Field of Science

Ami-, Ami-termes

Soldier of Amitermes, copyright Alexander Yelich.


I've referred before to my enthusiasm for termites, those wonderfully weird sociable scions of the cockroach clan. For today's post, I'm looking at one of the larger and most widespread termite genera, Amitermes.

There are over 100 species of Amitermes found in tropical regions around the world, though they are most diverse in Africa and Australia. They are members of the so-called 'higher termites' of the Termitidae, those termites with a gut microbiota dominated by bacteria rather than protozoa. Soldiers of Amitermes have long sickle-shaped mandibles with a more-or-less well-developed tooth on each mandible; these mandibles are used to slash at perceived threats, the effect of this direct attack being presumably exacerbated by offensive chemicals that seep from the fontanelle, a pore on the front of the head capsule. Members of the genus are diverse in habits: some build sizable mounds above ground whereas others live in small colonies in underground tunnels. Some show a distinct preference for living in the nests of other termites, either moving into abandoned mounds after the original owners have perished or squatting in some overlooked corner of an active nest. Nests may be built directly around a food supply, or workers may go out to forage for food to bring home. In the latter case, the workers may construct a covered tunnel for themselves as they go; these trails may commonly be seen running along the ground in areas where such termites are abundant. Many Amitermes species feed on wood but they may also take other vegetable matter such as grass. A number of species feed on the dung of herbivorous mammals such as cattle or horses (Gay 1968), digesting parts of the consumed plant matter that the original feeder could not. One West African species, A. evuncifer, is a significant pest of crops, attacking root vegetables or the roots of young trees. Hill (1942) noted that mound-building Amitermes could present difficulties beyond just their feeding habits, explaining that "The frequent destruction of nest of [this genus] is perhaps the most important task of those employed in the maintenance of certain northern aircraft landing grounds, for the removal of the original nest almost invariably is followed the erection of another of a size and consistency that contributed a potentially dangerous obstacle to landing or rising aircraft".

Magnetic termite mounds, copyright David King.


Perhaps the most famous members of this genus are the 'magnetic termites' of northern Australia. These are three species that build mounds that, instead of being conical or globular like the mounds of other species, are long and narrow, almost blade-like. Even more strikingly, they are lined up almost exactly along a North-South axis, with at most a 10° deviation. Experimental alterations of such mounds indicate that the termites are indeed sensitive to the direction of magnetic fields though other factors such as local climatic conditions may also play a part. The shape of magnetic mounds is usually interpreted as an adaptation for temperature regulation: at the cooler ends of the day, the mound is receiving the full effects of the sun but during the hot midday only the thin upper edge is in the line of the light. However elegant an explanation this may seem, however, it overlooks the detail that a more standard globular mound is actually better for heat regulation overall. Round mounds have a much lower surface area-volume ratio and hence a lower rate of heat diffusion. Blade-shaped mounds may absorb heat quickly in the morning but they also lose heat quickly at night. An alternative explanation for the mounds' shape may lie in where magnetic mounds are found. It is worth noting that only one of the Amitermes species concerned, A. meridionalis, is an obligate constructor of blade-shaped mounds; the other two species, A. laurensis and A. vitiosus, may build either conical or blade mounds depending on local conditions. Magnetic mounds are constructed on flat flood plains, so the termites living inside them build up stores of grass to provide food when flood-waters prevent them from foraging outside the nest. By allowing better air flow within the nest than a conical mound, the blade-shaped mounds allow food stores to remain edible for longer, reducing the risk of them expiring before flood-waters recede (Korb 2011). Temperature regulation is still the best explanation for the regular orientation, of course, but is probably not the primary cause for the mound form overall.

Drepanotermes rubriceps soldiers around a nest entrance, copyright Lochman Transparencies.


Phylogenetic analysis of the termites by Inward et al. (2007) indicated that the genus Amitermes as currently recognised is probably not monophyletic, being paraphyletic to at least the Australian genus Drepanotermes. Members of this latter genus are grass-feeders, particularly on the hard Triodia (spinifex) grasses that dominate large parts of arid Australia (and which few animals without the super-charged termite digestive system can eat). In my experience, Drepanotermes are one of the few termite genera that can be reasonably easily recognised from the workers alone, which are noticeably longer in the legs than other termites. I've often seen Drepanotermes workers out foraging at night; the entrance to the underground nest (a simple hole) can usually be found nearby. The soldiers do not usually emerge from the nest, but a group of them will sit in the entrance hole with their heads poking out to provide defence. When collecting specimens, I've found that the challenge is to move fast enough to grab a soldier before it zips back into the tunnel, escaping your grasp.

REFERENCES

Gay, F. J. 1968. A contribution to the systematics of the genus Amitermes (Isoptera: Termitidae) in Australia. Australian Journal of Zoology 16: 405–457.

Inward, D. J. G., A. P. Vogler & P. Eggleton. 2007. A comprehensive phylogenetic analysis of termites (Isoptera) illuminates key aspects of their evolutionary biology. Molecular Phylogenetics and Evolution 44: 953–967.

Korb, J. 2011. Termite mound architecture, from function to construction. In: Bignell, D. E., et al. (eds) Biology of Termites: A Modern Synthesis pp. 349–373. Springer.

First Supporter!

To be continued...


A big thank you to Paul Selden, who just became my first Patreon supporter! Remember, if you want to support Catalogue of Organisms, you can do so by signing up to my Patreon. Alternatively, because I've been asked about the possibility of one-off donations, I've added a Paypal donate button in the panel to the right. If the reader count is to be believed, I've got a bit under 300 readers at the moment; if each of you gave just $5.00 a month, I could just about make this a full time career! And in the meantime, thank you all for reading!

The Pseudoperisporiaceae: Fungi on Leaves, Fungi on Fungi

Leaves of savin juniper Juniperus sabina, with fruiting bodies of the pseudoperisporiaceous fungus Chaetoscutula juniperi visible as black spots, from Tian et al. (2014). Scale bar = 1 mm.


As has been noted on this site before, the world of microscopic fungi includes a bewildering array of species that may never come to your attention but are in fact all around you. These organisms quietly live out their lives, often serving to break down the refuse that larger organisms such as plants shed over the course of their lives. Sometimes they are not so patient, instead attacking the plant while it is still green and growing. The subjects of today's post, the Pseudoperisporiaceae, include examples of both.

The Pseudoperisporiaceae are a widespread group of minute fungi that are most diverse in the tropical parts of the world. Because of their small size and lack (so far as is known) of significant economic effects, they are rarely noticed and little studied. However, they are by no means rare; in fact, one species in the family, Raciborskiomyces longisetosum, has been shown by molecular studies to be a major component of the soil community (e.g. Valinsky et al. 2002). The majority of members of the family grow on the leaves of plants, either as saprobes on leaf litter or as parasites on live plants. Alternatively, they may be parasites of other fungi, particularly sooty moulds. The more or less globular fruiting bodies (which are at most about 200 µm in size) are superficial on the surface of the host substrate, and are surrounded by a brown mycelium (mass of vegetative strands). Other distinctive features of the family include fusoid-ellipsoid ascospores (i.e. sexually produced reproductive spores) that are minutely warty and have rounded, subacute ends (Tian et al. 2014).

Closer view of fruiting body of Wentiomyces, from Wilk et al. (2014). Note the ostiole towards the lower left, surrounded by bilobed setae. Scale bar = 20 µm.


Pseudoperisporiaceae belong to the class of fungi known as the Dothideomycetes, a major subdivision of the Ascomycetes. Dothideomycetes include the majority of what used to be called the loculoascomycetes, so-called because of the way their fruiting bodies grow. A distinctive hollow, or locule, forms in the vegetative mycelium of the parent fungus, and the fruiting body develops within this hollow. In most Dothideomycetes (including the Pseudoperisporiaceae), the resulting fruiting body is almost entirely closed with a single opening (the ostiole) at the top through which the spores are released. Pseudoperisporiaceae also resemble other Dothideomycetes in having fissitunicate asci: that is, the asci (which are finger-shaped structures inside the fruiting body in which spores are formed) have a double-layered wall, with the outer layer being more rigid than the inner. As the inner layer swells with moisture, it causes the outer layer to split and the spores end up being expelled from the end of the ascus. Dothideomycetes are not the only fungi to show locular development, hence the dropping of loculoascomycetes as a formal group; the Chaetothyriomycetidae also grow their fruiting bodies from locules (Hyde et al. 2013).

The exact relationships of the Pseudoperisporiaceae with other Dothideomycetes remain uncertain; in their review of dothideomycete families, Hyde et al. (2013) left Pseudoperisporiaceae unassigned to an order within the class. Indeed, it is unclear to what extent Pseudoperisporiaceae are even related to themselves. Few members of the family have been studied from a molecular perspective, and those few that have been have not come out in the same place in the dothideomycete family tree. At least one supposed member of the family, the genus Epibryon, turns out not to even be a dothideomycete but is instead a chaetothyriomycete (Stenroos et al. 2010). Not for the first time on this site, I find that a seemingly simple outer morphology may be disguising a much greater diversity.

REFERENCES

Hyde, K. D., E. B. G. Jones, J.-K. Liu, H. Ariyawansa, E. Boehm, S. Boonmee, U. Braun, P. Chomnunti, P. W. Crous, D.-Q. Dai, P. Diederich, A. Dissanayake, M. Doilom, F. Doveri, S. Hongsanan, R. Jayawardena, J. D. Lawrey, Y.-M. Li, Y.-X. Liu, R. Lücking, J. Monkai, L. Muggia, M. P. Nelsen, K.-L. Pang, R. Phookamsak, I. C. Senanayake, C. A. Shearer, S. Suetrong, K. Tanaka, K. M. Thambugala, N. N. Wijayawardene, S. Wikee, H.-X. Wu, Y. Zhang, B. Aguirre-Hudson, S. A. Alias, A. Aptroot, A. H. Bahkali, J. L. Bezerra, D. J. Bhat, E. Camporesi, E. Chukeatirote, C. Gueidan, D. L. Hawksworth, K. Hirayama, S. De Hoog, J.-C. Kang, K. Knudsen, W.-J. Li, X.-H. Li, Z.-Y. Liu, A. Mapook, E. H. C. McKenzie, A. N. Miller, P. E. Mortimer, A. J. L. Phillips, H. A. Raja, C. Scheuer, F. Schumm, J. E. Taylor, Q. Tian, S. Tibpromma, D. N. Wanasinghe, Y. Wang, J.-C. Xu, S. Yacharoen, J.-Y. Yan & M. Zhang. 2013. Families of Dothideomyctes. Fungal Diversity 63: 1–313.

Stenroos, S., T. Laukka, S. Huhtinen, P. Döbbeler, L. Myllys, K. Syrjänen & Jaakko Hyvönen. 2010. Multiple origins of symbioses between ascomycetes and bryophytes suggested by a five-gene phylogeny. Cladistics 26: 281–300.

Tian, Q., P. Chomnunti, J. D. Bhat, S. A. Alias, P. E. Mortimer & K. D. Hyde. 2014. Towards a natural classification of Dothideomycetes 5: The genera Ascostratum, Chaetoscutula, Ceratocarpia, Cystocoleus, and Colensoniella (Dothideomycetes incertae sedis). Phytotaxa 176 (1): 42–54.

Valinsky, L., G. Della Vedova, T. Jiang, & J. Borneman. 2002. Oligonucleotide fingerprinting of rRNA genes for analysis of fungal community composition. Applied and Environmental Microbiology 68 (12): 5999–6004.

Wilk, M., J. Pawłowska & M. Wrzosek. 2014. Wentiomyces sp. from plant litter on poor fen in northeastern Poland. Acta Mycologica 49 (2): 237–247.

Support Catalogue of Organisms!


Hi all. I've been writing posts here at Catalogue of Organisms for nearly nine years (nine years come Friday week, in fact). And in that time, I hope that you've been enjoying reading what I've had to say as much as I've enjoyed writing it. I've found some wonderful things in the course of writing this blog, and I've had a great time sharing them with you all. We've debated whether you can make a pillar out of a mat, contemplated whether wasps can have venomous claws, even seen massive reefs produced by single-celled organisms! Unfortunately...

Excuse me a moment, where did I put that violin? Ah, here we go...

Some of you may be aware that, in late 2014, I was made redundant as my university lost the contract that I was working on. Since then, regular employment has proven a little hard to come by. I worked for several months as a casual lab technician, but that has also since come more or less to a close. A combination of factors, including a strong economic downturn in this part of the world, a high level of competition for available positions, and just plain bad luck, have not made things easy.

With that said, I've taken the step of signing up for Patreon. If you would like to show your support for Catalogue of Organisms, and help to keep this site a going prospect, then please chuck a couple of bucks my way. And if enough people do so, then I have some rewards planned: I'll be writing a series of posts on the Patreon page that will be readable only by Patreon supporters. These posts will be a little different from the usual ones here at CoO, in that they'll focus in on an individual species. The first post, which I'll put up if we reach the $100 mark, will be on the so-called 'alien goldfish' of Mazon Creek, Typhloesus wellsi. The current plan is that a new post will appear for every $100 I earn from Patreon. If anyone has suggestions for anything they'd like to see further, then please let me know!

These exclusive posts will be on the Patreon page for a month, and then they'll be released into the wild on the main page here, which will continue to be free to all comers. I have no plans on stopping writing here any time soon; probably nothing short of a major coronary will stop that. And whatever happens, I'd like to thank you again for all the support you've shown me over the years. Thank you!

Bitubulites: Yeah, Nach

Several months back, I published a post on a decidedly obscure tubular fossil by the name of Serpularia: once described, completely forgotten. Is it possible to top that for inconsequentiality?

You betcha, because the subject I drew for today's post, Bitubulites irregularis, never even got a sketchy diagram to illustrate it. And once again, we have an early German palaeontologist to thank. In 1820, Ernst Friedrich, Freiherr von Schlotheim, published a book called Die Petrefactenkunde auf ihrem jetzigen Standpunkte durch die Beschreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzenreichs der Vorwelt erläutert, because they don't write book titles like they used to. As far as I can tell, the title basically translates as Got Some Great Fossils Here, Wanna See? As with Münster's Beiträge zur Petrefakten-Kunde that provided the source for the Serpularia post, Schlotheim's publication was basically a description of some of the fossils held in his own collection. His comments on B. irregularis appeared on p. 376, and were as follows:

Bitubulites irregularis.
Aus dem Muschelflötzkalk der Gegend von Weimar.

Einzelne cylinderförmige Stücke, von der Dicke eines mäſsigen Fingers, mit gröſstentheils concaven Durchschnittsflächen, auf welchen sich gewöhnlich ins Dreyeck gestellte kleine Öffnungen zeigen, welche mit durchgehenden Nervenröhren in Verbindung zu stehen scheinen. Äuſserlich ist die Oberfläche fein puncktirt.
Da sich mehrere übereinstimmende Stücke finden, so läſst sich nicht erwarten, daſs wir ein bloſses Naturspiel vor uns hätten. Zuweilen sind auch vier, aber alsdenn noch unregelmäſsiger gestellte Öffnungen, vorhanden. Bis jetzt haben sich, meines Wissens, noch keine ganz vollständigen und recht gut erhaltenen Exemplare aufgefunden.
And I'll be honest, I have very little idea what any of that means, because I don't read German beyond chucking stuff into Google Translate. The genus Bitubulites had established in 1803 by another German scientist, Johann Friedrich Blumenbach, for a different fossil, B. problematicus. Bitubulites problematicus was composed of two small conjoined tubes that Blumenbach illustrated thus:
Schlotheim's B. irregularis was presumably similar to Blumenbach's original; as far as I can work out, each tube was cylindrical and about the thickness of a finger. Small openings down the sides of the main tubes indicated the presence of smaller connecting tubes ("nerve-tubes") between them; the entire outer surface was finely punctate. The second paragraph of Schlotheim's states that he possessed several examples, indicating that the association between the tubes was not a mere accident. I think he says that the tubes were sometimes associated in fours rather than in pairs, but the overall confirmation remained the same. The "Muschelflötzkalk" refers to a Middle Triassic formation; both the two Bitubulites species came from the same formation.

Blumenbach had called his original fossil 'problematicus' because he had little idea what type of animal it represented. Schlotheim was none the wiser, listing Bitubulites among unclassifiable forms with no close analogues in the modern fauna. He did tentatively compare it to a couple of fossil mollusks, such as the straight-shelled cephalopods or the reef-forming hippuritid bivalves. And there Bitubulites lay for over a century, more or less forgotten by all except the most pedantic of cataloguers (ahem...)

In 1962, Walter Häntzschel included Bitubulites in his chapter on problematica for the Treatise on Invertebrate Paleontology. It was tucked away in the end, in a list of "Unrecognized and Unrecognizable "Genera"" that Häntzschel felt largely deserved nothing more than to be cast forever into the outer darkness. Nevertheless, he did suggest a possible identity for Bitubulites: Rhizocorallium, a fossil that can be found in deposits dating from the Cambrian all the way to the present, commonly looking like this (copyright Manuel Flöther):
Rhizocorallium is a trace fossil, a structure created by the activity of some animal and preserved in the geological record. Rhizocorallium takes the form of a U-shaped burrow, with the two arms of the burrow connected by fine cross-lines or fractures referred to as Spreiten (German for "spread"). The Spreiten are the result of the animal digging its burrow further into the substrate, with sediment being taken from the outer side of the tube and packed on the inner side. The burrows often run more or less parallel to what would have been the original surface of the sediment; they may have been primarily dwelling burrows, or they may have been feeding burrows extended as the animal searched for buried organic matter. Rhizocorallium-type burrows were probably made by many different types of animal, such as worms or arthropods, and their presence in a deposit is more indicative of environmental conditions than faunal composition.

At the time that Blumenbach and Schlotheim were writing their books, no-one had yet twigged what these kind of trace fossils were; neither author would have been alone in mistaking a burrow for a body fossil. Many structures that are now recognised as traces were described as fossil algae. It was not until the late 1800s that a Swedish and an American palaeontologist independently noted the similar between a number of these 'algae' and the structures left by marine organisms as they went about their daily life. Even today, this earlier misunderstanding has left its mark in the tradition of referring to particular trace fossils by binomial names, as trace 'genera' and 'species'. Nevertheless, trace fossils often provide us with a window into the past over and above what we can learn from body fossils alone, and they are an invaluable tool in developing a truly rounded understanding of life in ages past.

REFERENCES

Blumenbach, J. F. 1803. Specimen Archaeologicae Telluris terrarumque inprimis Hannoverarum. Henricum Dieterich: Göttingen.

Häntzschel, W. 1962. Trace fossils and problematica. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W177-W245. Geological Society of America, and University of Kansas Press.

Schlotheim, E. F. von. 1820. Die Petrefactenkunde auf ihrem jetzigen Standpunkte durch die Beschreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzenreichs der Vorwelt erläutert. Becker'schen Buchhandlung: Gotha.

Fishes be Crazy


Despite how it may look, there is absolutely nothing wrong with this fish. Butis butis is a moderately sized species of fish (up to about 14 cm in length) widespread in warmer waters around the Indian and western Pacific Oceans. They are found in shallow bays and mangrove swamps, often entering into estuaries and lower reaches of rivers. It is known by a range of vernacular names, including crimson-tipped gudgeon or duckbill sleeper. In the aquarium trade, it often goes by the name of crazy fish, in reference to its distinctive habit of swimming hanging vertically head-down or even swimming upside-down. Its predilection for such unusual angles assists it in remaining concealed from both predators and prey; Ryan (1981) noted that the addition of anaesthetic for collection purposes to a pool resulted in the sudden appearance of several specimens of which no sign had been previously seen. Their camouflage abilities are further enhanced by the ability to change colour to a certain degree, from pale to dark. Butis butis are ambush predators of smaller fish and invertebrates that they engulf in their broad jaws with rapid lunges.

Drawing of Butis butis, coloured from an original in Herre (1927) by M. L. Nievera.


The genus Butis belongs among the gobies, a somewhat notorious group of fish from a taxonomic perspective. In the words of the South African ichthyologist J. L. B. Smith, "The Gobioid fishes are one of the major trials of ichthyologists, and when general regional collections are worked up, these fishes tend to be pushed aside, and are apparently often identified with some impatience by those not specially interested" (Smith 1958). This notoriety is mostly due to the small size of many gobies, together with a tendency to the reduction of diagnostic features. Earlier authors classified Butis within the Eleotridae, a group of gobies (commonly known as sleepers, presumably due to their benthic habits) distinguished by having the pelvic fins separate from each other (in other gobies, the pelvic fins are united into a ventral sucker or disc). This, however, is a primitive feature only, and more recent molecular phylogenies have confirmed the paraphyly of Eleotridae in the broad sense. As a result, Butis and some of its nearest and dearest have been separated out into a separate family Butidae (Thacker 2011). However, while the separation of Eleotridae and Butidae seems to be fairly widely accepted, the two groups are still not clearly defined morphologically. Characteristic features of Butis relative to other gobies include (among others) the presence of a complete covering of scales, and a bony ridge above each eye (Smith 1958). In a number of species of the genus, including B. butis, the head is low and long, and the lower jaw distinctly protruding; however, the mudsleeper B. koilomatodon has a shorter, rounder head (this latter species, though originally native to a similar range to B. butis, has become invasive in more recent years in west Africa and Brazil, presumably carried in ballast water). Butis butis differs from other species in the genus in having small secondary scales at the base of most scales on the trunk, and the bony ridges above its eyes are more or less smooth (Herre 1927).

REFERENCES

Herre, A. W. 1927. Gobies of the Philippines and the China Sea. Philippine Bureau of Science Monographic Publications on Fishes 23: 1–352, 26 pls.

Ryan, P. A. 1981. Records of three new freshwater fishes from the Fiji Islands. Pacific Science 35 (1): 93–95.

Smith, J. L. B. 1958. The fishes of the family Eleotridae in the western Indian Ocean. Ichthyological Bulletin 11: 137–163.

Thacker, C. 2011. Systematics of Butidae and Eleotridae. In: Patzner, R. A., J. L. Van Tassell, M. Kovačić & B. G. Kapoor (ed.) The Biology of Gobies pp. 79–85. CRC Press.

Predatory Ribbons

Some of you may have seen something like this doing the rounds:

The animal in the clip is called a nemertean. The Nemertea, commonly known as ribbon worms, are a group of more than 1200 known species of mostly predatory worm-like animals. The majority of nemerteans are marine, but there are also species found in freshwater or even terrestrial environments (the clip above shows a terrestrial species). As their vernacular name suggests, the majority of ribbon worms are flattish, slender animals with little in the way of external elaborations. Most are small and unassuming, but there are exceptions: one ribbon worm species from coasts of northern Europe, Lineus longissimus, grows to estimated lengths of over 30 m and may even be the longest animal in existence*. The most characteristic feature of ribbon worms is a long proboscis that they use in capturing prey; when not being deployed, this proboscis is retracted within a cavity called the rhynchocoel that runs much of the animal's length. Other than this, nemerteans have little in the way of internal body cavities other than the gut. They do have a simple blood-vascular system consisting of a few blood vessels but no actual heart; instead, the blood just kind of sloshes back and forth as a result to the animal's body contractions as it moves.

*Some uncertainty over the exact lengths of Lineus longissimus specimens is inevitable because, despite their remarkable length, they are still only a centimetre or so wide. When you're trying to extract something like that from among a bunch of rocks, it's gonna stretch and break. Still, thirty metres is a fairly conservative estimate of its length; Wikipedia cites a supposed maximum nearly twice that. These mega-nemerteans are definitely one of those animals that make me wonder, how does this thing even exist? I mean, what is the point of being so incredibly long and slender? How does it collect enough food at the front end to nourish itself all the way to the back end? How does it not just fall apart of its own accord, let alone when subjected to any external pressure?

Lineus longissimus, from here.


The relationships of nemerteans to other animals are rather uncertain, and they have generally been classified as their own independent phylum. Because of their simple body plan, many early authors compared them to flatworms, at least on a grade level, but this fell out of favour as it became accepted that the rhynchoel and blood-vascular system probably correspond to anatomical structures in more complex animals. More recent evidence from molecular and other sources has converged on a position within the Lophotrochozoa, the major animal clade that also includes molluscs, brachiopods and annelids, but their exact placement within this clade remains open to debate.

Molecular data have also influenced our understanding of relationships within the Nemertea. An influential classification of the group divided them between the Enopla, in which the proboscis is usually armed with a stabbing stylet or stylets, and the Anopla, in which the proboscis is unarmed (members of this latter group often have the proboscis branched as in the clip above; I'm guessing that in the absence of a stylet the proboscis probably works through adhesion). The two groups also differ in that Anopla always have the proboscis emerging from a separate pore to the mouth, whereas in many Enopla the mouth and proboscis pore share a common opening (Kvist et al. 2014). The Anopla were further subdivided into the Heteronemertea, which have a distinctive tissue layer called the dermis underneath the outer epidermis, and the Palaeonemertea which lack such a differentiation of skin layers. However, one need not be an expert in nemerteans to spot that the Anopla and Palaeonemertea were mostly defined by their lack of derived features (no stylets, no dermis) and so it should come as little surprise that molecular studies of the group have failed to offer resounding support for their monophyly. Instead, a number of studies have suggested that the Heteronemertea and Enopla together form a clade that Thollesson & Norenburg (2003) dubbed the Neonemertea. When they did so it was on the basis of molecular data only, but later authors have identified possible synapomorphies of the Neonemertea in features of the nervous and blood-vascular systems. One family of 'Palaeonemertea', the Hubrechtidae, has been suggested to also belong within the Neonemertea as sister-taxon to the Heteronemertea. This is of interest because the Hubrechtidae and Heteronemertea share a distinctive type of ciliated planktonic larva called a pilidium (other nemerteans either develop directly or have a creeping planula-type larva). Ciliated planktonic larvae are known a number of groups of animals, such as the veliger of molluscs, the trochophore of annelids, or the tornaria of acorn worms, and there has been a lot of discussion over the years as to whether similarities between these larvae represent a shared ancestry, or whether they might have evolved independently. In the case of nemerteans, at least, the current evidence seems to favour the latter. As for the other 'palaeonemerteans', there seems to be less of a consensus as to whether they form a single clade or a paraphyletic series relative to the Neonemertea.

A polystiliferan, Drepanogigas albolineatus, copyright Peter Wirtz.


As for the Enopla, it appears to form a valid clade. Previous authors divided the enoplans between the Hoplonemertea, including the majority of species, and the Bdellonemertea, including the single distinctive genus Malacobdella. The Hoplonemertea were in turn divided between the Monostilifera, in which the proboscis has a single long stylet, and the Polystilifera, in which it bears a pad of small stylets, and molecular analyses support the separation of these groups. Malacobdella (which lacks proboscis stylets but has the conjoined mouth-proboscis pore) has a sucker at the posterior end of its body, by which it lives attached to the gills of a mollusc. Malacobdella is not a parasite of the mollusc, per se: instead, it feeds on food particles drawn in by water flowing through the mollusc's gills. However, the recent analyses have indicated that Malacobdella is in fact a derived monostiliferan, and a number of recent authors have used the Hoplonemertea as an equivalent name to the old Enopla.

Live individual of the pelagic nemertean Dinonemertes shinkaii (head towards the right), from here.


Also distinctive within the Hoplonemertea are two clades, the polystiliferan Pelagica and the monostiliferan Korotkevitschiidae, that have left the ocean floor and adopted a pelagic life style. Members of both these groups are gelatinous and eyeless; the Pelagica have lost further internal organs such as nephridia. The Korotkevitschiidae (which also lack a proboscis stylet) are found towards the surface of the ocean; the Pelagica are found in much deeper waters (Chernyshev 2003). The pelagic nemerteans are among the most poorly known of all ribbon worms; they are rarely encountered (about half of the 100 or so described species of Pelagica are known only from single specimens) and their relatively simple morphology makes them difficult to compare to other nemerteans. If the individual in the photograph is any indication, however, they are beautiful animals.

REFERENCES

Chernyshev, A. V. 2003. Classification system of the higher taxa of enoplan nemerteans (Nemertea, Enopla). Russian Journal of Marine Biology 29 (Suppl. 1): S57–S65.

Kvist, S., C. E. Laumer, J. Junoy & G. Giribet. 2014. New insights into the phylogeny, systematics and DNA barcoding of Nemertea. Invertebrate Systematics 28: 287–308.

Thollesson, M., & J. L. Norenburg. 2003. Ribbon worm relationships: a phylogeny of the phylum Nemertea. Proceedings of the Royal Society of London Series B—Biological Sciences 270: 407–415.