Parastenocaris

Parastenocaris brevipes, copyright A. Hobaek.

It's time for another consideration of the overwhelming diversity of stygofaunal copepods. Parastenocaris is a genus of copepods found on almost all the landmasses of the world except, presumably, Antarctica (New Zealand also stands out as an intriguing void in the genus' distribution). The majority of species in this genus are insterstitial, mostly found in soils saturated with fresh water; a small number of species are found in brackish habitats such as estuaries. A few species have also been found above ground, particularly in the tropics (Galasi & Laurentiis 2004). The type species of the genus, P. brevipes, has been found in sphagnum bogs (Karanovic 2005).

As commonly recognised, Parastenocaris is a pretty huge genus, with well over 200 species having been assigned to it over the years. However, the genus has been poorly defined and many authors have questioned its integrity. Galasi & Laurentiis (2004) suggested that Parastenocaris should be restricted to those species most closely related to the type species, P. brevipes. Such a group would still be pretty cosmopolitan; indeed, P. brevipes itself has a Holarctic distribution and is known from both Europe and North America (this stands in pretty stark contrast to the super-short ranges of some stygofaunal copepods). Distinctive features of this restricted P. brevipes group include a characteristic endopodal complex on leg 4 of the male, with the endopod hyaline and with one or two large claws. In contrast, the leg IV endopod in females is long and distally serrate.

Parastenocaris lacustris, from here

Members of the Parastenocaris brevipes groups are found closer to the soil surface than many other members of their family (Karanovic 2005). They are also relatively large, reaching the absolutely monstrous size (I'm sure) of half a millimetre or more. Karanovic (2005) suggested that this larger size could reflect the larger size of the sand grains they live among closer to the surface, or it could simply reflect their access to more reliable food sources that are available to their more deeply buried relatives.

REFERENCES

Galasi, D. M. P., & P. de Laurentiis. 2004. Towards a revision of the genus Parastenocaris Kessler, 1913: establishment of Simplicaris gen. nov. from groundwaters in central Italy and review of the P. brevipes-group (Copepoda, Harpacticoida, Parastenocarididae). Zoological Journal of the Linnean Society 140: 417–436.

Karanovic, T. 2005. Two new subterranean Parastenocarididae (Crustacea, Copepoda, Harpacticoida) from Western Australia. Records of the Western Australian Museum 22: 353–374.