Pecten afribenedictus Kilburn & Dijkstra, 1995
KILBURN, R. N. & H. H. DIJKSTRA. 1995. A new species of Pecten Müller, 1776, from South Africa, with a note on "Pecten sulcicostatus var. casa" van Bruggen, 1961 (Mollusca: Bivalvia: Pectinidae). Annals of the Natal Museum, 36: 271-279. [p. 172, figs. 1-9]
1995 Pecten afribenedictus Kilburn & Dijkstra, 1995
R. N. Kilburn & H. H. Dijkstra, 1995, figures 1-9.
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«Diagnosis: Shell height to 64 mm. Left valve somewhat concave, with 11-13 almost flat-topped main ribs, about half width of their intervals; concentric threads lamellar (in unworn shells reflexed to form a delicate secondary surface), more or less worn away on ribs; extemally pinkish brown to brownish pink with undulating dark brown lines, umbonal region pale pinkish, interior white, usually with narrow brownish border. Right valve strongly convex, with 14-16 flatly rounded main ribs, not bifid (rarely feebly so), intervals shallow; exterior glossy greyish brown, marked towards edge with darker brown, early part cream with pink or brown flecks or blotches; interior white, margin with a light to dark brown band.
Description: Shell medium-sized (up to 64 mm in height), broader than high, subequilateral, strongly inequivalve, moderately heavy. Left valve somewhat concave, usually with 11, occasionally 12-13, main radial ribs, and 1-2 rudimentary ribs near anterior margin, 2-3 nealr posterior margin; radial ribs in section moderately raised and almost flat-topped, mostly about half width of each interval. Fine, close-set, concentric lamellate threads (Fig. 7) cover entire disc, more or less worn away on ribs in adults; where unworn these lamellae are reflexed dorsally to touch the preceding lamella and form a delicate, chalky secondary surface. Anterior auricle usually slightly larger than posterior one, but ratio of posterior/anterior auricles varying from 0.84-1.02; edge rather concave, face of auricle bearing fine, close-set, slopingly erect, concentric lamellae, with or without 1-4 weak radial ridges near dorsal margin. Hinge line straight. Interior of valve bearing 12 concave ribs, evanescing towards centre of valve; surface of ribs concave between raised angular edges, which form pairs of denticles where they terminate on ventral margin; adductor muscle scar well-defined, sometimes slightly sunken, sometimes raised; resilium triangular; resilial, intermediate and dorsal teeth (crura) developed on both sides of resilium; an auricular tooth visible on each side near sinus. Right valve strongly convex, bearing 14-16 flatly rounded radial ribs (Fig. 8), plus 1-3 rudimentary riblets near anterior margin and l-2 near posterior margin; ribs 2-3 times width of shallow, concave intervals; each costa may be slightly concave medially, and in occasional specimens some anterior ribs may be bifid. Fine, closeset growth lines cover entire disc, somewhat more pronounced near margin than elsewhere. Anterior auricle bearing 5-9 fine, low, irregular radial riblets (Fig. 9), usually feeble or absent on posterior auricle, occasionally up to 6 very low riblets; crossed by close-set concentric threads (generally worn down in large examples), and coarse growth lines, which render dorsal margin somewhat squamose, particularly on posterior side. Dorsal margin somewhat raised. Interior of valve with 14-16 ribs, sharply-defined ventrally, weakening towards dorsal interior of valve, concavetopped (widely bifid) with raised, ridge-like edges, evanescing at ventral margin. Adductor muscle scar sometimes slightly sunken, glossy white. Resilial, intermediate and dorsal teeth (crura) present on both sides of resilium; no ctenolium in adult; byssal sinus small. Coloration: exterior of left valve brownish pink to pinkish brown, usually with wide, paler rays, crossed transversely by irregular, wavy lines of dark brown; auricles darker, umbonal region usually pale pinkish buff or flesh colour, often forming a discrete area that is edged by brown; ribs with an occasional inconspicuous cream bar or chevron; interior of valve silky white, ventral margin and edges of auricles with a narrrow brownish border. Exterior of right valve glossy greyish brown, with irregular, deep brown, obliquely transverse lines or blotches towards ventral margin in adult; colour shading to cream in umbonal area, sometimes remaining pale until half-grown, this area covered with pinkish to brown flecks or diffuse spots; interior of valve silky white, with a wide dark brown band (lighter brown in paler examples) around ventral margin and outer edge of auricles. Measurements: Height 56.0 mm, length 64.0 mm, depth 23.7 mm. Largest paratype: height 64.8 mm,length 76.5 mm, depth 26.4 mm. Distribution: Continental shelf of south-eastern Africa, from northern Zululand (Kosi Bay) to eastem Cape (East London area); living in 20-73 m, mainly on a bottom of fine to medium sand, disarticulated valves found from shoreline to 170 m or deeper. During the late Pleistocene occurred as far west as Knysna (Barnard 1962). (...) Notes: Pecten afribenedictus appears to be endemic to south-eastern Africa; although not yet reported from Mozambique waters, the dredging of live individuals as far north as Kosi Bay indicates that its range probably extends at least into southern Mozambique. Single valves are not uncommon, and occasionally wash ashore in southern Natal; living examples, however, are seldom seen, and only six are preserved in the NMSA collection, most collected during the Natal Museum dredging prograrnme. A complete juvenile shell dredged in 200-1220 m off the Matigulu River mouth, Zululand (NMSA 88962), is unlikely to have been living at that depth, and was probably washed from shallower depths or derived from deposits laid down during a Tertiary regression. Comparison: Three species of Pecten are known to inhabit the Indian Ocean, namely P. erythraeensis G. B. Sowerby (2nd), 1842, P. fumatus Reeve, 1852, and P. dorotheae Melvill in Melvill & Standen, 1907. Of these, the closest to P. afribenedictus is P. erythraeensis Sowerby, 1842, from the Red Sea. The latter species differs in its slightly narrower, higher and more rounded radial ribs on the right valve; in the rib intervals, weak, close-set concentric lamellae are visible, these being absent in P. afribenedictus. The left valve in P. erythraeensis is also slightly flatter, and its interior is more or less blotched or flecked with pinkish brown, at least dorsally, which is never the case in P. afribenedictus. External coloration also differs: the right valve of P. erythraeensis is uniform white except for reddish dots near the umbonal area, whereas even in the palest adult specimens of P. afribenedictus this valve shows a brown tinge. Also, in P. erythraeensis the ribs of the left valve are pigmented with delicate, inegularly placed, concentric pinkish brown dashes and the interior lacks the brown border that is always present in P. afribenedictus. Pecten dorotheae Melvill in Melvill & Standen, 1907, from the Persian Gulf and off Somalia differs in several features from P. afribenedictus. In dorotheae the radial ribs of the right valve are flat-topped and distinctly bifid, with some secondary radial grooves visible in mature specimens. In P. afribenedictus the radial ribs on the right valve are slightly rounded in t/s, and lack distinct radial grooves. The left valve in P. dorotheae is flatter and the ribs are higher and more tabulate, and their intervals bear an occasional secondary riblet, lacking in afribenedictus. The coloration is somewhat similar in both species, although P. dorotheae tends to be slightly paler. Pecten fumatus Reeve, 1852, from eastern to south-western Australia is very variable in form, sculpture and coloration, and in the past was treated by various authors as a complex of distinct species and/or subspecies. Recently, Woodburn (1987), using protein electrophoresis, concluded that all are synonymous; in this she was followed by Lamprell & Whitehead, (1992), whereas Waller (1991) provisionally proposed the existence of two species and one subspecies. Of the Pecten fumatus complex, specimens from eastem Australia are closest in form fo P. afribenedictus; however, in fumatus the radial ribs of the right valve are more rounded and higher than in afribenedictus, the left valve is more flattened, and coloration is different (more variable). Another allied species is Pecten excavatus Anton, 1838 (c.f. Fleming, 1957; Wang, 1989; Dijkstra, 799r), which ranges from the south-eastem Pacific to the northern region of Australia and southern Japan. One of us (H.H.D.) has examined syntypes of P. excavatus in the Staatliches Museum für Tierkunde, Dresden, and finds it indistinguishable from material from Japan, Philippines, Indonesia. The left valve in excavatus is more concave than in P. afribenedictus, with flatter-topped radial ribs, the ribs on the right valve are higher, more rounded, and bear fine radial striae, which are lacking in P. afribenedictus. Also, interstitial, close-set concentric lamellae occur in excavatus, which are absent in afribenedictus. Coloration is somewhat similar, although more heavily maculated with reddish brown in P. excavatus. Pecten benedictus Lamarck, 1819, of the Meditenanean Pliocene, according to the holotype in the Museum National d'Histoire Naturelle, Paris, differs from P. afribenedictus in the following characters: size somewhat larger (up to 70 mm), left valve less concave, main radial ribs lower, strongly flat-topped, right valve less convex, radial ribs fewer (11 + 1 rudimentary riblets anteriorly and 2 posteriorly), slightly rounded, with deeper and broader intervals. Finally, comparison must be made with Pecten sulcicostatus 'var. casa van Bruggen, 1961', described from a locality slightly west of the known range of P. afribenedictus; the types prove to differ from the latter species in their much shallower right valve and almost flat left valve, and in possessing concentric threads on both valves. The identity of this taxon is discussed below. Etymology: An African species, resembling Pecten benedictus Lamarck, 1819.» RICHARD NEIL KILBURN & HENK H. DIJKSTRA, 1995
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«HISTORY IN NEW ZEALAND: The history of Pecten in New Zealand apparently began with its arrival as planktonic larvae from the North Atlantic-Mediterranean area, via South Africa and the Antarctic Circumpolar Current, following the same route as the more numerous tonnoidean gastropod migrants such as Semicassis labiata (Perry, 1811) and Argobuccinum pustulosum (Lightfoot, 1786) (Beu 1976), of Lutraria (Lutraria) (see below), of mytilids such as Mytilus galloprovinialis (Lamarck, 1819) and Modiolula phaseolina (Philippi, 1844) (Daguin & Borsa 2000; Beu & Darragh 2001; Beu 2004; Saavedra & Peña 2004), and of Lutraria (Lutraria) grandis (see below). The two Pecten species, P. sulcicostatus G. B. Sowerby II, 1842 and P. afribenedictus Kilburn & Dijkstra, 1995, living in southern Africa as a result of this dispersal, were discussed by Kilburn & Dijsktra (1995) and Dijkstra & Kilburn (2001, p. 286), although the wide range of variation now recognised in Pecten species suggests that these may not be distinct.»
BEU, A. G. 2006. Marine Mollusca of oxigen isotope stages of the last 2 million years in New Zealand. Par 2. Biostrattigraphically usefull and new Pliocene to Recent bivalves. Journal of the Royal Society of New Zealand, 36 (4): 151-338, figs. 1-41. [p. 199]
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