著者

上島 励

出版者

日本貝類学会

雑誌

貝類学雑誌Venus : the Japanese journal of malacology (ISSN:00423580)

巻号頁・発行日

vol.54, no.3, pp.161-173, 1995-09-30

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"Succinea" lyrata Gould, 1859 and "S". horticola Reinhardt, 1877 are common succineid species that are widely distributed in Japan. Recently, these succineids have been assigned to the genus Neosuccinea, although they lack vaginal appendix which is diagnostic feature of Neosuccinea. Shinagawa & Yano (1983) pointed out similarities in male genitalia between these problematic succineids and N. kofui which has prominent vaginal appendix and suggested their close relationships. Since the current assignment of these problematic succineids to Neosuccinea is dubious, re-examination of their taxonomic relationships with N. kofui has been needed. However, taxonomic position of these succineids remained unsolved, because N. kofui could not been rediscovered after the original description. The present paper reports a rediscovery of N. kofui after 24 years absence in formal records. Although N. kofui had been recorded from no other place than the type locality, Kofu, Yamanashi Pref., the present study revealed that this species is widely distributed in the Kanto district. N. kofui seems to have been misidentified as "S". horticola in previous records, due to their close conchological similarities. The genital morphologies of "S". lyrata, "S". horticola and N. kofui are redescribed to clarify their taxonomic relationships. By comparing the genitalia of "S". lyrata and "S". horticola, I found no significant differences that warrant taxonomic separation. Since they are identical in conchological and anatomical traits, especially in their unique internal structure of penis, "S". horticola is synonymized with "S". lyrata. On the other hand, "S". lyrata is highly divergent from N. kofui not only in the absence of vaginal appendix, but also in internal morphology of penial complex, mode of insertion of vas deferens to epiphallus, internal structure of lower oviduct, morphology of vas deferens and unique connection between vagina and retractor muscle. Since penial complex of N. kofui and "S". lyrata are substantially different in their internal structures, their similarity in male genitalia is now proved to be superficial resemblance and hence their close relationships are not supported. Considering taxonomic significance of vaginal appendix together with many structural differences in various genital organs, the current taxonomy of "S". lyrata placed in Neosuccinea was rejected. Alternative generic assignment of "S". lyrata to Novisuccinea was also rejected. The current results show that "S". lyrata belongs to the genus Succinea (sensu lato).