Hyalopecten tydemani (Dijkstra, 1990)
DIJKSTRA, H. H. 1990. Three new pectinacean species from the Indonesian Archipelago collected
during the Siboga Expedition (1899-1900), with additional information and
corrections on the previous report (Mollusca: Propeamussiidae, Pectinidae).
Beaufortia, 40 (1): 1-14, pls. 1, 2. [p. 7, pl. 2, fig. 13]
1990 Palliolum (Hyalopecten) tydemani Dijkstra, 1990
H. H. Dijkstra, 1990, plate 2.
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«Material examined. Holotype: one left valve. Measurements: height 9.1 mm, length 7.5 mm (ZMA Moll. no. 3.89.009).
Locus typicus. SIBOGA stat. 178. Indonesia, Ceram Sea, 2°40' S, 128°37'.5 E. Deep sea trawl. 835 m. Blue muddy bottom. 2.IX. 1899. Description. Shell small, approximately 10 mm in height, and 8 mm in length, somewhat convex and elongate of proportion. Anterior and posterior auricles subequal, umbonal angle about 85°. The valve has strongly developed irregular concentric lamellae on the entire external surface, curved on the auricles and near the anterior and posterior margin. Anterior auricle more curved than posterior, especially near the byssal sinus. Internal surface is opaque up to the pallid area, but near the ventral margin translucent, making the external concentric lamellae visible. Hinge line straight with broad triangled resilial pit. No cardinal crurae are exposed. Etymology. The species is named after Rear Admiral G. F. Tydeman (1858-1939), commander of H. M. SIBOGA. Discussion. Palliolum (Hyalopecten) graui (Knudsen, 1970) from the east Pacific is more circular. It has a finer sculpture of concentric lamellae, which are less pronounced and not strongly curved, and there is a delicate radiating striation on the external surface of the left valve.» HENK H. DIJKSTRA, 1990
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«Distribution and ecology.— So far only known from Indonesia, where it has been collected dead from muddy bottoms at a bathymétrie range of 800-950 m .
Additional description.— Shell small, approximately 10 mm in height, strongly convex and elongate. Anterior and posterior auricles subequal, umbonal angle about 90°. The external surface of the valve is provided with strongly developed concentric lamellae. The anterior auricle also bears an obsolete radial striation. The hinge line is straight, and finely spinous. The byssal notch is rather deep; a few teeth (ctenolium) are developed on the suture, visible only on the inside of the shell. The suture overlaps the ctenolium. The shell is dirty white and opaque. Remarks.— The present specimen is the first collected right valve of H. tydemani, which is similar to the holotype in proportion and sculpture (ZMA 3.89.009, holotype). A closely related species is H. strigillatus (Dall, 1889), known from the western Atlantic, which is somewhat more prominently sculptured with concentric lamellae, and less elongated.» DIJKSTRA, H. H. 1991. A contribution to the knowledge of the pectinacean Mollusca (Bivalvia: Propeamussiidae, Entoliidae, Pectinidae) from the Indonesian Archipelago. Zoologische Verhandelingen, 271: 1-57, figs. 1-91. [p. 28]
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Hyalopecten tydemani Dijkstra, 1990; H. H. Dijkstra, 1991, A contribution to the knowledge of the pectinacean Mollusca from the Indonesian Archipelago, figure 88.
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