Leptopecten latiauratus (Conrad, 1837)
CONRAD, T. A. 1837. Descriptions of new Marine Shells, from Upper California. Collected by Thomas Nuttall. Journal of the Academy of Natural Sciences of Philadelphia, 7 (2): 227-268, pls. 17-20. [p. 238, pl. 18, fig. 9]
1837 Pecten latiauratus Conrad, 1837
1837 Pecten monotimeris Conrad, 1837
1844 Pecten tunica Philippi, 1844
1898 Pecten latiauritus [sic] var. fucicolus Dall, 1898
1898 Pecten (Chlamys) latiauritus [sic] var. fragilis Arnold, 1903
1906 Pecten (Chlamys) latiauritus [sic] var. delosi Arnold 1906
1906 Pecten (Chlamys) latiauritus [sic] var. cerritensis Arnold, 1906
1837 Pecten monotimeris Conrad, 1837
1844 Pecten tunica Philippi, 1844
1898 Pecten latiauritus [sic] var. fucicolus Dall, 1898
1898 Pecten (Chlamys) latiauritus [sic] var. fragilis Arnold, 1903
1906 Pecten (Chlamys) latiauritus [sic] var. delosi Arnold 1906
1906 Pecten (Chlamys) latiauritus [sic] var. cerritensis Arnold, 1906
T. A. Conrad, 1837, plate 18.
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«1. P. latiauratus. [Plate 18, fig. 9.] Shell inequilateral, thin, compressed; ribs fourteen, flattened on the back, slightly sulcated; interstices transversely striated; ears very wide, unequal, both acutely angulated at the extremity; colour reddish brown and white, variegated or spotted.
Inhabits below the efflux of the tide near Sta. Diego and Sta. Barbara.» TIMOTHY ABBOT CONRAD, 1837
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«Remarks.— Verrill (1897: 69) based his description of Leptopecten on only one species, Pecten monotimeris Conrad, 1837. A second species described by Conrad (1837), P. latiauratus, which has page priority over P. monotimeris, differs from the latter in lacking commarginal lamellae and in having a more prosocline form, thinner shell, lower, more rounded ribs, and shorter auricles. These two putative species have broadly overlapping geographic ranges along the California coast and have been regarded by more recent authors as either subspecies (e.g., Grau, 1959) or ecomorphs (e.g., Coan et al., 2000: 237). Clark (1971) provided evidence based on laboratory observations that their differences are under ecological control, possibly but not conclusively involving temperature relative to position in the water column.
The genus name Leptopecten has been applied to a wide array of Recent and extinct species living mainly in warm marine waters on both sides of the Americas, the main feature in common being the relatively large auricles, particularly the anterior auricles, the anterior extremities of which commonly project beyond the anterior extremities of the disks. The shell has a strongly prosocline pterioid shape, at least in early ontogeny, and a deep byssal notch bordered ventrally by a prominent active ctenolium that persists throughout ontogeny. Olsson (1961: 164) subdivided Leptopecten by introducing a new genus-group name, Pacipecten, for species said to differ from Leptopecten s. s. in being more equilateral and having heavier, thicker valves. Upon examining many species of Leptopecten, however, it can be seen that equilaterality, prosoclinity, and shell thickness vary greatly. Even the ecomorphs of L. latiauratus mentioned above diff er in shell thickness, with the lamellate form L. latiauratus having a thicker shell than the smooth form L. monotimeris. Difference in shell thickness also aff ects the degree to which the edges of plicae become thickened or carinate on the inner shell surface. Such internal carinae are absent in ultrathin L. monotimeris but present in thicker-shelled L. latiauratus. For these reasons, Pacipecten is regarded herein as a junior synonym of Leptopecten.» WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197, pls. 1-18. [p. 75]
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Examples of the two forms of Leptopecten latiauratus (Conrad) from G. R. Clark II, 1971, The influence of water temperature on the morphology of Leptopecten latiauratus (Conrad, 1837).
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«Description.— Shell averaging about 25 millimeters in altitude, about as long as high, inequivalve, compressed, inequilateral, disk obliquely produced posteriorily, thin; sides straight; margins smooth. Right valve more compressed than left, with 12 to 16 low, rather squarish ribs, separated by equal, more or less distinctly channeled interspaces; whole surface sculptured by numerous fine concentric lines; hinge line nearly as long as disk; ears subequal in length; anterior ear long and narrow, with 5 or 6 prominent radials and numerous fine concentric lines; byssal notch deep and distinctly separating ear from disk; posterior ear from rectangularly to acutely pointed, sculptured by obsolete radials and concentric lines. Left valve . somewhat more convex than right, otherwise similar to it; anterior ear generally shorter and more prominently sculptured than posterior.
Dimensions.— Alt. 25 mm.; long. 23 mm.; hinge line 20 mm.; diameter 9 mm.; umbonal angle 90º. This species is characterized by its small size, oblique disk, thinness, long hinge line, and deep byssal notch. The sculpture of the shell is usually well marked. The ribs are sometimes faintly medially sulcated, and the interspaces sometimes contain a faint intercalary riblet in the later stages of growth. The Pleistocene shells, as a rule, are rather more strongly ribbed than the living. A pair of valves in the U. S. National Museum (No. 96964), from U. S. 'Fish Commission Station No. 2840, Santa Barbara Islands, is labeled "P. tumbezensis Orb" This shell is probably an albino variety of P. latiauritus, having just a touch of color on the interior of the posterior ear of the left valve. The true P. tumbezensis is from the Peruvian part of the South American coasts. In the Third street tunnel, Los Angeles, P. latiauritus has been found associated with the following fauna: Pecten pedroanus, P. ashleyi, P. opuntia, P. stearnsii, Glyphis densiclathrata, Nassa n. sp.?, Macoma sp. indet., Arca multicostata, Lima hamlini, Buccinum sp. indet., Neverita recluziana, Astarte sp., Priene oregonensis, Ostrea veatchii, Pleurotoma sp. indet., and a carditoid. As this fauna indicates a horizon well down in the Pliocene, it extends the geologic range of P. latiauritus much further back than heretofore known. P. latiauritus is found living attached to kelp, those specimens inhabiting the deeper, quieter waters being less strongly sculptured than those which are subjected to a more strenuous existence nearer the shore.» ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, pls. 1-53. [p. 116]
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Pecten (Chlamys) latiauritus Conrad; R. Arnold, 1906, The Tertiary and Quaternary pectens of California, plate 46, figures 2, 2a, 3, 3a; Pecten (Chlamys) latiauritus Conrad var. monotimeris Conrad, figures 4, 5, 5a.
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