Pascahinnites pasca (Dall, 1908)
DALL, W. H. 1908. The Mollusca and the Brachiopoda. Reports on the Mollusca and Brachiopoda [U. S. Fish Commission Steamer ''Albatross'' during 1891 and 1905] region. Bulletin of the Museum of Comparative Zoology at Harvard University, 43 (6): 203-487, pls. 1-22. [p. 401]
1908 Pecten (Chalmys) [sic] pasca Dall, 1908
Pascahinnites pasca (Dall, 1908); B. K. Raines & G. T. Poppe, 2006, A Conchological Iconography, The Family Pectinidae, pl. 170, figs. 1-4.
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«Shell (left valve) flat, irregular distally, rose-pink and white, irregularly clouded, somewhat inequilateral; anterior car larger, with four crimson radial threads on a light pink background covered with the superficial reticulum; posterior ear smaller, with two or three radial obscure threads; disk with about fourteen radial ribs (none intercalary) subequal and equally spaced; the whole surface covered with a fine, closely woven reticulum of minute rectangular scales, when perfect coalescent at the surface, when the surface is eroded presenting a minute cellular reticulum, when this is eroded the surface still shows fine regular reticular markings. When the crust is perfect over a rib it appears keeled, when the crust is removed the rib itself is seen to be rounded, the interspaces also are not channelled but roundly excavated; interior polished, the coloration shining through; hinge margin straight, with a small medial pit, the margin showing conspicuous traces of the provincular striation; there are no crura, the peripheral margin of the disk is irregular. Alt. of valve, 16; lat. of valve, 13; of hinge line, 8 mm.
Collected on the beach at Easter Island, by the "Albatross" party. U. S. N. Mus. 110,765. This single valve would perhaps not have been worthy of description were it not that it seems to belong to the group of species called Hinnites, and possesses such a remarkable surface. I have elsewhere expressed the opinion that the different species of Hinnites are more intimately related to various groups of Pecten than they are to each other, and that probably there is no direct genetic relation between the fossil species. The "genus" Hinnites may be regarded as composed of "sports" from the Chlamys group of Pecten.» WILLIAM HEALEY DALL, 1908
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«Distribution.— Endemic for Easter Island.
Habitat.— DiSavo, Randall & Cea (1988) conducted a survey of the marine environment surrounding Easter Island and reported that many specimens of P. pasca were attached to Leptoseris paschalensis wells, 1972 (a species of hard coral), caught by a fisherman at 100 m depth. In the same report, it was noted that divers had experienced a thermal cline between 50-60 m. The present live taken specimen was cemented to hard substrate in open habitat, not nested in a crack or a hole. Remarks.— Semipallium coruscans (Hinds, 1845) is somewhat similar to juvenile P. pasca, but differs in having tripartite radial ribs on the left valve, with interstitial shagreen microsculpture, which is not commarginally arranged. The tri- or quadripartite radial ribs of the right valve are more regularly spaced than they are in P. pasca. Adult specimens of S. coruscans are byssaly attached to rocks or coral, but never cemented. It appears that P. pasca is actually a deep water species (in that habitat at least fully adult specimens are found), and that the single valves collected at shallower depths are a result of intertidal drift. This is supported by the fact that the island experiences a strong underwater surge even at depths of 20-30 m. This surging action does not lend itself to supporting sedentary fauna at shallower depths. The microsculpture, dissoconch and prodissoconch of both the smaller, regular shells and of the larger, distorted ones, were compared. It turned out that they are identical, confirming that the two forms are conspecific. The smaller immature specimens have an active ctenolium, which suggests that they are byssally attached at this stage.» DIJKSTRA, H. H. & B. K. RAINES. 1999. Pascahinnites n. gen. for "Pecten (Chalmys)" [sic] pasca Dall, 1908, a cemented Easter Island scallop (Bivalvia: Pectinidae). Basteria, 63: 199-203, figs. 1, 2. [p. 202]
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Pascahinnites pasca (Dall, 1908); H. H. Dijkstra & B. K. Raines, 1999, Pascahinnites n. gen. for "Pecten (Chalmys)" [sic] pasca Dall, 1908, a cemented Easter Island scallop, figures 1, 2.
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«REMARKS.—This species was previously known from only a single, somewhat beach worn, left valve. I have now been able to examine one complete specimen and 17 single valves found in drifted sand, of which 13 are left and 4 are right valves. The larger valves are unfortunately also beach worn and / or broken, and therefore I am figuring an immature specimen. In writing up this species I have fortunately been able to consult Dr. Thomas R. Waller, whose detailed description of Chlamys coruscans Hinds, 1845, has been of great help (Waller, 1972: 231-236). As mentioned above, this species is closest to Chlamys coruscans hawaiensis Dall, Bartsch, and Rehder.
Dall in his remarks mentions that the present species "seems to belong to a group of species called Hinnites," which he does not regard as a phylogentically natural group. This comment was apparently prompted by the fact that the older part of the valve shows an irregularity in growth and sculpture that I believe is due to the conditions under which it grew. I am including photographs of an additional left and a right valve to show this irregularity (Plate 13: figures 5, 6).» REHDER,
H. A. 1980. The Marine Mollusks of Easter Island (Isla de Pascua) and
and Sala y Gómez. Smithsonian Contributions to Zoology, 289: 167 p., pls. 1-14. [p. 109]
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Chlamys pasca (Dall); H. A. Rehder, 1980, The Marine Mollusks of Easter Island, plate 13, figures 3-6.
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