Delectopecten Stewart, 1930
STEWART, R. B. 1930. Gabb’s California Cretaceous and Tertiary type lamellibranchs. Academy of Natural Sciences of Philadelphia, Special Publication No. 3: 1-314 pls. 1-17. [p.118]
«PALLIOLLUM Monterosato 1884
DELECTOPECTEN new subgens
In not having the posterior ear differentiated, Delectopecten includes a group of small forms now living in the N. E. Pacific which have been classed as "Pseudamussium" by Dall (U. S. Nat. Mus. Bul. 112, 1921, p. 19, 20, pI. 1, fig. 4, 5), "Pecten" murrayi Smith from Australia (Rep. Challenger, Zool. v. 13, 1885, p. 303, pI. 22, fig. 1), and Palliolum vitreum (Verrill, Tr. Conn. Ac. Sc. v. 10, 1897, p. 66, pI. 18, fig. 6-13). "Pecten (Pseudamussium)" polyleptus Dall, from the Galápagos Islands and "P. (Pseudamusium)" panamensis Dall also belong to this group (Dall, Mus. Comp. Zool. Bul. 43, 1906, p. 403, 404, pI. 10, fig. 9, pI. 6, fig. 8, 10). Palliolum" vitreum, which is from the North Atlantic, was apparently included in the original Palliolum Monterosato (Nom. Gen. Conch. Medit., 1884, p. 5-6), but "Pecten" incomparabilis Risso, which has been designated as type species of Palliolum (Crosse, Jr. de Conch. v. 33, 1885, p. 140) seems to have a distinct posterior ear (Bucquoy, Dautzenberg and Dollfus, Moll. Roussillon v. 2, 1889, p. 109, pI. 16, fig. 18, 19). The type species of Delectopeeten is It "Pecten (Pseudamusium,)" vancouverensis Whiteaves, a living West Coast species (Ottawa Nat. v. 7, 1893, p. 133-4, pI. 1, fig. 1, a: Dall, U. S. Nat. Mus. Bul. 112, 1921, p. 20, pI. 1, fig. 4, 5). Although the radial ribs predominate, the "Camptonectes-sculpture" is evident beneath them. Camptonectes dubliensis and Pecten sarumensis Woods (1902, p. 162, pI. 29, fig. 8, p. 192, pI. 37, fig. 1-3) from the Cretaceous of England, lack the well-differentiated posterior ear, but do not seem to be unusually close to this group. However, it may be that Delectopecten will eventually be placed near Camptonectes "Agassiz" Meek (Smiths. Misc. CoIl. 177, 1865, p. 28, 39) the type species of which is the Jurassic "Pecten" lens Sowerby, designated by Stoliczka (1871, p. 425).
Hylopecten [sic] Verrill, which also lacks the distinctly setoff posterior ear, differs in having concentric undulations and is also said to lack the Camptonectes-sculpture (Verrill, Tr. Conn. Ac. Sc. v. 10, 1897, p. 71, pI. 18, fig. 5).» RALPH BENTLEY STEWART, 1930
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Pecten (Pseudamusium) [sic] Vancouverensis (Sp. nov.); J. F. Whiteaves, 1893. Notes on some marine invertebrata from the coast of British Columbia, plate 1, figures 1, 1a.
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Delectopecten fosterianus (Powell, 1933); H. H. Dijkstra & B. A. Mashall, 2008, The recent Pectinoidea of the New Zealand region, figures 40A, 40B, 40D-40F.
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«Genus Delectopecten Stewart, 1930
Delectopecten Stewart, 1930: 118. Type species (by original designation): Pecten (Pseudamusium [sic]) vancouverensis Whiteaves, 1893; Recent, off Maryland, 2603 m.
Diagnosis
Pectinidae with opaque or translucent, fragile, subcircular shell, up to ca. 30 mm in height, valves inequivalve and equilateral, smooth or sculptured with commarginal rows of scales or vesicles, spinose radial ridges and/or delicate antimarginal striae. Auricles unequal in size. Byssal notch moderately deep, functional ctenolium prominent. Distribution
Early Cretaceous to Recent. Worldwide at sublittoral to abyssal depths. Remarks
For discussion see Dijkstra (1995: 50), and Coan et al. (2000: 227).» DIJKSTRA, H. H. & B. A. MARSHALL. 2008. The recent Pectinoidea of the New Zealand region (Mollusca: Bivalvia: Propeamusiidae,Pectinidae and Spondylidae). Molluscan Research, 28 (1): 1-88, figs. 1-70. [p. 49]
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«Waller (1991, fig. 8) and Waller and Marincovich (1992: 219) indicated that the extant cosmopolitan genus Delectopecten Stewart, 1930, is a descendant of the extinct Jurassic-Cretaceous genus Camptonectes Agassiz in Meek, 1864, which in turn is derived from Pleuronectites von Schlotheim, 1820, of the Triassic. By this phylogenetic scheme, Delectopecten is a sister taxon of all other extant Pectinidae, with the last common ancestor in the early Middle Triassic (early Anisian), approximately 240 million years ago. New research by the author on Middle Triassic pectinids has led to a new concept of Pleuronectites as an evolutionary dead-end that underwent its main evolutionary change within the Muschelkalk Basin of southwestern Europe. In the course of its evolution within this basin in the Triassic, the genus reached gigantic size and became more inequivalved, with the right valve nearly flat and the left valve becoming greatly inflated (Hagdom 1995). All Pleuronectites thus far examined lack antimarginal microsculpture throughout ontogeny, indicating that these are an unlikely phylogenetic source for the earliest Camptonectes, which have fine but persistent antimarginal microsculpture. The earliest Camptonectes thus far reported are Late Triassic (Carnian-Norian) in age and are from the Boreal-East Asian Province of Japan and eastern Siberia (Hayami 1989: 6). Their likely origin is in the Triassic Chlamys group, possibly in the genus Praechlamys
Allasinaz, 1972. Delectopecten, as a phyletic descendant of Camptonectes, thus still remains as the sister group of all other extant Pectinidae, but the divergence point should now be dated from the early Late Triassic (Carnian), in the time range of approximately 225 to 230 million years ago (Harland et al. 1990).» WALLER, T. R. 2006. New phylogenies of the Pectinidae (Mollusca: Bivalvia): reconciling morphological and molecular approaches. In: S.E. Shumway & G.J. Parsons (Ed.), 2006: Scallops: Biology, Ecology and Aquaculture, 1-44, figs. 1.1-1.4. [p. 10]
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«Genus Delectopecten Stewart, 1930
Delectopecten Stewart, 1930: 118. Type species (by original designation): Pecten (Pseudamusium [sic]) vancouverensis Whiteaves, 1893; Recent, VClncouver Island, British Columbia, Canada.
Remarks: Grau (1959: 38) and Beu (1970: 117) synonymised Catillopecten Iredale, 1939 with Delectopecten. Waller (1984: 214), however, treated Catillopecten as a distinct genus of Propeamussiidae. Schein (1989: 81) placed Catillopecten in Propeamussiinae Abbott, 1954 of Pectinidae and mentioned that Bathypecten Schein-Fatton, 1985 is closely related to Catillopecten. Recently Waller & Marincovich (1992: 219) placed Delectopecten in Camptonectinae Habe, 1977.»
DIJKSTRA, H. H. & B. A. MARSHALL. 1997. Pectinoidea (Mollusca: Bivalvia: Propeamussiidae: Pectinidae) of Lord Howe Island, Norfolk Island and the Kermadec Islands. Molluscan Research, 18 (1): 73-114, figs. 1-13. [p. 88]
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Cyclopecten (Delectopecten) vancouverensis (Whiteaves) 1893; G. Grau, 1959, Pectinidae of the eastern Pacific, plate 15.
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Subgenus DELECTOPECTEN Stewart 1930
Delectopecten Stewart, 1930, p. 1J8. [Proposed as a subgenus of Palliollum.] Type species: Pecten (Pseudamusium) vancouverensis Whiteaves, 1893, p. 133, pI. 1, figs. 1-1a; type locality: Forward Inlet, Quatsino Sound, Vancouver Island, British Columbia, Canada, in ten to twenty fathoms, mud. [For geographical range see Cyclopecten (Delectopecten) vancouverensis, this paper. Whiteaves, Dall and several other authors invalidly emended Pseudamussium to Pseudamusium.]
Arctinula Thiele, 1934, p. 806. [Proposed as a section of Palliolum.] Type species: Pecten Greenlandicus Sowerby, 1842, p. 57, pl. 13, fig. 40; type locality: Greenland. Catillopecten Iredale, 1939, p. 370. Type species: Pecten murrayi E. A. Smith, 1885, p. 303, pI. 22, figs. 1-1a; type locality: Challenger station 184, east of Cape York, Queensland, Australia, in 1400 fathoms. Original diagnosis: In not having the posterior ear differentiated, Delectopecten includes a group of small forms now living in the N. E. Pacific which have been classed as "Pseudamussium" by Dall..., "Pecten" murrayi Smith from Australia ..., and Palliolum vitreum..., "Pecten (Pseudamussium)" polyleptus Dall, from the Galapagos Islands and "P. (Pseudalmusium)" panamensis Dall also belong to this group... [panamensis Dall, 1908; panamensis Dall, 1898 = zacae Hertlein, 1935.] Palliolum vitreum, which is from the North Atlantic, was apparently included in the original Palliolum Monterosato (1884, p. 5-6), but "Pecten" incomparabilis Risso, which has been designated as type species of Palliolum (Crosse, 1885, p. 140) seems to have a distinct posterior ear... The type species of Delectopecten is "Pecten (Pseudamusium)" vancouverensis Whiteaves, a living West Coast species... Although the radial ribs predominate, the "Camptonectes-sculpture" is evident beneath them.
Additional diagnosis; Shells very thin, translucent and uncolored; without "ribs" (see below); left valve usually more convex than right; height and length identical or nearly so; valves identical in size except for Cyclopecten greenlandicus, in which right is smaller; disks occasionally having obscure and varying number of low concentric folds in umbonal region (in Hyaloptcten folds are functional and more pronounced, occurring throughout disk). Posterior auricles poorly defined; in Cyclopecten greenlandicus their lateral margins are oblique, slanting from submargin to hinge line, in all other species margins are continuous with outlines of disks; ctenolium always present. Disks unsculptured only in C. randolphi, other species having either concentric rows of scales or vesicles, spinose radial ridges, or fine radial striae; right valve never concentrically lamellated or ridged as in Cyclopecten, although C. vitreus has unique form of minute ridges,
Remarks: DeIectopecten differs from Cyclopecten s.l. in the shape of the aurides, the unflexed right valve (except in Cyclopecten greenlandicus), the absence of concentric lamellae or ridges on that valve (except in C. vitreus), the always-present ctenolium, and the translucency of all species.
The author cannot agree with Woodring (1938, p. 35), who assigned Delectopecten subgeneric rank under Hyalopecten Verrill (1897, p. 71). The latter was proposed as a genus, primarily because of the concentric undulations of the disks; while obviously separable from Cyclopecten, its other similarities make it more appropriately a subgenus under that unit. Arctinula is synonymized here because the slight distinctions between its type and most species of Delectopecten are not felt to be of sufficient importance to warrant separation at more than specific level. Since the type of Catillopecten, Pecten murrayi, was one of the species cited by Stewart, and since it agrees so well with the diagnosis of Delectopecten, Iredale's genus is also synonymized. In addition to the species cited above and others included in this paper, the following are also referable to Delectopecten: abyssorum Lovell (north Atlantic to West Africa and probably Mediterranean); parvulinus Locard (Bay of Biscay); translucens and micaceus Dautzenberg & Bavay (Makassar Strait, Indonesia); distinctus E. A. Smith (Marion Island, Prince Edward Islands, South Indian Ocean).» GRAU, G. 1959. Pectinidae of the eastern Pacific. Allan Hancock Pacific Expeditions, 23: viii, 308 p., pls. 1-57. University of Southern California Press. Los Angeles, California. [p. 38, 39]
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