Pecten waikikius Dall, Bartsch & Rehder, 1938
DALL, W. H., P. BARTSCH & H. A. REHDER. 1938. A manual of the Recent and fossil marine pelecypod mollusks of the Hawaiian Islands. Bernice P. Bishop Museum Bulletin, 153: i-iv, 1-233, pls. 1-58. [p. 95, pl. 24, figs. 5-6]
1938 Pecten waikikius Dall, Bartsch & Rehder, 1938
W. P. Dall, P. Bartsch & H. A. Rehder, 1938, plate 24.
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«Shell moderately large, white, variegated with old rose color, the latter being particularly in evidence in the middle of the disk. The upper valve (a left valve) is very deeply cupped with the wings of almost equal size. The right wing terminates in an almost straight line at its lateral edge. It is marked by five slender radiating threads which occupy the posterior three fifths of the wing, the last or fifth thread being weaker than the other four. The left wing is moderately arched at its lateral margin and is crossed by three radiating threads, which are confined to the posterior fifth of the wing. In addition to this, both wings are marked by very closely spaced, incremental lines which in reality are slender lamellae. The spaces that separate them are about as wide as the slender lamellae. The right and left wings are concave. The central portion of the shell adjoining the wings is strongly convexly rounded on both sides. On the right side it is marked by five moderately strong radiating cords, which are about twice as wide as the spaces that separate them. On the left side two cords are present near the inner margin, the outer one being considerably smaller than the inner one. The central, decidedly concave portion of the shell is marked by 11 strong, somewhat flattened, radiating ribs, which appear as flutings. These are a little less wide than the spaces that separate them and may be feebly medially grooved. These radiating ribs, as well as the spaces that separate them, are crossed by numerous thin lamellae, which are only about one fourth as thick as the spaces that separate them. The ventral margin of the shell is rendered scalloped by the ribs. The interior of the shell is porcelaneous. The hinge has the dorsal margin almost straight; the ligamental pit is deep and triangular, and its
attachment rough. The anterior and posterior portion of the hinge bears five oblique folds, of which the dorsal one parallels the dorsal margin of the hinge and is much longer than the rest, which tend to a more vertical position. These folds are crossed by slender vertical lamellae which probably correspond to the external growth sculpture referred to for the wings. The attachment for the muscle is decidedly elevated and thickened. The type (an upper valve), U.S.N.M. Cat. No. 337523, was dredged by Thaanum (Coll. No. 8320) off Waikiki, Oahu, in 33-50 fathoms. It measures: height, 40.8 mm.; length, 47.6 mm.; diameter of upper valve, 7.3 mm. U.S.N.M. Cat. No. 335668 contains a very poor specimen, an upper valve, but unmistakably belonging to this species, badly worn, dredged by the U. S. Bureau of Fisheries Steamer Albatross at Station 4061 off the northeast coast of Hawaii in 24-83 fathoms on coral, sand, coralline nodules and foraminifera bottom; surface temperature 77º F. U.S.N.M. Cat. No. 337524, another upper valve, collected by Thaanum (Coll. No. 8320a) off Mala Bay, Maui, in 4-8 fathoms. This species differs from Pecten diomedeus in having the wings radially ribbed and the concentric lamina much coarser and more distantly spaced.» WILLIAM HEALEY DALL, PAUL BARTSCH & HARALD ALFRED REHDER, 1938
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«AFFINITIES: P . j. waikikius differs from jacobaeus s.str. and from the subspecies keppelianius, byronensis, byoritsuensis, and meridionalis in its high beak and inflation, strongly concave left valve, and distinctive left adductor scar. In sculpture it most closely resembles the ornamented phase of the extinct New Zealand Pleistocene form P. j. toi, but the latter is larger (up to 131 mm long), less inflated (29.5% compared with 44%), has a normal muscle scar, and is diphasic. In its rounded ribs, P, j. waikikius approaches subspecies of P. maximus, but this resemblance is probably homeomorphy.
In studying the relationships between different living and extinct populations of Pacific Pecten, the writer was led to the conclusion that members of the jacobaeus group were capable of hybridising with members of the benedictus group, when they came into geographical proximity, despite the evidence that the two groups had long been differentiated in the Mediterranean and had maintained themselves as distinct for most of Upper Tertiary time. For this reason, the subgenus Oppenheimopecten von Teppner, 1922, proposed for Pecten subbenedictus Fontannes, cannot be maintained. A member of the benedictus group, P. benedictus excavatus Anton (of authors, = sinensis Sowerby) lives in the China Sea, Formosa, and Japan, is present at the Philippine Islands as dead valves (U.S. Nat. Mus., Bur. Fisheries Sta. 5162, 230 fathoms off Sanga Sanga Island), and perhaps formerly ranged far enough east to influence the Hawaiian population. It is even possible, as noted below, that a form of benedictus still lives at Hawaii. The characters of waikikius that could be attributed to interbreeding with a benedictus population are its extreme inflation, concave left valve, and rounded ribs. The peculiar adductor muscle scar of waikikius resembles that of a specimen of sinensis from Japan, but this character probably has a functional relationship to the extreme inflation of the right valve and is not necessarily an indication of close affinity» FLEMING, C. A. 1962. On the hawaiian scallops of the genus Pecten Muller (Pelecypoda). Pacific Science, 16: 181-185, fig. 1. [p. 183]
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Pecten jacobaeus waikikius Dall, Bartsch, and Rehder; C. A. Fleming, 1962, On the hawaiian scallops of the genus Pecten, figure 1.
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