Semipallium aktinos (Petterd, 1886)
PETTERD, W. F. 1886. New species of Tasmanian marine shells. Papers and Proceedings and Report of the Royal Society of Tasmania, 1885: 320-321 [p. 320]
1886 Pecten aktinos Petterd, 1886
1887 Pecten bednalli Tate, 1887
1887 Pecten bednalli Tate, 1887
Semipallium aktinos (W. F. Petterd, 1886); B. K. Raines & G. T. Poppe, 2006, A Conchological Iconography, The Family Pectinidae, plate 184, figures 1-8.
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«Shell of moderate thickness, irregularly, elongately, and somewhat obliquely orbicular, depressed, marked with irregular prominent lines of growth, ornamented with numerous —fourteen to eighteen— radiating perceptibly imbricated riblets, which are alternatley large and small, and again covered with smaller lirae; cellular structure, distinctly visible under the lens, towards the base; ears unequal, moderately prominent; colour, pink to bright rose, with irregular light or dark bands, and again peculiarly marked with numerous small sharply angular patches of white to pink, shaded with deep brownish-red; interior, shining pinkish-white, with exterior colouration faintly showing through.
Long.— 42 mill.
Lat.— 36 „ Alt.— 15 „ Habitat.— North-West Coast.
Though very distinct from the other Tasmanian forms, this species shows an approach to the common P. asperrimus Lam, but may be at once recognised by its form, smaller size, and very different colouration. It appears to be of rare occurrence, for, although I have seen numerous valves, but two perfect examples have come under my notice. It is probably a deep water form.» WILLIAM FREDERICK PETTERD, 1886
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«Description. Shell up to c. 42 mm high, most specimens under 30 mm; elongate, moderately prosocline, weakly inflated, valves almost equally convex, auricles highly unequal in shape and size, umbonal angle c. 85°; colour variable, yellow, purple, pink to reddish and brown, with patches and streaks, interior shining white or tinted pink.
Left valve sculptured with 9–11 low, narrow, widely spaced primary radial costae or weak plicae, variable in prominence, more subdivided on right valve into 18–20 narrow costae, increasing by intercalation to 60–80 delicate, narrow, closely spaced, weakly squamous radial riblets near ventral margin. Shagreen microsculpture present throughout. Anterior auricles much larger and longer than posterior, bearing c. 8–10 radial riblets on left valve and c. 6 on right; posterior auricles bearing fewer, weaker riblets. Byssal notch relatively deep, byssal fasciole rather narrow. Functional ctenolium well-developed, with c. 5 teeth. Internal plicae with carinate edges around ventral margin. Hinge with moderately prominent resilial and dorsal teeth. Dimensions. Illustrated specimen: SA, Port Stanvac, under rock slabs (AM C.303773): rv: H 38.4, L 32.4 mm; lv: H 38.6, L 31.5 mm; D 11.5 mm.
Habitat. Living cryptically in the littoral zone, byssally attached under rocks or on ledges, and hidden in reef crevices, many specimens covered with sponges.
Distribution. This endemic species is most common in temperate waters, and is not recorded from the tropical Indo-West Pacific outside Australia. Present specimens alive in the intertidal zone to 15 m.
Remarks. A closely similar congeneric cryptically living species is Semipallium hallae (Cotton, 1960), known only from South Australia. Semipallium hallae differs from S. aktinos in its larger size (up to c. 55 mm high, S. aktinos up to 42 mm), in having a more nearly circular shape (S. aktinos is more elongate), in having larger posterior auricles (in S. aktinos very small, almost rudimentary), in having 7–8 broad primary radial plicae on both valves (S. aktinos has 9–11 narrow plicae on the left valve, more subdivided on the right valve), and in its purplish, almost monochrome coloration (S. aktinos is more polychrome).»
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. 261-263]
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Semipallium aktinos (Petterd); H. H. Dijkstra & A. G. Beu, 2018, Living scallops of australia and adjacent waters, figures 80A, 80B.
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