The present paper deals with the results of observations performed with the purpose of identifying larval and spat shells of Pinctada margaritifera. Material used in this observation was artificially reared ones from fertilized eggs induced by thermo-stimulation from October to December, 1968, in Okinawa. The developmental stages are shown in Table 1. The outline, texture and hinge apparatus are shown in Plate 7 and sizes of the larvae in Table 2. It was found that the coloration of the larvae of this species differs clearly from those of allied form, P. fucata, i.e. the former is distinctly brownish in color, while the latter has no special coloration. The present results afford the first clue for the collection of natural seeds of this pearl-oyster in Kabira Bay, Ishigaki Is., Okinawa.

View full abstract

Author got on board the Tansei-Maru, Research Vessel of the Ocean Research Institute, University of Tokyo, in September 1969, and made a through investigation into the group of Molluscan shells, using the Nakai-type beam trawl, at the archibentha where were 492 to 504 meters and 120 to 1250 meters in depth, off Sanriku, coast of the Mainland (North Pacific Ocean), and collected 13 species of sea snails, 2 species of tusk shells and 2 species of bivalves. After investigating these materials, there are almost irrelevant to the fauna between the archibenthal group of Molluscan shells, recently investigated, and these inhabited at the continental shelf off Akkeshi, Hokkaido, enforced in 1968.

View full abstract