Equichlamys bifrons (Lamarck, 1819)
LAMARCK, J. B. 1819. Histoire naturelle des animaux sans vertèbres, présentant les caractères généraux et particuliers de ces animaux, leur distribution, leurs classes, leurs familles, leurs genres, et la citation des principales espèces qui s'y rapportent. Tome sixième, Premier partie, 343 p. Chez l'Auteur, au Jardin du Roi. De l'imprimerie de A. Belin. Paris, 1819. [p. 164]
1819 Pecten bifrons (Lamarck, 1819)
1882 Pecten subbifrons Tate, 1882
1886 Pecten consobrinus Tate, 1886
1886 Pecten palmipes Tate, 1886
1882 Pecten subbifrons Tate, 1882
1886 Pecten consobrinus Tate, 1886
1886 Pecten palmipes Tate, 1886
Pecten bibrons; B. Delessert, 1841, Recueil de coquilles décrites par Lamarck, pl. 15, figs. 5a-5c.
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«4. Peigne double-face. Pecten bifrons.
P. testâ subaequivalvi, utrinque convexiusculâ, albidâ, intus purpureo-nigricante; radiis subseptem longitudinaliter sulcatis, supernè evanidis.
Habite les mers australes et de la Nouvelle Hollande. Péron. Mus. nº. Mon cabinet. Coquille très-distincte, à oreillettes un peu inégales, et ayant des côtes peu nomhreuses, sillonnées longitudinalement et dans leurs interstices. Les côtes de dessus sont plus larges et simplement convexes; celles de dessous semblent presque carénées. Largeur, 105 millimètres.» JEAN BAPTISTE LAMARCK, 1819
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«Description. Shell up to 135 mm high (Huber, 2010), most specimens smaller than 80 mm; solid, circular, right valve slightly more convex than left, to equally inflated; somewhat equivalve and equilateral, auricles almost equal, umbonal angle c. 100–115°; cream with purplish radial streaks, most specimens purplish, a few orange or brownish, interior of most specimens purplish.
Both valves sculptured with 7–11 obvious, evenly spaced radial plicae (most specimens with 8–10), varying greatly in prominence, narrowly angular to more broadly rounded. Interspaces of left valve each wider than one plica, plicae of right valve each wider than one interspace. Numerous widely to closely spaced radial riblets on plicae and interspaces; coarse shagreen microsculpture throughout on juveniles and some unabraded adults, more developed into commarginal lamellae near ventral margin on some adults. Auricles with 6–10 weak, narrow radial riblets. Byssal notch moderately shallow, byssal fasciole very weak. Functional ctenolium present in juveniles, lacking in adults. Internal rib carinae prominent near ventral margin. Dimensions. Illustrated specimens: TAS, off Hobart (AM C.102328): rv: H 103.5, L 106.5 mm; lv: H 103.8, L 107.5 mm; D 33.4 mm; SA, Henley Beach (AM C.097523), larger specimen: rv: H 79.4, L 83.7 mm; lv: H 81.9, L 88.0 mm; D 27.5 mm; smaller: rv: H 65.5, L 67.0 mm; lv: H 68.0, L 68.9 mm; D 23.6 mm.
Habitat. In South Australia living free in the littoral to sublittoral zones on soft sediment, prefering clean sand, and on seagrass, Zostera (“ribbon weed”). In Tasmania on silty-muddy bottom conditions amongst shell rubble, generally in deeper water. Wolf & White (1997) discussed the factors affecting the distribution of Equichlamys bifrons in fishing grounds in D’Entrecasteaux Channel, Tasmania. Mendo et al. (2014) also commented on the environments preferred by the three commercial scallops E. bifrons, Mimachlamys asperrima (Lamarck, 1819) and Pecten fumatus in D’Entrecasteaux Channel. They concluded that P. fumatus is associated with fine-grained sediment, shells and macroalgae, and is affected by the abundance of the invasive seastar Asterias amurensis. Equichlamys bifrons is strongly associated with macroalgae and seagrass cover, and abundant M. asperrima is strongly associated with sponge cover.
Distribution. Southernmost New South Wales, Victoria, Tasmania, South Australia westwards to the Great Australian Bight, SE Western Australia (present data; Raines & Poppe, 2006: 190). Present specimens alive at 3–91 m (minimum depth range).
Remarks. For synonymy and comparison with fossil species see Beu & Darragh (2001: 57). The present species is aquacultured and utilized for commercial consumption. Dix (1976) and Cragg (2016) described the unusual lecithotrophic development of Equichlamys bifrons, which contrasts strongly with the planktotrophic development and correspondingly long larval life of most other common shallow-water scallops. Cragg (2016: 36) noted that “Lecithotrophic development occurs in a temperate-water pectinid (Equichlamys), sublittoral cave-dwelling cyclochlamydids and propeamussiids … the coral reef Caribachlamys … the hydrothermal vent Catillopecten (= Bathypecten) vulcani and bathyal to abyssal pectinids (Hyalopecten) and propeamussiids … Planktotrophic development is the dominant mode in euphotic waters, but where suspended particulate food is limited … or where the parental environment is extremely patchy … lecithotrophic development may improve the chances of survival to settlement in the parental environment. Lecithotrophic development may also correlate with small adult size”. Another southern Australian species, Notochlamys hexactes (Lamarck, 1819), also has lecithotrophic development, acquired independently. Presumably this mode of development is responsible for the great range of variation shown by both E. bifrons and N. hexactes, because of the lack of genetic exchange between distant populations.
DIJKSTRA, H. H. & A. G. BEU. 2018. Living scallops of Australia and adjacent waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae). Records of the Australian Museum, 70 (2): 113-330, figs. 1-102. [p. 234, 235]
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Equichlamys bifrons (Lamarck); H. H. Dijkstra & A. G. Beu, 2018, Living scallops of australia and adjacent waters, figures 63B, 63D-63H, 65A-65C, 65F.
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«Remarks. The range of variation of Equichlamys bifrons has troubled paleontologists from Tate (1882) to Ludbrook (1984). Tate (1886), with little knowledge of the Recent population, assumed that the several forms present in young rocks around Adelaide were distinct species. However, not having the present knowledge of ages of Cenozoic rocks in South Australia, he also confused some older forms with E. bifrons, from the Oligocene Port Willunga Formation near the mouth of the Onkaparinga River, near Adelaide. His type material of Pecten consobrinus includes two strongly plicate and unusually strongly costate specimens of E. bifrons from Hallett Cove Sandstone (Pliocene) (Fig. 14B, C), and two specimens of Notochlamys squamundata sp. nov. (Fig. 15G, H), and two of a more Chlamys-like taxon from Onkaparinga. These latter four specimens differ from E. bifrons in their narrower umbonal angle, in two having narrower and more evenly rounded plicae whereas two have low costae without plicae, in their costal sculpture of low, closely spaced scales and, on the RV, a much larger anterior auricle and a deep byssal notch. However, Tate’s confusion is understandable, as both the plicate specimens have 10 plicae (a similar number to that on many large E. bifrons, which have c. 7-11 plicae) and the LV bears persistent shagreen microsculpture in the intercostal spaces.
Cotton (1947) suggested that Equichlamys subbifrons and E. palmipes were probable synonyms of E. consobrinus (Tate) and Ludbrook (1978) reduced Tate’s ‘species’ to ‘subspecies’ of E. bifrons, but this merely provides names for the more extreme variants within a single population. Comparison with the large collections available from commercial fisheries (NMV, AMS) showed that all these forms intergrade in the present-day fauna, and within a collection dredged from a single locality. The variation of the Pliocene population seems no different from that of the present-day one, and we regard Tate’s names as synonyms of E. bifrons. The color, also, is variable within the present-day population. Whereas most specimens are pale purple or violet, particularly on the interior (the exterior is whitish to pale brown on some specimens with complete shagreen), about 10% of the population is pale orange.» BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1–205. [p. 57, 58]
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Equichlamys bifrons (Lamarck); A. G. BEU & T.A. Darragh, 2001, Revision of southern Australian Cenozoic fossil Pectinidae, figure 13 (Recent juvenile).
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«Pecten bifrons Lamarck, 1819
References: LAMARCK 1819: 164, nº 4 (Orig. descr.); DESHAYES in Lamarck 1836: 131, nº 4; DELESSERT 1841: pl. 15, figs. 5a-c, text; CHENU 1843: 3, pl. 22, figs. 3, 3a-b; CHENU 1862: 184, figs. 925- 926. Type locality: "Les mers australes et de la Nouvelle Hollande. Péron". [Only known from southern Australia, det. Dijkstra] Type material: Specimens cited : "Mus. nº." [MNHN], "Mon cabinet" [MHNG] Size given : "Largeur [= width], 105 millimètres".
REMARKS:
Lamarck mentioned Péron in the original text, indicating that this material from southern Australia was collected by the French expedition (1800-1804) to Australia. Although two specimens of P. bifrons are in the Lamarck collection (MHNG), having been isolated from the Delessert collection as Lamarck's specimens, only one was mentioned by Rosalie de Lamarck, and was figured by Delessert and Chenu. CURRENT TAXONOMIC POSITION AND DISTRIBUTION: P. bifrons Lamarck is the type species of Equichlamys Iredale (1929 : 162). This species occurs in shallow water off southern New South Wales, Tasmania and South Australia.» DIJKSTRA, H. H. 1994. Type specimens of recent species of Pectinidae described by Lamarck (1819), preserved in the Muséum d'Histoire Naturelle of Geneva and the Muséum National d'Histoire Naturelle of Paris. Revue Suisse de Zoologie, 101 (2): 465-532, 30 pls. [p. 472, 473]
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P. Bifrons Lamarck; J. C. Chenu, 1842-1854, Illustrations conchyliologiques, plate 22, figures 3, 3a, 3b.
Pecten bifrons Lamarck, 1819; H. H. Dijkstra, 1994, Type specimens of recent species of Pectinidae described by Lamarck, plates 2, 3.
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