Five new limid bivalves from the eastern Pacific Ocean are described. They are, Limaria valdiviesae from northern Chile, 100m deep ; Limatula macleani from off San Pedro, southern California, 560m deep ; L. californica from off Santa Catalina Island, southern California, 144m deep ; Plicacesta nasca from off Shoal Guyot, west of Chile, 228m deep ; and Limatuletta coani from off Patton Escarpment, southern California, 3706-3806m deep.

View full abstract

Recent dredgings in waters around New Caledonia revealed two new Conus species which are described as Conus richeri, n. sp. and Conus plinthis, n. sp. Both new species are compared to closely related species and their variability is enumerated.

View full abstract

The new bathyal bivalve Calyptogena (Ectenagena) australis n. sp. collected at a depth of about 1400m off the coast of central Chile (lat. 37°35′S ; long. 73°50′W) is described. Its anatomical characteristics include a notably reduced stomach, a very short, almost straight intestine, vestigial labial palps and large gills of dark colour. These features, typical of such giant clam, suggest restricted habitats and strategies similar to those reported for other species of the family Vesicomyidae. A very particular trophic strategy was proposed for Calyptogena (E.) magnifica Boss and Turner, 1980 from the Galapagos hydrothermal vents, with gills appearing notably enlarged due to symbiosis with chemoautotrophic bacteria living within the gill tissue. As the presence of hydrothermal vents in the bathyal slopes of central Chile is unlikely, it is assumed that these bivalves could use the energy of sulphide-rich deep soft bottoms to drive CO_2 fixation, a mechanism already proposed for other bivalves.

View full abstract

A new species, Morula pacifica is described. Although this new species has been confused with species of the Fasciolariidae, radular character indicates that this species belongs to the Muricidae. This new species is characterized by the prominent spiral sculpture. The shell is grayish or yellowish white.

View full abstract

Radular characters are described or supplemented for Testudivolva orientis, T. nebula, Dentiovula mariae, D. takeoi, Pseudosimnia nubila, A. takae, Crenavolva draperi and C. tigris. Taxonomic comments or new distributional records are given to Habuprionovolva aenigma (syn. Galeravolva basilia), Dentiovula septemmacula (syn. Crenovolva conspicua), D. spectabilis, D. cobra, Aperiovula pontia, A. testudiana, Crenavolva periopsis and C. minabeensis.

View full abstract

Anatomical features of Hirasea (s.s.) diplomphalus Pilsbry is described. On the basis of the anatomical characters, the genus Hirasea is transferred from the family Endodontidae to the family Helicarionidae, subfamily Euconulinae. Although this genus has long been considered to be originated in tropical Pacific Islands, close relationship of Hirasea to Japanese Euconuli especially to Gastrodontella is strongly suggested. Among land snails endemic to Bonin (Ogasawara) Islands, Hirasea is the first example suggesting the Palaearctic origin.

View full abstract

Frequency of incubation of a freshwater mussel. Anodonta woodiana, in a small pond was studied by continuous observation on the outer demibranchs. The female shells were slightly opened to investigate once or twice every month from November 1985 to November 1986. The results suggested that incubation was performed through the whole year, except for July to August. During the period from winter to spring, some females were observed by 5 or 7 times in succession to hold larvae in final developmental stage, while others were observed not to start the new incubation for relatively short periods and released the glochidia. During the periods from spring to autumn, some females seemed not to repeat incubation if once she released the larvae in May to June, while some females repeated to incubate except for July to August, and others did not incubate throughout the entire observation. This paper clarified that some females of A. woodiana repeat incubation and discharge of larvae at short intervals, while others maintain the incubation over a long period.

View full abstract

Mark-recapture experiments revealed significant differences in the daily patterns of the capture rates of Mesodon normalis (Pilsbry), Triodopsis albolabris (Say) and T. dentifera (Binney) in sympatry ; M. normalis is much less nocturnal than T. albolabris and T. dentifera. The mean proportions of M. normalis, T. albolabris and T. dentifera in yearly captures were 76.9, 21.3 and 1.8% in the daytime but 23.2, 68.3 and 8.5% at night, respectively. Although Mesodon and Triodopsis belong to separate subfamilies of the Polygyridae, M. normalis and T. albolabris are remarkably convergent in the morphology of the shell. There was no detectable difference in microhabitat between the two species. In contrast, T. dentifera, which has a rather different shell, showed no difference from T. albolabris in the daily pattern of the capture rate. The adaptive significance of the differences in activity pattern is discussed as a possible mechanism to reduce interspecific competition between M. normalis and T. albolabris.

View full abstract