The distribution, abundance and shape of Dotilla myctiroides (Ocypodidae) burrows were investigated on a south-east shore of Phuket Island, Thailand (7°50'N; 98°24'E). At the lower area of its habitat where the seagrass, Enhalus acoroides, occurred in small isolated patches, the burrow density of D. myctiroides was higher on small mounds located on the landward side of Enhalus patches than in flat areas. The crabs constructed burrows densely on artificial mounds lacking Enhalus, while no burrows were observed in shallow depressions located on the seaward side of Enhalus patches, and in artificial depressions. Two shapes of burrow, tube-and "igloo"-type burrows, were observed in the Enhalus zone. The relative proportion of tube-type burrows increased with height of substratum surface, i.e., in the order of flat area, artificial mound and Enhalus mound. D. myctiroides, when making a burrow, may prefer a higher substratum, and construct a tube-type burrow there.

View full abstract

On an intertidal sand flat in west Kyushu, Japan, populations of the ghost shrimp Callianassa japonica ORTMANN and the snake eel Pisodonophis cancrivorus (RICHARDSON) were found to inhabit the upper and lower tidal zones, respectively, in August, 1979. Ghost shrimp distribution later expanded greatly, and in September, 1987, when almost the entire sand flat was densely populated by ghost shrimps, the density of snake eels was found to have increased significantly from that recorded in 1979. This may have resulted from immigration of adult snake eels onto the sand flat from elsewhere. Possible beneficial effects of ghost shrimps with regard to snake eels are : 1) an increase in softness and underground water content of the sediment owing to the turnover of sediment by and the presence of burrows of ghost shrimps. Such bioturbation is more favorable for snake eels' penetration of and resting in sediment ; and 2) ghost shrimps are a preferred food of snake eels. Both 1979 and 1987 studies recorded ghost shrimps as prey of snake eels, larger-sized shrimps being almost the exclusive prey item in 1987. The predation impact of the snake eel population on the ghost shrimp population is estimated to be trivial.

View full abstract

Living specimens of the lumbrinerid polychaete Lumbrineris flabellicola (FAGE, 1936) were firstly collected from Japanese water, Southwest off Shikoku Island at depths of 277-317m. The species lived in a mucous tube attached to the ahermatypic coral Caryophyllia decapali (YABE & EGUCHI, 1942). The morphological characters of the polychaete were briefly reported.

View full abstract

The infections of the parasitic isopod Bopyrus squillarum on Palaemon pacificus and P. serrifer were studied during 1987 to 1989 in Tateyama Bay, Chiba Prefecture. One of 7913 P, pacificus and 278 of 7097 P. serrifer were infected. B. squillarum exhibits some degree of host specificity for the host P. serrifer. B. squillarum retarded the growth of the secondary characters of male hosts, such as the number of segments of the inner branch of the bifurcated outer flagellum of the antennuler, the rostral length, the exopod and the endopod of the first and the second pleopods. On the other hand, B. squillarum castrated the female host, but did not affect the secondary sexual characters.

View full abstract

A bivalve-inhabiting hydrozoan Eugymnanthea japonica KUBOTA, 1979 (Thecata, Leptomedusae, Eirenidae), commensal with the blue mussel Mytilus edulis galloprovincialis LAMARCK collected from 20m in depth, 200m off Nishikigaura, Shizuoka Prefecture, Japan on December 1, 1990, is the deepest recorded occurrence of this species. The association rate with this host (60%, N=40) is as high as that with the same host species located in the intertidal region at Atami, Shizuoka Prefecture, Japan. Thus the present species also occurs in subtidal waters, as is the case with the related species Eutima japonica UCHIDA, 1925 distributed in Japan. The polyp bearing more than two stalks of medusa buds is an uncommon and previously unreported type of zooid for this species, and is illustrated. Eighty medusae 1 day old and 1 medusa 2 days old, which were liberated as mature medusae from polyps taken from a total of 13 hosts, were examined within 8 days after collection of the hosts. The morphology of the mature medusae is not different from that of medusae released from polyps found in the intertidal region or just below it in Japanese waters, except for the most modified individual, which had only one radial canal and one gonad.

View full abstract

About 50 individuals of Neaxius acanthus were collected in the seagrass beds of Papua New Guinea, and their morphological variations and quantitative characteristics such as the diameter of living holes, carapace length, body length, dry body weight and ash-free dry weight were examined. The present results reaffirm that N. acanthus var, mauritiana is not distinguishable from N. acanthus.

View full abstract

Age structure and growth pattern of Yoldia notabilis in Otsuchi Bay, northeastern Japan were studied using samples collected monthly during the period between December 1989 and December 1990. Y. notabilis has growth rings on external shell surface, and it was found that the formation of the “major ring” occurs annually during late winter to early spring. Age of Y. notabilis can be determined up to seven years old by counting number of the major rings, whereas only four younger year classes are separable from size-frequency histograms. Mean shell lengths of the four youngest year classes separated by the two methods are identical to each other. The growth rate of Y. notabilis is very slow at 0 year old ; achieving only 1.3mm in shell length by the first winter. The growth becomes rapid after the first year and the animal reaches 32.0mm at the age of seven years old. The obtained growth curve shows a sigmoidal pattern and the Gompertz growth equation gives a best fit for the data.

View full abstract