A population of the supralittoral Orchestia gammarellus (Pallas) (Amphipoda: Talitridae), living in a percolating filter of a sewage treatment works has been studied over 12 months. The population showed a seasonal pattern of occurrence, few animals being collected during the winter. The sex ratio was biased significantly to females except during the breeding season when it did not deviate significantly from 1:1. Ovigerous females, never collected in high numbers (1–14 per month), were found from April to August, with peak occurrence in May/June. Juveniles were present throughout the year, but peak recruitment occurred in summer, following the period of reproduction by females. The smallest ovigerous female had a body length of 12.6 mm and the largest measured 20.0 mm. Egg numbers (5–31 per brood) increased with increasing female size and egg volume more than doubled during embryonic development. These findings are discussed in relation to the possible methods of colonization of this unique habitat and the influence of sewage on crustacean life-history traits.

Populations of the prosobranch gastropod Rissoa parva (da Costa) have been investigated from Wembury, Devon, and a number of localities in south-west England and Wales. The distribution of individuals on the shore at, and subsequent to, settlement has been found to be greatly influenced by the anatomical characteristics of algal substrata, animals being more commonly encountered among the fronds of filamentous algal forms. Only during the summer months were individuals found in any appreciable numbers on the more simple forms such as the Fucus spp.While individuals of R. parva generally avoid areas of excessive sedimentation a positive correlation between increased population density of this species and increased sediment content of the algal substratum has been shown for populations collected from the filamentous red algae Lomentaria articulata Lyngb. and Plumaria elegans Schimtz. A similar, though not so marked, correlation is also found for populations living on Gigartina stellata Batt. On Fucus serratus L. no such correlation was evident.The nature of the algal substraum affects the seasonal variation in population density: on the mat-like growth forms of Corallina officinalis L. and Lomentaria articulata population densities remain fairly high, even increase in some instances, over the winter months, whereas on other algal substrata a sharp decline in density closely follows an August/ September maximum.Recently settled individuals are evident throughout the year, though settlement intensity varies, being highest during August 1972 at Wembury. The post-settlement phase of the life-cycle varies between 3 and 9 months, according to the season, and as many as six generations per annum have been recorded.

No abstract

The classification of the Rissoidae has been, and continues to be, based largely upon shell characters. In a group of small animals of variable form this has resulted in a state of considerable taxonomic confusion. Ponder (1965, 1967, 1968), in his works on the New Zealand Rissoidae, attempted to clarify, what he termed, the existing ‘pigeon-hole classification’ in the light of more detailed anatomical investigation. He observed (Ponder, 1967) that ‘many wrong assumptions can be drawn from the study of the shell alone’. In an earlier work Johansson (1939) had also tried to relate the taxonomy of the Rissoidae to anatomical features.