Laevichlamys boninensis (Dijkstra & Matsukuma, 1993)
DIJKSTRA,
H. H. & A. MATSUKUMA. 1993. Chlamys ('Hinnites') boninensis (Biv.: Pectinidae) from Osagawara
Islands, Japan. Venus [Journal of the Malacological Society of Japan], 52 (3):
179-181, pls. 1-2; text-figs. 1, 2. [p. 182, pl. 1, figs. 1, 2; text-figs. 1A, 2]
1993 Chlamys ("Hinnites") boninensis Dijkstra & Matsukuma, 1993
H. H. Dijkstra & A. Matsukuma, 1993, plate 1.
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«Type Material: Holotype: NSMT-Mo 69619, Chichijima Island, Ogasawara Islands (Kawamura Collection). Paratypes: NSMT-Mo 69622-69624, Miyanohama beach, Chichijima Island, Ogasawara Islands, collected by T. Osato in August 1986, three living specimens cemented on a colony of coral in 10 m deep (ex Okutani Collection).
Diagnosis: Shell medium, not exceeding 50 mm in length, heigher than long, with small apical angle. In early growth stage similar to Chlamys with a large byssal notch and a ctenolium, later the shell attached to substrate by the right valve and developing irregular form like Spondylus. Outer surface ornamented with radial ribs, shagreen microsculpture, and Camptonectes microsculpture. Description: Shell medium, approximately 42 mm in height and length, thin, nearly circular, with narrow apical angle, in mature stage irregularly distorted by cementation to substrate. Hinge line with narrow hinge ligament straight and umbo located nearly at midpoint of hinge line. Hinge ligament area having fine wrinkles (Fig. 1A, hla). Umbonal angle about 90°. Juvenile "Chlamys stage" 16-21 mm high and 12-20 mm wide, with about 35 irregularly arranged radial costae.
Left valve more convex than the right, having diverged microscopic radial striae on and between obsolete radial riblets. The striae are identical with the Camptonectes microsculpture figured by Waller (1972b: 229, fig. 11). Anterior and posterior auricles nearly equal in size and shape. About 12 radial riblets on anterior auricle, with white shagreen microsculpture (Fig. 2) among them. Posterior auricle nearly smooth excepting about 4, low, radial costae with shagreen sculpture and concentric growth striae. Coloration of the left valve darker than that of right, creamy yellowish to light brown, near umbo with brown-purple spots and large, irregular, white streaks, like those of Chlamys squamata (Gmelin, 1791). Right valve slightly larger than the left, nearly similar in sculpture to the left valve, radial costae somewhat smaller compared with those in the left valve, with more closely set lamellae. On anterior auricle, there are nearly obsolete radial and concentric riblets, without intermediate microscopic shagreen sculputre. Posterior auricle smooth. A non-functional ctenolium with several teeth is exposed on the suture. Byssal faciole approximately 1.5 mm near byssal notch. Color yellowish, pale orange or pale pink, with small brown spots near umbo.
ln "Spondylus stage", shell heavily distorted by cementation of the right valve to substrate. Left valve irregularly undulated with nearly obsolete radial costae and concentric growth ridges near the anterior marginal region. Near the ventral margin, radial costae are more pronounced with heavily developed lamellae. Anterior and posterior auricles smooth. Interior surface irregularly undulated and distorted by cementation. Resillial pit triangular. Near antero- and postero-dorsal margins of right valve there are large auricular crura and heavily developed scales, both of which are absent on hinge line of left valve. Color creamy purplish. Right valve undulated with irregularly developed concentric lamellae. Anterior and posterior auricles heavily developed with large scales, which are also in the byssal gape. A functional ctenolium is located on the anterior margin below the byssal notch (Fig. 1A, ct).
Type Locality: Chichijima Island, Ogasawara Islands, Japan (lat. 27°N, long. 142°8).
Distribution: So far only known from Ogasawara Islands, Japan. Remarks: Following living 'Hinnifes' species are known: 'Hinnites' distortus (da Costa, 1778) from the eastern Atlantic, 'H.' absconditus Fischer, in Locard, 1898, from western and southwestern Africa, 'H.' corallinus Sowerby, 1827, from southwestern Africa, Crassodoma gigantea from the northeastern Pacific, and Chlamys ('Hinnites') boninensis from Japan. No living species of 'Hinnites' and Crassadoma are known from the Indo-West Pacific and Australasia, except C. ('H.') boninesis. 'Hinnites distortus' is distribqted from southern Iceland to the Iberian Peninsula, the Mediterranean and Azores, south to the Gulf of Guinea. Outer surface of the shell is ornamented with more numerous and stronger radial ribs than those of C. ('H') boninensis n. sp. Chlamys ('Hinnites') boninensis n. sp. clearly differs from 'Hinnites' absconditus by the following characteristics. Shells of 'H.' absconditus from off Cape Manuel, Senegal (HHD1175) have larger Chlamys stage, attaining 30 mm in height. They are ornamented with stronger radial ribs with fine oblique striae on and interstices of ribs (Adam, 1690: pl. 2, fig. 1a) and lack shagreen microsculpture. ln Spondylus stage they are ornamented with more distantly spaced, stronger concentric lamellae. Kensley (1985) reported,'Hinnites' specimens in a late Pleistocene sediments at Cape Province, South Africa and non-fossil specimens from Namibia. The shells are thick and large, attaining 160 mm in height, and are ornamented with squamose ribs. The Cape fossils are noted that they more closely resemble the Miocene to Pliocene Chlamys ercolaniana (Kensley, 1985: 631), which is considered by Adam (1960: 8) to be a senior synonym of '.H.' absconditus. Young individuals of Chlamys ('Hinnites') boninensis n. sp. are somewhat similar to 'H.' corallinus. The holotype specimen of 'H.' corallinus (BM(NH)1842.10.19.2) is large and thick. The shell of 'H.' corallinus attains occasionally up to 140 mm in height. The Chlamys stage of 'H.' corallinus is approximately 20 mm in height, its umbonal area is translucent, and the Comptonectes microsculpture is finer than that of C. ('H.') boninensis n. sp. 'Hinnites' corallinus lacks the shagreen microsculpture and fine wrinkles on the hinge area. Outer shell surfaces of both species are ornamented with fine radial fibrous structure (Newell and Boyd, 1985: 4), which is Camptonectes microsculpture figured by Waller (1972b, p. 229, fig. 11). According to Waller (1972a: 53), radial corrugations appear to develop within foliated calcite of outer shell layer only. Both species seem to have same shell structure in the outer shell layer. External coloration of 'H.' corallinus, i.e. light orange to purple, is darker than that of C. ('H') boninensis n. sp. The umbonal areas of 'H.' corallinus occasionally show fine radial threads forming reticulate patterns (Pl. 2, figs. 1c, 1f). In Spondylus stage right valve of 'H.' corallinus is ornamented with stronger concentric lamellae. Chlamys ('Hinnites') boninensis n. sp. also differs from Crassadoma gigantea (Gray, 1825) of the eastern Pacific. The latter species has larger (up to 180 mm in length), heavier and more strongly distorted shells. Crassadoma gigantea has more numerous, closely set radial riblets with sharp scales and the Camptonectes microsculpture. Crassodoma gigantea differs from C. ('H.') boninensis n. sp. by lacking the shagreen microsculpture between the radial riblets in auricles and by possessing prominent resilial teeth in the right valve (SBMNH26044, 33487). Gray (1825) described the species first as a member of Lima, then placed it in Hinnita (Gray, 1826), which is a junior synonym of Hinnites. Bernard (1983: 25) placed the species in the genus Chlayms, and later proposed the genus Crassodoma for it (Bernard, 1986: 70). Pecten (Chlamys) multirugosus Gale, 1928 is a junior synonym of C. gigantea (Gray, 1825) (Roth and Coan, 1978: 297). Both auricles of C. gigantea have approximately 15 radial riblets. Exterior color is usually creamy white to brownish, the interior glossy white, occasionally with brown spots or concentric bands near ventral margin and purple color on the near dorsal margin. According to Bernard (1986: 73), fossil specimens of C. gigantea are known in western North America as early as the Miocene, and are not known from Japan or northwestern Pacific. Chlamys hastata (Sowerby, 1842) from the eastern Pacific is said to be the most closely related species (Waller, 1991: 23). Fossil species of 'Hinnites' from New Zealand and Australia, including 'Hinnites' trailli Hutton, 1873 from New Zealand Eocene to Miocene and 'H.' corioensis McCoy, 1879 from southern Australian Miocene, have a very distinct shagreen microsculpture and may be constitute a monophyletic group (Beu and Maxwell, 1990: 179). The microsculpture of C. ('H.') boninensis n. sp. suggests that it is not closely related to Hinnites crispus (Brocchi, 1814), type species of Hinnites, or to Crassadoma gigantea, type species of Crossadoma, but is most probably related to the Australasian species group. Dijkstra (1989: 29) described Pseudohinnites levii from New Caledonia. This is a bathyal species with translucent fragile shells, and the juvenile has the same conchological features as the adult. Juvenile uncemented specimens of C. ('H.') boninensis n. sp. are somewhat similar to Chlamys irregularis (Sowerby, 1842), Chlamys lemniscata (Reeve, 1853), and Chlamys squamosa (Gmelin, l79l), which have also the Camptonectes microsculpture on the outer shell surface. The microscopic shagreen sculpture on the anterior and posterior auricles of C. ('H.') boninensis n. sp. is somewhat similar to some Chlamys species from the Indo-Pacific, including Chlamys farreri (Jones and Preston, 1904) and Chlamys livida (Lamarck, l8l9). Shagreen sculpture of Chlamys farreri is much pronounced. Sometimes C. irregularis, C. lemniscata, and C. livida are somewhat distorted in shape, caused by byssal attachment to substrate such as coral, but they are never cemented like C. ('H.') boninensis n. sp. Although the holotype of 'Hinnites' spectabilis von Cosel and Gofas, 1984, from Angola has numerous radial riblets on the right valve similar to those on the left one, the species is possibly identical with Hinnites corallinus because heavy, reddish brown shell with fine radial striations on internal surface outside the pallial line is common to 'H.' corallinus and 'H.' spectabilis. 'Hinnites' pasca (Dall, 1908) is known from Easter Island, southeastern Pacific, but Rehder (1980: 109) pointed out that this species belongs to Chlamys, it is somewhat similar to Chlamys coruscans (Hinds, 1845). 'Hinnites' adamsi Dall, 1886, reported from 573 fms of the Lesser Antilles is recently placed in Pseudohinnites by Dijkstra (1989:32). Etymology: The species is named after Bonin Islands.» HENK H. DIJKSTRA & AKIHIKO MATSUKUMA, 1993
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«This species has been assigned to Hinnites corallinus, originally from southwest Africa. but is now regarded as distinct. Shell small or medium-sized, yellowish brown. Immature shell is very similar to Chlamys, having deep byssal notch and distinct ctenolium, but adult individuals stick to rocks and corals by the right valve, characterized by wide commarginal lamellae and irregular shell shape. Ogasawara Islands, southward to tropical West Pacific, subtidal rocky bottom.»
OKUTANI, T. (Ed.). 2000. Marine mollusks in Japan. xlviii, 1173 p. Tokai University Press. Tokyo. [p. 901]
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Hinnites boninensis (Dijkstra & Matsukuma. 1993); T. Okutani (Ed.), 2000, Marine mollusks in Japan, pl. 447, fig. 16.
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