Recording schemes

The hypogean (subterranean) Crustacea recording scheme is a small scheme dealing with the subterranean macro-Crustacea (Malacostraca) found in the groundwater and aquatic cave habitats of the British Isles, including Ireland. The scheme only encompasses the (mostly) larger Crustacea specifically evolved to exist in underground aquatic habitats (stygobites). Adaptations to the underground aquatic environment typically involve a lack of pigment (i.e. specimens are white in colour), a lack of eyes and over-development of antennae and legs. Most species are also quite small and/or have a thin body shape for squeezing between small water-filled crevices in underground rock strata and water-logged gravels.

Specimens of the ubiquitous epigean (surface-dwelling) freshwater shrimp Gammarus pulex are often recorded in caves but are usually washed in from the surface, although some isolated stygophilic populations have been recorded. In Ireland a similar case exists with Gammarus duebeni celticus. Both of these species are not included in the scheme.

The scheme also does not cover the micro-Crustacea (Copepoda, Ostracoda, Cladocera etc.). Amongst the micro-crustaceans there are several species that have been recorded from cave and groundwater habitats but it is thought that the copepod Acanthocyclops sensitivus is the only true sygobitic copepod in Britain, whilst the stygobitic ostracods Fabaeformiscandona breuili and F. wegelini have also recently been recorded from Ireland and Britain (Knight & Mori, 2022). Proudlove et. al. (2003) includes the various micro-Crustacea besides the subterranean Malacostraca, and discusses their distributions and hypogean status, as well as the occurrence of Gammarus species underground.  Knight & Mori (2022) update the records of subterranean Ostracoda, including seveeral important new records from the last two decades.

The eleven stygobitic Malacostraca Crustacea recorded from Britain and Ireland are listed below.