Mystery Animal for Today

Take a close look at the photo above. What kind of animal do you think this is? [The photo comes from here, but don't look there just yet, because that would be cheating.]

Some of the more observant among you may have noticed the five rays visible on the animal, and so you would have correctly decided that this is an echinoderm, seen from the underside. Echinoderms are the phylum of marine animals that includes crinoids (sea lilies and feather stars), asteroids (sea stars or starfish), ophiuroids (brittle stars), echinoids (sea urchins) and holothuroids (sea cucumbers). The five rays are the ambulacra - furrows lined with the tube feet that the echinoderm uses for walking on, or for passing food particles to the central mouth. Before I reveal exactly what kind of echinoderm this is, though, I'll show you another photo of the same specimen (from the same site) seen from the side:



By now, it should be pretty obvious which of the five living classes of echinoderms this is. So if you guessed "starfish"* - you're absolutely right. This specimen is, in fact, the type specimen of Podosphaeraster toyoshiomaruae Fujita & Rowe, 2002. Podosphaeraster is an extremely unusual asteroid known from the western Pacific and north-east Atlantic that has abandoned the typical star-shape of most members of its class, and adopted a near-spherical form much more similar to that of an echinoid. If you were to look closely at the specimen, you would be able to see a difference from a typical echinoid in that the ambulacral furrows only go halfway up the side of the sphere, rather than all the way up as in echinoids.

*Kevin Zelnio is going to kill me for calling it a starfish instead of a sea star. Tough.

The way in which Podosphaeraster has evolved its unusual form is relatively simple. The development of the plates that normally form the dorsal (aboral) surface of the flattened star has been greatly reduced relative to those that form the ventral (oral) surface. The reasons why this unusual morphology has evolved in Podosphaeraster, however, are unknown. Though five species have been described to date, specimens of Podosphaeraster are few and far between. All species are small (the largest specimens are little over a centimetre in diameter) and there is evidence that they live in habitats that are not conducive to easy collecting - among sponges or rocky ground in depths of 85 - 615 m. It may be adapted to living in cracks or crevices in these habitats.

For all its unusualness, Podosphaeraster is not unique. A fossil family of asteroids, the Sphaerasteridae, also developed a similar globose form by the reduction of the aboral surface. Also, Smith (1997) suggested that echinoids could have also evolved from a star-like ancestor in just this way. If true, what might seem an interesting but inconsequential oddity in the asteroid world could actually be very significant in understanding how another of the major modern animal groups came into being.

REFERENCES

Fujita, T., & F. W. E. Rowe. 2002. Podosphaerasteridae fam. nov. (Echinodermata: Asteroidea: Valvatida), with a new species, Podosphaeraster toyoshiomaruae, from southern Japan. Species Diversity 7: 317-332.

Smith, A. B. 1997. Echinoderm larvae and phylogeny. Annual Review of Ecology and Systematics 28: 219-241.

On Hybrid Birds

Fuller, E. 1995. The Lost Birds of Paradise. Swan-Hill Press.

The 19 "lost" birds of paradise that Errol Fuller describes in this book are forms that are mostly only known from very few specimens, often with very little supporting information. What makes them "lost", however, is that despite all but one of them being described as new species, all of them were later reinterpreted as hybrids between better-known species. Fuller's motivating question is whether these specimens are indeed hybrids, or represent valid species that might occupy unknown restricted ranges somewhere in the depths of New Guinea, or may perhaps have slipped into extinction without ever getting the recognition they deserved.

Most of the specimens reached Europe through the plume trade. Specimens of birds of paradise were purchased from native collecters and then shipped back to the West for use in the fashion industry (the first country to ban the import of birds of paradise for plumes, according to Fuller, was the US in 1913, a development that probably had less to do with the developing conservation movement than with the increasing unfashionability of wearing plumes*). As a result, the available collection data on most specimens is decidedly hazy - few bear more specific information than "Dutch New Guinea" (the western part of New Guinea that is now controlled by Indonesia). Even if a more specific locality is recorded, it is often unreliable - specimens could be passed through a number of different native tribes before eventually reaching the European traders. Throughout the book, we get introduced to many of the figures involved in the collection and study of these mystery birds.

*To add further complexity, a major factor in the decline of popularity of plumes was actually the rise in popularity of the motor-car - ornate plumed hats being decidedly impractical for wearing in open-topped cars.

'Paradisaea mirabilis', a possible hybrid of Paradisaea minor (lesser bird of paradise) and Seleucidis melanoleuca (twelve-wired bird of paradise). 1902 lithograph by Bruno Geisler.

Throughout Fuller's book, we get introduced to many of the personages involved in the collection and study of the specimens (including the spectacularly named Captain Neptune Blood*). A significant number passed through the collection of Lord Walter Rothschild, a somewhat eccentric enthusiast who amassed one of the world's largest private natural history collections (Darren Naish wrote a piece two years ago on Rothschild and his unusual enthusiasm for cassowaries), though many of Rothschild's bird of paradise specimens were included in the collection he was blackmailed into selling to the American Museum of Natural History**. The "hybrid" specimens were largely identified as such in 1930 by Erwin Stresemann. Fuller accuses Stresemann of overzealousness in embracing his hybrid theory of origin for "species" known only from one or two specimens, essentially assuming from the start that all such species must be hybrids of known species and identifying "parents" from the available options no matter how poorly supported.

*Seriously.

**Probably not, I hasten to add, by the American Museum of Natural History.

'Diphyllodes gulielmitertii', almost certainly a hybrid between Diphyllodes magnificus and Cicinnurus regius. Unlike most of the other forms described by Fuller, this hybrid occurs fairly commonly, with more than two dozen known specimens. Lithograph by J. Gould and W. Hart.

Unfortunately, many of Fuller's reinterpretations of the supposed hybrids end up falling a little flat. Fuller accepts a hybrid origin for some forms, refutes it for others, but in many cases it is debatable whether his interpretations are any better than Stresemann's. Because all Fuller has to go on is examination of specimens, most of his arguments for valid species status amount to little more than replying to Stresemann's statement that "Species A has features intermediate between those of B and C, and is therefore a hybrid between the two" with "No it doesn't, so it isn't". In two cases where Fuller does accept hybrid status, 'Loborhamphus ptilorhis' and 'Lamprothorax wilhelminae', the reasons for linking them to their supposed parents seem decidedly unconvincing (which, of course, does not eliminate the possibility that they could still be hybrids between other species), while 'Cicinnurus lyogyrus', which Fuller hesitatingly accepts as a hybrid of the king bird of paradise (Cicinnurus regius) and the magnificent bird of paradise (Diphyllodes magnificus) seems more likely to be simply an aberrant variant of Cicinnurus regius. In contrast, 'Janthothorax bensbachi', which Fuller suggests is a valid species, seems more likely to be a hybrid. Probably DNA analysis of the specimens would be the only way to convincingly decide the question one way or another - Fuller suggests this would be difficult because the close relationships of the parent species would make results unconvincing, but resolution of molecular analyses has decidedly improved since 1995. The main barrier would be that DNA extraction from museum specimens, especially ones that have been in storage since the 1800s (and were probably not exactly fresh when they first reached the museum) is a difficult process, with little guarantee of success.

Loborhamphus nobilis, regarded by Stresemann (1930) as a hybrid between Paradigalla carunculata and Lophorina superba, but by Fuller as a probable valid species. Unlike the other bird of paradise species mentioned in this post, the less sexually dimorphic Paradigalla species are not polygamous breeders, and form permanent pair bonds. They therefore strike me as less likely to produce hybrids.

The Lost Birds of Paradise is certainly a lavishly illustrated book, reproducing paintings by Gould and other spectacular bird illustrators (some of which I've taken the liberty of re-reproducing), as well as numerous photos and drawings. The distribution and subjects of these illustrations are often a little erratic, however - what's with the naked man in the bath on page 76? - and this same erraticism extends to the text. I can't escape the impression that most of the essays on the various birds were composed separately, with little cross-checking between chapters when the book was compilated. The story of Stresemann's 'overzealous' revisions is repeated a number of times in different chapters, for instance, while many chapters include rather tangential passages on matters related to birds of paradise in general, but not necessarily directly relevant to the specific form the chapter is devoted to (not surprisingly, this is particularly noticeable in some forms known only from single specimens for which otherwise Fuller probably just wouldn't have had that much to say). Probably this eclecticism is most marked in the chapter on 'Paradisaea mixta', in which we are treated to a lengthy quotation from the autobiography of Errol Flynn (complete with full-page photograph) and a description of his experiences trying to start a career collecting birds of paradise in New Guinea some years before he became an actor. And what does this have specifically to do with 'Paradisaea mixta'? As it happens, absolutely nothing.

Still, The Lost Birds of Paradise is easily readable, and at least highlights that the identity of many of the "hybrid" birds of paradise is not as firm as might be thought. A commentor on one discussion thread makes the comment that Fuller obviously really wants there to be overlooked species of birds of paradise, which may lead him to be a bit more hasty in his judgements than he probably should be. Nevertheless, New Guinea, especially the western half, is a surprisingly unexplored place, and as the recent discovery/rediscovery of unknown or near-unknown mammal species there shows, it would be wise to not rule anything out just yet.

The Stately Herons

Taxon of the Week this week may overstep its bounds a little. This is because of a somewhat surprising amount of disagreement about what exactly the taxon in question covers, despite being familiar to people the world around. Prepare to meet the Ardeinae, the herons.

Herons belong to the family Ardeidae, which also includes the bitterns. When I was young and reading Ausich (1961), the division of this family was simple - the bitterns formed the subfamily Botaurinae, while everything else fell into Ardeinae. Since then, however, the picture has become a bit more complicated. The bitterns are almost certainly nested within this broad picture of Ardeinae, and most authors have tended to restrict Ardeinae to birds more closely related to the genus Ardea than to the bitterns. Unfortunately, because different authors have found differing positions for the bitterns within heron phylogeny (McCracken & Sheldon, 1998), this has resulted in differing contents for Ardeinae.

One point that most authors have agreed on is that the family Ardeidae can be divided into four main groups, whatever their inter-relationships might be. These groups are the day-herons (Ardea and its relatives), night-herons, bitterns and tiger-herons. There are also two single-species genera of more uncertain relationships, Cochlearius and Agamia. The South American tiger-herons have been regarded in the past as closely related to the day-herons on the basis of osteological data (Payne & Risley, 1976), but DNA-DNA hybridisation and vocal data position them as the basalmost group in the Ardeidae (McCracken & Sheldon, 1998). Unfortunately, heron phylogeny does not appear to have been given much attention since the DNA-DNA hybridisation days, and the only study I found referred to that used (barely) more advanced molecular methods (Chang et al., 2003) seems to have not included tiger-herons. Payne & Risley (1976) took a conservative approach that referred to each of the four groups as separate subfamilies, while Kushlan & Hancock (2005) included both the night-herons and day-herons in the Ardeinae and placed the other two groups in separate subfamilies. Kushlan & Hancock (2005) also recognised a separate subfamily each for Cochlearius and Agamia, but I suspect this more reflects their uncertain relationships rather than any positive idea about their positions.



The day-herons (Ardeinae proper or tribe Ardeini, depending on whom you ask - Kushlan & Hancock, 2005, divide them into two tribes Ardeini and Egrettini, but that isn't an approach I've seen elsewhere) are the best-known of the groups, and include what most people associate with the name "heron" - long-necked, long-legged, stately birds. The image at the top of this post (from Wikimedia) shows a fairly typical example, the white heron or great egret (Casmerodius albus), while the photo just above (from here) shows the Chinese pond-heron (Ardeola bacchus). As well as the herons of the genus Ardea, this group also includes the egrets (Egretta) and the pond-herons in Ardeola and Butorides. As the common name indicates, the day herons are largely diurnal. The males of a number of day heron species (most notably members of the genus Egretta) produce long decorative plumes in the breeding season, as can be seen in the photo of Casmerodius.



The night herons (Nycticoracini or Nycticoracinae) of the genera Nycticorax and Gorsachius are generally shorter, stouter birds than the day herons, with relatively shorter beaks, as well as (obviously) being nocturnal or crepuscular. Osteological data suggest that the night herons are closely related to the bitterns, while molecular data would place them closer to the day herons (McCracken & Sheldon, 1998). One night heron genus, the American Nyctanassa, is included by Kushlan & Hancock (2005) among the day herons as opposed to with the other Old World night herons.



The boat-billed heron (Cochlearius cochlearius - shown above in an photo stolen from Brian Switek) and the agami heron (Agamia agami - photo below from Arthur Grosset) are both South American oddballs that have been particularly difficult to place among the herons. In the case of Cochlearius, it was regarded as distinct enough that Wetmore placed it in its own separate family. Cochlearius differs from other herons in its unique beak structure and the number of powder-down patches on the chest (four as opposed to three). However, Cracraft (1967) claimed that, except for features directly connected with the beak, Cochlearius was little different osteologically from Nycticorax, and in fact resembled Nycticorax more closely than the other night-heron genus Gorsachius did! While osteological data might indicate that Cochlearius is simply a very specialised night heron, DNA-DNA hybridisation data indicated a more basal position, around the level of the tiger-herons (though unresolved as to which of the two was the basalmost clade - McCracken & Sheldon, 1998). Whichever is the true position, it is clear that the boat-billed heron is highly specialised, though we have little idea what, in fact, it is specialised for - Biderman & Dickerman (1978) found little apparent difference in diet and foraging behaviour of boat-billed herons from more typical heron species, and were only able to suggest somewhat half-heartedly that the oversized beak might be related to courtship displays.



The agami heron (Agamia agami) seems to be a specialist bank feeder (Payne & Risley, 1976). In proportions, it is much like a day heron, and osteological data also associates it with that group. However, if it is a day heron, it differs in a number of characteristics from the other members of that group. As can be seen in the photo above, it is a particularly colourful bird, and it is distinct from the day herons in many features of its adult and juvenile plumage. It also has a particularly slender, needle-like bill. The relationships of Agamia do not seem to have yet been investigated molecularly.

REFERENCES

Austin, O. L., Jr. 1961. Birds of the World: A survey of the twenty-seven orders and one hundred and fifty-five families. Paul Hamlyn: London.

Biderman, J. O., & R. W. Dickerman. 1978. Feeding behavior and food habits of the boat-billed heron (Cochlearius cochlearius). Biotropica 10 (1): 33-37.

Chang Q., Zhang B.-W., Jin H., Zhu L.-F. & Zhou K.-Y. 2003. Phylogenetic relationships among 13 species of herons inferred from mitochondrial 12S rRNA gene sequences. Acta Zoologica Sinica 49 (2): 205-210.

Cracraft, J. 1967. On the systematic position of the boat-billed heron. The Auk 84 (4): 529-533.

Kushlan, J. A., & J. Hancock. 2005. Herons. Oxford University Press.

McCracken, K. G., & F. H. Sheldon. 1998. Molecular and osteological heron phylogenies: sources of incongruence. The Auk 115 (1): 127-141.

Payne, R. B., & C. J. Risley. 1976. Systematics and evolutionary relationships among the herons (Ardeidae). Miscellaneous Publications, Museum of Zoology, University of Michigan 150: 1-115.

Linnaeus' Legacy #4

Linnaeus' Legacy #4 is up and running at The Other 95%. This month's keywords: everyone's war against everyone; nine men in the bride's chamber, with one woman; provides suction; every brachyuran; mysteries of the platypus; evil geneticists; Roy Orbison; giganormous rodent; LOLcats; Aetogate.

Giant Cannibal Algae from the Watery Ditch

I didn't think I was going to post anything today - nothing had really grabbed my attention over the last couple of days to write about. But then I look in my e-mail and find a notice about something I really couldn't resist - giant cannibal algae!

Chrysophytes (also known as "golden algae" due to the colour of their chloroplasts) are a class of unicellular algae found in pretty much any aquatic habitat. Your average chrysophyte is not particularly prepossessing - a single cell with one or two flagella emerging from one end and a scattering of chloroplasts within the cell. The image at the top of the post (from here) shows a couple of individuals of one such chrysophyte, Ochromonas. Some chrysophytes produce a covering lorica or coating of scales, while some live in small gelatinous colonies. Chrysophytes can produce resistant statospores or cysts when conditions become unfavourable (in at least some species, this may be induced by increasing population density rather than external environmental conditions), and as a result active populations of chrysophytes often show marked cycles between bloom and quiescent periods. The spore structure of chrysophytes is unique to this group, with a wall composed mostly of silica opening through a collared pore plugged with polysaccharides. Almost all chrysophytes can become heterotrophic (feeding on other organisms) if light conditions are not good enough for photosynthesis, and a number of chrysophytes have ditched chloroplasts altogether and are obligate heterotrophs.

A paper just out today by Yubuki et al. (2008) describes the life cycle of one such colourless chrysophyte, belonging to the genus Spumella. I wasn't able to find a picture of Spumella on the web, but if you imagine Ochromonas without chloroplasts you won't be too far off. Unfortunately, the organisms concerned are not identified to species. This could potentially be a problem as Spumella may be polyphyletically derived from chrysophyte lines that have independently lost chloroplasts (Cavalier-Smith & Chao, 2006). Whatever the species examined actually was, it was recovered from an ephemeral ditch where it would have had to survive periods of drying out.

The single cell that hatched out through the pore of a resistant spore was initially non-motile, but soon sprouted flagella and started to swim. It then produced a gelatinous sphere around itself, which it continued to swim in. The cell then started reproducing by binary cell division at a rapid rate (doubling time at 22°C was about two and a half hours), with the growing cells feeding on bacteria growing within the matrix of the gelatinous sphere, which continued to increase in size as the number of inhabiting cells increased. Eventually, after about two days, the sphere broke down, releasing the swimming cells into the surrounding medium.

Some hours after leaving the sphere, the cells began congregating in swarms of up to forty individuals. It was then that things turned nasty. Some cells within the swarm began capturing others and engulfing them*. Growth of these cannibal cells was rapid, and they soon became two or three times the size of their unfortunate siblings. Finally, the enlarged cannibal cells dropped their flagella and produced their own dormant cysts, waiting for the next stage in the cycle.

*If you can access the original paper, there's an absolutely fantastic sequence of photos of this. You can practically hear the cannibal cell smacking its lips (if it had them) after swallowing its sibling.


Figure from Yubuki et al. (2008), showing the life cycle of Spumella.

The first remarkable thing about this cycle was how quickly it all happened - from initial hatching to re-encystment took only three days. This rapidity is probably an adaptation to the unstable habitat that the organism lives in - reproduction and encystment has to be complete by the time the water supply dries up. The gelatinous matrix inhabited by the growing cells seems to facilitate this rapid life cycle by encouraging the growth of bacteria and providing the cells with a ready food supply (offhand, such a gelatinous matrix in which the cells are free-swimming has previously been described from only a single other organism - another chrysophyte, Chromulina nebulosa). The cannibalism within the swarm may also serve the same purpose. Cannibalism has been recorded in other protist species, but seems in those cases to be an opportunistic response to disappearing food supplies. In Spumella, cannibalism may be obligate - when individuals of two other protist species, Bodo and Ochromonas, both comparable in size to the cannibalised Spumella, were added to the medium, they were completely ignored and the cannibal Spumella continued to feed only on members of their own species.

Chomp.

REFERENCES

Cavalier-Smith, T., & E. E.-Y. Chao. 2006. Phylogeny and megasystematics of phagotrophic heterokonts (kingdom Chromista). Journal of Molecular Evolution 62 (4): 388-420.

Yubuki, N., T. Nakayama, & I. Inouye. 2008. A unique life cycle and perennation in a colorless chrysophyte Spumella sp. Journal of Phycology 44 (1): 164-172.

Tangled Bank

The Tangled Bank is a fortnightly carnival that highlights the best in science and medicine blogging. This week's edition is up at Quintessence of Dust.

Also, a reminder that Linnaeus' Legacy is scheduled to happen at The Other 95% tomorrow. If you've got any last minute submissions, get in quick!

Sculpins Go Wild

Yokoyama, A., & A. Goto. 2005. Evolutionary history of freshwater sculpins, genus Cottus (Teleostei; Cottidae) and related taxa, as inferred from mitochondrial DNA phylogeny. Molecular Phylogenetics and Evolution 36 (3): 654-668.

Freshwater sculpins of the genus Cottus are a widespread Holarctic group of smallish fishes, belonging to the suborder Cottoidei (the image at top, from Wikimedia, shows Cottus gobio). While most members of the Cottoidei are marine, there are a number of freshwater taxa - about 40 species in Cottus, three in Myoxocephalus (a genus also including marine species), the monotypic genera Mesocottus and Trachidermus, and 33 species divided between three families and 12 genera found in Lake Baikal in central Siberia. Species of Cottus show a wide diversity of life histories, from catadromous (species that live in fresh water before travelling to the sea to spawn) to amphidromous (species that can move between fresh and salt water, but don't do so specifically to spawn - the amphidromous Cottus species are freshwater spawners) to species that are permanently freshwater. As such, Yokoyama and Goto (2005) investigated the phylogeny of this genus using the mitochondrial 12S rRNA and CR (control region) genes to discover its biogeographical history and how the different life histories have evolved.

Previously, the catadromous life cycle has been thought to be ancestral for Cottus, both because freshwater cottoids as a whole are certainly derived from marine ancestors, and because the catadromous Trachidermus fasciatus was identified on morphological groups as the sister group to Cottus. The amphidromous lifestyle was thought to have arisen next, from which increasing specialisation for freshwater habitats had given rise to the purely fluvial (river) or lacustrine (lake) species. The results of Yokoyama and Goto did not contradict the basal position of catadromy, but added a twist - the single catadromous species, Cottus kazika, did not group with the remaining Cottus species, but instead was sister (with high support) to Trachidermus fasciatus, making Cottus polyphyletic (Shedko & Miroshnichenko (2007) have since moved C. kazika out of Cottus as a result, resurrecting an old genus name to label it Rheopresbe kazika). The role of catadromy in the evolution of Cottus therefore becomes a bit more uncertain.

The remaining, freshwater-spawning species of Cottus were supported as a clade, admittedly with low support though the shared life history makes the clade credible. As for whether the amphidromous life style was indeed ancestral to the purely freshwater, Yokoyama and Goto's results seemed to suggest the exact opposite, with the amphidromous species scattered through the various clades of purely freshwater species, and not particular basal within those clades. However, the authors themselves were a little more agnostic about their results - they point out that repeated parallel loss of amphidromy could give a falsely parsimonious appearance of derived amphidromy. Biogeography-wise, their results supported the traditional view of an origin of Cottus somewhere in eastern Eurasia, where the greatest diversity of species is found. Four reasonably well-supported clades of freshwater-spawning species were identified - two restricted to eastern Eurasia and Japan, one found across Eurasia, and one (their clade E) including both Eurasian and North American species.



The non-monophyly of Cottus goes further than just one wayward species, though. You recall that I mentioned the diverse fauna of freshwater cottoids endemic to Lake Baikal? In the past, species of this fauna were divided between three families - some in Cottidae with the other freshwater sculpins, some in an endemic family Abyssocottidae, and a separate family for the unique genus Comephorus. However, molecular analysis (Kontula et al., 2003) had discovered that the Baikal cottoids formed a single clade, and had probably originated from a single colonisation of the lake by an ancestral species. Once in the lake, the cottoids had diversified rapidly (molecular clock calculations, for what they're worth*, estimate an age of 1.2 to 6.2 million years for the Baikal radiation) to occupy a number of niches, including some not occupied by sculpins anywhere else in the world. The pictures above give some indication of the diversity of Baikalian cottoids - the pelagic Cottocomephorus inermis (from here) on the right, an unidentified benthic species reasonably similar to a typical cottid (from here) in the centre, and the highly derived pelagic Comephorus on the left (image from here).

*Okay, so I don't trust molecular clocks as far as I can throw them or the researchers who calculate them. In this case, unfortunately, they're all the evidence we have.

The point where it all becomes really interesting, though, is that not only does this diversity derive from a single point, but it is actually nested within the genus Cottus! This had previously been suggested by Kontula et al. (2003), and so Yokoyama & Goto (2005) took the opportunity to test Kontula et al.'s results against their more extensive dataset by including the data from the earlier study. While support was not impressive, the Baikalian radiation seems to be nested within Yokoyama & Goto's clade E.

As usual, though, I did come away from this paper with a few questions. Yokoyama and Goto used only one marine species and a member of Myoxocephalus as outgroups, and while they did find the Trachidermus + Rheopresbe clade as sister to the freshwater-spawning clade, support was very low and the position was not statistically supported. Is there actually a direct connection between these two clades, or did the catadromous species gain their freshwater lifestyle independently from the freshwater species? Answering this question will be vital to understanding what (if any) role catadromy may have played in the transition of the ancestors of Cottus from marine to freshwater habitats. And what of the untested freshwater Mesocottus haitej? Does this Siberian species represent another independent movement into freshwater, or does the paraphyly of Cottus extend even further?

REFERENCES

Kontula, T., S. V. Kirilchik & R. Väinölä. 2003. Endemic diversification of the monophyletic cottoid fish species flock in Lake Baikal explored with mtDNA sequencing. Molecular Phylogenetics and Evolution 27 (1): 143-155.

Shedko, S. V., & I. L. Miroshnichenko. 2007. Phylogenetic relationships of sculpin Cottus volki Taranetz, 1933 (Scorpaeniformes, Cottidae) according to the results of analysis of control region in mitochondrial DNA. Voprosy Ikhtiologii 47 (1): 27-30 (transl. Journal of Ichthyology 47 (1): 21-25).