this abundance, Australia's ants also come in a variety of distinctive forms, many of them unique to this country.

One distinctively Australian group of ants are the 'epopostrumiforms'. This is a small group of genera belonging to the tribe Dacetonini of the subfamily Myrmicinae (in the past the epopostrumiforms have been formally recognised as the subtribe Epopostrumiti, though Bolton eschewed the use of formal subtribes in his 1999 review of the Dacetonini). The Dacetonini are all predatory ants, with a distinctive large process inside the base of the mandibles that helps to lock them closed when holding struggling prey. The mandibles may be particularly long and slender, sometimes with only a few teeth present at the end. Where their habits are known, epopostrumiforms are predators of springtails; these are the most typical prey for the Dacetonini as a whole though some species of the tribe are more catholic in their tastes. Dacetonins live in small colonies, commonly in secluded habitats such as leaf litter; the epopostrumiforms include species that nest and forage either above or below ground (Brown & Wilson 1959). Dacetonins hunt their prey by stealthily sneaking up to it with the mandibles held open, followed by a quick lunge combined with snapping the mandibles shut. Once the prey has been successfully grabbed, those dacetonins with shorter mandibles rapidly bring the sting forward to quell it. Even after using the sting, however, hunters of springtails may find themselves flung into the air by flicks of the springtail's furca a couple of times before the venom takes full effect (hence the need for a firm mandibular lock). Dacetonins with longer mandibles may also deploy their sting or they may simply lift the prey above their heads until it gives up the ghost.

The African Microdaceton tanyspinosum, copyright April Nobile.


As already indicated, the majority of epopostrumiforms are endemic to Australia (one genus, Colobostruma, includes a few species found in New Guinea and the Solomon Islands). The only non-Australasian taxon to be assigned to the Epopostrumiti is an African long-mandibulate genus Microdaceton. Features uniting Microdaceton with the Australasian epopostrumiforms include the presence of lateral outgrowths on the petiole and postpetiole (the first two nodular segments of the metasoma) and the position of the petiolar spiracle (Bolton 1999) but some authors have suggested a closer relationship of Microdaceton to other dacetonin genera. Even if correctly positioned, Microdaceton is at most the sister taxon to the Australasian clade, members of which are united by features such as reduced antennae and an enlarged labrum.

Face of Colobostruma alinodis, copyright Estella Ortega.


Bolton (1999) divided the Australasian epopostrumiforms between three genera: Colobostruma, Mesostruma and Epopostruma. Less than fifty species of this clade have been described to date though others probably remain to be named. Even among the known species, many are rare and/or cryptic and some are known from only a very few specimens. Epopostruma resembles Microdaceton in having elongate mandibles with only a small number of interlocking teeth at the end (two in Epopostruma, three in Microdaceton). When hunting, Epopostruma may open their mandibles to a full 170°. Colobostruma has much shorter, triangular mandibles with numerous teeth; Mesostruma has triangular mandibles somewhat intermediate between the other two genera. The mandibles of both Colobostruma and Mesostruma cannot be opened to the same degree as those of Epopostruma; rather, species of these two genera will open their mandibles to a maximum angle of 90° when hunting. Whether the Dacetonini involved long mandibles on a single occasion, with a number of sub-lineages reverting to shorter mandibles afterwards, or whether the short-mandibled Dacetonini retain the ancestral morphology and long mandibles evolved on multiple occasions within the tribe, remains a question occasioning some debate.

REFERENCES

Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). Journal of Natural History 33: 1639–1689.

Brown, W. L., Jr & E. O. Wilson. 1959. The evolution of the dacetine ants. Quarterly Review of Biology 34 (4): 278–294.

The Monkey Orb of Asia

Just a quick entry for this week. And for the second week in a row, today's post will somehow involve monkeys.

Female monkey orb-weaving spider Neoscona punctigera, copyright Akio Tanikawa.


The orb-weavers of the family Araneidae are a highly diverse group of spiders, with well over 3000 known species. They are also one of the most familiar spider groups, often being relatively large as well as visible due to their construction of exposed and characteristic webs. The lady in the picture above represents one of the more moderately sized species, being about a centimetre in length (Tikader & Bal 1981). Neoscona punctigera is a widespread species in Asia, with a range extending from Madagascar and surrounding islands to Japan, as well as south into New Guinea and northernmost Australia. Vernacular names for the species include ghost spider or monkey orb-weaver. Like many other orb-weavers, N. punctigera only puts up its web at night; it sits in the web head downwards. When morning comes, the spider consumes the previous night's web and finds a concealed spot to hide until evening. On the underside of the body, N. punctigera has one or two pairs of bright white spots. When the spider is hunkered down for the day, these spots are concealed but when the spider is out on its web at night they are very visible; Chuang et al. (2008) found that these bright spots appear to attract prey, as spiders who had had their spots painted over caught less moths than usual.

Male Neoscona punctigera, copyright Suresh Kumar.


The name 'monkey orb-weaver' refers to the appearance of the male, which like the males of other orb-weavers is quite a bit smaller than the female (I have no idea where the name 'ghost spider' comes from; perhaps something to do with the spider's appearance on a web?) Resting males tend to adopt a pose with the front legs bent close together and the rear legs crossed behind the abdomen (as in the photo just above). Combined with eye-like spots on the abdomen, the overall effect has been compared to a monkey lying back with its legs crossed and its hands behind its head.

Orb-weaver taxonomy can often be confusing. Early authors tended to dump a large number of orb-weavers in a broad genus Araneus; though this genus is now used in a much narrower sense, many orb-weaver genera are difficult to distinguish without examining the genitalia. Individual species can also be quite variable in superficial appearance with a lot of variation in colour pattern, so many species were initially described under a number of names. Female Neoscona differ from Araneus in the presence of a longitudinal groove on the cephalothorax, as well as the presence of one or two lateral lobes at the base of the scape (a projecting process over the epigyne, the sclerotised structure around the female genital openings). Distingushing N. punctigera from other species of Neoscona requires even closer inspection of the genitalia. In a number of older sources the species now generally referred to as Neoscona punctigera (including in the World Spider Catalog) is commonly referred to as 'Araneus lugubris'. Confusingly enough, the latter name actually has priority (it dates to 1841 whereas the name pectinigera was only published in 1857) but has fallen out of disuse since Grasshoff (1986) stated that it was preoccupied in a review of African Neoscona. I'm not sure if he was correct—I suspect that he thought it was antedated by Aranea lugubris, published in 1802 for what is now a species of wolf spider, but as the 1841 species was originally placed in the now-obsolete genus Epeira I don't think they actually conflict. Nevertheless, the rules governing how preoccupation affects the use of older names can be complicated and if N. pectinigera has been settled as standard then it may be best to let it be.

REFERENCES

Grasshoff, M. 1986. Die Radnetzspinnen-Gattung Neoscona in Afrika (Arachnida: Araneae). Annalen Zoologische Wetenschappen 250: 1–123.

Chuang, C-Y., E.-C. Yang & I.-M. Tso. 2008. Deceptive color signaling in the night: a nocturnal predator attracts prey with visual lures. Behavioral Ecology 19 (2): 237–244.

Tikader, B. K., & A. Bal. 1981. Studies on some orb-weaving spiders of the genera Neoscona Simon and Araneus Clerck of the family Araneidae (=Argiopidae) from India. Records of the Zoological Survey of India, Occasional Paper 24: 1–60.

Sorting Monkeys: Dissecting Mimulus

New Zealand musk Thyridia repens, one of the species previously included in Mimulus section Paradanthus, copyright Jon Sullivan.


Long-time readers of this site will know that often, when I pull out the name from the virtual hat of my subject taxon for the week, I find that the greatest challenge lies in determining just what that name applies to. I knew that I was in for another one of these challenges as soon as I established that this week's post would be on the section Paradanthus of the plant genus Mimulus.

Mimulus, as it is most commonly recognised, is a genus of about 120 species found in many parts of the world but with by far the greatest diversity in western North America (where about three-quarters of the recognised species are found). They are commonly known as monkeyflowers or muskflowers in reference to the appearance and scent of the flowers of some species. Because of their diversity (in a well-studied part of the world), monkeyflowers have attracted a fair bit of interest as a model system for studying processes of evolution and speciation. Most Mimulus species are herbs though some are small shrubs. However, even shrubby forms do not have extensive root systems, and they are mostly annual or seasonal; perennial forms usually die off above ground over winter, growing back from the rootstock when conditions improve. These perennial forms may also propagate vegetatively through drooping stems putting down new rootstock where they contact the ground (Grant 1924). Mimulus species primarily grow in damp habitats; some will even grow in standing water.

Nepal monkeyflower Erythranthe nepalensis, copyright Qwert1234.


Until fairly recently, Mimulus was primarily classified in the family Scrophulariaceae. Members of this family (including Mimulus) were united by the possession of a flower type referred to as a 'scroph'; examples of plants with scroph flowers that may be familiar to you include snapdragons or foxgloves. Characteristic features of a scroph include having the calyx and corolla each fused basally. The corolla is hence more-or-less tubular at the base, then divided towards the top into five out-turned lobes corresponding to the petals (usually with two above and three below; the flower is therefore zygomorphic or bilaterally symmetrical). This flower type is primarily adapted to pollination by insects such as bees that use the lower lobe (or lip) as a 'landing ramp' when visiting the flower. After pollination, the flower develops into a dehiscent, many-seeded capsule. The advent of molecular phylogenetic analysis has established, however, that scroph-flowered plants belong to several lineages within the order Lamiales; the scroph has apparently evolved (and been lost) on a number of occasions. As a result, Mimulus is now placed in a separate family Phrymaceae with a handful of small, closely related genera.

Muskflower Erythranthe moschata, copyright Nick Moyes.


Mimulus was divided into two subgenera and ten sections by Grant (1924); with minor modifications, her system remained in place until recently. The two subgenera, Synplacus (or Mimulus proper) and Schizoplacus, were recognised based on whether the flower's placenta was united or divided, respectively. Four of Grant's sections were placed in the subgenus Mimulus; one of these was Paradanthus. Grant's system was not entirely phylogenetic as we would understand the term today: she did provide a diagram of suggested relationships between the sections but it did not cleanly separate the two subgenera. The section Paradanthus, in particular, was explicitly established as a convenient holding-place for a number of "small closely allied associations which, however, were not sufficiently distinct to warrant being placed in sections by themselves". Most had relatively unspecialised flowers, mostly (but not always) with funnel-shaped corollas and more or less equal lobes. Grant also somewhat unceremoniously dumped the majority of non-American Mimulus species into Paradanthus. She confessed that this section was "a collection of groups not necessarily related to one another and in all probability most of them have been derived from members of the other sections".

Phak taptao Mimulus orbicularis, one of the few true Mimulus species under the system of Barker et al. (2012), from here.


It therefore came as no surprise whatsoever when later phylogenetic analyses did not uphold the section Paradanthus as monophyletic. Instead, the primary division within Mimulus found by Beardsley & Olmstead (2002) was between a clade centred on western North America and one containing the majority of species from elsewhere in the world, with the Paradanthus species falling in either clade depending on their distribution (many of Grant's other sections, in contrast, do correspond to monophyletic groups). Perhaps more unexpected was the finding that Mimulus as a whole was not monophyletic. Instead, other genera of Phrymaceae were nested in Mimulus, including Phryma, a genus of one or two species found in eastern North America and eastern Asia in which the fruit is a single-seeded achene instead of a multi-seeded capsule, and Leucocarpus, a Central American genus in which the fruit is a fleshy berry.

The non-monophyly of Mimulus raised the question of whether these other genera should be subsumed within a broadened Mimulus (in which case the genus Mimulus and the family Phrymaceae would potentially become identical in content). An alternative tack was proposed by Barker et al. (2012) who divided the 'traditional' Mimulus into several genera corresponding to monophyletic clades separated by the previously recognised segregate genera. Of the 120 or so original species, only seven remain in the restricted Mimulus (species of Grant's section Paradanthus end up divided between no less than four genera). None of the western North American species remain in Mimulus; instead, species from this region are divided between the genera Diplacus and Erythranthe.

Only time will tell whether this proposed reorganisation will gain acceptance. I can see there being a lot of resistance to the idea that many of the most familiar 'Mimulus' species should no longer be included in Mimulus, particularly in non-academic circles. Nobody likes being made a monkey by monkeyflowers.

REFERENCES

Barker, W. R., G. L. Nesom, P. M. Beardsley & N. S. Fraga. 2012. A taxonomic conspectus of Phrymaceae: a narrowed circumscription for Mimulus, new and resurrected genera, and new names and combinations. Phytoneuron 2012-39: 1–60.

Beardsley, P. M., & R. G. Olmstead. 2002. Redefining Phrymaceae: the placement of Mimulus, tribe Mimuleae, and Phryma. American Journal of Botany 89 (7): 1093–1102.

Grant, A. L. 1924. A monograph of the genus Mimulus. Annals of the Missouri Botanical Garden 11 (2–3): 99–388.

All the Skinks of the Rainbow

Breeding male southern rainbow skink Carlia tetradactyla, copyright Will Brown.


Australia is home to a diverse and distinctive array of reptiles, most of which are unique to the continent. Perhaps the most famous of these are its venomous snakes and gigantic crocodiles, but the continent also possesses its fair share of lizards. Among these are the subjects of today's post, the rainbow skinks of the genus Carlia.

Carlia is primarily a genus of the north of Australia, particularly northern Queensland. They are moderately-sized skinks, with a snout-to-vent length of up to seven centimetres (indicating a total length of about half a foot). The vernacular name 'rainbow skink' refers to the bright colours, red, green, blue and/or black, exhibited by males of this genus during the breeding season. Females (and non-breeding males) are duller in coloration and commonly have a white stripe along the side of the body (Dolman & Hugall 2008). Only one of the more than twenty Australian species, the southern rainbow skink C. tetradactyla, is found in the southern half of the continent (specifically in a band from southernmost Queensland to northern Victoria). More than a dozen other species are found in New Guinea and neighbouring islands of eastern Indonesia; one species, C. peronii, is found on the island of Timor. Many Carlia species are difficult to distinguish without close examination and new ones continue to be described on a regular basis.

Closed-litter rainbow skink Carlia longipes (perhaps a non-displaying male?), copyright Greg Schechter.


Carlia can be easily distinguished from most other skink genera in the region by counting the toes, of which there are four on the forefoot and five on the hind foot (Storr 1974). Some authors have included all such Australo-Papuan skinks in this genus, but following a molecular phylogenetic analysis Dolman & Hugall (2008) recognised three genera of four-toed skinks in Australia: Carlia and the two smaller genera Lygisaurus and Liburnascincus. Lygisaurus species are generally more slender than Carlia and often have smaller legs. Liburnascincus includes three species of large skinks with sprawling legs found living around rocks. Both these genera lack the contrast in coloration between the sexes found in Carlia; at most, male Lygisaurus will become reddish around the head or tail.

Male rainbow skinks maintain territories from which they will vigorously exclude other males; a male may hold the same territory for several years (Langkilde et al 2004). Breeding males display themselves by flattening the body and tilting to one side, in order to optimise their apparent size and strikingness. Of the two Carlia species for which behaviour has been studied in detail, the black-throated rainbow skink C. rostralis is most likely to perform this display to other males, presumably as an act of intimidation. The lined rainbow skink C. jarnoldae, on the other hand, is more likely to perform its tilting display in the presence of a female (Langkilde et al. 2003). They may also display in this way towards predators, presumably to make themselves appear less digestible. Other displays performed by rainbow skinks include moving the head to display the coloration of the throat, or flicking the tail (this latter appears to be primarily a defensive display, being performed in the presence of predators or encroaching males). Langkilde et al. (2003) also found rainbow skinks to 'play dead' when captured, a rare behaviour in skinks (though known from other lizards).

Admiralty brown skink Carlia ailanpalai, from Lardner et al. (2013). This species lacks the sexual dichromatism of other Carlia species.


Rainbow skinks are also present in islands of western Micronesia, where they have been introduced by human activity. They were first recognised in Micronesia in the early 1960s, subsequently becoming abundant and seemingly supplanting native skinks in more disturbed areas. On Guam, they are also believed to have played a part in the spread of the brown tree snake Boiga irregularis: the healthy population of introduced skinks provided a reliable food source for the introduced snake. Because of the aforementioned difficulties in Carlia taxonomy, the exact identity of Guam's 'curious skink' was uncertain for many years though it was certainly part of the New Guinean 'Carlia fusca' group. A molecular analysis of Micronesian Carlia by Austin et al. (2011) confirmed that the species in question was the Admiralty brown skink C. ailanpalai but also found that skinks from different parts of Micronesia where connected genetically to different parts of the New Guinean archipelago. Rainbow skinks from Guam, for instance, were related to populations on Manus and New Ireland, whereas Palau skinks were more closely akin to New Britain residents. Austin et al. noted a correlation between the sources of each of the inferred separate invasions in Guam, Palau and the Northern Marianas and troop movements during World War II. While machinery and equipment was being transported to Micronesia for use in the Pacific theatre of war, skinks were apparently hitching rides. Alternatively, some could have reached Micronesia with equipment being returned to permanent military bases from New Guinea after the war's close. The resulting seed populations would have presumably been small, explaining why it took another twenty years or so before they were noticed.

REFERENCES

Austin, C. C., E. N. Rittmeyer, L. A. Oliver, J. O. Andermann, G. R. Zug, G. H. Rodda & N. D. Jackson. 2011. The bioinvasion of Guam: inferring geographic origin, pace, pattern and process of an invasive lizard (Carlia) in the Pacific using multi-locus genomic data. Biol. Invasions 13: 1951–1967.

Dolman, G., & A. F. Hugall. 2008. Combined mitochondrial and nuclear data enhance resolution of a rapid radiation of Australian rainbow skinks (Scincidae: Carlia). Molecular Phylogenetics and Evolution 49: 782–794.

Langkilde, T., L. Schwarzkopf & R. Alford. 2003. An ethogram for adult male rainbow skinks, Carlia jarnoldae. Herpetological Journal 13: 141–148.

Langkilde, T., L. Schwarzkopf & R. A. Alford. 2004. The function of tail displays in male rainbow skinks (Carlia jarnoldae). Journal of Herpetology 39 (2): 325–328.

Storr, G. M. 1974. The genus Carlia (Lacertilia: Scincidae) in Western Australia and Northern Territory. Records of the Western Australian Museum 3 (2): 151–165.

Typhloesus: The 'Alien Goldfish' of Bear Gulch

The following post first appeared on May 19th on my Patreon page, available only to subscribers. If you would like to show your support for Catalogue of Organisms, and potentially gain access to future Patreon-exclusive content, please become a subscriber for as little as $1 a month!

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Above: Typhloesus wellsi, external appearance, and the same with major anatomical details shown. Based on figure of specimen U.M. 6027 in Conway Morris (1990).


Recently, the interwebs became all agog at the suggestion that the hitherto-mysterious Carboniferous fossil Tullimonstrum gregarium could possibly represent a vertebrate, distantly related to modern lampreys. But there are other fossil animals whose relationships remain inexplicable and one of these is another child of the Carboniferous, the so-called 'alien goldfish' Typhloesus wellsi.

When I announced my plan to write this post, I referred to Typhloesus as coming from Mazon Creek, the fossil deposit from whence comes Tullimonstrum. This, as it turns out, was a mistake on my part: Typhloesus actually comes from a different deposit, Bear Gulch in Montana. Bear Gulch is perhaps most famous for its fossils of early fish, such as symmoriiform sharks (the ones with the weird shoebrush headgear) and heavily armoured palaeoniscoids. Indeed, compared to other Carboniferous deposits, Bear Gulch is unusual for its preponderance of swimming rather than benthic animals. Typhloesus is represented in the deposit by a number of individuals in varying states of preservation.

In some ways, Typhloesus is more famous for what it is not than for what it is. It was one of the first body fossils found in association with conodonts, minute teeth-like fossils that had been subject to much speculation as to what sort of animal they might have come from. Initially, there was much excitement that the conodont animal may have finally been found, but it did not take very long for questions to be raised about the nature of this association. By the time Typhloesus was reviewed in detail by Conway Morris (1990), it was clear that the conodont fossils had been preserved within its gut, not its mouth, and Typhloesus was a conodont-eater rather than a conodont-bearer (it has since been found that conodont animals were eel-like chordates).

Externally, Typhloesus was a fairly simple, cigar-shaped animal, with its body laterally compressed and higher than wide. It grew to a decent size, with the largest specimens being a little under ten centimetres in length. There is no sign of eyes or any other prominent sensory structure, and so far as is known the external skin or cuticle was smooth and unornamented. The most distinctive external feature is a large 'tail-fin' at the rear. This fin was supported by an arrangement of criss-crossing rods or fibres, and would have been fairly stiff in life. Another pair of folds or fins ran along most of the underside of the body with a noticeable gap towards the rear. Typhloesus probably swam in a not dissimilar manner to an active modern fish, using sweeps of the tail-fin to provide thrust; the ventral fins may have provided stability and steerage. The visible line of the foregut comes to a halt slightly before reaching the front of the body, and it seems that the mouth would have been slightly ventral and contained within a 'hood'. Though its overall conformation and known gut-contents (most commonly conodonts, but sometimes worm jaws or fish scales) suggest an active predator, I am at a loss to understand how it located its prey without eyes. Perhaps the hood contained some sort of chemical sensors in life.

When it was first found, it was thought that its overall appearance suggested a relationship of Typhloesus to the chordates. However, Conway Morris (1990) saw its internal anatomy as incompatible with this view. Fossils of this animal show a narrow foregut leading into a voluminous, sack-like midgut. Below the midgut is a pair of dark, disc-shaped organs showing a concentration of iron deposits called the ferrodiscus; though a striking element of all Typhloesus fossils, the function of this structure is completely unknown. What Conway Morris found conspicuous by its absence, however, was an anus: there appeared to be no sign of any gut structures in the rear of the animal. The gut was a blind sack, with the only way out being the same as the way in. The absence of a through-gut would be unprecedented in a chordate, or indeed in many animals except jellyfish or flatworms. Conway Morris was also unable to identify other chordate-specific structures such as muscle-blocks, gill openings or a notochord; though he confessed that the first two might be obscured by the vagaries of decay, he felt that the third at least should have left more of a sign. It was this combination of an overall fish-like appearance with a very un-fish-like anatomy that led Conway Morris to later dub Typhloesus the 'alien goldfish'.

With the exclusion of a chordate connection as a possibility, Conway Morris found himself at a loss as to just where Typhloesus fitted into animal evolutionary history. Finned swimmers are also known among molluscs, nemerteans and chaetognaths, but Typhloesus is no more like any of these than it is like a chordate. Conway Morris felt himself compelled to declare the affinities of Typhloesus completely unknown. Personally, though, I can't help wondering if the 'alien goldfish' might not be so alien after all: maybe it is a chordate. The overall similarities of Typhloesus to a chordate are remarkable; in particular, the hooded mouth is very similar to that of a lancelet. But what about that missing anus, you say? Where is that all-important butthole? To which I respond, is it really missing? Looking at the figures of Typhloesus fossils in Conway Morris (1990) (which is of course a poor competitor to Conway Morris' ability to look directly at the fossils themselves), I see that directly below the midgut is the ferrodiscus. And directly below that is a streak running between the ferrodiscus and the animal's venter. Conway Morris saw this structure (which he called the 'midventral strand') as some sort of connection between the ferrodiscus and the exterior, but could it in fact be the tail-end of the reargut? It is certainly not unknown for the anus in chordates to not be right at the very rear of the animal; in some fish (such as the scorpionfish-like Aploactinidae) it is even moved so far forward as to be almost underneath the head. And the missing notochord? Considering that despite the presence of specimens numbering in the thousands, a notochord was only announced in Tullimonstrum within the past year, maybe on that front Typhloesus could reward a second look.

REFERENCE

Conway Morris, S. 1990. Typhloesus wellsi (Melton and Scott, 1973), a bizarre metazoan from the Carboniferous of Montana, U.S.A. Philosophical Transactions of the Royal Society of London Series B 327: 595–624.

Zemacies: A Toothless Wonder

The Recent species Zemacies queenslandica, photographed by Jan Delsing.


What makes an organism a 'living fossil'? The phrase is one that has been thrown about a bit over the years but whose actual definition can be ambiguous. Many people use it to refer to a species that is supposedly little changed from its distant ancestors. An alternative interpretation, however, and I suspect the phrase's original inspiration, would be something that was first discovered as a fossil, only to be found alive at a later date. The coelacanth, of course, would be the textbook example of such a case (without necessarily being a good example). But you might be surprised at some of the animals that could be called a 'living fossil' under this definition. The white-tailed deer would be one, as would the bush dog of South America. And so would the subject of today's post.

Zemacies is a genus of conoid gastropods known from the south-west Pacific. It is relatively large as conoids go, with some growing over three inches in length. Shells are a slender, fusiform shape, often with prominent nodules on the whorls. The first known species, Z. elatior, was described from the Miocene of New Zealand. Over time, additional species were described from New Zealand and Australia, extending the age range of the genus from the Palaeocene to the Pliocene (Powell 1969). It wasn't until 2001, however, that living species of Zemacies were recognised in the deep sea around New Caledonia and Queensland.

Figure from Fedosov & Kantor (2008) showing appearance of pyriform organ in foregut of Zemacies excelsa (left), with cross-section of organ to show internal structure (right). Abbreviations: bl, bulb-like structure; gt, glandular tissue; ms, muscles; sgp, semicircular glandular pad; tf, tall folds underlain by glandular tissue; tn, tentacles.


The discovery of living specimens (or, at least, living until the time of their collection) led to the revelation that Zemacies was a very intriguing genus, in a way that would have probably never been guessed from fossil material alone. As has been described previously, one of the great innovations of conoids was the modification of the radula into a system for the injection of paralysing toxins. When researchers investigated the soft anatomy of Zemacies excelsa, however, they discovered that it turned away from this trend. Zemacies has lost both the radula and its associated poison glands, as well as the associated proboscis. In their place, one side of the foregut has grown a pear-shaped outgrowth, referred to as the pyriform organ, that is covered with glandular tentacles (Fedosov & Kantor 2008). This structure is so unusual that its initial discovery lead to the proposal of a new subfamily to separate Zemacies from all other conoids (it has since been placed by Bouchet et al., 2011, as a distinctive member of the family Borsoniidae).

Unfortunately, the bathyal habitat of living Zemacies means that we as yet have no idea of its preferred prey and consequently little idea of how the pyriform organ is used when feeding. The internal cavity of the pyriform organ contains an array of longitudinal muscles, suggesting that it can be extended out the front of the animal in place of the usual proboscis. The tentacles may function to grasp or adhere to the prey, and/or the glandular tissue underlying them may secrete toxins or digestive enzymes, while the action of the pyriform organ against the foregut wall during withdrawal of the prey may serve to crush it (I wonder what the efficacy of this arrangement may be against something with a strong but not calcified cuticle, such as a deep-water crustacean). A similar foregut structure (also associated with loss of the radula and proboscis) has been identified in another conoid genus, Horaiclavus, though phylogenetic analysis of the Conoidea indicates that the two genera almost certainly evolved these structures independently. Horaiclavus also differs from Zemacies in that the muscular foregut outgrowth lacks any associated glandular tissue and is presumably entirely mechanical in its action (Fedosov & Kantor 2008). Perhaps one day someone will finally observe one of these deep-sea genera in their native habitat and provide us with a solution to the mystery of their life styles.

REFERENCES

Bouchet, P., Y. I. Kantor, A. Sysoev & N. Puillandre. 2011. A new operational classification of the Conoidea (Gastropoda). Journal of Molluscan Studies 77: 273–308.

Fedosov, A., &. Y. Kantor. 2008. Toxoglossan gastropods of the subfamily Crassispirinae (Turridae) lacking a radula, and discussion of the status of the subfamily Zemaciinae. Journal of Molluscan Studies 74: 27–35.

Powell, A. W. B. 1969. The family Turridae in the Indo-Pacific. Part 2. The subfamily Turriculinae. Indo-Pacific Mollusca 2 (10): 215–415.

Click! Goes the Beetle

The click beetle Athous haemorrhoidalis, copyright André Karwath.


There have been occasions when I've found myself complaining of the difficulty of recognising particular beetle families. It almost goes without saying, however, that this difficulty does not apply across the board. Whereas some beetle families may indeed be generically small and brown, there are others that are almost instantly recognisable. One such family, for the most part, is the click beetles of the Elateridae.

Click beetles are a cosmopolitan family with well over 900 known species. The majority of click beetles adhere to a consistent basic form: they have elongate, slender bodies, often with distinct longitudinal grooves running down the elytra. The front part of the body (the prothorax) is relatively large, and more or less acutely pointed at the back corners. Between the prothorax and the next part of the body (the mesothorax), the body is strongly constricted top to bottom so that the beetle can be flexibly bent. This distinguishes the Elateridae from most other beetle families (except for a few close relatives), and this is where the 'click' comes in. If the beetle finds itself lying on its back (or wishes to escape from a threat), it is able to arch itself so that the thoracic junction is lifted upwards. On the rear margin of the underside of the prothorax is a notched peg that sits against the front of the mesothorax, holding the two sections apart like the stick in a cartoon crocodile's jaws. This builds up a lot of potential energy that the beetle is able to hold in place until it suddenly releases the peg, which then slams back into a ventral groove at the front of the mesothorax with an audible 'click'. The effect of this sudden release of energy, followed by an equally sudden stop, is to cause the beetle to rapidly bend forwards, much in the manner of a person folding over as they receive a powerful punch to the gut. This self-inflicted gut punch results in the beetle being flung in the air, somersaulting to a hopeful landing on its feet. Evans (1972) conducted an analysis of the click-jumping of the elaterid Athous haemorrhoidalis, which is about a centimetre-and-a-half in length, and found that it could be lifted over a foot above the ground, tumbling several times over the course of a single jump. He calculated that during the jump it could be subjected to an acceleration of up to 3800 ms-2, equivalent to a force of 380 G, one of the highest acceleration forces known in the animal kingdom (a human subjected to a similar force would soon end up like a satchel of instant pudding). Ribak & Weihs (2011) subsequently found, however, that the beetle has no actual control over its movements once flung and is just as likely to end up flat on its back again as the right way up, requiring it to attempt a second jump.

Fire beetle Pyrophorus sp., copyright Andreas Kay.


Adult click-beetles feed on the juices from plants but larvae may be more diverse in habits, including phytophagous, saprophagous or predaceous forms. Some burrowing phytophagous larvae, known as wireworms, can be notable pests, feeding on the roots and buried seeds of crop plants. Predatory forms, on the other hand, can be quite beneficial: the eyed elater Alaus oculatus of North America, for instance, has larvae that feed on the larvae of other beetles burrowing in wood. The Elateridae also include the fire beetles of South and southern North America, belonging to the tribe Pyrophorini. These beetles have a pair of large bioluminescent spots on their back at the rear of the prothorax. The larvae and even the eggs of fire beetles are similarly bioluminescent, and my guess is that the bioluminescence provides some sort of defense against predation.

Larva of Drilus on a snail, copyright Cécile Bassaglia.


Not all elaterids match the family's standard morphology, however. An analysis of elaterid phylogeny by Kundrata & Bocak (2011) found that a few groups that had previously been classified as separate families were in fact derived subgroups of the Elateridae. The 'Cebrionidae' (possibly a polyphyletic assemblage in the elaterid subfamily Elaterinae) are softer-bodied than other elaterids and lack the ability to click (presumably because their cuticle does not provide the resistance for a clicking mechanism to work). Female cebrionids may be flightless, with reduced wings and/or elytra. Even more dramatically altered are the females of the tribe Drilini (previously recognised as the Drilidae), the false firely beetles, which are larviform in appearance with only the head metamorphosing to an adult appearance. The larvae of Drilini feed on snails, and have a lifestyle that straddles the boundary between predator and parasite. Rather than killing and eating the prey snail immediately, they crawl into its shell and feed on it slowly; it may take several days for the larva's victim to actually meet its demise.

REFERENCES

Evans, M. E. G. 1972. The jump of the click beetle (Coleoptera, Elateridae)—a preliminary study. Journal of Zoology 167: 319–336.

Kundrata, R., & L. Bocak. 2011. The phylogeny and limits of Elateridae (Insecta, Coleoptera): is there a common tendency of click beetles to soft-bodiedness and neoteny? Zoologica Scripta 40: 364–378.

Ribak, G., & D. Weihs. 2011. Jumping without using legs: the jump of the click-beetles (Elateridae) is morphologically constrained. PLoS ONE 6 (6): e20871. doi:10.1371/journal.pone.0020871.