Parvamussium marmoratum (Dall, 1881)
DALL, W. H. 1881. Reports on the results of dredging..... “Blake”..... XV. Preliminary report on the Mollusca. Bulletin of the Museum of Comparative Zoology at Harvard University, 9 (2): 33-144 [p. 117]
1881 Amussium [sic] lucidum marmoratum Dall, 1881
1886 Amusium (Propeamusium) [sic] pourtalesianum Dall, 1886
1886 Amusium (Propeamusium) [sic] pourtalesianum striatulum Dall, 1886
1886 Amusium (Propeamusium) [sic] pourtalesianum Dall, 1886
1886 Amusium (Propeamusium) [sic] pourtalesianum striatulum Dall, 1886
Pecten (Propeamusium) Pourtalesianus Dall, var. marmoratus; W. H. Dall, 1886, Report on the Mollusca, Part I. Brachiopoda and Pelecypoda. Reports on the results of dredging, under the supervision of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in the Caribbean Sea (1879-80), by the U.S. Coast Survey Steamer “Blake”…, plate 4, figure 3.
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«Amussium lucidum JEFFREYS.
Pleuronectia lucida Jeffreys, Depths of the Sea, p. 464, fig. 78. Station 2, 805 fms.; Station 21, 287 fms.; Yucatan Strait, 640 fms.; Station 5, 229 fms.; Station 35, 804 fms.; Station 3, 243 fms.; Station 19, 310 fms.; Station 47, 331 fms.; Sigsbee, off Havana, in 119, 127, 243, 450, and 480 fms.; off Morro Light, 292 fms.; Station 7, off Cape San Antonio, 424 fms.; Station 44, 539 fms.; Gulf of Mexico, west of Florida, 30 fms.; Charlotte Harbor, Florida, 13 fms.
This is one of the most common and pretty of the abyssal species in the Antillean and Gulf region. Variety marmoratum, from all depths, is beautifully mottled with scarlet, opaque white, and orange; many specimens are dotted all over with opaque white dots. I have reason for suspecting that this, or a nearly allied species, attains a much greater size, perhaps two or three inches in length. It will be observed that the ordinary form ranges from a few fathoms on the coast of Florida to the greatest depths of the region; and there is no difference whatever between the specimens from shallow and those from deep water. The same may be said of Gouldia cubaniana.» WILLIAM HEALEY DALL, 1881
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«Amussium lucidum marmoratum Dall, 1881: 117.
Amusium (Propeamusium) pourtalesianum marmoratum Dall. Dall, 1886: 212, pl. 4, fig. 3. Amusium (Propeamusium) pourtalesianum striatulum Dall, 1886: 212; 1889: 34. Propeamussium pourtalesianum (Dall, 1886). Abbott, 1974: 449, fig. 5207. Description.--Parvamussium of small size, commonly <15 mm Ht, prosocline, margin of disks unevenly circular, with posterior somewhat extended, anterior auricles longer than posterior, LV more convex than RV, disk flanks of both valves low but steep, disk gapes absent; exterior of right disk formed by columnar prismatic calcite with alternating bands of large, radially elongate prisms and much smaller polygonal prisms, with regularly spaced commarginal lirae formed on larger-prism bands; right anterior auricle with rounded anterior margin and moderately deep, ontogenetically persistent byssal notch without ctenolium, surface of auricle with single radial costella demarcating flat byssal fasciole, rarely with finer radial costae crossed by commarginal lamellae present on auricular surface; posterior margin of posterior auricle sigmoidal to nearly straight, forming acute angle with dorsal margin, dorsal margins of both right auricles commonly dentate, caused by projections of commarginal lamellae; ventral border of RV commonly flexed when valves are tightly closed, made possible by projection of flexible prismatic outer layer beyond distal tips of internal ribs and beyond distal margins of inner shell layers; surface of left disk underlain by foliated-calcite, initially smooth and glossy from beak to 2-3 mm Ht, then with matte surface that is either smooth or with very fine radial costellae varying in number and spacing and increasing distally by intercalation; left disk flanks low and steep, commonly roughened by dense lamellae and minutely scabrous radial costellae; anterior margin of left anterior auricle nearly straight, forming acute angle with dorsal margin, either lacking radial costae or with weakly developed costellae and projecting commarginal lamellae in ventral sector; posterior margin of posterior auricle as on RV. Interiors of disks of both valves commonly with 10, rarely 9 or 11, regularly spaced inner ribs consisting of fibrous calcite embedded in crossedlamellar
aragonite inner shell layer; additional riblet or knob at border of disk and auricle on each side but commonly somewhat stronger on posterior side, and commonly an additional riblet or knob on posterior auricular surface dorsal to basal auricular riblet; intercalated inner ribs common on disk in late ontogeny of large individuals, when present most commonly in posterior sector; hinge plate simple, apposition zones roughened but without cross-ridging even in early ontogeny, hinge teeth absent. Type material.— Dall (1881: 117) did not specify a holotype
for his Amussium lucidum variety marmoratum, and his type series from the dredging expeditions of the U.S. Coastal Steamer "Blake" is now divided among the collections of the USNM(IZ) and the Museum of Comparative Zoology in Cambridge, Massachusetts. Because I have not studied all of the potential syntypes, I am not designating a lectotype. Type locality.— Dall (1881: 117) did not specify a particular locality for his variety marmoratum, and later (Dall, 1886: 212) stated that this variety occurs at all depths and throughout the range of the nominal species. This is a broad area that includes the Gulf of Mexico and Caribbean and a very broad depth range, said by Dall (1886: 211) to be 13-805 fathoms (24-1,472 m).
Other material.— Recent: 85 lots of Recent Parvamussium marmoratum s. l., in the USNM(IZ), from the western Atlantic region; Dominican Republic Neogene: 7 RV, 8 LV, from 4 localities (Table 4).
Remarks.— The species Parvamussium pourtalesianum (Dall, 1886) was subdivided by Dall (1886) into three varieties (subspecies in the sense of the ICZN): P. pourtalesianum s.s., P. p. marmoratum (Dall, 1881), and P. p. striatulum (Dall, 1886). However, because Dall's 1881 name has priority, the correct nominal species name is P. marmoratum, and the subspecies in Dall's sense are thus P. m. marmoratum, P. m. pourtalesianum, and P. m. striatulum. Further collecting and study since Dall's time have resulted in the synonymy of the first two subspecies (Abbott, 1974: 449), and indeed this synonymy was anticipated by Dall (1886: 212), who noted, "The variety marmoratum, with its brilliant mottling of orange, scarlet, brown, bright yellow, and opaque white dots or flecks, appeared indifferently at most of the stations in company with the pale translucent typical form."
On the other hand, there is no general agreement on the status of Parvamussium marmoratum striatulum. This putative subspecies differs from the other two subspecies in having weak radial costellae on its left valve that originate at the boundary between the proximal glossy zone and distal matte zone on the exterior surface, these costellae commonly fading out before reaching the ventral margin. Additionally, the pigment patterns on the left valves of the costellate form are commonly weaker, lacking the bold white spots present on many P. marmoratum s.s. The right valves of the two subspecies are indistinguishable, because they do not develop radial costellae. Although some samples from some localities have left valves that are all of the costellate form, a few samples contain both non-costellate and costellate forms. There is no demonstrable geographic boundary that separates costellaebearing populations from non-costellate ones, the former occurring in the Gulf of Mexico as well as in the Antilles and in the tropical western Atlantic as far south as Brazil (USNM 752646, specimens collected alive), although costellate specimens are absent from samples from the Atlantic side of the southeastern United States. This distribution suggests that the costellate form is the result of discontinuous genetic variation within populations and that P. m. striatulum cannot be viewed as a geographic subspecies. For these reasons, this taxon is regarded as a junior synonym of P. marmoratum. In the USNM(IZ) collections of extant Parvamussium marmoratum, the total depth range is 44-548 m. The vast majority (81%) of samples, however, are from depths of 70-200 m. The occurrence of this species in the Neogene of the Dominican Republic (Table 4) is consistent with a deepwater origin for the sediments in which it occurs. At localities TU 1227, 1227A, and 1250 there is evidence of deep-water turbidity-flow deposits (E. Vokes & D'Attilio, 1980: 52; E. Vokes, 1989: 12). An exuberant entry in the original Tulane University Locality Register (now in Department of Paleobiology, Smithsonian Institution) reads, "Deep water Gurabo (600 m!)." Comparisons.— All of the left valves of the fossil specimens from the Dominican Republic identified with Parvamussium marmoratum have radial costellae. They differ from extant members of the species in having a slightly more extensive proximal glossy zone before the start of radial costellae (ca. 4 mm in the fossil specimens as compared to 2-3 mm in extant specimens). The fossils also appear to have a somewhat thicker inner crossed-lamellar aragonitic layer that dampens the relief of the proximal ends of the internal ribs. Specimens from TU 1357 are all small (5-6 mm Ht), and because they are all right valves, they cannot be positively identified. Two of three valves that have accessible interiors have 11 internal disk ribs, the third having 10.
Amusium (Parvamussium) spendulum Woodring, 1925, from the Bowden beds of Jamaica, was said by Woodring to be remarkably similar to P. pourtalesianum (= P. marmoratum herein). Although the holotype, a right valve, is poorly preserved, it differs from P. pourtalesianum in lacking a distinct byssal notch and fasciole, in being higher than long in spite of its small size (7.6 mm Ht), and in having a different prism arrangement in its outer shell layer, with a less clear alternation of bands of prisms of different sizes. If I have interpreted the configuration of its anterior auricle correctly, it is more likely a young specimen of Propeamussium. Evolution.— So far as known, this is the first report of Parvamussium marmoratum in the fossil record, and there is insufficient material for assessing evolutionary trends.
Occurrence.— In the Dominican Republic, Parvamussium marmoratum is known only from the upper Gurabo Formation, early Pliocene.
Distribution.— Fossil representatives of Parvamussium marmoratum are thus far unknown outside of the Dominican Republic.»
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. 25-27]
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Parvamussium marmoratum (Dall, 1881); T. R. Waller, 2011, Neogene Paleontology of the Northern Dominican Republic, 24, Propeamussiidae and Pectinidae, plate 1, figures 13-16.
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«Amussium (Propeamussium) pourtalesianum DaIl.
Lam. 1. Fig. 12-15. 1886 Dall, Blake Rep. l, pág. 211, lám. 4, fig. 3, lám. 5, fig. 12, con sinonimia.
1889 Dall, Cat. Mll. a. Brach. SE. U. S., pág. 34, lám. 4, fig. 0, lám. 5, fig. 12. Concha pequeña, delgada, transparente, suborbicular, algo oblicua, poco convexa, en el lado exterior cubierta con finas estrías concéntricas, en el interior adornada con 9 costillas radiantes, altas y delgadas, que comienzan como hilos finos cerca de la charnela, se ensanchan y se hacen más gruesas hacia el borde cerca del cual terminan en forma de masa, la oreja posterior es corta, la anterior está destruida.
Dimensiones: altura, 15 mm.; ancho, 14.5 mm,; grueso, 2 mm. A nuestra especie se asemeja principalmente el A. lucidum, Jetfr. pero se distingue por su mayor tamaño y su forma más larga y oblicua; A. lucidum se conoce del Atlántico oriental y A. pourtalesianum del mar de las Indias Occidentales. Conocemos algunos parientes de nuestra forma en el Terciario, especialmente en el Eoceno, como Amussium squamula, Lam. [1] y Amussium Alabamensen, Aldr. [2] pero las dos formas son mucho más pequeñas que nuestra forma y mucho menos oblicuas. Nuestra forma es la conexión entre los Propeamussium del Eoceno y las especies recientes. Localidad: Km. 124 del Ferrocarril de Tehuantepec.» [1] Harris, Lignitic stage, I, pág. 236 (44), lám. 7, fig. 2, 2 a. 3, 1897.
[2] Harris, Midway Stage, pág. 162 (48) lám. 2, fig. 3, 1896. BÖSE, E. 1906. Sobre algunas faunas terciarias de Mexico. Boletín del Instituto Geológico de México, 22: 5-96, pls. 1-12. [p. 52, 53]
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Amussium [sic] (Propeamussium) pourtalesianum Dall: E, Böse, 1906, Sobre algunas faunas terciarias de Mexico, plate 1, figures 12-15.
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