Hemipecten forbesianus Adams & Reeve, 1849
ADAMS, A. & L. A. REEVE. 1849. Description of a new genus of acephalous Mollusca, of the family Pectinacea, collected by Capt. Sir Edward Belcher during the voyage of H.M.S. "Samarang". Proceedings of the Zoological Society of London, 16: 133-134, pl. 1, fig. 2. (25 April); Annals and Magazine of Natural History, (2) 4: 371–372 (1 November) [p. 133, pl. 1, fig. 2]
1849 Hemipecten forbesianus Adams & Reeve, 1849
1898 Pecten difformis Odhner, 1917
1898 Pecten difformis Odhner, 1917
A. Adams & L. A. Reeve, 1849,
plate 1. |
«HEMIPECTEN FORBESIANUS. Hem. testâ orbiculari, Anomiaeformi, tenuissimâ, hyalinâ, concentricè lineatâ, linearum interstitiis eximiè reticulatis; valvâ inferiore planulatâ, posticè auriculatâ, auriculâ longitudinaliter radiatâ, sinu infra profundo, margine opposito subtiliter denticulato; valvâ superiore convexâ, extus interdum decussatim rugosâ, vix auriculatâ; cardine edentulo, ligamento angusto, marginali, cartilagine parvo solido in cavitatem centralem superficiariam valvis ambabus ligamentum intersecante; pellucido-albâ, valvâ superiore interdum rufo-aurantio radiatâ.
Hab. Sooloo Archipelago, Eastern Seas.
The subject of the foregoing description, which constitutes an extremely interesting discovery in the acephalous family Pectinacea, is an inequivalve shell, partaking of the characters of Pecten and Anomia. Like Anomia, it is a thin, hyaline substance, of which the upper valve is a rude convex plate, distorted according to its situation of growth, but slightly notched on one side. Like Pecten, the under valve is characterised by a prominent auricle on the left side, the sinus beneath being very deeply cut in the direction of the hinge-margin, and furnished along the edge with a row of fine erect denticles. The hinge, similar to that of Pecten, consists of a slight marginal ligament intersected in the middle by a solid triangular cartilage, situated in the hollow of a superficial depression in each valve. Apparently the nearest approximation to this shell may be found in some of the fossil Pectens of the carboniferous limestone, distinguished by a nearer relation with Anomia, of which it presents a reversed condition of growth. From the circumstance of one of the valves being perforated by a deep sinus, of which there is no corresponding growth in the other, it may be compared with Pedum, but there is no indication of the umbonal area which characterises the hinge of that genus, and it does not appear to be the production of an animal of the same peculiar habits. In texture and composition the valves consist of a transparent, semipearlaceous lamina, exhibiting a series of closely-arranged concentric lines, the interstices between which are minutely rayed with much finer lines. If any importance can be attached to the variations in the microscopic structure of shells for the purposes of classification, the observations with which we have been kindly favoured by Dr. Carpenter on the genus, tend rather to show its affinity with Pedum. There is some uncertainty in the result. "The flat valve," says Dr. Carpenter, "in both specimens is permeated by copious tubuli, a character in which the species agrees with Pedum and with certain species of Lima, and differs from Pecten. This tubularity exists also ia the convex valve of the colourless specimen, but is absent in the other (at least in the portion of it which the Bryozoon covering its surface allows me to examine), and I would direct your attention to the fact that the coloured shell possesses a rudimentai sculpturing over the whole of its visible external surface, which is totally wanting in the other. Is not this suffcient as a specific difference?" The two specimens here spoken of, collected during the voyage of the Samarang, were dredged by Captain Sir Edward Belcher in the Sooloo Sea, from a coral and stony bottom, at a depth of about fourteen fathoms. The under valve of each is smooth, showing it to have been attached; the upper valve, covered in part in both specimens with particles of coral and parasitic shells, is in one individual smooth and colourless, in the other decussately corrugated, delicately rayed with reddish-orange. The two shells so entirely agree in all other respects that we have not ventured to describe them as distinct species. Trusting that this interesting subject may assist the developmental views of Professor Edward Forbes, we have the pleasure of distinguishing the species by his name.» ARTHUR ADAMS & LOVELL AUGUSTUS REEVE, 1849
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«Remarks. The present specimens are very variable in shape (circular to oblong and oblique), probably caused by their constricted living position on the scleractinian coral Turbinaria (Yonge, 1981: 29). The shell characters of the immature type specimens of Pecten difformis from Western Australia are identical to those of Hemipecten forbesianus at the same size. For descriptions of soft parts of this species see Yonge (1981) and, for the gills, Beninger & Decottignies (2008).
Petit (2007: 99–101) pointed out that the name Venilia concentrica was proposed for this species accidentally, in an anonymous report, with a recognisable description (“the lower valve having a remarkable lateral incison on the left side, after the manner of Pedum, whilst the hinge partakes of the structure of Pecten and Avicula; both valves are, moreover, of the same fragile tenuity as the Placuna placenta”) but that Venilia is a junior homonym. The name Hemipecten forbesianus was then proposed for it first by Adams & Reeve (1849: 133, pl. 1, fig. 2; 25 Apr 1849), later by Reeve (1849: Hemipecten monograph, sole species; text dated Sept 1849), and only in 1850 by Adams & Reeve (1850: 72, pl. 20, figs 1a–c, 2a–d; 31 Aug 1850) in the zoology of the “Samarang” voyage. In the chresonomy above we list the more than 25 usages of the name H. forbesianus (as the presumed valid name for this species by at least 10 authors during the last 50 years) that are required to make this name a nomen protectum under ICZN Article 23.9.1, and we declare Venilia concentrica a nomen oblitum.» 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. 237]
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Hemipecten forbesianus A. Adams & Reeve; H. H. Dijkstra & A. G. Beu, 2018, Living scallops of australia and adjacent waters, figures 65D, 65E, 67A, 67C.
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«Description. — Shell up to c. 40 mm high, most specimens smaller, up to 20 mm; semi-transparent or opaque, milky white or cream to reddish brown, fragile, flattened; left valve slightly convex, right valve flat; highly irregular in shape (almost circular to obliquely oblong), inequivalve, inequilateral; auricles unequal in size and shape. Both valves with very delicate antimarginal scratches (Camptonectes-like microsculpture) throughout, macrosculpture lacking. Anterior auricle of right valve somewhat declined, separated from disc by suture, bearing weak radial riblets; other auricles not differentiated from disc. Byssal notch extremely deep, curving towards umbo, byssal fasciole small; ctenolium present throughout ontogeny, with 8-12 well developed teeth; outer ligament rather broad, stationary; resilium narrow.
Distribution. — Tropical Indo-West Pacific, from southern Japan southwards to northern Australia, westwards into the Indian Ocean to Réunion, and eastwards into the Pacific to New Caledonia (ZMA, unpublished data; Raines & Poppe, 2006: 70). Present specimen from the Philippines alive at 4-30 m. Bathymetric range of live-taken specimens is 9-56 m (ZMA, unpubl. data). Living attached to the scleractinian coral Turbinaria (Yonge, 1981: 29), forming large lettuce leaf-like formations amongst rubble and weed on sand intertidally to sublittorally. Usually found in groups of 5-20 specimens, covered with epiphytic growths on the left valve. Remarks. — The present specimens are very variable in shape (circular to oblong and oblique), probably caused by their constricted living position on the scleractinian coral Turbinaria (Yonge, 1981: 29). The shell characters of the immature type specimens of Pecten difformis from Western Australia are identical to those of H. forbesianus at the same size. For descriptions of soft parts of this species see Yonge (1981) and, for the gills, Beninger & Decottignies (2008).» DIJKSTRA, H. H. 2013. Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from the Panglao region, Philippine Islands. Vita Malacologica, 10: 1-108, pls. 1-32. [p. 61]
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Hemipecten forbesianus A. Adams & Reeve, 1849; H. H. Dijkstra, 2013, Pectinoidea from the Panglao region, Philippine Islands, plate 16, figures 2a-2d.
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«Distribution and ecology. Throughout the Indo-Pacific region. Live specimens are bysally attached to scleractinian corals, and usually covered by epiphytic growths on the left valve. Recorded from sublittoral depth.
Remarks. Dautzenberg & Bavay (1912) did not discuss this species, although Pelseneer (1911: 31) mentioned it: "Un seule espèce, H. forbesianus, représentée par un seul exemplaire, se trouvait dans les collections du SIBOGA" in his anatomical report. Waller (1972: 256) stated that the only species of Hemipecten is morphologically distinct from other representatives of Pectinidae. Habe (1977: 88) placed the genus Hemipecten in a new subfamily Hemipectinae. Semipecten Fischer, 1886 (in Man. Conch., X: 945) is an invalid emendation for Hemipecten A. Adams & Reeve, 1849, with the same type species.» DIJKSTRA, H. H. 1990. Three new pectinacean species from the Indonesian Archipelago collected during the Siboga Expedition (1899-1900), with additional information and corrections on the previous report (Mollusca: Propeamussiidae, Pectinidae). Beaufortia, 40 (1): 1-14, pls. 1, 2. [p. 7]
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Hemipecten forbesianus A. Adams & Reeve, 1849, Three new pectinacean species from the Indonesian Archipelago collected during the Siboga Expedition, plate 2, figures 11, 12.
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