Field of Science

The Live-Bearing Brotulas

Black brotula Stygnobrotula latebricola, photographed by Thomas W. Doeppner.

The subject of today's post is the Bythitidae, a family of mostly marine fishes referred to as the live-bearing brotulas. Bythitids belong to the Ophidiiformes, a group of more or less elongate fishes with long soft dorsal and anal fins. They differ from most other ophidiiforms in that the males have an external intromittent organ and they are mostly live-bearers rather than egg-layers (though at least one species, Didymothallus criniceps, is potentially an egg-layer: Schwarzhans & Møller 2007). Bythitids do share these features with the deep-water Aphyonidae, which are however particularly elongate, lack scales and a swim bladder, and have loose translucent skin in contrast to the firm skin of bythitids (Nielsen et al. 1999).

Bahamian cave fish Lucifuga spelaeotes, photographed by Joe Dougherty.

Bythitids are often thought of as deep-water fishes, but there is also a reasonable diversity of them in shallower habitats such as coral reefs. The shallower-living species are mostly very cryptic in their habits and may be only rarely encountered; deeper-water species may occupy more open habitats or be found in association with hydrothermal vents. Some species of the genera Lucifuga and Ogilbia are found in freshwater caves in the Caribbean (Lucifuga species), the Yucatan (Ogilbia pearsei) and the Galapagos (O. galapagosensis); other species are found in marine caves such as the 'blue holes' of the Bahamas. New species of bythitid continue to be described at a reasonable rate of knots (over 100 species have been described in the last ten years alone). They vary in size from small (Microbrotula species are about four centimetres in length) to very large (Cataetyx laticeps reaches over 75 cmm; the Fishes of Australia website states that bythitids grow up to 2 m, but I haven't been able to find which species this refers to).

Yellow cuskeel Dinematichthys iluocoeteoides, from here.

Because of their cryptic habits, the lifestyles of most bythitids remain poorly known. They are predators of invertebrates and other fish. The few identified larvae have been collected in the epipelagic zone (Nielsen et al. 1999) but bythitids are believed to have relatively low fecundity rates (presumably as only small numbers of embryos have been found in gravid females). Reef-dwelling species, as far as is known, have only small ranges, and many may be endangered by habitat degradation.


Nielsen, J. G., D. M. Cohen, D. F. Markle & C. R. Robins. 1999. FAO species catalogue. Volume 18. Ophidiiform fishes of the world. An annotated and illustrated catalogue of pearl-fishes, cusk-eels, brotulas and other ophidiiform fishes known to date. FAO Fisheries Synopsis 125 (18): I–XI + 1–178.

Schwarzhans, W., & P. R. Møller. 2007. Review of the Dinematichthyini (Teleostei: Bythitidae) of the Indo-west Pacific. Part III. Beaglichthys, Brosmolus, Monothrix and eight new genera with description of 20 new species. The Beagle, Records of the Museums and Art Galleries of the Northern Territory 23: 29-110.

Limpets of the North-east Atlantic

The common limpet Patella vulgata, photographed by Rokus Groeneveld.

When Linnaeus published the tenth edition of his Systema Naturae in 1758, he defined the genus Patella as having a subconical shell with a single valve and without a respiratory opening. Starting from this fairly minimal set of criteria, it is not surprising that a very broad range of limpets from all over the world ended up passing through Patella at various times. However, as time goes by the definition of Patella became further refined, and currently both morphological (Ridgway et al. 1998) and molecular (Nakano & Ozawa 2004) studies have tied the name Patella to a clade of limpets found only in coastal waters of the north-east Atlantic Ocean and the Mediterranean.

The giant limpet Patella ferruginea, up to eight centimetres in diameter, photographed by E. Volto.

This restricted sense of Patella includes nine or ten recognised species, though discussions are ongoing about whether given populations should be regarded as conspecific or not, and a large number of subspecies have been described. Limpets are fairly conservative animals morphologically, offering a fairly narrow range of characters for taxonomic study. Matters are further confused by a certain degree of environmentally-related plasticity: individuals living higher in the tidal zone tend to be larger and higher-spired than individuals living subtidally (Weber & Hawkins 2002). Patella limpets are generally believed to be protandrous, starting their lives as males and eventually metamorphosing into females; however, a study monitoring sex changes in P. vulgata identified one individual that changed from female to male (Le Quesne & Hawkins 2006). Patella limpets have been used for food by humans in many parts of their range, and collection pressure is regarded as a significant threat to the endangered western Mediterranean species P. ferruginea.

Blue-rayed limpets Patella pellucida, from here.

Within the family Patellidae, the distribution of Patella is notably unusual: this genus is largely geographically isolated from other patellids in southern Africa and the Indo-Pacific. Only a single other patellid species, the western African Cymbula safiana, has a range overlapping with Patella species (Ridgway et al. 1998). The fossil record contains little evidence how this separation came about: patellids are rarely preserved, living as they do in high-energy environments, and their morphological simplicity makes them difficult to identify though genera can be distinguished by their shell microstructure. Patella proper has not been reliably identified earlier than the Pliocene (Ridgway et al. 1998). It has been suggested that the ancestors of Patella either migrated up the western coast of Africa, or became separated from other patellids by the closure of the Tethys Sea that once connected what is now the Mediterranean with the Indian Ocean. However, molecular analyses have placed Patella as the sister taxon to all other patellids; if correct, this could push its separation back past the Upper Cretaceous as a Japanese fossil from that time has been assigned to the patellid genus Scutellastra. This would be too early for the African dispersal or Tethyan explanations, and new proposals are required.


Le Quesne, W. J. F., & S. J. Hawkins. 2006. Direct observations of protandrous sex change in the patellid limpet Patella vulgata. Journal of the Marine Biological Association of the United Kingdom 86: 161-162.

Nakano, T., & T. Ozawa. 2004. Phylogeny and historical biogeography of limpets of the order Patellogastropoda based on mitochondrial DNA sequences. Journal of Molluscan Studies 70: 31-41.

Ridgway, S. A., D. G. Reid, J. D. Taylor, G. M. Branch & A. N. Hodgson. 1998. A cladistic phylogeny of the family Patellidae (Mollusca: Gastropoda). Philosophical Transactions of the Royal Society of London Series B 353: 1645-1671.

Weber, L. I., & S. J. Hawkins. 2002. Evolution of the limpet Patella candei d’Orbigny (Mollusca, Patellidae) in Atlantic archipelagos: human intervention and natural processes. Biological Journal of the Linnean Society 77: 341-353.

Bryaxis on the Prowl

Pselaphine, probably Bryaxis bulbifer, photographed by Krister Hall.

Bryaxis is a large genus, with over 400 described species and subspecies (Hlaváč 2008), of small beetles belonging to the group known as the Pselaphinae, a subgroup of the Staphylinidae. In older references, you'll see the pselaphines referred to as a separate family Pselaphidae from the staphylinids, but most authors now include it in the latter as it has become clear that the pselaphines are not only related to the staphylinids but nested well within them. It is not so surprising that this was not immediately recognised: your average staphylinid looks something like this:

Paederus riparius, from here.

Bryaxis species are mostly found living in leaf litter, where they are predators of other micro-arthropods such as springtails. If you look at the top photo, you will be see two appendages with paddle-shaped endings attached to the head just behind the antennae. These are the maxillary palps, often enlarged in pselaphines (sometimes ridiculously so). Glands on the inside of the palp 'paddle' produce a sticky secretion, and the palps are used to grab the prey when hunting. The process of prey capture in Bryaxis puncticollis was illustrated by Schomann et al. (2008):
Prey detected!

Palps at the ready...


The final parts of the process. The springtail is held tail-upwards so that it can't escape or injure the beetle using the forked furca, the 'spring' underneath its abdomen.

As befits a large genus, Bryaxis has a truly headache-inducing taxonomic history, summarised by Besuchet (1966). The genus was first named by Kugelann in 1794. Kugelann's work can't have been that widely publicised, however, because in 1817 Leach gave the name Bryaxis to a different genus of pselaphine. Most subsequent authors used Bryaxis in the sense of Leach, and included Kugelann's original Bryaxis in the genus Bythinus, until this was corrected by Raffray in 1904. Raffray treated Bythinus as a junior synonym of Kugelann's Bryaxis, and placed Leach's 'Bryaxis' under the name Rybaxis. Even so, some European authors persisted in using Leach's Bryaxis.

It wasn't until the 1950s and 1960s that the usage of Bryaxis became stabilised, but there was one further wrinkle to the story. When Raffray identified Bythinus as a synonym of the true Bryaxis, he separated out a few previous Bythinus species as a new genus Bolbobythus. However, one of those was the type species of Bythinus. So, as finally laid out by Besuchet (1966): what had been called 'Bolbobythus' was really Bythinus, 'Bythinus' was really Bryaxis, and 'Bryaxis' was really Rybaxis! What could be simpler?


Besuchet, C. 1966. Bryaxis Kugelann, 1794 and Bythinus Leach 1817 (Insecta, Coleoptera): proposed addition to the Official List in their original sense. Bulletin of Zoological Nomenclature 23 (2-3): 114-116.

Hlaváč, P. 2008. A new cavernicolous species of the genus Bryaxis (Coleoptera: Staphylinidae: Pselaphinae) from the island of Mljet. Natura Croatica 17 (1): 1-8.

Schomann, A., K. Afflerbach & O. Betz. 2008. Predatory behaviour of some Central European pselaphine beetles (Coleoptera: Staphylinidae: Pselaphinae) with descriptions of relevant morphological features of their heads. European Journal of Entomology 105: 889-907.

The Psocoptera of Barrow Island

Courtenay Smithers, courtesy of the Sydney Morning Herald.

Gunawardene, N. R., C. K. Taylor & J. D. Majer. 2012. Revisiting the Psocoptera (Insecta) of Barrow Island, Western Australia. Australian Entomologist 39 (4): 253-260.

Our lab has just recently added to its publication list with the above title, which is part of a special issue of the Australian Entomologist printed in memory of the late Courtenay Smithers, who passed away last year. For many years, Courtenay was one of Australia's leading entomologists, particularly for those unfairly overlooked animals the bark-lice (non-parasitic Psocodea). An obituary for him can be found here.

We wanted to include this paper as a tribute to Courtenay, as it basically presents some identification work that he had done for us in the last few years. As some of you already know, we've been working for the last few years on surveying the terrestrial invertebrates of Barrow Island, off the north-west coast of Australia. Courtenay had first surveyed the bark-lice of Barrow back in 1982, when he collected only five species of Psocodea all up, including the cosmopolitan synanthrope Liposcelis entomophila (Smithers 1984). Because Barrow Island is a very arid habitat, with little to no standing fresh water, Courtenay felt that "The small size of the fauna is probably a reality not an illusion".

A cute litte critter from our collection that still only goes by the name of 'Pteroxanium sp. A'.

As it turns out, he was wrong. At least 26 species of Psocodea have been found on Barrow so far (the paper says 25, but we've had at least one more turn up since it was accepted for publication). Most of these have currently only been identified as morphospecies: identification of bark-lice is often a difficult task, and many Australian species probably remain undescribed (as an example, Courtenay's 1996 tally of the total described Australian Psocodea for the Zoological Catalogue of Australia includes less species of Liposcelididae than have been collected on Barrow Island alone). Three of the recorded species are synanthropes collected in buildings on the island; as far as we know, these species are not found in unmodified habitat. One of these, Dorypteryx domestica, was particularly interesting to me as it had not been recorded previously from Australia (and was my first real success at identifying a psocodean right down to species level, hurrah!), though Tim New (Australia's remaining bark-louse expert) informed us that its presence has always been expected. I have to say, while bark-lice in general are among the cutest of all insects, but the little jumping Dorypteryx really amps the cuteness right up there.

And here it is! (Photo from Gunawardene er al. 2012.) Dorypteryx domestica is probably found worldwide, but records are scattered because of its unassuming nature.

Unfortunately, Courtenay's passing highlights that a large proportion of taxonomic expertise currently resides in the minds of retired individuals (of the experts who have made identifications of material from the Barrow Island project, nearly a third were either retired or amateur taxonomists working in their spare time). There is no shortage of material out there, but we still need the people to tell us what it is.

Suspiciously posed-looking photo, used in Gunawardene et al. (2012), of yours truly supposedly demonstrating an insect collection method.


Smithers, C. N. 1984. The Psocoptera of Barrow and Boodie Islands, Western Australia. Entomologica Scandinavica 15: 215-226.

Smithers, C. N. 1996. Psocoptera. In: Wells, A. (ed.) Zoological Catalogue of Australia. Psocoptera, Phthiraptera, Thysanoptera pp. 1–79. CSIRO Publishing: Melbourne.