Members of the genus Provanna are abundant and widely distributed in deep-sea chemosynthetic environments. Around Japan provannids inhabit a wide range of depths and substrates. In this study, we report additional species of Provanna from vents and a seep in the Nansei-shoto area. Shell morphological and molecular phylogenetic analyses showed that there are four new species: (1) P. subglabra is characterized by an inflated smooth shell and is most abundant in vent fields in the Okinawa Trough; (2) P. clathrata has a roughly sculptured shell and is distributed in vents in the southern Okinawa Trough; (3) P. lucida possesses a thin smooth shell with a deep suture and is limited to vents on the Minami-Ensei Knoll in the northern Okinawa Trough; and (4) P. kuroshimensis,which is distinguished by an olive-colored periostracum and is endemic to a seep site on the Kuroshima Knoll. In contrast to shell and molecular characters, radula morphology does not show clear differences among these species. The present study revealed a high species diversity of Provanna in a relatively limited area in southwestern Japan. The diversification of the genus might be correlated with complex topographic features in the Nansei-shoto area including the Okinawa Trough and Ryukyu Arc.
The northwestern Pacific species of the genus Epidendrium Gittenberger & Gittenberger, 2005, and those previously assigned to the genus Alora are reviewed based mainly on the conchological characters. The species previously identified as Alorabilleeana (DuShane & Bratcher, 1965) in this area is correctly identified herein as E. aureum Gittenberger & Gittenberger, 2005, and another species in the genus, E. sordidum Gittenberger & Gittenberger, 2005, is recorded for the first time in the Japanese waters. Alora reticulata (Habe, 1962) is transferred to the genus Epidendrium, and an additional new species is described as E. parvitrochoides n. sp. from Japan. Alora annulata (Kuroda & Ito, 1961) is retained in the genus Alora following most recent works, and Alora kiiensis Nakayama, 2000 is transferred to the genus Tuba Lea, 1833 in the basal heterobranch family Mathildidae based on the characteristic heterostrophic protoconch and overall teleoconch features.
A new subspecies of Entemnotrochus rumphii (Schepman, 1879) from the middle Miocene Shikiya Formation, Kumano Group, at Uematsu, Kushimoto-cho, Higashimuro-gun, Wakayama Prefecture, central Japan is described herein as E. rumphii kushimotoensis n. subsp. This new subspecies is distinguished from E. rumphii rumphii by having a lower spire, a selenizone situated below mid-whorl and a larger number of spiral cords above the selenizone. Judging from the geographical distribution and the morphological affinities of the living E. rumphii rumphii, the new subspecies seems to be an ancestral form of the Recent species.
Based on mitochondrial DNA barcoding, we identified the Dianbai oyster Crassostrea dianbaiensis from the Hiki River in Wakayama Prefecture, which is located on the Kii Peninsula on the Pacific coast of central Japan. Our sampling site represents the northern- and easternmost habitat of this species reported to date. Out of our 21 Crassostrea specimens examined, 20 were identified as C. dianbaiensis with one individual of the Pacific oyster C. gigas. In the field, C. dianbaiensis attached intertidally and subtidally to concrete blocks in brackish water (approximately 1 km upstream from the river mouth), where Saccostrea spp., C. gigas, Isognomon ephippium and Hormomya mutabilis were found in sympatry. Our specimens showed various shell sizes, implying that C. dianbaiensis successfully reproduces at the newly found habitat. Although C. dianbaiensis has so far been considered a tropical or subtropical oyster, there is a possibility that this species recently extended its habitat northward, in line with the increasing observations of southern species of marine benthos along the southwestern coast of the Kii Peninsula since the 1980s.