Cratis kanekoi Hayami & Kase, 1993

Raines, Bret & Huber, Markus, 2012, 3217, Zootaxa 3217, pp. 1-106 : 22

Cratis kanekoi Hayami & Kase, 1993

Figures 10 A–G

Cratis kanekoi Hayami & Kase, 1993: p. 36 , figs. 103–110.

Cratis kanekoi Hayami & Kase, 1993 — Hayami & Kase, 1996: p. 61; Okutani, 2000: p. 861, pl. 428, fig. 2; Tröndlé & Boutet, 2009: p. 5.

Material examined. Eleven single valves from SyG, and one badly worn valve from EI (1.8 to 2.77 mm) (BK).

Diagnosis. Shell small (up to 2.77 mm in height), polygonal-ovate, thick and not fragile. Umbones located anteriorly, with a large, hat-shaped prodissoconch which is characterized by a low conical central base and coarsely frilled brim margin, ca. 260 µm length and 250 µm height. Exterior surface with 7–9 beaded radial ribs crossed by regular commarginal lamellae. Intervals between ribs are broadly concave. Interior margin with a few strongly marked interlocking tubercles restricted to postero-ventral area. Hinge consisting of a large tubercular tooth in the anterior of each valve and numerous perpendicular denticles placed dorsally and interrupted by the ligament, resulting in a row of anterior and posterior denticles. Color translucent white and sparse orange blotches in adults.

Remarks. From the ten described philobryid genera, Cratis matches well by exhibiting the strong cap, clear dentition, trigonal ligament pit, dorsal denticles and pinctadoid shape. The sculpture of the EI material, however, is less beaded than in the type species and in most of the congeners. Internally, the posteroventrally 4–5 marked interlocking tubercles are similarly found in Cratis delicata Bergmans, 1970 , which, has a very distinct hinge and dentition. The type species C. progressa has similar tubercles also placed anteroventrally, and a much stronger dentition as well as a strong, narrowly beaded sculpture.

Nothing known from the Hawaiian Islands resembles this species, and from the nine described Pacific Cratis species , only one merits close comparison, namely, C. kanekoi Hayami & Kase, 1993 , from Miyako Island. All other species are at once separated by sculpture and/or stronger dentition and/or missing or additional tubercles.

Cratis kanekoi is identical in shape and in sculpture with widely spaced radials and lamellate commarginals. Position and sculpture of the cap are indistinguishable. Internally, the posterodorsal tubercles are very similarly arranged. At first glance the hinges seem to differ in that the tooth socket is placed left or posterior to the large cardinal of the scarce Okinawan material. However, in the numerous EI and SyG material studied both conditions were encountered, with the socket placed left or right of the prominent tubercular tooth. This is consistent with Tevesz’s (1977: 15) observation of high intraspecific variability of the Cratis dentition. Thus, no significant morphological differences to C. kanekoi remain.

The EI and SyG material, however, does provide C. kanekoi a new maximum size of 2.77 mm, variability in position of cardinal tooth and socket, as well as an additional feature in adult specimens, that it is occasionally being found with orange blotches. The availability of the material also suggests it has a more common occurrence than originally recorded by Hayami and Kase (1993).

Habitat. Apparently common from SyG, but less so on EI, in sand, from 20 m.

Distribution. Cratis kanekoi was originally described from Okinawa, but has been recorded from the Society Islands and the Tuamotu Archipelago as well. Easter and Salas y Gómez Islands are now considered a range extension— E4.