Rochefortina sandwichensis (Smith)

Figures 311-320

1885. Ervilia sandwichensis Smith, Rep. Sci. Res. Voy. H. M. S. Challenger, Zool., vol.13, p.81, pl.25, figs.5-5b.

1924. Rochefortina semele Dall, Proc. Biol, Soc. Wash., vol.37, p.88.

1938. Rochefortina sandwichensis: Dall, Bartsch and Render, Bernice P. Bishop Mus., Bull. 153, p.l69,pl.44, figs.9-12.

1953. Spondervilia rubra Laseron, Rec. Anstr. Mus., vol.23, p.52.

1973. Rochefortina sandwichensis: Sakurai and Habe, Venus, vol.32, p.7.

1979. Ervilia sandwichensis: Kay, Hawaiian Marine Shells, sec.4, p.558.

1992. Rochefortina cf. sandwichensis: Kase and Hayami, Jour. Moll. Studies, vol.58, p,448, listed.

Material.— RM19533 (dead) from "Devil's Palace", RM19534 (living) from "Fool's Palace", RM19535 (living) from "Witch's House", RM19536 (dead) from "Toriike", RM19537 (dead) from "Black Hole" of Shimoji Islet. RM19538 (dead) from "Lunch Hole", RM19539 (living) from "L-arch", RM19540 (living) from "Cross Hole" of Irabu Islet. RM19541 (dead) from "Shodokutsu" of Ie Islet.

Description.— Shell small, scarcely exceeding 3.5 mm in length, variable in coloration (white, yellow and pink) when alive, oblong, moderately thick and convex, 1.3- 1.4 times longer than high, commonly whitish or yellowish but sometimes tinted with three brownish or pinkish radiating bands. Umbo slightly prosogyrous, located a little posterior from mid-length of shell. Antero-dorsal margin long, a little concave in front of umbo; postero-dorsal margin comparatively short, roundly arcuate, passing gradually into posterior margin. Escutcheon depressed, narrow but distinct. Surface covered with numerous crowded, increasingly radial riblets and fine commarginal lamellae which reveal cancellate appearance. Numerous microscopic wrinkles and punctations distributed on whole surface of dissoconch. Inner margin not crenulated. Resilium situated in a depressed triangular pit just below umbo, bordered by a pair of ridges in RV. A narrow prosoclinal cardinal tooth present in RV; a tubercular tooth in front of the resilium and a thick triangular tooth behind the resilium in LV. Lateral tooth, if present, weak and indistinct. Pd I small, 75-85 µm in maximum diameter, followed by Pd II which is hemispherical, brownish or pink in color; veliconch (Pd I + Pd II) 240-248 µm in maximum diameter.

Remarks.— In every macroscopic characteristic and shell size the present material is indistinguishable from Ervilia sandwichensis Smith, 1885, the type-species of Rochefortina, from the Hawaiian Islands, though we have not yet done SEM observations of the Hawaiian specimens. The holotype of this species, in the British Museum (Natural History), is a left valve collected from the bottom (40 fathoms) off the reefs at Honolulu, Oahu Island. Dall, Bartsch and Render (1938) and Kay (1979) gave more detailed descriptions of this species. Moreover, Smith (1885) and Dall, Bartsch and Rehder (1938) noticed the presence of well-demarcated and colored prodissoconch, which corresponds well with the features of the Pd II in the present material. The maximum shell size and polymorphic coloration of the shell are also comparable with those of the Hawaiian, specimens.

Spondervilia rubra Laseron, 1953, from New South Wales, as pointed out by Sakurai and Habe (1973), is probably identical with Rochefortina sandwichensis, though detailed comparison should be based on SEM observation of original specimens.

The present species is not necessarily an indigenous cryptic bivalve, because abraded valves have been found occasionally in beach sand in southern Japan. The abundant occurrence of living specimens in these caves, however, is remarkable.

Distribution.— Common in many sublittoral caves of Ie, Shimoji and Irabu Islets, Ryukyu Islands. This species also occurs in "Balicasag cave" off Panglao Islet of Bohol Island, the Philippines. It has been recorded from many localities (Amami, Goto and Hachijo Islands and Kii Peninsula) of southern Japan in addition to the Hawaiian Islands and Australia.

Superfamily Arcticoidea Newton, 1891
Family Kelliellidae Fischer, 1887

Genus Kelliella Sars, 1870

The genus Kelliella is represented by about a dozen minute species, most of which have been known from abyssal to hadal depths in three major oceans (Knudsen, 1970; Bernard, 1989), even though it seems to have inhabited shallower waters until the Middle Miocene (Studencka, 1987). The occurrence of a representative of this genus from an upper sublittoral cave in subtropical region is, therefore, very remarkable. The cave species, as well as Kelliella nakayamai Habe, 1953, from the Holocene fossil bed of Kyushu, shares the cyprinoid hinge teeth, well-demarcated lunule and other diagnostic characters of this genus with deep-water species. Knudsen (1970) mentioned the presence of a fine furrow running along the circumference of valves in Kelliella brunni (Filatove, 1969) and K. indica Knudsen, 1970. Such a furrow is clearly observed in RV of the type species of Kelliella (Warén, 1989) and the present cave species (Figures 312, 319).