Excellichlamys spectabilis (Reeve, 1853)
REEVE, L. A. 1852-1853. Monograph of the genus Pecten. In: L. A. Reeve (Ed.), 1843-1878, Conchologia Iconica; or illustrations of the shells of molluscous animals, vol. 9. [unnumbered pages], pls. 1-18. London. [pl. 29, fig. 128]
1835 Pecten parvus G. B. Sowerby I, 1835
1853 Pecten spectabilis Reeve, 1853
1985 Semipallium (Excellichlamys) xishaensis Wang, 1985
1998 Excellichlamys sowerbyi Dijkstra, 1998
1853 Pecten spectabilis Reeve, 1853
1985 Semipallium (Excellichlamys) xishaensis Wang, 1985
1998 Excellichlamys sowerbyi Dijkstra, 1998
L. A. Reeve, 1853, plate 29.
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«PECTEN SPECTABILIS. Pect. testâ ovatâ, flabelliformi, aequilaterali, inaequivalvi, valvâ sinistrâ planatâ, costis duodecim subirregularibus, elevatis, supernè rotundatis et concentricè annulato-liratis, radiatâ; valvâ dextrâ convex^s, costis latioribus annulato-liratis, interstitiis in valvis ambabus tenuiscabrosis; albâ, costis alternatim nigricante et minio tessellatis; auriculis grandibus, sub-aequalibus, rufipunctatis.
THE REMARKABLE PECTEN. Shell ovate, fan-shaped, equilateral, inequivalve, left valve flattened, rayed with twelve somewhat irregular ribs, rounded and concentrically ring-ridged at the upper part; right valve convex, ribs broader, ring-ridged, interstices in both valves finely scabrous; white, ribs alternately tessellated blackish and vermilion; ears large, nearly equal, red-dotted. Hab. — ? A very beautifully sculptured and peculiarly coloured species, remarkably distinct from any hitherto described.» LOVELL AUGUSTUS REEVE, 1853
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«Remarks. Iredale (1939: 366) mentioned this species from the Great Barrier Reef, but did not specify the locality. Cotton (1964: 10) listed a valve from Yirrkalla (NT). However, no live records are known from that region. The present material from Queensland and Western Australia resembles the holotype, although the auricles of Australian specimens are more unequal (typically almost equal in size) and they have more prominent intercostal radial riblets (typically almost without secondary riblets). Auricles and secondary interstitial radial riblets are highly variable in this species and intermediate variants are also observed.
Wang (1985: 504) described a species from Jinqing Island (China), Semipallium (Excellichlamys) xishaensis, which resembles E. spectabilis but has strongly unequal auricles (the posterior ones are rudimentary) and fewer primary radial plicae. This form is identical to the French Polynesian morph, Pecten parvus G. B. Sowerby I, 1835 (preoccupied by Da Costa (1778: 153), renamed by Dijkstra (1998b: 247) as Excellichlamys sowerbyi. The tropical western Pacific species Excellichlamys histrionica (Gmelin, 1791) differs from E. spectabilis in lacking costae in the interspaces between plicae or in developing them weakly in the late growth stage. The plicae of most specimens are narrower and of even amplitude, and the interspaces are broader than in E. spectabilis.» 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. 192]
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Excellichlamys spectabilis (Reeve),; H. H. Dijkstra & A. G. Beu, 2018, Living scallops of australia and adjacent waters, figures 38E, 38F.
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«Type data. — Pecten parvus Sowerby: Holotype (H 20.3 mm, pv) BMNH 197011, refigured by Waller (1972: pl. 6 figs 97-102). Type locality: French Polynesia, Tuamotu Archipelago, Actaeon Group, Lord Hood’s Island (now Marutea), in coral sand on the reefs.
Pecten spectabilis Reeve: Holotype (H 22.8 mm, pv) UMZC 1461 (Jane Saul collection). Type locality unknown. A sample consisting of three articulated specimens (BMNH, not registered) from Mauritius is similar to the holotype of Pecten spectabilis and could have come from the same lot as the Saul collection. According to labels written by S. Morris, these specimens have no type status. Semipallium (Excellichlamys) xishaensis Wang: Holotype (H 21 mm, pv) IOAS M25777. Type locality: China, South China Sea, Xishi Islands, Jinqing Island, intertidal, leg. F. Xu, 1.v.1958. Description. — Shell solid, up to c. 30 mm high, most specimens to about 20 mm, circular to slightly oblong, inequivalve, right valve more convex than left, equilateral, auricles unequal to almost equal in size, umbonal angle c. 90˚; plicae unpigmented or pinkish, with brown maculations, umbones tinted red; right valve paler; interior white. Both valves sculptured with about 12 variable high plicae with rounded crests, bearing strongly developed recurved squamae; radial grooves with intercalated radial riblets commencing at about 10 mm shell height and increasing in prominence to ventral margin, subdividing plicae into bifid or trifid groups after about 20 mm shell height. Microsculpture of closely spaced commarginal lamellae on plicae and interspaces, weak on anterior auricle of left valve. Auricles with 4-10 radial costae (anterior 4-9, posterior 4-10), stronger on dorsal areas than on lower areas of auricles near disc. Byssal notch moderately deep, byssal fasciole rather wide, functional ctenolium with 3-5 teeth. Hinge teeth very weak or lacking. Hinge surface with minute, irregularly formed, transverse grooves. Internal plicae with carinate riblets near margin. Distribution. — Throughout the tropical Indo-West Pacific, from southern Japan to northern Australia, westwards into the Indian Ocean to Mauritius and Réunion and the Red Sea, and eastwards into the central Pacific to the Tuamotu Archipelago (Waller, 1972: 249-250, fig. 6; Dijkstra, 1998a: 20; Dijkstra & Knudsen, 1998: 58; Raines & Poppe, 2006: 110; Raines, 2010: 606). Present specimens from the Philippines alive at 19-90 m. Living byssally attached to undersides of coral slabs or amongst coral rubble on soft sediments (sand or muddy sand). Remarks. — Wang (1985: 504) described species from Jinqing Island (China), Semipallium (Excellichlamys) xishaensis, which resembles E. spectabilis but has strongly unequal auricles (the posterior ones are rudimentary) and fewer primary radial plicae. This form is identical to the French Polynesian morph, E. spectabilis parva (Sowerby 1st, 1835) (see also Waller, 1972: 248), and is part of the variation of E. spectabilis. The tropical western Pacific species E. histrionica (Gmelin, 1791) differs from E. spectabilis in lacking costae in the interspaces between plicae or in developing them weakly in the late growth stage. The plicae of most specimens are narrower, of even amplitude and the interspaces broader than in E. spectabilis.» DIJKSTRA, H. H. 2013. Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from the Panglao region, Philippine Islands. Vita Malacologica, 10: 1-108, pls. 1-32. [p. 38, 39]
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Excellichlamys spectabilis (Reeve, 1853); H. H. Dijkstra, 2013, Pectinoidea from the Panglao region, Philippine Islands, plate 8 figures 2a-2d; plate 9 figures 3a-3b (juvenile).
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«Type material: Holotype UMZC 1461.
Type locality: Unknown. Material examined: The type material. RED SEA: Etat, 1 spm., 1 v, MO28534; Elat, 3 v, HUJ 21581; Elat, 1 spm. + 5 v, HUJ 35730; Elat, 4-8 m, among coral nIbble, live, 1 spm., HD 177; S of Elat, 6-8 m, among coral rubble, live, 1 spm., HD 398; 20 km S of Elat, 10-15 m, amongst coral, live, 2 spms., HD 3021; Aqaba, 2 v, HUJ 35731; Aqaba, 3 v, HUJ 35732. Distribution: Red Sea, east coast of Africa to South Africa, Réunion, Mauritius, extending eastwards to southern Japan and New Caledonia. Subtidal to sublittoral depths, living byssally attached under rocks or corals or amongst coral rubble on sand. Remarks: Present material from the Red Sea is variable in radial costae (3-5 prominent radial costae with lower intercostal ribs, which are also variable in number). In some specimens the left valve is more convex than in the type material, and compressed near the ventral margin. The auricles are very unequal, but not as strongly as in Polynesian material. Excellichlamys xishaensis (Wang, 1985) from the tropical western Pacific is morphologically similar to Polynesian specimens, known as Excellichlamys parva (G.B. Sowerby 1st, 1835), which name is preoccupied by Da Costa (1778). E. xishaensis differs from the present species in its strongly unequal auricles and fewer primary radial costae. For description of the present species see Waller (1972: 247).» DIJKSTRA, H. H. & J. KNUDSEN. 1998. Some Pectinoidea (Mollusca: Bivalvia: Propeamussiidae, Pectinidae) of the Red Sea. Molluscan Research, 19 (2): 43-104, pls. 1-10. [p. 58]
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Excellichlamys spectabilis (Reeve, 1853); H. H. Dijkstra & J. Knudsen, 1998, Some Pectinoidea of the Red Sea, plate 6, figures 26, 27.
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«Pecten parvus G. B. Sowerby 1st, 1835, here included in the synonymy of Excellichlamys spectabilis, differs from typical E. spectabilis in several features. Pecten parvus has only 10 primary plicae, a less flaring shell with a narrower umbonal angle, and posterior auricles that are much smaller compared to the anterior auricles (Figures 97-102; Table 9). Because relative size of auricles and umbonal angle are variable features within E. spectabilis, these differences would seem to be of no more than subspecific significance. Furthermore, the presence of these differences at the eastern edge of the geographic range of E. spectabilis is paralleled by the existence of similar morphoIogical differences within Chlamys coruscans at the eastern edge of its range. Atthough specimens of C. coruscans from the Hawaiian Islands are recognized as a geographic subspecies, a parallel taxonomic treatment of the Tuamotu representatives of E. spectabilis cannot be justified with the materials on hand. These are only 2 lots, one consisting of Sowerby's type of Pecten parvus (BM(NH) 197011), the other consisting of 4 right valves (USNM 613230). The treatment of P. parvus Sowerby as a subspecies of Excellichlamys spectabilis would require a new name, for Pecten parvus was previously used for another species (DA COSTA, 1778, p. 153
Excellichlamys spectabilis closely resembles its congener, E. histrionica (Gmelin, 1791), with which it has been frequently confused (see following remarks on classification). The latter species (Figures 6, 103 - 106; Table 10) differs from E. spectabilis in lacking costae in the interspaces between plicae or in developing them very late, usually after a pronounced growth ring. Excellichlamys histrionica also has narrower plicae of more even amplitude and spacing and an outer ligament that is longer relative to length of shell. (See also comparison of Gloripallium pallium.) A second species that may be included in Excellichlamys, Pecten concinnus Reeve, 1853, from the Red Sea (Figures 107 - 110), resembles E. spectabilis even more closely than does E. histrionica. Compared to E. spectabilis, E. concinna has a considerably narrower umbonal angle and 10 or 11 plicae that are more uniform in both amplitude and spacing. In addition, the Red Sea species does not have squamae that extend across the crests of plicae beyond shell heights of 10 to 15 mm. Remarks on Synonymy
Excellichlamys spectabilis has been commonly confused with E. histrionica (Gmelin), which it resembles in morphology and overlaps in geographic range (off southern Japan, Figure 6). REEVE (1853, species 128 and 130), KUSTER & KOBELT (1888, pp. 61,128), and lREDALE. (1939, p. 366), correctly separated the two species, and IREDALE (op. cit.) discussed other past treatments. The original concept of Pecten histrionicus held by GMELIN (1791, p. 3326) probably included P. spectabilis Reeve, to judge by the highly stylized illustrations in references chosen by Gmelin to represent his species. His first reference, that of BONANNO (1684, section 2, fig. 14), poorly illustrates a specimen that is probably without costae between plicae and that probably represents Excellichlamys histrionica as here used. Gmelin's other references (KNORR, 1770, prt. 4; plt. 12, fig. 3; BORN, 1780, plt. 6, fig. 3; and CHEMNITZ, 1784, pit. 65, fig. 614) are also very poor illustrations and may well represent Pecten spectabilis rather than P. histrionicus.
According to the International Code of Zoological Nomenclature (1964, Article 73), the specimens represented by the illustrations referred to by Gmelin represent syntypes, and Bonanno's illustrated specimen would normally be selected as the lectotype because it is the first cited. However, the actual specimen illustrated by Bonanno almost 300 years ago has, to my knowledge, not been preserved. In view of the uncertain identity of the other figures cited by Gmelin, and in the interest of nomenclatural stability, the specimen illustrated as Pecten histrionicus by REEVE (1853, plt. 29, fig. 130) is here designated the neotype of Pecten histrionicus Gmelin. It is an articulated shell bearing the number 1454 in the Saul Collection of the Cambridge Museum, which is also the depository for the type specimen of P. spectabilis Reeve. With regard to generic classification, IREDALE (1939, p. 366) erected the genus Excellichlamys with Pecten spectabilis Reeve as type species. HERTLEIN (1969, p. 366, fig. C88), in attempting to picture the type species of Excellichlamys, chose an illustration from DUNKER (1882, plt. 11, figs. 12, 13), which is E. histrionica, not E. spectabilis. Hertlein's relegation of Excellichlamys to a subgenus of Semipallium is unacceptable because the vastly different microsculpture of the two taxa appears to be taxonomically significant at least at the generic level.» WALLER, T. R. 1972. The Pectinidae (Mollusca: Bivalvia) of Eniwetock Atoll, Marshall Islands. The Veliger, 14 (3): 221-264, pls. 1-8. [p. 248, 249]
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Excellichlamys spectabilis (Reeve, 1853); T. R. Waller, 1972, The Pectinidae of Eniwetock Atoll, plate 5, figures 87-92 (above); plate 6, figures 93-102 (below).
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