Semipallium rapanense ( Bavay, 1905 )

Dijkstra, Henk H. & Maestrati, Philippe, 2010, Pectinoidea (Mollusca, Bivalvia, Propeamussiidae, Entoliidae and Pectinidae) from the Austral Islands (French Polynesia), Zoosystema 32 (2), pp. 333-358 : 347-348

Semipallium rapanense ( Bavay, 1905) ( Fig. 4 A-F)

Pecten rapanensis Bavay, 1905: 25 , pl. 2, figs 10-13.

Semipallium rapanense – Dijkstra 1989a: 16, 17, fig. — Tröndlé & Boutet 2009: 7.

MATERIAL EXAMINED. — Austral Islands. Rapa, holotype spm ( BMNH 8606.9.889).

Marotiri. BENTHAUS, stn DW 1879, 27°55’S, 143°30’W, 52 m, 2 spms. — Stn DW 1880, 27°55’S, 143°29’W, 90-94 m, 1 spm, 1 lv, 1 rv. — Stn DW 1881, 27°55’S, 143°29’W, 112-121 m, 2 rv. — Stn DW 1884, 27°54’S, 143°33’W, 570-620 m, 1 rv. — Stn DW 1886, 27°51’S, 143°32’W, 620-1000 m, 4 fragments.

Rapa. Atelier RAPA, stn 8, 27°36.5’S, 144°17.7’W, 52-57 m, 1 spm, 22 lv, 32 rv. — Stn 11, 27°37.2’S, 144°18.2’W, 2 m, 1 spm. — Stn 15, 27°38.1’S, 144°21.1’W, 20 m, 1 lv. — Stn 26, 27°33.0’S, 144°19.1’W, 53 m, 1 spm. — Stn 31, 27°38.2’S, 144°18.2’W, 6 m, 2 spms, 1 lv, 1 rv. — Stn 38, 27°37.4’S, 144°18.4’W, 2 m, 1 lv. — Stn 43, 27°36.8’S, 18.3’W, 45 m, 1 spm, 29 lv, 18 rv. — Stn 44, 27°36.3’S, 144°18.2’W, 30 m, 1 spm, 1 lv, 4 rv. — Stn 45, 27°36.7’S, 144°18.9’W, 35 m, 17 lv, 14 rv. — Stn 46, 27°36.8’S, 144°19.2’W, 10-42 m, 8 spms. — Stn 47, 27°36.7’S, 144°19.1’W, 33 m, 16 lv, 10 rv, 2 fragments. — Stn 48, 27°34.1’S, 144°22.1’W, 36 m, 3 spms, 5 lv, 1 rv. — Stn 52, 27°36.8’S, 144°19.9’W, 23-25 m, 2 lv, 4 rv. — Stn 54, 27°36.6’S, 144°19.3’W, 12-20 m, 1 spm, 1 rv. — Stn 56, 27°36.7’S, 144°18.1’W, 25-30 m, 4 lv. — Stn 57, 27°36.8’S, 144°19.5’W, 20-30 m, 2 lv. — Stn 62, 27°36.6’S, 144°20.5’W, 20 m, 2 lv, 1 rv. — Stn 71, 27°37.0’S, 144°19.9’W, 20-25 m, 1 spm.

BENTHAUS, stn DW 1890, 27°39’S, 144°16’W, 800-822 m, 1 fragment. — Stn DW 1894, 27°40’S, 144°22’W, 100 m, 6 spms. — Stn DW 1903, 27°27’S, 144°04’W, 400-800 m, 1 lv, 1 rv. — Stn CP 1910, 27°38’S, 144°15’W, 840-1200 m, 1 lv. — Stn CP 1911, 27°38’S, 144°15’W, 900-1300 m, 1 rv.

Récif Neilson. BENTHAUS, stn DW 1913, 27°02’S, 146°00’W, 120 m, 1 lv. — Stn DW 1917, 27°03’S, 146°04’W, 50-60 m, 5 spms. — Stn CP 1920, 27°04’S, 146°04’W, 120-203 m, 2 lv. — Stn DW 1923, 27°01’S, 146°05’W, 360-840 m, 1 spm. — Stn DW 1924, 27°01’S, 146°05’W, 340-800 m, 1 rv. — Stn DW 1925, 27°00’S, 146°05’W, 560-790 m, 1 lv.

Banc Président Thiers. BENTHAUS, stn DW 1926, 24°38’S, 146°01’W, 50-90 m, 2 spms. — Stn DW 1927, 24°39’S, 146°02’W, 95-105 m, 1 spm, 1 lv. — Stn DW 1932, 24°41’S, 146°02’W, 500-800 m, 4 lv, 3 rv. — Stn DW 1933, 24°41’S, 146°01’W, 500-850 m, 1 rv. — Stn DW 1936, 24°40’S, 145°57’W, 80-100 m, 2 spms. — Stn DW 1937, 24°40’S, 145°56’W, 469-500 m, 1 lv, 1 rv.

Tubuai. BENTHAUS, stn DW 1958, 23°20’S, 149°30’W, 80-150 m, 2 spms, 6 lv, 4 rv, 2 fragments. — Stn DW 1959, 23°20’S, 149°30’W, 95-380 m, 1 rv. — Stn DW 1960, 23°20’S, 149°31’W, 230-262 m, 1 lv. — Stn DW 1961, 23°21’S, 149°34’W, 470-800 m, 1 lv.

Banc Arago. BENTHAUS, stn DW 1985, 23°26’S, 150°44’W, 100-107 m, 1 spm, 1 lv.

Rurutu. BENTHAUS, stn DW 1995, 22°29’S, 151°22’W, 212-450 m, 1 rv, 1 fragment. — Stn DW 1999, 22°25’S, 151°22’W, 270-500 m, 1 lv. — Stn DW 2003, 22°28’S, 151°19’W, 250-330 m, 1 lv, 2 rv.

Rimatara. BENTHAUS, stn DW 2013, 22°39’S, 152°50’W, 80-93 m, 3 spms.

DISTRIBUTION. — Known from Rapa Island, now also extended to the neighbouring region. Present material taken alive at 2-360 m depth.

DESCRIPTION

Shell up to c. 25 mm high, weakly inflated, left valve slightly more convex than right valve, higher than wide, somewhat inequivalve, equilateral, auricles strongly unequal in size and shape, umbonal angle c. 90°, colour yellowish, purplish or orangereddish.

Left valve sculptured with 9 shallow primary radial lirae, commencing 1 mm of the umbonal top, dividing by 2 longitudinal grooves (tripartite lirae) in late growth stage, with very weak nodules (also lacking) on the central part of the lirae. Interstitial secondary lirae (2-4) in late growth stage to the ventral margin. Shagreen microsculpture throughout, less developed on posterior auricle. Anterior auricles with 5 or 6 prominent radial lirae, posterior auricle with 3 scaled riblets.

Right valve with similar sculpture, although the primary radial lirae are more flattened, broader and more divided into quadri- to hexapartite radial lirae and 2 interstitial secondary lirae with more prominent scales. Interstices narrower than those of left valve. Anterior auricle with 7 squamous radial riblets, posterior with 2 scaled riblets. Byssal notch deep, byssal fasciole rather broad. Functional ctenolium with about 7 teeth.

REMARKS

The largest specimen (BENTHAUS, stn DW 1925, lv) is 43 mm in height, which is remarkably larger than the holotype (18 mm).

Semipallium rapanense is morphologically close to Semipallium fulvicostatum (A. Adams & Reeve, 1850) , from the tropical south-western Pacific to French Polynesia, but differs in having a more circular shape (more elongate in S. fulvicostatum ) and is somewhat more compressed. Moreover, the anterior auricle of the right valve is smaller than in S. fulvicostatum and the latter is more brightly coloured.

Figures

FIG. 4. — A-F, Semipallium rapanense (Bavay,1905);A, B, external and internal views of the left valve;C, D, external and internal views of the right valve; E, details of the left valve;F, details of the right valve;G-L, Mimachlamys erycina n. sp.; G, H, holotype, external and internal views of the left valve; I, J, holotype, external and internal views of the right valve; K, prodissoconch of the left valve (SEM); L, details of the left valve (SEM). Scale bars: E, F, L, 1 mm; K, 100 μm.