File:American malacological bulletin (1988) (17533758424).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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128 AMER. MALAC. BULL. 6(1) (1988)
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Figs. 61-72. Notoplax arabica sp. nov. Figs. 61-63. Valves I (4.0 mm wide) V (5.4 mm wide) and VIII (4.0 mm wide) respectively, dorsal view. Fig. 64. Valve VIII, ventral view (4.0 mm wide). Fig. 65. Heads of major lateral teeth. Fig. 66. Spatulate uncinal tooth. Fig. 67. Cen- tral and first lateral radula teeth. Fig. 68. Dorsal girdle spicules. Fig. 69. Marginal spicule. Fig. 70. Spicule from sutural tuft. Fig. 71. Spicule from girdle bridge. Fig. 72. Ventral spicules (Figs. 65-67, scale bar = 100 /tm; Figs. 68-72, scale bar = 10 Pm). Tegmentum microscopically granulose, end valves and lateropleural areas of intermediate valves sculptured with large, strongly raised, convex, widely spaced, irregularly oval to decidedly elongate, radially oriented pustules, those near valve margins overhanging or projecting past valve, on some valves pustules vaguely arranged in irregular, longitudinal rows, jugal areas raised, smooth to naked eye, ornamented with extremely fine, longitudinal, beaded riblets, accompanied by shallow, longitudinal excavation on both sides. Articulamentum slightly translucent, tegmental color shining through, apophyses strongly forwardly produced, rounded, jugal sinus moderately to strongly convex, insertion plates long, slit formula 5/1/ 6, slits shallow, those of tail valve inequidistant, slit rays hardly or not indicated, teeth of head and intermediate valves long, sharp, weakly striate dorsally, those of tail valve short, blunt, strongly striate. Girdle dorsally covered with small, straight to slightly bent, sharply pointed, faintly longitudinally striate spicules, 56-62 ^m long, 8-10 /xm thick (Fig. 68), on girdle bridges in- terspersed with long, slender, straight, smooth spicules, 110 x 8 nm (Fig. 71), sutural tufts composed of stout, straight, sharply pointed spicules, 100 x 14 ^m, weakly longitudinally striate on distal half (Fig. 70). Marginal spicules (Fig. 69) small, decidedly obese, blunt-pointed, finely longitudinally striate, 52 x 14 fim. Girdle paved ventrally with very small, slender, straight spicules, 40 x 3 ^m (Fig. 72). Central tooth of radula (Fig. 67) tulip-shaped, with straight blade, first lateral tooth somewhat shorter, narrowly aliform, without blade, major lateral with tricuspid head, den- ticles pointed, central one longer than others (Fig. 65), spatulate uncinal tooth bent, smooth, distal end rounded. DISCUSSION: By its peculiar sculpture of large, elongate, convex, widely spaced pustules, N. arabica differs markedly from all known Notoplax spp. in the Indian Ocean, its closest relatives being N. elegans Leloup, 1981, from Madagascar, which has a greater number of close set, subcircular, con- cave granules, N. alisonae (Winckworth, MS; Kaas, 1976), from Sri Lanka, which has a much greater number of tear-shaped, flat to slightly concave granules, and N. coarctata (Sowerby, 1841), from the Philippines, in which the tegmentum of in- termediate valves is flask-shaped. ETYMOLOGY: The name of this species reflects its presence in the Arabian Gulf. DISCUSSION The most striking phenomenon among the present material is the discontinuous distribution of Lepidozona luzonica, hitherto known only from Luzon, Philippines, the Java Sea and Singapore. Its occurrence in the Arabian Gulf remains inexplicable except for transport resulting from human intervention via navigation. This is the case with Chaetopleura angulata (Spengler, 1797) and Acanthochitona fascicularis (Linnaeus, 1767). Another striking fact is the ab- sence of Chiton huluensis (Smith, 1903), also discontinuously distributed, covering a vast area from the Tasman Sea through the Torres Straits, the Moluccas, the Timor Sea, the Maldive Islands, Sri Lanka, the western coast of Madagascar, the coast of Mozambique, the Red Sea and through the Suez Canal to the Mediterranean coast of Israel. It should be remembered, however, that the bulk of material we studied was collected in intertidal or shallow subtidal areas, except for some specimens collected in 15-20 m depths by SCUBA. Ferreira (1983) concluded that "at least as far as chiton faunas are concerned, the tropical western Indian Ocean con- stitutes a definite zoogeographic province, which includes the Red Sea, the East African coast southward to Natal, and the adjacent islands eastward to Mauritius (60°E)." Undoubtedly the chiton fauna of the western Indian Ocean is far richer in species than is that of the Indo-Arabian side. However, 50% of the species found in the Gulf and on the Oman coast also are found on the African coast, and all but one also occur in the Red Sea. On the other hand, Callistochiton adenensis

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