Peringia

Abstract: In 1933 an examination of Peringia ulvœ for larval trematodes was under-taken at Plymouth (Rothschild, 1936). No actual measurements were made at the time, but there appeared to be a relation between the species of trematode and the size of the individual infected snails. Thus the commonest species, Cercaria oocysta Lebour, 1907 (14% infection), and C. ubiquita Lebour, 1907 (4% infection), were found in 75% of the largest snails, while the rarer species, such as C. ephemera Lebour, 1907 (non Nitsch) (2% infection), and C. pirum Lebour, 1907 (0–1% infection), occurred most frequently in medium sized individuals.

Abstract: Many workers have reported that the adult population of the small prosobranch Peringia (=Hydrobia) ulvae reaches its maximum density on muddy-sandy shores in a broad belt at approximately mid-tide level. Yet it has also been reported that some float for at least part of the tidal cycle and at low tide burrow in the sand. Experiments in the laboratory and observations on the shore suggest that under natural conditions the animals float on the surface film of the water by means of a mucoua raft, which also acts as a food net. After a time, which is geared to the tidal oscillation, they submerge at mid-tide level. When the tide has receded, the animals crawl about on the surface of the mud then burrow in the sand for several hours, resurface, and launch themselves on the surface film of the water between the ripple marks. By this time the tide is approaching mid-tide level again and the cycle of behaviour is completed. Thus these animals, formerly regarded as mainly benthonic, spend part of their time as pelagic plankton feeders.

Abstract: In order to investigate whether the genus Hydrobia should be subdivided, three species representing the nominal genera involved (Hydrobia, Ventrosia, and Peringia) were compared on the basis of allozyme data. Based on genetic distances, anatomical and ecological data, as well as data on reproductive biology, it is argued that (1) there is no reason to split the genus Hydrobia into different genera, (2) Hydrobia can be subdivided into the subgenera Hydrobia s. s. and Peringia, and (3) Ventrosia has to be considered synonymous with Hydrobia. The analysis of the genetic structure of the three populations investigated revealed heterozygote deficiencies in practically all polymorphic loci in one case, and low, respectively complete lack of variability in the remaining two populations