FRESHWATER AND TERRESTRIAL CRUSTACEA
P.A. Gainey, C.J. Neil and S.M. Turk
(Anostraca & Amphipoda by P.A. Gainey,
Cladocera & Ostracoda by S.M. Turk and Isopoda by C.J. Neil)
1. Branchiopoda: Anostraca
Chirocephalus diaphanus Fairy Shrimp
2. Water Fleas (Cladocera)
There are 92 British species of water-fleas listed by Hearn (1974), 43 of them being present in Cornwall. Hearn (1986) did some intensive recording on the Lizard Peninsula (including Loe Pool) between 1971 and 1985 when he found 24 species. All the Cornish species are widespread and common with the following exceptions:
3. Copepods (Copepoda)
Compared with at least 1280 British species of marine copepods, there are only 50 or so to be found in terrestrial (usually subterranean or in moss) and freshwater habitats. In all three habitats there are free-living, commensal and parasitic representatives. They are usually less than 0.5mm, and except for those following a parasitic life, they are a distinctive shape. Harding and Smith (1974) provide notes on the general British distribution as well as keys to the species.
4. Bean animalcules (Ostracoda)
Henderson (1990) lists 85 British species. There seems to have been no special study of the Cornish freshwater ostracods since 1905 when Rupert Vallentin collected at several sites for A.M. Norman and T. Scott who were responsible for identifying them (Norman & Scott, 1906). Consequently there are only 16 species known from Cornwall, and none listed for the Isles of Scilly. Two of these are Nationally Scarce.
5. Amphipoda (Freshwater)
Two species typically found in underground/interstitial water are Niphargus aquilex Schibdte, the commonest British niphargid, recorded in wells at Saltash and St. Stephen-in-Brannel by Canon J.H. Adams in 1930 but not recorded since, and Niphargus glenniei, described below.
Niphargus glennei South-western Groundwater Shrimp
6. Woodlice (Isopoda)
Woodlice are amongst the most accessible groups of animals to study; there can be few households which do not contain at least one species. However, without doubt our present knowledge of the status and distribution of woodlice within Cornwall is sketchy and very much shaped by recorder bias. Woodlice belong to the order Isopoda which is dominated by the marine species. All 37 species of terrestrial Isopods found in Britain belong to the suborder Oniscidea. 26 species of non-marine Isopods (including two aquatic species) have been recorded from Cornwall with Trichoniscus pusillus, Oniscus asellus, Philoscia muscorum and Porcellio scaber being ubiquitous. The splash zone of the sea shore is an area rich in woodlice, though many species are difficult to find because of their small size (frequently less than 4mm in length); the largest British species Ligia oceanica (up to 30mm long) is common all along the coast. Cornwall is also a stronghold for Porcellionoides cingendus, which is common in coastal grasslands, while another large species Armadillidium vulgare (up to 18mm long) is very tolerant of dry conditions and is common in coastal sand dunes. Two species which are probably very common but may be overlooked because of their small size are Trichoniscus pygmaeus and the striking rosey-pink Androniscus dentiger; both are likely to occur anywhere in damp soil and leaf litter, the latter particularly around man-made structures. The unusual little blind white woodlouse Platyarthrus hoffmannseggi is a frequent resident of ant nests particularly near the coast. Our two aquatic species Asellus aquaticus and Asellus meridianus are commonly found in a variety of freshwater pools, lakes, streams and rivers. Identification of all British species is covered by Hopkin (1991). The newsletter and Bulletin of the British Myriapod and Isopod Group provides useful up-to-date information and promotes the study of this under-recorded group of invertebrates. An account of the woodlice found in Cornwall is given in Jones (1987); the Isles of Scilly have been covered by Jones and Pratley (1987). A good general introduction to woodlice can be found in Sutton (1972). Harding & Sutton (1985) provided extensive information on distribution in the first atlas for British woodlice and provided a list of Red Data woodlice, including two species which have been found either in Cornwall or in the Isles of Scilly, Armadillidium album and Halophiloscia couchii. This listing has been altered subsequently following further survey work and Bratton (1991) dropped both species. Nationally, records are now compiled through the Isopod Recording Scheme which is part of the British Myriapod and Isopod Group (http://groups.google.com/group/bmigroup/web/index-2). Recent information on national distribution is available from the Interim Isopod Dataset through the British Myriapod and Isopod Group website. A new checklist of non-marine isopods for Britain and Ireland has been compiled (Gregory, 2008) and a new atlas is currently being produced from which national rarity status will be re-assessed. Reference to national Red Data status has not therefore been included here.
Non-native Isopod species
Twelve species of non-native terrestrial woodlouse have been listed for Britain and Ireland in the new checklist (Gregory, 2008). They have been recorded from heated greenhouses and have, no doubt, been imported on foreign plant material. In Cornwall a number have been recorded from the Eden Project (SX05) including Trichorhina tomentosa Budde-Lunde and, for the first time in Britain and Ireland, the tropical/subtropical species Venezillo parvus Budde-Lunde (Gregory, 2009).