Cyclopecten ryukyuensis Hayami & Kase, 1993
HAYAMI, I. & T. KASE. 1993. Submarine cave Bivalvia from the Ryukyu Islands: Systematics and evolutionary significance. The University Museum, The University of Tokyo, Bulletin, 35: 1-133, figs. 1-374. [p. 59, figs. 193-201]
1993 Cyclopecten ryukyuensis Hayami & Kase, 1993
I. Hayami & T. Kase, 1993,
figures 193-201. |
«1992. Cyclopecten sp. A and B, Kase and Hayami, Jour. Moll. Studies, vol. 58, p. 448, listed.
Type and material.— Holotype: RM19463a, a living specimen, from the bottom sediments of "Cross Hole" of Irabu Islet, Miyako Islands. Paratypes: RM19456 (dead) from "Devil's Palace", RM19457 (dead) from "Fool's Palace", RM19458 (dead) from "Witch's House", RM19459 (dead) from "Toriike", RM19460 (dead) from "Black Hole", RM19599 (dead) from "Coral Hole" of Shimoji Islet. RM19461 (dead) from "W-arch", RM19462 (dead) from "L-arch", RM19463 (living) from the type locality of Irabu Islet. RM19464 (dead) from "Shodokutsu", RM19570 (dead) from "Daidokutsu" of Ie Islet.
Diagnosis.— Small-sized, comparatively low and paedomorphic species of Cyclopecten, characterized by deep byssal notch, long dorsal margin, poorly defined posterior auricle, and coarsely cancellate ornaments in addition to persistent Camptonectes-striae in LV. Description.— Shell small, rarely exceeding 2.5 mm in length, very thin, translucent, nearly acline, weakly convex, a little longer than high. Umbo located near midpoint of dorsal margin. Dorsal margin long, occupying nearly the whole shell length. Byssal notch deep. Posterior auricle large, rectangularly truncated but poorly defined from disk. Disk of RV covered with dense commarginal lamellae and numerous fine rectangular interstitial threads representing regular arrangement of simple quadritic prismatic crystals of outer layer. Byssal auricle bears several weak radial ribs, while posterior auricle often has a strong radial rib and coarse commarginal lamellae. Disk and both auricles of LV marked with widely spaced and strong commarginal lamellae and several irregular radial rlbs. Camptonectes-striae of LV persistent until later dissoconch. No internal ribs. Resilium pit spoon-shaped, projecting downward. Numerous denticles of provinculum persistent throughout growth. Pd I large, D-shaped, ranging 165-204 μm in maximum diameter; Pd II absent. Remarks.— In a preliminary study (Kase and Hayami, 1992), we identified two unnamed species of Cyclopecten in tine bottom sediments of "shodokutsu"; a strong radial ribs occurs on the middle of the posterior auricle in one species and not in the other. However, the difference between the two forms is actually gradational and is regarded here as due to intrapopulational variation. The morphology of this species is somewhat similar to that of the juvenile stage of Parvamussium crypticum sp. nov. but is clearly distinguishable from it by fewer radial ribs, more persistent Camptonectes striae in LV (at similar size) and absence of internal ribs throughout growth. The long dorsal margin, poorly defined posterior auricle and coarse cancellate ornaments at a glance constitute criteria for characterizíng this species, but these features are shared by juvenile specimens of many species of Cyclopecten (and Parvamussium). Distribution.— Common in many sublittoral caves of Ie, Shimoji and Irabu Islers, Ryukyu Islands. This species also occurs in "Balicasag Cave" off Panglao Islet of Bohol Island, the Philippines.» ITARU HAYAMI & TOMOKI KASE, 1993
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