イノウエヤマトガイの三重県北部における新分布記録

抄録

A rare terrestrial gastropod species, Japonia inouei, is newly recorded from Mie Prefecture, central Honshu, Japan. A living specimen was collected in Ogisu Valley, Suzuka City, in 2013. A brief morphological examination was carried out on this specimen, and compared with conspecific and allied species collected from adjacent areas. Five diagnostic characters were recognized in the present specimen: 1) two rows of petal-like periostracal hairs on the periphery of the body whorl, 2) blackish coloration of the head-foot, 3) a taenioglossate radula with relatively few cusps, 4) a grayish white penis with dully acute tip, 5) ball-like feces containing plant tissues in the intestine. Examination of additional specimens of J. inouei collected from the Kii Peninsula revealed that there is a considerable variation in the morphology of the petal-like periostracal hairs. Although the present specimen possesses distally expanding hairs with a smooth surface, most specimens from the Kii Peninsula possess similarly shaped hairs but with a striated surface. In addition, larger and more aged specimens from the Kii Peninsula tend to have narrower hairs, suggesting age-related change in their shape. However, a population from Kushimoto-cho comprises specimens of similar sizes with both wide and narrow hairs, and it is also probable that the difference may be ascribed to intraspecific variation. The present record represents a considerable north- and eastward range expansion of this species to Mie Prefecture. The lack of previous records in this area can be attributed to the fact that the morphology of the periostracal hairs is the only morphological character that distinguishes this species from its allies, and specimens possessing hairs in good condition are extremely rare, like the species itself. It is thus necessary to reconsider the distributions of this and allied species in the western part of Honshu, where more than two species are potentially distributed sympatrically, based on the careful examination of periostracal hairs.