Asellus aquaticus (Linnaeus, 1758)
GB IUCN status: Least Concern
Asellus aquaticus can usually be distinguished from the frequent Proasellus meridianus by the pattern of pigmentation of the head, with two pale spots at the back separated by a central dark pigmented area. However, head pigmentation can vary and the two species are frequently confused. The shape of the male first pereopod (leg) is diagnostic.
Asellus aquaticus is abundant throughout Britain (but under-recorded in Wales and Scotland) and probably across Ireland (where is seems to be badly under-recorded).
It occurs in a wide variety of water-bodies, including small urban garden ponds, ditches, lakes, canals and rivers.
Specimens can be found among water plants, under stones and submerged bits of dead wood, among the roots of riparian trees and on the stonework of bridges. It is tolerant of organically polluted waters, high salinities, low pH and high metal concentrations.
This summary is based on the detailed account in Gregory (2009).