Synonyms
Asellus coxalis Dollfus, 1892
Status:
GB IUCN status: Not applicable (non-native)
ID Difficulty
Identification
Waterlice (Asellidae) are distinguished from the terrestrial woodlice by their plate-like pleotelson, consisting of four pleonites and the telson fused together.
Adult Proasellus coxalis are similar in size to P. meridionalis, with males reaching 10mm and females, 8mm. This contrasts with the larger Asellus aquaticus, which can measure up to 20mm.
The pale marking along the posterior head margin can be used to differentiate P. coxalis from the other waterlice. Both Proasellus species have a single, continuous marking, while A. aquaticus usually has two distinct rectangular markings separated by an area of pale dots. In P. meridionalis, the marking has a neatly delineated border, whereas in P. coxalis the pale area has an ill-defined, speckled border (see image to right).
Although a useful feature, head markings can be variable and difficult to discern, especially in young specimens. To reach a definitive identification, it is necessary to microscopically examine the first and second male pleopods.
Text prepared by Dr. Stephanie Skipp.
