Comprehensive Description

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Description

Chlamys phalara sp. nov.

 

Pl. 6, fig. 1-4

 

 

[?] Chlamys amandi (Hertlein): Soot-Ryen, 1959: 30, pl. 1, fig. 7-8.

 

 

Description: Shell thin, subcircular, more or less oblique in outline; compressed, left valve slightly more inflated than right. Right valve sculptured with about 30 to 40 low, rounded ribs, many of which split into groups of two or three riblets; ribs smooth near the beak and very finely concentrically frilled on the outer portion of the disk; interspaces as wide or wider than ribs, crossed by fine, concentric lamellae, covered by minute, irregularly anastomosing, radial lineolation, and occasionally bearing low central riblets, particularly near margins of the valve; auricles unequal, anterior one larger, bearing about five scaly to nodulose radial riblets, with a well-developed byssal notch; margin below the notch with 4 to 6 free pectinidial teeth; posterior ear obtuse, with about five riblets bearing sharp, imbricating spines and microscopic lineolation over all; the first three or four marginal ribs below this ear may have similar spines. Left valve with narrower, sharper ribs which rarely bifurcate and are either smooth or sparsely ornamented with short, raised scales, variably distributed over the disk; interspaces sculptured about as on right valve; auricles unequal, anterior one without byssal notch, its anterior margin nearly perpendicular to hinge line, bearing about seven finely nodulose riblets; posterior auricle sometimes without ribs; both auricles microscopically wrinkled; hinge line imbricately scaled. Color of exterior of valves variously white, cream-color, yellow, orange-brown, or rosy-red, singly or in combination, the left valve always the more deeply colored. Ribs often darker than interspaces. Valve margins below the auricles typically with a narrow streak of reddish brown, the same color sometimes appearing inside, along the hinge line. White mottling, characteristically composed of chevron-shaped markings pointing towards the beaks, often occurs over part of one or both valves.

 

 

The entire left valve, and portions of the right, are coated with en­crusting sponge in many of these specimens; a few have lepadomorph barnacles attached.

 

 

Type locality: California Academy of Sciences locality No. 41568, trawled off Juan Fernandez Island (Isla Más á Tierra), Chile, in 80-200 metres, R/V Anton Bruun, 15 December 1965. The log of the Anton Bruun's Cruise 12, during which the collections were made, records that on the date in question the ship was at 33° 29-42' S lat., 78° 55' W long., and that eight hauls were made with a 12 m shrimp trawl (E. H. Vokes, personal communication). Thirty-four specimens examined.

 

 

Dimensions: Holotype, length 38.4 mm; height perpendicular to hinge line 38.6 mm; diameter (joined valves) 9.2 mm. Measured paratypes: (a) length 33.2 mm; height 34.0 mm; diameter 7.3 mm; (b) length 32.1 mm; height 32.5 mm; diameter 6.9 mm; (c) length 32.5 mm; height 32.0 mm; diameter 7.4 mm.

 

 

Type material: Holotype, right and left valves, No. 54752, Department of Geology, California Academy of Sciences, San Francisco. Paratypes, Nos. 54753-54754, same institution. Additional paratypes are deposited in the following institutions: Museo Nacional de Historia Natural, Santiago, Chile; National Museum of Victoria, Australia; U.S. National Museum of Natural History, Washington, D.C.; and Los Angeles County Museum of Natural History, California.

 

 

Distribution: Mainland Chile: Calbuco to Chonos Archipelago, in 5-300 metres (Soot-Ryen, 1959). Juan Fernandez Islands.

 

 

Etymology: From the Greek phalaros - having a white patch.

 

 

Commentary: The present specimens are in all probability conspecific with those cited and figured by Soot-Ryen (1959: 29-30, pl. 1, figs. 7, 8) as Chlamys amandi from numerous stations, on a variety of bottom types, in the vicinity of Chiloe Island and the Golfo de Ancud, Chile. This new record, therefore, represents a northwestward range extension of some 600 miles. Previous reports on the molluscan fauna of the Juan Fernandez Islands (Dall, 1909; Odhner, 1922) have not listed any Pectinidae. Of a total of 39 marine molluscan species then known to occur at Juan Fern­andez, Odhner (1922) cited 13 as also occurring along the west American mainland; to this group is now added C. phalara.

 

 

Chlamys phalara differs from all other species of Chlamys known to be living in the eastern Pacific region in its oblique outline, thin shell texture, and fineness of ribbing. The color pattern is also unique among regional Pectinidae, although the white, chevron-shaped markings recall in a vague way those of Chlamys (Leptopecten) monotimeris (Conrad, 1837) (figured by Grau, 1959, pl. 35, fig. 2; as C. [L.] latiauratus monotim­eris). Argentinian specimens of Chlamys patriae (Doello-Jurado, 1918) in the California Academy of Sciences collection show somewhat the same type of microsculpture, fine concentric lamellae in spaces between the ribs, traces of reddish brown on valve margins below the auricles, and — rarely — faint, opaque, white clouding on the left valve near the beak, similar to the white chevrons of C. phalara. From the new species, C. patriae differs in having single, not fascicled, ribs on the right valve, which are separated by deeper interspaces; and a sturdier shell with both the concentric lamellae and microscopic lineolation more strongly developed.

 

 

Chlamys phalara should also be compared with the Pliocene Chlamys moerickei (Hertlein, 1936) (replacement name for Pecten tenuicostatus Hupé, 1854, non Mighels & Adams, 1841), described from "los faluns de Chiloé," but best known from Tubul (Philippi, 1887; Möricke, 1896). Both species are thin-shelled, inequivalve and moderately to strongly inequilateral, with short hinge line and fine ribs which do not markedly indent the margin of the shell. The microsculpture of both consists of anastomosing radial lineolation overriding the scales on the ribs and the lamellae in the interspaces. The ribs of the right valve of C. moerickei show considerable variation in size and degree of fasciculation; some specimens are much like C. patriae in having large, single ribs. These three species seem to be phyletically closely related. Chlamys moerickei is a plausible ancestor of both C. patriae and C. phalara, which are prob­ably allopatric differentiates of the more variable C. moerickei stock. Chlamys phalara differs from C. moerickei principally in having less de­veloped microsculpture and a tendency towards narrower apical angle. The material at hand suggests that smaller maximum size and reduced variability of right-valve ribbing are other differences.

 

 

Herm (1969: 104, text-fig. 41) considered Chlamys vidali (Philippi. 1887) from the Chilean Pliocene to be similar and possibly ancestral to "Chlamys amandi," accepting Soot-Ryen's (1959) concept of the latter species; but I do not believe the relationship to be very close. Chlamys vidali differs from C. phalara in being equilateral, thicker shelled, more strongly ribbed, and approximately twice as large. Its hinge has strong bosses on either side of the ligamental pit, which are absent in C. phalara.”

 

 

 

(Roth, 1975: 82-84)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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