Oxynoe kabirensis Hamatani, 1980

Description

A sap-sucking sacoglossan of the family Oxynoidae. Living animals are limaciform and superficially resemble Oxynoe viridis; the body is 20-30 mm long when extended (holotype 25 mm), with a slightly smaller head and a very long, somewhat flattened tail whose margins undulate and whose dorsal midline lacks a longitudinal crest. Several to about a dozen delicate, usually bifid or trifid papillae are scattered over the dorsal surface of the body, but only rarely on the tail. The shell siphon is usually displaced slightly to the right of the body midline.
Ground colour varies from greenish yellow through pale green and dull yellow green to pale yellow. A large triangular area, deep green in the holotype and paratypes 1 and 4 and light green in paratypes 2, 3 and 5, lies on the outside of the parapodium with its base along the parapodial base and its apex near the middle of the parapodial free margin. Small light brownish spots are scattered over the dorsal surface, except on the head, the greenish parapodial triangle and the basal half of the rhinophores; the papillae bear a few small chocolate-brown spots. The shell is calcified but thin and fragile, milky white and glossy, similar in shape and size to that of O. viridis, but readily separable by the sutural panel: its free margin extends out from the sunken apex within the hollow collared by the outer lip in a gentle arc, without the recurvature seen in O. viridis. The radula is uniseriate and of typical ascoglossan style; paratype No. 3 has 23 teeth in total (17 ascending + 6 descending + 5 pre-radular).

Distribution

Type locality: Kabira Bay, Ishigaki-jima Island, Yaeyama Islands, Okinawa, Japan (27°27.5′N, 124°08.6′E). The original type series comprises four specimens from Kabira Bay and adjacent Kuro-shima Island (Yaeyama Islands, March-May 1977) and one specimen from Bansho-zaki near the Seto Marine Biological Laboratory, Wakayama Prefecture, central Japan (collected by K. Kitao, 30 July 1979), demonstrating a continuous range from the Yaeyama Islands to the central Pacific coast of Honshu.

Etymology

The specific epithet kabirensis is a toponymic adjective referring to the type locality, Kabira Bay (川平湾) on Ishigaki-jima Island, Okinawa Prefecture, Japan. The original description does not include a separate etymology section; Hamatani 1980 states the type locality verbatim as Type locality: Kabira Bay of Ishigaki-jima Island (27°27.5′N and 124°08.6′E). and proposes the Japanese name as (Japanese name: Kabirano-tsuyu, nov.).

Notes

Like its congeners, Oxynoe kabirensis is tightly associated with the green alga Caulerpa racemosa, on which it feeds. The Yaeyama specimens were collected from colonies of C. racemosa var. clarifera f. macrophysa growing at the low water level on projecting reefs, while the Wakayama specimen was obtained from C. racemosa var. occidentalis at 1.5 m depth. As in other species of the genus, the tail is readily autotomised and a regenerated tail develops from the remaining basal portion. Hamatani 1980 distinguishes this species from O. viridis by four lines of evidence: features of the soft body and papillae, the radula, the sickle-shaped penis with a rounded protuberance at its bending point, and the structure of the shell sutural panel.

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References

• Kabirano-tsuyu, nov., Hamatani I. (1980). ON THE SPECIES OF THE GENUS OXYNOE RAFINESQUE, 1819 FROM JAPAN, INCLUSIVE OF A NEW SPECIES (OPISTHOBRANCHIA : ASCOGLOSSA). Publications of the Seto Marine Biological Laboratory. 25(5-6): 349-360. https://doi.org/10.5134/176004