Development, hatching and brood size in Bathyporeia pilosa and B. pelagica (Crustacea: Amphipoda)

Abstract

The haustoriid amphipods Bathyporeia pilosa and B. pelagica are common in intertidal sand deposits around the British Isles. Both species live in the surface sediments and B. pilosa is typically a high-shore species, while B. pelagica is restricted to beach levels below the high-water mark of neap tides. Gravid females are readily identified by the presence of blue-pigmented eggs held in the brood pouch where they undergo direct development. The extent of the breeding season varies with locality (Salvat, 1967; Fish & Preece, 1970) and on the west coast of Wales B. pilosa breeds throughout the year and B. pelagica from March to October (Fish & Preece, 1970). At this locality, however, the breeding cycles of the two species are similar in that they show reproductive peaks in spring and autumn and it has been suggested that the spring peak is caused by breeding of the overwintering generation, the progeny of which mature to reproduce in the autumn of the same year (Fish & Preece, 1970). In common with many amphipod species, brood size of Bathyporeia is related to body length. Salvat (1967) has shown that the brood size of B. pelagica on the west coast of France doubles from February to April, but apart from his study adequate data on brood size are lacking. This paper describes embryonic development, hatching and brood size of overwintering and summer generations of both species.