Serratovola angusticostata Dijkstra, 2008
DIJKSTRA, H. H. 2008. A new species of Recent scallop of the genus Serratovola (Bivalvia, Pectinidae) from the tropical Indo-West Pacific. Basteria, 72 (1-3): 57-63 [p. 60, figs. 7-12 ]
2008 Serratovola angusticostata Dijkstra 2008
H. H. Dijkstra, 2008, figures 1-12.
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«Description.— Shell up to ca. 35 mm high, circular, inequivalve, equilateral. Left valve flat or slightly inflated; right valve convex. Auricles nearly equal in size, unequal in shape. Umbonal angle ca. 115º. Left valve creamy red-brownish with commarginal brownish maculations and brownish radial streak on the ribs; right valve off-white with minute red-brownish dots near the umbo, inside whitish with large brown dot near adductor scar.
Left valve sculptured with 18, regularly spaced, narrow angular radial costae with hollow sections laterally, separated by a solid central radial keel. The interspaces (2.5 mm) are broader than the radial ribs (1.5 mm) near the central part of the ventral margin. The anterior (11.9 mm) and posterior (11 mm) hinge of the auricles are nearly equal in size. The anterior auricle is slightly smaller than the posterior one (antero-margin 7 mm, postero- margin 9 mm); both auricles have a few very weak radial ridges (2 anterior, 3 posterior) and a closely spaced commarginal lamellar sculpture near the disc of the anterior auricle. Antimarginal microsculpture is present in the intercostal spaces. Right valve with 19, regularly spaced, angular radial ribs with a tripartite appearance by ‘dentrition’, also with hollow sections laterally and separated by a solid central radial keel. Interspaces (1.5 mm) somewhat narrower than the radial costae (2 mm) near the ventral margin with closely spaced (7-8 per mm) commarginal lamellae. Anterior and posterior auricles with 3-4 very weak radial ridges. Byssal notch shallow. Functional ctenolium lacking. Measurements of the type material.— Holotype: H 34.7 mm, W 37.1 mm, C 10.4 mm. Paratypes: height 14.6-32.4 mm. Distribution.— Tropical Indo-West Pacific: Taiwan, Philippines, Indonesia, westwards to Thailand and eastwards to Papua New Guinea. Depth range 30-150 m, living on soft bottom assemblages. Comparison.— Serratovola angusticostata is morphologically close to S. gardineri, but the present species has a slightly more inflated left valve when juvenile. Serratovola gardineri is flat and differs in having smaller radial costae and wider intercostal spaces on both valves; it has broad ribs and narrow interspaces. The commarginal microsculpture on the left valve of S. angusticostata is only present on the anterior auricle near the disc and throughout the left valve in S. gardineri. An antimarginal microsculpture is present in the interspaces of the left valve of S. angusticostata, and a commarginal microsculpture in S. gardineri. Moreover, the groundcolour of the left valve of S. angusticostata is reddish brown with minute brownish commarginal dots, versus creamy with red scattered markings in S. gardineri. The internal colour of S. angusticostata is whitish with a large brown spot, and uniform white in S. gardineri. Serratovola angusticostata differs from the sympatric S. rubicunda in having slightly smaller radial costae, with broader hollow sections laterally and a smaller central keel. Serratovola rubicunda has wider, more flat-topped ribs and smaller hollow sections laterally and a broader central keel. Serratovola angusticostata has a commarginal sculpture on the anterior auricle of the left valve and S. rubicunda has a prominent commarginal sculpture throughout on ribs, interstices and auricles. The radial ridges on the auricles are weaker and less numerous in S. angusticostata (anterior 2, posterior 3) versus S. rubicunda (anterior 5, posterior 6). Moreover, the ribs of the right valve are solid and rounded, with a delicate or without a commarginal sculpture in the interstices in late growth stage of S. angusticostata, and angular with hollow sections and a prominent commarginal sculpture in the interstices of S. rubicunda. The groundcolour of S. angusticostata is red-brownish and creamy, and creamy in S. rubicunda. Serratovola angusticostata has minute dots in early growth stage, versus scattered prominent dots on both valves in S. rubicunda. The internal colour of S. angusticostata is whitish or yellowish white with a large brown spot and white throughout in S. rubicunda. Serratovola angusticostata is clearly larger than S. pallula, measuring ca. 35 mm versus ca. 17 mm in height. The left valve of S. angusticostata is slightly inflated in early growth stage, whereas that of S. pallula is slightly concave. Serratovola angusticostata has small ribs and wide interstices, and S. pallula broad ribs, lacking the intercostal spaces in early growth stage and very narrow interstices when fully grown. The microsculpture of the left valve of S. angusticostata is commarginal, partly on the anterior auricle and antimarginal in interstices, whereas fully grown S. pallula has a commarginal microsculpture on both auricles and interstices. Serratovola angusticostata has commarginal dots in intercostal spaces and brown streak on keel, whereas S. pallula has more scattered dots on the ribs and interstices. Etymology.— With small ribs (Latin, adj.), alluding to the radial macrosculpture on both valves.» HENK H. DIJKSTRA, 2008
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