The Terrestrial Fauna of Barrow Island

Nihara R. Gunawardene, Jonathan D. Majer, Christopher K. Taylor & Mark S. Harvey (eds) 2013. The Terrestrial Invertebrate Fauna of Barrow Island, Western Australia. Records of the Western Australian Museum, Supplement 83. 406 pp.

For several years now, my colleagues and I have been monitoring terrestrial invertebrates on Barrow Island here in Western Australia. Some of you will have already heard of Barrow Island; for anyone that hasn't, Barrow is the second-largest island off the coast of WA (it's about 25 km long and 12 km wide). It has two main claims to fame: (a) it has been a recognised nature reserve for over 100 years, with thriving populations of a number of animals that are rare or extinct elsewhere, and (b) for the last 50 years, it has also been a working oil field, most recently managed by the oil company Chevron. It also lies close to large offshore natural gas deposits, and in 2003 Chevron and its associates were given permission to build a processing plant on Barrow Island for extraction of the gas. This permit, however, carried strong caveats: development of the plant is not to compromise the value of Barrow as a nature reserve. That's where we come in: on a regular basis, we travel to the island to look for any undesirables that may have managed to slip through the stringent quarantine requirements that have been placed on transport to Barrow (nothing so far, touch wood). Before plant development was begun, a large-scale survey was also conducted to identify the pre-existing invertebrate fauna of Barrow Island: before you can say whether something isn't there, you need to be able to say what is.

Over the course of these surveys, a sizeable collection of material has been accumulated from an area that had previously been only sporadically sampled. Over two dozen taxonomic experts were consulted in the process of identifying this material, a lot of which represented species potentially new to science. And so, some time in 2012, we asked the people who had been involved with the project if they would like to contribute to a collection of papers on Barrow Island invertebrates. The response was mostly positive, and The Terrestrial Invertebrate Fauna of Barrow Island, Western Australia was released to the world a couple of weeks ago.

We're very pleased with how it turned out. Some of the contributors provided overviews of their taxon of interest; others provided descriptions of new species. Authors came from both the academic and private sectors, and we're grateful to everyone who put time and effort into answering our calls. In the end, we had 22 chapters on hand, including material on animals from arachnids to isopods to ants, and 25 new species: one snail, two spiders, a silverfish and 21 flies. Not all of these new species were from Barrow Island alone: the chapter on Dolichopodidae (long-legged flies) by Dan Bickel represents a review of the fauna of the entire Pilbara region.

The book is available for purchase from the Western Australian Museum, but I've noticed that their site doesn't provide an article listing. Therefore, I'm including one below, with the abstracts for each article. Contact details for the corresponding authors have been included as hyperlinks, if you want to ask them about their articles. And again, thank you to everyone involved.

The camaenid snail Rhagada barrowensis. The identity of Barrow Island's common Rhagada species has been subject to a bit of confusion over the years; Johnson et al. describe it as a new species in this book.

Dorian Moro and Russell Lagdon, pp. 1-8.
History and environment of Barrow Island

Barrow Island represents a unique island ecosystem off north-western Australia. It has ecological affinities to the Cape Range region of the Australian mainland, and it also supports an oil and gas resource industry. The island hosts a long-unburnt vegetation complex, and a diverse community of vertebrate and invertebrate fauna occupy the disturbed and undisturbed habitats of the island. In the absence of non-indigenous predators or herbivores, without extensive land clearing, and with an instituted level of island quarantine, these environmental values have persisted to make Barrow Island an important environmental asset for Australia, and an example where island ecology functions in the presence of resource extraction. To date, almost 2,800 species of terrestrial and subterranean species have been consistently recorded from Barrow Island. These include 378 native plant species, 13 mammal species (including two species of bats), at least 119 species of terrestrial and migratory birds, 43 species of terrestrial reptiles, one species of frog, three subterranean vertebrates, at least 34 species of subterranean invertebrates, and the most speciose of all, over 2,200 terrestrial invertebrates.

Russell Lagdon and Dorian Moro, pp. 9-11.
The Gorgon gas development and its environmental commitments

Chevron has made an important contribution to our knowledge and understanding of the Barrow Island flora and fauna, and to the Australian economy. This knowledge has been primarily founded from the investigations and commitments of joint venture partners associated with the environmental impact assessment for the Gorgon Gas Development. The Gorgon Gas Development is one of the world’s largest natural gas projects and the largest single natural gas project in Australia’s history. Development has been balanced between energy needs and environmental management. Through plans, procedures, programs and research, Chevron Australia and its joint venture participants have established a benchmark for environmental management of this important island reserve. Furthermore, the Gorgon Joint Ventures have contributed to one of the largest biodiversity offset and Net Conservation Benefit programs in Western Australia.

Jonathan D. Majer, Shae K. Callan, Karl Edwards, Nihara R. Gunawardene and Christopher K. Taylor, pp. 13-112.
Baseline survey of the terrestrial invertebrate fauna of Barrow Island

Barrow Island is Western Australia’s second largest offshore island and its flora and fauna have been able to evolve without major human disturbances. Chevron Australia Pty Ltd and its Joint Venture Participants made an application to construct a plant to liquefy natural gas on the island in 2001. One of the conditions under which approval was granted was the implementation of a rigorous biosecurity effort to ensure that no non-indigenous species (NIS) are introduced or allowed to establish on the island. To fulfil this condition it was first necessary to characterise what was already present on the island. A series of surveys have been performed using a purpose-designed sampling protocol in order to provide baseline data on the existing terrestrial invertebrates on Barrow Island. A total of 1,873 morphospecies were sampled but subsequent surveys and taxonomic developments have increased the count to 2,397. This compares with an estimated species richness of 2,481 terrestrial invertebrate species on the island. Composition of the fauna varied considerably between the wet and dry seasons and between years, even when samples were taken during the same month. Composition also varied with distance from the coast, which may be associated with soil type and vegetation association. Twenty five non-indigenous species and seven putative non-indigenous species have been found, all of which are believed to have been present prior to commencement of the Gorgon Gas Development project.

Peter Whittle, Frith Jarrad and Kerrie Mengersen, pp. 113-130.
Design of the quarantine surveillance for non-indigenous species of invertebrates on Barrow Island

The Ministerial conditions for regulatory approval for the Gorgon gas project on Barrow Island included a quarantine surveillance program having detection power of 0.8 for non-indigenous species of terrestrial invertebrates, vertebrates and plants. No method was available for design of such a program, so we developed a new method and designed surveillance systems that were implemented successfully in 2010−11 for the first of four years over the construction period. Here we describe the method and outline the invertebrate surveillance system, after the experience of the first year. We discuss a set of issues that characterised the design problem, which we consider typical of many surveillance applications. We suggest that the method is broadly applicable for objective design of surveillance, for biosecurity and other settings.

Ken Walker, pp. 131-134.
Providing web based diagnostics for the Barrow Island baseline survey

During the years of 2005 to 2007, an extensive baseline study of the Barrow Island invertebrate fauna was conducted. This survey included more than 50 sample sites across the island and multiple collecting techniques were used at each site. Over 14,000 specimens were collected during this survey. Taxonomic specialist who examined this material nominated over 2,000 morphospecies of which about 300 could be placed to species rank. Having done all of this collecting and identification, the question then was how best to access and use this valuable resource. All of the specimens were stored in two institutions in Perth – several thousand kilometres south of Barrow Island. Manual access to these specimens was slow which hindered the decision making processes needed when a suspected non-indigenous species was found on the island. The decision was made to digitise the diagnostic characters for representative of each morphospecies. These images were to be made available through a website called PaDIL (Pests and Diseases Image Library). Each species was to have its own webpage containing at least 4 diagnostic images of each species and all of the species collection points to be displayed on an interactive Google Map. Species, as well as higher ranks, could be queried alone or against sample localities or against Indigenous or Non-Indigenous status. Individual species pages could be opened and comparative images tables could be pre-defined and presented or users could build their own comparative image tables in real time. The development of the Barrow Island PaDIL website made the results of the entire Baseline Study accessible to anyone with a web browser from anywhere with an internet connection. The Barrow Island PaDIL website is a major part of the Quarantine efforts of Chevron on Barrow Island.

Christopher K. Taylor, pp. 135-144.
Annotated bibliography for Barrow Island terrestrial invertebrates

A bibliography is provided of publications treating terrestrial invertebrates on Barrow Island. A brief overview is also given of natural history and invertebrate collections on Barrow Island.

Garth Humphreys, Jason Alexander, Mark S. Harvey and William F. Humphreys, pp. 145-158.
The subterranean fauna of Barrow Island, north-western Australia: 10 years on

Barrow Island, situated off the north-west Australian coast, is well recognised for its subterranean fauna values. Sampling for both stygobitic and troglobitic fauna has taken place on the island since 1991, and Humphreys (2001) summarised the then current state of knowledge of the island’s subterranean fauna. Sampling for impact assessment purposes on the island over the past decade has substantially increased the recorded species richness of Barrow Island. The number of documented stygal taxa has more than doubled since 2001, from 25 to 63 species now known. Troglobitic diversity has also substantially increased, with six species known in 2001 and 19 troglobitic taxa known today. The total recorded subterranean species richness for Barrow Island at this time stands at 82 species. It is likely that considerably more species remain to be recorded, as even the additional surveys of the past decade leave many areas of the island unsampled.
The distributions and minimum area of occupancy for many species known from Barrow Island in 2001 have also been significantly expanded by the sampling efforts of the last decade. This includes specially protected species listed under State and Commonwealth Government legislation. The available data suggest the fauna of the island may number in the hundreds of species, many of which are endemic, confirming its status as internationally significant for subterranean biota.

Michael S. Johnson, Sean Stankowski, Corey S. Whisson, Roy J. Teale and Zoë R. Hamilton, pp. 159-171.
Camaenid land snails on Barrow Island: distributions, molecular phylogenetics and taxonomic revision

Three species of camaenid land snails occur on Barrow Island: Quistrachia barrowensis and two previously unassigned species of Rhagada. Based on morphological re-evaluation and analysis of sequences of the mitochondrial gene COI, we have revised the taxonomy of these species, providing a clearer understanding of their geographic distributions and origins. The supposed Barrow Island endemic Q. barrowensis is synonymous with Q. montebelloensis from the Montebello and Lowendal Islands. The small species of Rhagada, confined to the northern tip of Barrow Island, is conspecific with R. plicata, whose distribution also includes the Montebellos and the Lowendals. The large species of Rhagada is described here as R. barrowensis sp. nov., known only from Barrow Island and adjacent Pascoe Island. The three camaenids represent deeply divergent lineages with different geographic origins, indicating that the local diversity on Barrow Island has come about through a complex history. With maximum geographic spans of only 22 to 70 km, the short-range endemism of these species highlights the conservation significance of Barrow Island.

Volker W. Framenau and Anna E. Leung, pp. 173-184.
Costacosa, a new genus of wolf spider (Araneae, Lycosidae) from coastal north-west Western Australia

A new genus of wolf spider (family Lycosidae Sundevall, 1833), Costacosa gen. nov. is described from north-west Western Australia to include C. torbjorni sp. nov. (type species) and C. dondalei sp. nov. The genus belongs to the subfamily Lycosinae Sundevall, 1833 and differs from all other Australian genera in this subfamily with similar somatic morphology, in particular Venator Hogg, 1900 and Knoelle Framenau, 2006, mainly in genitalic characters. The tegular apophysis of the male pedipalp has a pronounced ventral spur, a distinct ventral edge of species-specific shape and serrations along its apical edge. The female epigyne has an elongated triangular atrium and the medium septum is longer than the posterior transverse part. Costacosa are medium-sized wolf spiders of overall brown colouration and with broad light median and sublateral bands on the carapace and a black patch in the frontal two-thirds of the venter. Costacosa torbjorni is the most commonly recorded wolf spider on Barrow Island, from where currently seven species of Lycosidae are known.

Simon Judd and Giulia Perina, pp. 185-207.
An illustrated key to the morphospecies of terrestrial isopods (Crustacea: Oniscidea) of Barrow Island, Western Australia

This paper presents an illustrated key to eighteen morphospecies of terrestrial isopods from Barrow Island with a brief summary regarding their currently known distribution and potential endemicity to the island. Six described species are recorded, Ligia exotica (family Ligiidae), Alloniscus pallidulus (Alloniscidae), Laevophiloscia yalgooensis (Philosciidae), Porcellionides pruinosus (Porcellionidae), Barrowdillo pseudopyrgoniscus, Buddelundia hirsuta (both Armadillidae), but the identifications of most need to be confirmed following genus-level revisions and examination of type- or topotypical material. The key includes twelve undescribed species and at least two undescribed genera from the family Armadillidae, one of which is apparently restricted to Barrow Island. Although there is still considerable taxonomic work required to evaluate distributions, it appears that at least six of the eighteen species are potential short-range endemics (SRE).

Catherine A. Car, Megan Short, Cuong Huynh and Mark S. Harvey, pp. 209-219.
The millipedes of Barrow Island, Western Australia (Diplopoda)

Six species of millipedes are recorded from Barrow Island, including three species of pin-cushion millipedes of the order Polyxenida, Lophoturus madecassus (Marquet and Condé, 1950) (Lophoproctidae), Unixenus mjoebergi (Verhoeff, 1924) (Polyxenidae) and Phryssonotus novaehollandiae (Silvestri, 1923) (Synxenidae), a single species of the order Spirobolida, Speleostrophus nesiotes Hoffman, 1994 (Trigoniulidae), and two species of the order Polydesmida, Boreohesperus dubitalis Car and Harvey, 2013 (Paradoxosomatidae) and one species of the family Haplodesmidae (genus and species indet.). Lophoturus madecassus is circum-tropical in distribution, Unixenus mjoebergi and Phryssonotus novaehollandiae are found also on mainland Australia, but the other three species are endemic to the island. Speleostrophus nesiotes is a highly modified troglobiotic species, currently listed as threatened by the Western Australian government. It is unclear at present whether the haplodesmid specimen is a troglobite.

Penelope Greenslade, pp. 221-228.
Composition of Barrow Island collembolan fauna: analysis of genera

Collembola have been collected from Barrow Island for the first time; a maximum of seventy one species were detected, of which a high proportion are undescribed. Only four non-indigenous species (NIS) species have been collected, three in very small numbers but one was a large population introduced to the island in lengths of timber which were subsequently sent off the island. Despite few of the species being described, most have been collected before and endemism is low. One new genus record for Australia, Calx, was found. The presence of a species of Temeritas is unusual in that the males showed strong sexual dimorphism, and a species of Acanthocyrtus that lacked any pigment was collected in reasonable numbers. Collections from bore holes were rich in species. Five species were recorded only from bore holes and may be island endemics. The intertidal fauna was also rich in species with 14 found, all restricted to this habitat. Soil fauna density of Collembola was found to be high, with a mean average potential density of nearly 47,000/m². A proportion of the terrestrial Collembola fauna is active under all weather conditions but other species are only active after rain. In general, the terrestrial fauna shows a dominance of the families Isotomidae and Bourletiellidae, which is typical for the wet/dry tropics where trees are absent.

Graeme Smith, pp. 229-240.
A new species of Heterolepisma from Barrow Island (Zygentoma: Lepismatidae)

The silverfish fauna of Barrow Island is discussed and Heterolepisma parva sp.nov. is described from extensive material collected mostly in pitfall traps or Winkler sac leaf litter samples.

David T. Jones, pp. 241-244.
The termites of Barrow Island, Western Australia

Forty years ago D. H. Perry, the renowned termite expert, published a checklist of 18 species that he had collected on Barrow Island. That checklist is now updated with the results of a recent invertebrate survey of the island, and a literature search for additional records. The updated list now runs to 27 species, all of which appear to be indigenous to the island.

Christopher K. Taylor, pp. 245-252.
The genus Lithoseopsis (Psocodea: Amphientomidae) in the Western Australian fauna, with description of the male of Lithoseopsis humphreysi from Barrow Island

The Australian Amphientomidae species Seopsis incisa Smithers, 1989 and S. humphreysi New, 1994 are transferred to the genus Lithoseopsis Mockford, 1993 as L. incisa new combination and L. humphreysi new combination, as a result of the discovery of speciens of L. humphreysi from Barrow Island, Western Australia. The male of L. humphreysi is described for the first time, and both macropterous and brachypterous individuals are described. The genus Lithoseopsis was previously known from North America only, and the addition of the Western Australian species significantly increases its range. A key is provided to the genera of Amphientomidae.

David Gopurenko, Murray Fletcher, Holger Löcker and Andrew Mitchell, pp. 253-285.
Morphological and DNA barcode species identifications of leafhoppers, planthoppers and treehoppers (Hemiptera: Auchenorrhyncha) at Barrow Island

The hemipteran suborder Auchenorrhyncha comprises a rich assemblage of plant feeding species, many of which are widespread in distribution and act as vectors of viral and fungal diseases affecting plants. Species level identifications in this group generally are possible only by examination of male specimens; prior DNA barcode analyses of a limited range of Auchenorrhyncha indicate that this approach may provide an expedient means to identify species within this diverse group. In this study we explored the utility of DNA barcoding for identification of a wider range of Auchenorrhyncha species than has been examined previously. Diverse fulgoroid (planthopper) and membracoid (leafhopper and allies) Auchenorrhyncha were sampled from Barrow Island, Western Australia, and identified to the least inclusive taxonomic units using morphology. DNA barcodes from 546 adult specimens were obtained and analysed using a General mixed Yule – Coalescent (GMYC) modelling approach to genetically delimit putative species, as a comparison to the morphospecies identifications. Additional DNA barcodes (N = 106) were obtained from nymphs and these were compared to adult DNA barcodes to identify species present among immature specimens.
Among adult specimens, 73 species were congruently delimited by morphology and genetic analyses when modelled using a single threshold GMYC. Congruence between morphological and molecular species assignments was greatly reduced when the Yule – Coalescent transition was allowed to vary across genetic lineages. In a separate DNA barcode analysis of all specimens using neighbour joining distance metrics, nymphs and physically degraded specimens were in most cases genetically linked to adult conspecifics. Ten genetic clades detected among the nymphs were not observed among adults and did not match pre-existing sequence accessions in GenBank or DNA barcode records in BOLD.
Of the 73 adult Auchenorrhyncha species congruently identified by DNA barcoding and morphology, most were Cicadellidae (N = 53 morphospecies), the remaining 20 morphospecies were sparsely representative of ten other families. Formal identifications to species level were available for only 36% of these 73 morphospecies, owing mainly to an absence of diagnostic male specimens within many of the delimited species. Indeterminate species detected among adults and nymphs are designated with interim species codes.
The work presented here demonstrates that DNA barcoding is likely to be a powerful investigative tool for identifying and understanding species limits in the Auchenorrhyncha, particularly if it is used within an integrative taxonomic framework.

Laurence A. Mound, pp. 287-290.
Thysanoptera (Insecta) of Barrow Island, Western Australia

Almost 50 species of the insect order Thysanoptera are here listed from Barrow Island, Western Australia, of which several are known only from this island. This cannot be interpreted as indicating that any species is endemic to the island, because almost nothing is known of the Thysanoptera fauna of the nearby mainland.

Daniel J. Bickel, pp. 291-348.
The family Dolichopodidae (Diptera) of the Pilbara region, Western Australia in its Australasian biogeographic context, with the description of 19 new species

The Dolichopodidae (Diptera) of the Pilbara Region (here also including Barrow Island and Cape Range), Western Australia are described, keyed and illustrated. The fauna comprises 41 species, including three with generic names only, being represented by females or badly damaged males. The following 19 species are newly described: Pseudoparentia canalicula sp. nov., Pseudoparentia niharae sp. nov., Paraclius manglar sp. nov., Medetera junensis sp. nov., Corindia gascoynensis sp. nov., Thinophilus eboricoxa sp. nov., Thinophilus yarraloola sp. nov., Chaetogonopteron capricorne sp. nov., Chaetogonopteron vexillum sp. nov., Sympycnus colliepa sp. nov., Sympycnus lacrimulus sp. nov., Sympycnus pistillus sp. nov., Sympycnus weano sp. nov., Sympycnus ephydroides sp. nov., Sympycnus hamulitarsus sp. nov., Diaphorus karijini sp. nov., Diaphorus garnetensis sp. nov., Chrysotus austrotropicus sp. nov. and Chrysotus pilbarensis sp. nov. Paraclius obtusus Hardy, 1939 is regarded as a new senior synonym of Paraclius albodivisus Parent, 1941, syn. nov. The Pilbara fauna is treated in the context of the wider Australian fauna, and many extralimital records are included. Many Pilbara species are found across tropical northern Australia, and sometimes into adjacent Melanesia. However, some species have a trans-continental distribution south of the monsoonal belt and also occur in central Northern Territory and subtropical interior Queensland suggesting a biogeographic track that now comprises favorable relictual habitats in a largely arid region. The Millstream site along the Fortescue River is particularly rich in species, and it is the only known locality of the isolated monotypic genus Pilbara Bickel.

David K. Yeates and Stefanie K. Oberprieler, pp. 349-354.
Two new species of the Australian bee fly genus Comptosia (Diptera: Bombyliidae) from Barrow Island, Western Australia

Two new species of the bee fly genus Comptosia Macquart from Western Australia, C. barrowensis and C. karijinii, are described.

Nicholas B. Stevens, Syngeon M. Rodman, Tamara C. O’Keeffe and David A. Jasper, pp. 355-374.
The use of the biodiverse parasitoid Hymenoptera (Insecta) to assess arthropod diversity associated with topsoil stockpiled for future rehabilitation purposes on Barrow Island, Western Australia

This paper examines the species richness and abundance of the Hymenoptera parasitoid assemblage and assesses their potential to provide an indication of the arthropod diversity present in topsoil stockpiles as part of the Topsoil Management Program for Chevron Australia Pty Ltd Barrow Island Gorgon Project. Fifty six emergence trap samples were collected over a two year period (2011 and 2012) from six topsoil stockpiles and neighbouring undisturbed reference sites. An additional reference site that was close to the original source of the topsoil on Barrow Island was also sampled. A total of 14,538 arthropod specimens, representing 22 orders, were collected. A rich and diverse hymenopteran parasitoid assemblage was collected with 579 individuals, representing 155 species from 22 families. The abundance and species richness of parasitoid wasps had a strong positive linear relationship with the abundance of potential host arthropod orders which were found to be higher in stockpile sites compared to their respective neighbouring reference site. The species richness and abundance of new parasitoid wasp species yielded from the relatively small sample area indicates that there are many species on Barrow Island that still remain to be discovered. This study has provided an initial assessment of whether the hymenoptera parasitoid assemblage can give an indication of arthropod diversity. However, further work would still be required to more robustly establish the use of the hymenoptera parasitoid assemblage as indicators of arthropod diversity.

B. E. Heterick, pp. 375-404.
A taxonomic overview and key to the ants of Barrow Island, Western Australia

This work characterises the ant (Hymenoptera: Formicidae) fauna of Barrow Island, Western Australia, and provides a key to the workers and several unique reproductives of the 117 species recorded from the island thus far. In all, 11 of the 13 subfamilies of Western Australian ants have been recorded from Barrow Island, but Myrmeciinae and Heteroponerinae are absent. At a generic level, the fauna of the island is less rich, holding 36 of the 71 genera currently known from Western Australia. The ant fauna is characteristic of the Eremaean Botanical Province of the Pilbara, rather than that of the Carnarvon Basin from which Barrow Island is geologically derived. Ninety-three ant species (79.5% of the total on Barrow Island) are shared with the ant fauna of the Pilbara region on the adjoining mainland, but only 52 species (44.4% of the total) are shared with the ant fauna of the Carnarvon Basin. The island is very rich in unspecialised and thermophilic ant species. Five such genera, i.e., Iridomyrmex (14 spp.), Monomorium (13 spp.), Polyrhachis (12 spp.), Melophorus (10 spp.), and Camponotus (nine spp.) make up almost 50% (i.e., 49.6%) of the island’s ant fauna. Very few ants appear to be endemic to Barrow Island. The relative proportions of the two major subfamilies (Formicinae and Myrmicinae, together comprising 61.5% of the total ant richness) are similar to the proportions found in the South-west Botanical Division for these two subfamilies (i.e., 65.9%), with Barrow Island having a slightly lower ratio of formicines to myrmicines than is found in the south-west of the state. An estimate of the total number of ant species likely to occur on Barrow Island, using the Estimate-S program (Colwell 2009), suggests that a maximum of fourteen additional species may be as yet unrecorded.

Jonathan D. Majer, Nihara R. Gunawardene, Christopher K. Taylor and Mark S. Harvey, pp. 405-406.
A last word

The work reported on in this volume is the culmination of nine years of data gathering stemming from the original baseline surveys on Barrow Island. Not surprisingly, this has resulted in one of the most comprehensive terrestrial invertebrate surveys ever performed on an offshore island on this continent. There are other substantial surveys, but these have generally focussed on specific taxonomic groups, rather than the whole spread reported here.

Proasellus: Life Under Water

Proasellus slavus, photographed by Hans Jürgen Hahn K. Grabow (see comments below re credits).

The animal in the picture above is not quite the animal that I was planning on telling you about today, but I couldn't find an image of my particular target species. As long-time readers of this page will know, once a week I pick some random taxon to look at, and for this week I picked out the freshwater isopod Proasellus vignai. Most of you will know isopods as the woodlice that you may find in your garden, but the woodlice are really only one small part of the broad range of mostly aquatic isopod diversity. Proasellus belongs to a group of isopods known as the Asellota; as you can see in the picture above, asellotes differ from woodlice in (amongst other things) having the dorsal shields of each segment less tightly pressed together.

Proasellus is a genus of freshwater asellotes found around the Mediterranean: Europe, western Asia, northern Africa. Proasellus vignai is one of a number of species of Proasellus that are found in subterranean habitats, like P. slavus shown above. Both P. slavus and P. vignai, like most other subterranean animals, have lost the pigment and eyes of their surface-dwelling relatives. However, not all subterranean habitats are equal, and not all subterranean animals live in 'caves' as you might usually imagine them. Some Proasellus species are indeed found living in caves, but P. vignai and P. slavus are inhabitants of the hyporheic zone, the ground around rivers and streams where the water from the river soaks into the surrounding groundwater. Cave-dwelling Proasellus species tend to be broader and have more elongate limbs, so that they can maximise their chances of finding food in the nutritionally sparse cave waters. Hyporheic species, on the other hand, are narrower and more elongate, making them better suited for squeezing through the gaps between sediment particles.

Proasellus vignai seems to be a little known species (hence the lack of an available illustration). It is only known from the hyporheic zone of the Melfa river, in the Appenine mountains of the Lazio region of Italy (Bodon & Argano 1982). The Melfa is not a long river, only about 40 km long, so P. vignai may be a very localised species. It is a close relative of P. slavus, which lives in the water catchment of the Danube River. Other related species include P. ligusticus in the Ligurian Alps, P. sketi in Greece and P. boui in Languedoc in southern France. The scattered nature of the species of the P. slavus group, all of them hyporheic, suggests a certain degree of relictualism. Like other habitats that represent the edge of things, the hyporheic environment can be an uncertain one, vulnerable to outside influences. Should something change the nature of the Melfa river, Proasellus vignai might be taken with it.

REFERENCE

Bodon, M., & R. Argano. 1982. Un asellide delle acque sotterranee della Liguria orientale: Proasellus ligusticus n.sp. (Crustacea, Isopoda, Asellota). Fragm. Entomol. 16 (2): 117-123.

Life Among a Shrimp's Gills

Female of Schizobopyrina bombyliaster from Williams & Boyko (2004), with red box added on ventral view to indicate position of small male.

For today's random subject, I drew the marine isopod genus Schizobopyrina. Schizobopyrina is a genus in the family Bopyridae, and females of this genus were distinguished by Markham (1985) from those of the related genus Bopyrina by the presence of palp on the maxilliped (part of the mouthparts), by its more elongate oostegites (the lamellae forming the brood pouch in which eggs and larvae are incubated), and by the fusion of the pleomeres (posterior segments) on one side of the body. About ten or so species have been assigned to this genus from warmer waters around the world.

Mature bopyrids are parasites of shrimps and other crustaceans (Schizobopyrina has been found on hosts of the families Palaemonidae, Gnathophyllidae and Hippolytidae). Schizobopyrina and related genera are found in the branchial (gill) cavities of their host. Shrimp gills are developed from side-branches of the base of the legs, and are covered by an overhanging shelf of the carapace (if anyone is familiar with the process of preparing a crayfish or lobster, the gills are the 'dead man's fingers' that you have to remove before serving the crayfish). In a shrimp that is host to Schizobopyrina, the branchial cavity will become greatly protruding, as can be seen in this photo of a bumblebee shrimp Gnathophyllum americanum parasitised by Schizobopyrina bombyliaster (from Williams & Boyko 2004; scale bar equals 1.0 mm):

Bopyrids are released from the parent host as larvae that initially attach themselves to copepods. When they are approaching maturity, they leave the copepod and find an appropriate adult host. The first larva to attach itself to an appropriate shrimp will develop into a female, while any subsequent larva to attach itself will develop into a male (Cash & Bauer 1993). As can be seen in the figure at the top of this post, the female is considerably larger than the male. She is also noticeably asymmetrical in her body form, though a single species may include individuals bent to either the left or the right (Markham 1985). The female bopyrid attaches herself to her host before it reaches maturity: this puts her at risk of losing her place as the host moults, but studies of another branchial parasite bopyrid, Probopyrus pandalicola, indicate that as the host cuticle tears away during the process of moulting, the female is able to reattach herself to the new cuticle underneath and keep her place (Cash & Bauer 1993). The smaller male looks very different to the female, and is much more symmetrical. He attaches himself to the female, but whether or how he feeds is unknown. In Probopyrus pandalicola, the female moults, then produces eggs, after each moult of her host; the male has been observed crawling at this point into the brood pouch of the female, where he presumably fertilises her eggs.

Just as a further aside, the recent description of the species featured in the figures used in this post, Schizobopyrina bombyliaster Williams & Boyko 2004, was of further interest because the type specimen of this parasitic isopod was itself host to a hyperparasitic isopod, the cabiropid Cabirops bombyliophila. Which gives me an idea for a matryoshka design...

REFERENCES

Cash, C. E., & R. T. Bauer. 1993. Adaptations of the branchial parasite Probopyrus pandalicola (Isopoda: Bopyridae) for survival and reproduction related to ecdysis of the host, Palaemonetes pugio (Caridea: Palaemonidae). Journal of Crustacean Biology 13 (1): 111-124.

Markham, J. C. 1985. A review of the bopyrid isopods infesting caridean shrimps in the northwestern Atlantic Ocean, with special reference to those collected during the Hourglass cruises in the Gulf of Mexico. Memoirs of the Hourglass Cruises 7 (3): 1-156.

Williams, J. D., & C. B. Boyko. 2004. A new species of Schizobopyrina Markham, 1985 (Crustacea: Isopoda: Bopyridae: Bopyrinae) parasitic on a Gnathophyllum shrimp from Polynesia, with description of an associated hyperparasitic isopoda (Crustacea: Isopoda: Cabiropidae). Proceedings of the California Academy of Sciences 55 (24): 439-450.

Burrowing Beaky Amphipods

Oediceroides emarginatus, photographed by Gauthier Chapelle.

I've been out in the field for a couple of weeks, hence the momentary absence of regular posts. But I have returned, and shall kick off with a brief introduction to the Oedicerotidae.

The oedicerotids are another cluster within the systematic morass that is the gammaridean amphipods (other gammaridean families featured here and here). Members of the Oedicerotidae are marine benthic burrowing forms, appropriately solidly built (for an amphipod, at least), and most readily distinguished from most other gammarideans by their particularly long fifth pereiopods (the last pair of legs on the main body) (Barnard 1969). They also usually have a long peduncle on the third uropods (the 'tail' appendages), though one distinctive genus Metoediceros lacks the third uropod entirely (Barnard 1974). In many oedicerotids, the eyes have also moved upwards to become coalesced along the dorsal midline and the head often possesses a prominent rostrum. However, these features are absent from a number of Southern Hemisphere and deep-sea taxa (the latter of which generally lack eyes altogether).

Dorsal view of the head of Monoculodes borealis, showing the coalescent eyes, from Andrey Vedenin.

Oedicerotids of the genus Synchelidium have been shown to be predators of harpacticoid copepods (Yu & Suh 2006). The abundance of this food appears to determine their reproductive behaviour, as females produce larger broods in the spring when harpacticoids are more abundant than in the fall.

REFERENCES

Barnard, J. L. 1969. The families and genera of marine gammaridean Amphipoda. United States National Museum Bulletin 271: 1-535.

Barnard, J. L. 1974. Evolutionary patterns in gammaridean Amphipoda. Crustaceana 27 (2): 137-146.

Yu, O. H., & H.-L. Suh. 2006. Life history and reproduction of the amphipod Synchelidium trioostegitum (Crustacea, Oedicerotidae) on a sandy shore in Korea. Marine Biology 150: 141-148.

Flower-tails

The patterned anthurid Mesanthura astelia, from Museum Victoria.

Anthuroidea (or Anthuridea, depending on where you look) are small marine isopods that get up to a couple of centimetres in length. Anthuroids are distinguished from other isopods by their particularly narrow, elongate body form, as well as (in most species) their tail-fans with the component uropods arranged in a manner reminiscent of a 'five-petalled flower' (hence the name of the group, 'flower-tails'). The one exception is the recently described Leipanthura casuarina in which the uropod branches are cylindrical rather than flattened; Leipanthura is a very small species (less than 3 mm long) and probably represents a neotenous form retaining a juvenile tail morphology into adulthood (Poore 2009).

The question of whether this group should be called Anthuridea or Anthuroidea relates to different proposals on their phylogenetic position. The name 'Anthuridea' is older (replacing an even earlier name, Aberrantia, that does not appear to have any recent usage) but was changed to Anthuroidea by Brandt & Poore (2003) when they reclassified anthuroids from a separate 'suborder' of isopods to a 'superfamily' within the suborder Cymothoida. In a more recent analysis by Wilson (2009), the monophyly of Cymothoida was supported by morphological data alone, but not by molecular data or combined analysis (in particular, several parasitic 'cymothoid' families such as Gnathiidae and Bopyridae formed a clade in the latter analyses that was sister to all other isopods). As the composition of the anthuroids has never altered under either name, the question of orthography is largely academic.

Individual of Paranthura elegans, photographed by Peter J. Bryant. Paranthura belongs to a separate family (Paranthuridae) from Mesanthura (Anthuridae); the families are distinguished by the mouthparts of Paranthuridae being modified into piercing stylets, as opposed to the chewing mouthparts of Anthuridae.

Anthuroids live hidden among sponges, corals, seaweeds, etc. or burrowed into sand, where they are active hunters of smaller invertebrates (as evidenced by their raptorial forelimbs). They have most commonly been recorded from shallow waters, but are also known from the deep sea (Kensley 1982). It is unclear whether their supposed rarity in deep-sea collections reflects poorer investigation, or whether the morphological conservatism of anthuroids compared to other isopod groups has restricted their ecological diversity. At least some species are protogynous sequential hermaphrodites (Brusca et al. 2001), that is, they begin life as females and transform later into males.

REFERENCES

Brandt, A., & G. C. B. Poore. 2003. Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics 17 (6): 893-923.

Kensley, B. 1982. Deep-water Atlantic Anthuridea (Crustacea: Isopoda). Smithsonian Contributions to Zoology 346: 1-60.

Poore, G. C. B. 2009. Leipanthura casuarina, new genus and species of anthurid isopod from Australian coral reefs without a “five-petalled” tail (Isopoda, Cymothoida, Anthuroidea). ZooKeys 18: 171–180.

Wilson, G. D. F. 2009. The phylogenetic position of the Isopoda in the Peracarida (Crustacea: Malacostraca). Arthropod Systematics and Phylogeny 67 (2): 159-198.

Snail Mimics and Marine Symbionts (Taxon of the Week: Pleustidae)

The pleustid amphipod Incisocalliope aestuarius. Photo by Marco Faasse.

The Pleustidae are a family of marine amphipods, distributed around the world. However, despite their seemingly cosmopolitan distribution and abundance, it has been surprisingly difficult to find information about this family online. Pleustids are one of the many families in the largest of the amphipod suborders, the Gammaridea (gammarideans include the sandhoppers and other sandhopper-looking crustaceans that are what most people think of when they think of an amphipod). Gammaridean interrelationships are a great tangled mess, and in many places fall into a state that we scientists technically refer to as "buggered beyond belief". Only slowly are researchers beginning to draw some sense out of things, and they'll probably be at it for a long time yet. For those who wish to track them down (for the most part, I haven't seen them), the main revisions of Pleustidae were published by Bousfield & Hendrycks (1994 and following) in Amphipacifica*. Stock (1986) (who very tentatively assigns three oddball stygobiotic species from Japan to the Pleustidae) gives the defining characters of the family as "the rudimentary condition of the accessory flagellum of the first antenna, the biramous third uropod (rami lanceolate), the elongate telson, the weak and more or less similar gnathopods 1 and 2, and... the bilobed condition of the labrum". Bousfield & Hendrycks (1994, 1995) divided the family into a number of subfamilies.

*The short-lived journal Amphipacifica ended up with three volumes published between 1994 and 2001 (I haven't found any indications that a planned fourth volume ever made an appearance). While I haven't found a complete contents listing, it appears that most (if not all) articles had the chief editor, Edward Bousfield, as author or co-author, and the majority were on amphipod taxonomy. Perhaps unjustly, the journal is not remembered for its contributions to crustacean systematics as much as it is for Bousfield's perhaps unwise foray into vertebrate taxonomy. Yes, this was the journal that saw the publication of the infamous Bousfield & LeBlond (1995), and the name Cadborosaurus wellsi - a paper so controversial that two of the journal's editors promptly handed in their resignations in protest. For more details, see Darren Naish's 2006 review.

Not having the resources on hand to give you a a decent overview of the family (sorry), I'm just going to give you a couple of the highlights that I have been able to locate - (as it says in the title) the snail mimics and the symbiotic taxa.


Pleustes panopla, a close relative of one of the snail-mimicing pleustids. Photo via here.

Snail mimicry has been recorded for two pleustids, Pleustes platypa and unidentified species of Stenopleustes (Field, 1974). Pleustes platypa lives in kelp beds and mimics the marine gastropod Mitrella carinata. Mimetic Stenopleustes (it is not known how many species are involved) live in beds of Zostera (seagrass) and mimic various species of snails of the genus Lacuna. Different Stenopleustes individuals may have different colour patterns, each matching a different Lacuna species. The amphipod clings tightly to the seagrass, moving slowly to match the speed of a snail. Occassional rocking back and forth mimics the rocking movement of the snails. And while amphipods are perfectly adept swimmers, snail-mimicing Stenopleustes would only swim under extreme provocation, preferring to crawl to the other side of the seagrass blade instead when possible. Obviously, starting to swim would quickly give away that the animal was not a snail!

Other intriguing pleustids are the species that live as symbionts (generally commensals) of larger marine invertebrates. Commensipleustes commensalis is a symbiont of crabs, with enlarged spines on the underside of the forelimbs against which the dactylus (claw) can be folded back, allowing the amphipod to hang onto the host's setae. Members of the genus Dactylopleustes, on the other hand, live on sea urchins, and their legs have notched claws that can be placed around the host's spines. Another species, Mesopleustes abyssorum, clings to the legs of sea spiders. But most remarkable of all is the lifestyle that has been inferred for the species Myzotarsa anaxiphilius (Cadien & Martin, 1999). Like Commensipleustes, Myzotarsa is a symbiont of crabs (in this case, king crabs of the genus Paralithodes), but while most crab-symbiotic amphipods live around the densely setose mouthparts, Myzotarsa lives underneath the crab's recurved abdomen. Without setae to cling on to, the claws on the walking legs of Myzotarsa bear special suckers to allow the animal to latch on. What makes Myzotarsa really remarkable is that not just any crab will make a suitable host - instead, the amphipod shows a strong preference for crabs that are parasitised by rhizocephalans (out of 179 specimens of Myzotarsa referred to by Cadien & Martin, 1999, 167 came from parasitised hosts while only six came from a non-parasitised host [the remainder came from hosts whose parasite status was not recorded). It seems that the diet of the little Myzotarsa is the eggs being incubated underneath the abdomen. While healthy crabs will only be carrying eggs if they're female and if it's the right season, the chemically-castrated, feminised (if male) and mind-controlled infected crabs will be carrying externa filled with yummy rhizocephalan eggs all year round...

REFERENCES

Bousfield, E. L., & E. A. Hendrycks. 1994. A revision of the family Pleustidae (Crustacea: Amphipoda: Leucothoidea). Part I. Systematics and biogeography of component subfamilies. Amphipacifica 1: 17-57.

Bousfield, E. L., & E. A. Hendrycks. 1995. The amphipod family Pleustidae on the Pacific coast of North America: Part II. Subfamilies Parapleustinae, Dactylopleustinae, and Pleusirinae. Systematics and distributional ecology. Amphipacifica 2: 65-133.

Bousfield, E. L., & P. H. LeBlond. 1995. An account of Cadborosaurus willsi, new genus, new species, a large aquatic reptile from the Pacific coast of North America. Amphipacifica 1 (Supplement 1): 3-25.

Cadien, D. B., & J. W. Martin. 1999. Myzotarsa anaxiphilius, new genus, new species, an atylopsine amphipod (Gammaridea: Pleustidae) commensal with lithodid crabs in California. Journal of Crustacean Biology 19 (3): 593-611.

Field, L. H. 1974. A description and experimental analysis of Batesian mimicry between a marine gastropod and an amphipod. Pacific Science 28 (4): 439-447.

Stock, J. H. 1986. Amphipoda: Pleustidae. In Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) (L. Botosaneanu, ed.) pp. 560-561. E. J. Brill / Dr. W. Backhuys: Leiden.

Another Case of Mistaken Identity

Just the other day, Adam Yates showed us a couple of photos of a fossil that had been identified as dinosaurian, but actually belonged to a fish. Identifying isolated pieces of things can be a hazardous activity, and a mistaken identification can become something of a self-fulfilling prophecy - once the idea of a certain identity for your specimen has developed, you will tend to find "characters" that support your identification. Palaeontology, of course, presents researchers with no shortage of fragmentary remains, and it is not entirely surprising that a few snafus have occured. Adam referred to the case of Aachenosaurus multidens, a "hadrosaur" described in 1888 that was soon reidentified as a piece of petrified wood. A similar fate befell the "sauropod jaw" Succinodon putzeri (making the first four letters of the species name even more apropos). But while the most famous (and most dramatic) examples of such misidentifications involve fossils, studies of recent organisms have not been entirely free of impostors.



The figure above from Huys (2001) shows two views of the paratype of Megallecto thirioti, described by Gotto in 1986. The two specimens originally assigned to this species came from a plankton haul off the coast of Mauretania. Gotto identified them as parasitic copepods belonging to the family Splanchnotrophidae, and suggested that their hosts might be pteropods from the same haul.

Parasitic copepods can certainly be very strange creatures. While free-living males (and larvae of both sexes) may look like fairly ordinary copepods, the parasitic females may have highly derived morphologies that barely resemble crustaceans, let alone copepods. Consider the female of another splanchnotrophid, Arthurius elysiae (also from Huys, 2001):



When Huys (2001) revised the Splanchnotrophidae, however, he discovered that Gotto's Megallecto was (A) not a splanchnotrophid, and (B) not even a copepod. In fact:



'Megallecto' was nothing but a large chunk of the detached head of Phrosina semilunata, a pelagic amphipod. Phrosina belongs to a group of amphipods known as Hyperiidea. Most hyperiids feed on gelatinous plankton such as jellyfish or salps. They may or may not feed on pteropods.

REFERENCES

Huys, R. 2001. Splanchnotrophid systematics: A case of polyphyly and taxonomic myopia. Journal of Crustacean Biology 21 (1): 106-156.

Southern Crustacean Relicts

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

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

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

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


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

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

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

REFERENCES

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

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

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

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

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

Taxon of the (this) week - Holarctic subterranean amphipods, Batman!

Yesterday, after much grousing, I introduced you to last week's belated taxon of the week. So as not to get caught out like that again, today I'm introducing this week's title-holder - the amphipod genus Crangonyx. The image at left comes from here.

Crangonyx is the type genus of the family Crangonyctidae. Crangonyctidae is an entirely Holarctic family (Holsinger, 1986) that shows an interesting tendency towards a subterranean lifecycle. When Holsinger reviewed the family in 1986, 126 of the 154 known species where stygobionts (exclusively cave-dwelling). More species have been described since then, but the proportion of stygobionts is probably still roughly the same. Even those species that are not stygobionts are cold-stenothermal (only able to tolerate cold water temperatures) and photonegative (keep away from light). Many are stygophilic (not exclusively cave-dwelling, but often found in cave habitats). Crangonyx, with 47 species, is one of only three genera of crangonyctids with epigean (surface-dwelling) species (the others are Synurella and the monotypic Lyurella hyrcana, which may be a species of Synurella - Holsinger 1986). Epigean species of Crangonyx have small but distinct eyes and pigmentation between light brown and pale green in colour, while stygobiont species may retain vestigial eyes and traces of pigmentation (in contrast to exclusively stygobiont crangonyctid genera, which are invariably eyeless and colourless). The greater number of known Crangonyx species come from North America, with only a few from Eurasia - however, I would be inclined to suspect (admittedly without real evidence) that a certain degree of researcher bias may be at fault here.* Perhaps the most widely distributed species is Crangonyx pseudogracilis, shown above in a photo from Bioimages (copyright Malcolm Storey, 2004). Originally native to North America, this species has been introduced to Europe.

*The vast majority of species of organisms on this planet remain undescribed - there are probably about 1.5 million described species, and while it is difficult to estimate how many species remain to be discovered, estimates of 20 million are not impossible (Harrison et al. have a brief review here). As a result, there are many higher taxa for which the current known species distribution does not accurately reflect reality. Major factors influencing this discrepancy will be collection and study bias - for instance, if most of the researchers on a given taxon have been North American, then there might be expected to be an inflated view of North American diversity as opposed to elsewhere. In the case of Crangonyx, 24 of the known species were erected in a recent review of the North American fauna (Zhang & Holsinger, 2003), and one can't help wondering what would be uncovered if, say, the Siberian fauna received the same treatment.

One species of Crangonyx, C. islandicus Svavarsson & Kristjánsson, 2006 was recently described as part of the Icelandic subterranean fauna. This has interesting implications for the biogeographical history of Crangonyctidae - due to the family's exclusively freshwater, stringent habitat requirements, it is believed to have originated prior to the tectonic separation of Europe and North America and spread by vicariance as the continents divided. The Crangonyctidae are certainly very old - Palaeogammarus from Baltic amber is essentially indistinguishable from modern crangonyctids. Iceland is far younger than the opening of the Atlantic. However, Kristjánsson & Svavarsson (2007) indicate that Crangonyx, as well as the ancestors of the endemic Icelandic Crymostygiidae (Kevin Z has already commented on this here) may have spread along the Greenland-Iceland ridge as the geological hotspot that is responsible for the formation of Iceland drifted east, if at least a part of the ridge was above sea-level and held groundwater during that time (note that it does not have to have always been the same part - if extra land was raised above sea-level in the east at about the same rate as land eroded below sea-level in the west, that'd do).

REFERENCES

Holsinger, J. R. 1986. Holarctic crangonyctid amphipods. In Stygofauna Mundi: A faunistic, distributional, and ecological synthesis of the world fauna inhabiting subterranean waters (including the marine interstitial) (L. Botosaneanu, ed.) pp. 535-549. E. J. Brill/Dr. W. Backhuys: Leiden.

Svavarsson, J., & B. K. Kristjánsson. 2006. Crangonyx islandicus sp. nov., a subterranean feshwater amphipod (Crustacea, Amphipoda, Cranonyctidae) from springs in lava fields in Iceland. Zootaxa 1365: 1-17.

Kristjánsson, B. K., & J. Svavarsson. 2007. Subglacial refugia in Iceland enabled groundwater amphipods to survive glaciations. American Naturalist 170: 292-296.

Zhang, J., & J. R. Holsinger. 2003. Systematics of the freshwater amphipod genus Crangonyx (Crangonyctidae) in North America. Virginia Museum of Natural History, Memoir 6: 1–274.