Isopoda

Phreatoicus typicus, copyright NIWA.

Belongs within: Eumalacostraca.
Contains: Scuticoxifera, Asellota, Microcerberidae, Phreatoicidae, Amphisopidae

The Phreatoicidea are a group of isopods currently found in Australasia, India and South Africa. Modern species are freshwater dwellers (including a number of stygobiotic species), though fossil phreatoicids include marine species. Epigean phreatoicids are superficially amphipod-like in appearance, with high-vaulted, narrow bodies; stygobiotic species are more elongate.

Southern crustacean relicts
Published 5 May 2008
Eophreatoicus from Kakadu in the Northern Territory of Australia. Image from here.

This page’s subject 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). Scale 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.

<==Isopoda [Euisopoda, Normalia, Polygonata, Pterygibranchia, Quatuordecempedes, Tetracera]BP03
    |--+--ScuticoxiferaBP03
    |  `--+--CalabozoaL86 [Calabozoida, CalabozoideaBP03]
    |     |    `--*C. pellucida Van Lieshout 1983L86
    |     `--+--AsellotaBP03
    |        `--MicrocerberideaBP03
    |             |--MicrocerberidaeMD01
    |             `--Atlantasellus Sket 1979HLM86 [AtlantasellidaeMD01]
    |                  `--A. cavernicolus Sket 1979HLM86
    `--PhreatoicideaBP03
         |  i. s.: SynamphisopusK86
         |         Phreatomerus latipesK86
         |--PhreatoicidaeK86
         |--AmphisopidaeK86
         |--Nichollsia Chopra & Tiwari 1950 [Nichollsidae]K86
         |    |--N. kashiense Chopra & Tiwari 1950K86
         |    `--N. menoni Tiwari 1955K86
         `--PalaeophreatoicidaeBWW93
              |--Hesslerella shermani Schram 1970BWW93
              |--Palaeocrangon problematicus (von Schlotheim 1820)BWW93
              `--Palaeophreatoicus Birstein 1962K86
                   `--*P. sojanensis Birstein 1962K86
Isopoda incertae sedis:
  AlbunioneB02
    |--A. australiana Markham & Boyko 1999B02
    `--A. indecora (Markham 1988)B02
  Syscenus infelixK-M02
  Holotelson tuberculatusKBC03
  Hydroniscus lobocephalusB88
  Urda Münster 1840 [Urdidae]BWW93
    |--U. punctata Münster 1842GH05
    `--U. rostrata Münster 1840GH05
  IsocladusHS01
    |--I. armatusHS01
    `--I. dulciculusHS01
  Batedotea elongatusHS01
  Notatolana albicaudataHS01
  Pentheus tuberculatus [=Armadillo tuberculatus]S77
  Proteolepas bivinctaG87
  Oxyuropoda ligioidesH47
  Nodoplanulis Hussey 1943LT64
    `--*N. elongata Hussey 1943LT64
  CampecopeaR26
    |--C. bituberculata Risso 1826R26
    |--C. corallina Risso 1826R26
    |--C. hirsutaPP64
    |--C. spinosaR26
    |--C. trigonaR26
    `--C. vulgaris Risso 1826R26
  Ischyromene lacazeiPP64
  Zenobiana prismaticaPP64
  Amphoroidea australiensisH15
  Quantanthura pacificaPG98
  Albanthura stenodactylaPG98
  Neastacilla levisPG98
  Papuasoniscus holthuisiH83
  Pseudarmadillo [Pseudarmadillidae]P92
    |--P. cristatusP92
    `--P. tuberculatusP92
  LeptosomaR26
    |--L. appendiculata Risso 1826R26
    `--L. lanceolataR26
  Hebe Risso 1826 non Jussieu 1789 (ICBN)R26
    `--*H. punctata Risso 1826R26
  Armida Risso 1826R26
    |--A. bimarginata Risso 1826R26
    |--A. pustulata Risso 1826R26
    `--A. viridissimaR26
  Zenobia Risso 1826R26
    |--Z. mediterranea Risso 1826R26
    `--Z. prismatica Risso 1826R26
  Oliska Risso 1826R26
    `--*O. penicellataR26
  NelociraR26
    |--N. brongniartiiR26
    `--N. navicularisR26
  CanoliraR26
    |--C. oestroidesR26
    `--C. ottoR26
  Olympia Risso 1826R26
    |--O. moyonia Risso 1826R26
    |--O. ricinoidesR26
    |--O. rugulosa Risso 1826R26
    |--O. viviania Risso 1826R26
    `--O. vulgaris Risso 1826R26
  Helena Risso 1826R26
    `--*H. spinola Risso 1826R26
  Sophone Risso 1826R26
    `--*S. nicaeensis Risso 1826R26
  Osirusa Risso 1826R26
    `--*O. petagniana Risso 1826R26

*Type species of generic name indicated

References

[B88] Boxshall, G. A. 1988. A new genus of tantulocaridan (Crustacea: Tantulocarida) parasitic on a harpacticoid copepod from Tasmania. Bulletin of the British Museum (Natural History), Zoology series 54 (6): 271–274.

[B02] Boyko, C. B. 2002. A worldwide revision of the recent and fossil sand crabs of the Albuneidae Stimpson and Blepharipodidae, new family (Crustacea: Decapoda: Anomura: Hippoidea). Bulletin of the American Museum of Natural History 272: 1–396.

[BP03] Brandt, A., & G. C. B. Poore. 2003. Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics 17: 893–923.

[BWW93] Briggs, D. E. G., M. J. Weedon & M. A. Whyte. 1993. Arthropoda (Crustacea excluding Ostracoda). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 321–342. Chapman & Hall: London.

[GH05] Gaillard, C., P. Hantzpergue, J. Vannier, A.-L. Margerard & J.-M. Mazin. 2005. Isopod trackways from the Crayssac Lagerstätte, Upper Jurassic, France. Palaeontology 48 (5): 947–962.

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 measurement. Biological Journal of the Linnean Society 81: 235–253.

[G87] Grygier, M. J. 1987. New records, external and internal anatomy, and systematic position of Hansen’s y-larvae (Crustacea: Maxillopoda: Facetotecta). Sarsia 72: 261–278.

[H83] Hammen, L. van der. 1983. Contribution to the knowledge of the soil-fauna of New Guinea. Zoologische Verhandelingen 206: 1–36.

[H47] Hatch, M. H. 1947. The Chelifera and Isopoda of Washington and adjacent regions. University of Washington Publications in Biology 10 (5): 155–274.

[HS01] Hayward, B. W., A. B. Stephenson, M. S. Morley, W. M. Blom, H. R. Grenfell, F. J. Brook, J. L. Riley, F. Thompson & J. J. Hayward. 2001. Marine biota of Parengarenga Harbour, Northland, New Zealand. Records of the Auckland Museum 37: 45–80.

[H15] Hedley, C. 1915. Presidential address. Journal and Proceedings of the Royal Society of New South Wales 49 (1): 1–77, pls 1–7.

[HLM86] Henry, J.-P., J. J. Lewis & G. Magniez. 1986. Isopoda: Asellota: Aselloidea, Gnathostenetroidoidea, Stenetrioidea. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 434–464. E. J. Brill/Dr. W. Backhuys: Leiden.

[KBC03] Kashin, I. A., E. V. Bagaveeva & S. F. Chaplygina. 2003. Fouling communities of hydrotechnical constructions in Nakhodka Bay (Sea of Japan). Russian Journal of Marine Biology 29: 267–283.

[K-M02] Klein-MacPhee, G. 2002. Grenadiers. Family Macrouridae. In: Collette, B. B. & G. Klein-MacPhee (eds) Bigelow and Schroeder’s Fishes of the Gulf of Maine 3rd ed. pp. 212–216. Smithsonian Institute Press: Washington.

[K86] Knott, B. 1986. Isopoda: Phreatoicidea. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) 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.

[L86] Lieshout, S. E. N. van. 1986. Isopoda: Calabozoidea. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 480–481. E. J. Brill/Dr W. Backhuys: Leiden.

[LT64] Loeblich, A. R., Jr & H. Tappan. 1964. Sarcodina: chiefly “thecamoebians” and Foraminiferida. In Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt C. Protista 2 vol. 2. The Geological Society of America and The University of Kansas Press.

[MD01] Martin, J. W., & G. E. Davis. 2001. An updated classification of the Recent Crustacea. Natural History Museum Los Angeles County, Science Series 39: 1–124.

[PP64] Peres, J. M., & J. Picard. 1964. Nouveau manuel de bionomie benthique de la mer Mediterranee. Recueil des Travaux de la Station Marine d’Endoume, Bulletin 31 (27): 5–137.

[P92] Poinar, G. O., Jr. 1992. Life in Amber. Stanford University Press: Stanford.

[PG98] Probert, P. K., & S. L. Grove. 1998. Macrobenthic assemblages of the continental shelf and upper slope off the west coast of South Island, New Zealand. Journal of the Royal Society of New Zealand 28: 259–280.

[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.

[S77] Schmalfuss, H. 1977. Eine neue Nagurus-Art aus der Süd-Agäis (Crustacea: Isopoda: Oniscoidea: Trachelipidae). Senckenbergiana Biologica 57 (4–6): 359–365.

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

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