A new species of Solenogastres, Anamenia amabilis is described from southern Japan, at depths from 27–96 m. The new species is distinguishable from congeners by the long straight esophagus and thin, elongate wedge-shaped denticles of the radula, as well as the peculiar pattern of short transverse reddish orange bands on the dorsum of the animals. All specimens were exclusively found clinging on the alcyonacean soft coral Scleronephthya gracillima.
Hypermastus ryukyuensis n. sp. is described based on specimens from the clypeasteroid echinoid Echinodiscus tenuissimus caught at 10 m in depth in Oura Bay, Okinawa Prefecture, Japan. Of 30 currently valid species in the genus, H. tenuissimae, H. serratus and H. auritae resemble the new species, which is, however, distinguished from these three species by having a mucronate protoconch of nearly 2.5 whorls, apical teleoconch whorls abruptly increasing in diameter, indistinctly convex teleoconch whorls, a smaller aperture and prosocline outer lip mar-gin, which is not sinuate below the suture. In addition to the new species, H. peronellicola and H. tokunagai are known to occur in Japanese waters, and H. tenuissimae has been reported from E. tenuissimus from Thailand.
Two species of the eulimid genus Hypermastus are redescribed based on specimens recently collected from sand dollars caught in the Seto Inland Sea and the type specimens: Hypermastus peronellicola (Kuroda & Habe, 1950) from Peronella japonica, and H. tokunagai (Yokoyama, 1922) from Scaphechinus mirabilis. These two eulimid species are very similar in their shell morphology but are distinguished from each other based on characters such as the proportions of shell length to several dimensions of the shell, width/length ratios of each teleoconch whorl, the protruding part of the outer lip margin, and the coloration of the visceral mass that can be seen through the translucent shell in living specimens. H. peronellicola was attached to the host by inserting the proboscis into the host's body, whereas no proboscis penetration was observed in H. tokunagai.
The host species for the glochidia of the freshwater unionid mussel Inversiunio jokohamensis were identified by determining whether these glochidia had infected the following fish taxa collected from a paddy field ditch in Tochigi Prefecture, Kanto area, central Japan: Nipponocypris spp., Gnathopogon elongatus, Carassius spp., Misgurnus anguillicaudatus, Cobitis biwae, Lefua echigonia, and Rhinogobius sp. OR (orange type). The fishes were kept in tanks for 10 or 11 days, and the numbers of glochidia and metamorphosed juveniles detached from the hosts were counted. Living juveniles detached from the bodies of only Nipponocypris spp., L. echigonia, and Rhinogobius sp. OR. The number of glochidia infecting the fishes, the infection site, and the rate of glochidial encystment were determined using formalin-fixed specimens of N. temminckii, N. sieboldii, G. elongatus, Ca. buergeri subsp.1, M. anguillicaudatus, Co. biwae, L. echigonia, Rhinogobius sp. OR, and the frog Hyla japonica (tadpole). Glochidia had infected 3 host species i.e. L. echigonia, Rhinogobius sp. OR, and N. temminckii. Most glochidia were attached to the gills and fins of the fishes. More glochidia were attached to and encysted on L. echigonia and Rhinogobius sp. OR than on N. temminckii. L. echigonia was identified as a new host species for the glochidia of I. jokohamensis in addition to Rhinogobius sp. OR and N. temminckii.
To clarify the relationship between reproductive behavior and pair formation in the egg cowry Ovula ovum (Linnaeus, 1758), field research was carried out from May 2004 to October 2006 at a small cove in Bonotsu, Minami-Satsuma City, Kagoshima, southern Kyushu, Japan, on the East China Sea, which is a subtropical area. Four types of pair formation by egg cowries were observed: (1) two egg cowries lying in close proximity and spending most of their time feeding on soft corals (common pairs); (2) copulating pairs; (3) one egg cowry lying beside brooding egg cowries; and (4) a female producing egg capsules while a male introduces its penis into the female mantle cavity. There was a significant relationship between the number of pairs and reproductive activities. The distances between the paired individuals were significantly shorter during reproductive periods than during non-reproductive periods. The number of observed pairs was also significantly higher during reproductive periods than during non-reproductive periods. During reproductive periods, egg cowries frequently produced transparent belts from the foot using pedal mucus, which might play an important role in locating a mating partner. Of the pair formations observed, 44% were related to reproductive activities. These observations suggest that pair formation in the egg cowry is closely related to reproductive activities.
The eulimid gastropod Hypermastus tokunagai is an ectoparasite that utilizes the sand dollar Scaphechinus mirabilis as a host on the sandy bottom in Japan. The distribution patterns of H. tokunagai in populations of S. mirabilis were studied in the western part of the Seto Inland Sea, Japan. The density (= number of individuals per m2) of H. tokunagai was significantly higher in the central region where there is a higher host abundance. On the other hand, a higher prevalence (= percentage of infected hosts) and mean abundance (= number of parasites per host) were recorded in the marginal regions where there is a lower host abundance. These results suggest that eulimid larvae are widely dispersed in a host population but settle largely in a host-abundant area. The infection also showed higher levels in inshore regions than offshore.