Habitat Preferences and Interspersion of Species within the Superspecies Jaera albifrons Leach (Crustacea: Isopoda)

Abstract

Within the 'species' Jaera albifrons Leach (= J. marina Bate & Westwood = Oniscus marinus Fabr. nec Linnie) there is considerable variation in the form of the secondary sexual characters of the male (Sye 1887; Kesselyak 1938), on the basis of which Forsman (1944, 1949) recognized four distinct morphological races. Bocquet (1950, 1953, 1954) elevated these and two additional races to the rank of species within the superspecies Jaera marina and named each one on a trinomial system thus: J. marina albifrons Leach, J. m. forsmani Bocquet, J. m. ischiosetosa Forsman, J. m. posthirsuta Forsman, J. m. praehirsuta Forsman, and J. m. syei Bocquet. All of these except J. m. posthirsuta, which is North American, have been recorded in Britain under the superspecific name J. albifrons (Naylor, Slinn & Spooner 1961). In separating continental European forms of J. albifrons, both Forsman (1944, 1949) and Bocquet (1953, 1954) have described distinct habitat preferences for each species, which do not overlap and which also appear to be clearly zoned on the shore according to tidal level. So far in Britain it has not been possible to generalize about the habitat preferences of each species, partly owing to regional differences and partly owing to the fact that the ranges of each species often overlapped (Naylor, Slinn & Spooner 1961). The present investigation was therefore carried out to demonstrate the habitat preferences and the extent of habitat interspersion amongst the species of J. albifrons in a limited area in order to make more careful comparisons with what is known of their distribution elsewhere.