Order ISOPODA Latreille, 1817

Isopod

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Order ISOPODA Latreille, 1817

Compiler and date details

30 April 2005 - Gary C.B. Poore (Editor)

Introduction

The Isopoda have the most diverse range of body plans of all the peracaridans if not of all crustacean orders. Although they are often said to be "dorsoventrally flattened" while amphipods are "laterally flattened," there are many exceptions; some are cylindrical, others laterally compressed, and parasitic forms take many shapes.

The suborder is predominantly marine but is also well represented in estuarine and fresh waters. One suborder, the Oniscidea, is the only large group of Crustacea which is truly terrestrial. Freeliving predators, filter feeders, scavengers, and various parasitic forms are represented. The literature on the systematics and biology of the Isopoda is scattered and few efforts have ever been made in recent times to draw it together. Regional faunas have been summarised by Hurley (1961) for New Zealand, Schultz (1969) for North America, Naylor (1972) for the UK, Kensley (1978) for southern Africa, Brusca & Iverson (1985) for Costa Rica, Kensley & Schotte (1989) for the Caribbean, and Saito et al. (2000) for Japan. Wägele (1991) provided keys and illustrations for the Valvifera of Antarctica. Expedition reports, in particular those of Nierstrasz & Brender à Brandis (1923), Nierstrasz (1931, 1941) on the isopods of the Siboga Expedition, Nordenstam (1933) on the Swedish Antarctic Expedition, and Menzies (1962) on the isopods of Chile, are valuable resources. For readers of Russian, Kussakin's four volumes on the isopods of the north Pacific are comprehensive (Kussakin 1979, 1982, 1986, 1999).

Kaestner (1980) and Schram (1986) have provided chapter-length discussions on general biology. Internal anatomy was covered in detail by Wägele (1992). More recently, the Isopoda have been dealt with in French as chapters of the Traité de Zoologie (Roman & Dalens 1999; Trilles 1999).

The world's described species of marine and freshwater isopods total about 5300 species according to Kensley, Schotte & Schilling (www.nmnh.si.edu/iz/isopod/). The number of terrestrial species on this list is about 4600. Their website at the Smithsonian Institution, National Museum of Natural History lists all the species plus a bibliography of isopod literature. The Australian isopod fauna is especially rich and diverse and, with 1009 species described, comprises almost 10% of the known species. Poore, Just & Cohen (1994) described the ecological distribution of 357 species from the continental slope of south-eastern Australia showing it to be one of the most diverse regions ever studied. Only 10% of the species in this collection were identifiable to species. This Catalogue lists only a small fraction of the species known to exist. Some groups are especially poorly known, e.g. the Asellota where only 46 species out of the hundreds in museum collections have been described.

Our Catalogue includes species from the Australian subantarctic islands, Macquarie Island and Heard Island. Lists of isopods from all the subantarctic and Antarctica were provided by Kussakin (1967), for nearby New Zealand by Hurley (1961) and for the Indian Ocean (including Western Australia) by Kensley (2001). Synonymies list only junior synonyms used for Australian records and for the few non-endemic species a reference to a complete synonymy is given. Hale's (1929) keys are useful for southern Australia but are now incomplete and some of the specific names are outdated. Most modern Australian authors include keys to genera and species.

The traditional division of the Isopoda has been into suborders and infraorders (e.g. Hurley 1961; Bowman & Abele 1982; Martin & Davis 2001) but it is now recognised that this does not reflect their phylogeny. Wägele (1989) and Brusca & Wilson (1991) have presented two competing phylogenies neither of which is fully resolved and neither leads clearly to a more modern classification. We recognise the following monophyletic suborders supported by these and later analysis: Phreatoicidea, Asellota, Microcereberidea (not known from Australia), Calabozoidea (not known from Australia), and Oniscidea. The remaining families have traditionally been placed in the monophyletic Anthuridea, Gnathiidea, Epicaridea and Valvifera, and paraphyletic Flabellifera.

A phylogenetic analysis completed in 2001 by A. Brandt & G.C.B. Poore, but as yet unpublished, has resolved many of the problematic clades but retains the major elements of the Wägele (1989) and Brusca & Wilson (1991) hypotheses. A classification derived from this analysis is used here. Instead of "Flabellifera", four suborders are proposed: Valvifera as in the usual sense, Cymothoida including Anthuridea, Gnathiidea and Epicaridea, Limnoriidea, and Sphaeromatidea.

Inclusion of Anthuridea in a cymothoidan clade was suggested by both Wägele (1989) and Brusca & Wilson (1991); the group is monophyletic and treated here as a superfamily. The same is true of Epicaridea but their two superfamilies are retained for the time being. The close relationship of Bopyridae to Cymothoidae was supported by molecular data by Dreyer & Wägele (2001). The Gnathiidea comprise a single family. It and most other "flabelliferan" families are placed in a paraphyletic superfamily, Cymothooidea while the monophyly of the families themselves and their relationships are undecided. Cirolanidae are placed in a separate superfamily, Cirolanoidea. Two families have never been reported from Australia: Anuropidae Stebbing, 1893 (a small group of oceanic species) and Protognathiidae Wägele & Brandt, 1988.

The relationships of the three families of Limnoriidea was agreed by both Wägele (1989) and Brusca & Wilson (1991) but the new analysis of Brandt & Poore places them as a distinct clade from Sphaeromatidea.

Wägele's (1989) Sphaeromatidea is divided here into two superfamilies, Seroloidea and Sphaeromatoidea. The higher classification of Plakarthriidae may be disputed in the future and the monophyly of the Sphaeromatidae remains doubtful. Tecticipitidae Iverson, 1982 (for species in one genus formerly referred to Sphaeromatidae) have not been recorded from Australia.

The authorities of many family names have often been given incorrectly; we have made a conscious effort to trace the correct authorities carefully.

The published catalogue (Poore 2002) relied for its taxonomy of the Isopoda on work then in preparation but now published (Brandt & Poore 2003).An interactive key to the families of Isopoda in Australia is to be found at Keable et al. (2002).

Database Notes

Updated by Gary C.B. Poore, 30 April 2005.

Diagnosis

Carapace absent; thoracomere 1 fused to head (bearing maxillipeds). Eyes sessile. Antenna 1 typically uniramous. Antenna 2 uniramous or with small exopod. Maxillipedal basis with mesial endite distally directed, epipod lateral. Thoracopods 2– 8 (pereopods 1– 7) uniramous, coxae with dorsal plates sometimes fused to tergites (on pereopod 1 almost always so), sometimes with ventral plates. Pleopods 1– 5 usually biramous, respiratory, second and sometimes first modified in males. Sixth pleonal limb modified as uropod. Telson fused to pleonite 6. Young released from brood pouch at a manca stage (without pereopod 7). Insemination internal; male with paired penes on coxal plates 7 or fused plate on pereonite 7 or pleonite 1, appendices masculinae on mesial or distal margin of endopod of pleopod 2; female gonopores on pereonite 5.