Cyclochlamys australensis, Dijkstra & Maestrati, 2010

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 : 341-342

Cyclochlamys australensis n. sp.

( Fig. 3 A-E)

TYPE MATERIAL. — Rapa. Atelier RAPA stn 32,Vavai, 27°35’S, 144°23’W, 15-20 m, holotype spm ( MNHN 21379). — Same data, paratypes, 17 spm ( MNHN 21380), 4 spm ( ZMA Moll. 4.09.013), 2 spm ( NMNZ M.287779).

TYPE LOCALITY. — Austral Islands, Rapa Island, Vavai, 27°35’S, 144°23’W, 15-20 m (Atelier RAPA stn 32).

ETYMOLOGY. — From the Austral Islands.

OTHER MATERIAL EXAMINED. — Rapa. Atelier RAPA, stn 4, 27°34.3’S, 144°22.1’W, 18 m, 1 spm, 3 lv, 1 rv. — Stn 5, 27°05.6’S, 144°18.5’W, 8 m, 13 spms, 3 lv. — Stn 6, 27°36.8’S, 144°16.7’W, 42 m, 4 spms, 1 lv, 1 rv. — Stn 8, 27°36.5’S, 144°17.7’W, 52-57 m, 3 spms, 80 lv, 1 rv. — Stn 9, 27°37.3’S, 144°22.2’W, 3-24 m, 8 spms, 13 lv, 1 rv. — Stn 11, 27°37.2’S, 144°18.2’W, 2 m, 10 spms, 8 lv, 10 rv. — Stn 21, 27°34.2’S, 144°20.6’W, 5 m, 2 spms. — Stn 22, 27°33.9’S, 144°21.7’W, 18-22 m, 3 spms. — Stn 25, 27°38.4’S, 144°18.9’W, 3 m, 23 spms, 7 lv, 3 rv. — Stn 28, 27°38.4’S, 144°20.6’W, 30 m, 9 spms, 2 lv. — Stn 30, 27°38.2’S, 144°18.2’W, 16-20 m, 1 spm, 4 lv. — Stn 31, 27°38.2’S, 144°18.2’W, 6 m, 13 spms, 1 lv. — Stn 33, 27°34.8’S, 144°18.6’W, 30 m, 4 spms, 4 lv. — Stn 36, 27°33.5’S, 144°20.8’W, 27 m, 1 spm, 1 lv. — Stn 41, 27°36.3’S, 144°22.7’W, 5 m, 3 spms, 15 lv, 6 rv. — Stn 43, 27°36.8’S, 144°18.3’W, 45 m, 42 lv, 5 rv. — Stn 44, 27°36.3’S, 144°18.2’W, 30 m, 2 spms, 22 lv, 4 rv. — Stn 47, 27°36.7’S, 144°19.1’W, 33 m, 18 lv. — Stn 48, 27°34.1’S, 144°22.1’W, 36 m,> 100 valves. — Stn 61, 27°37’S, 144°18.6’W, 10-15 m, 2 lv. — Stn 98, 27°34.8’S, 144°22.8’W, 16-18 m, 6 lv, 2 rv.

DISTRIBUTION. — Austral Islands, alive at 3-52 m depth.

DESCRIPTION

Shell up to c. 1.80 mm high, nearly circular to strongly oblique, inequivalve, inequilateral (valves sometimes strongly deformed), left valve more inflated than right valve, higher than wide, translucent or opaque whitish.

Left valve disc and auricle sculpture commencing immediately by irregularly spaced very weak antimarginal threads, multiply on disc by intercalation. Prominent commarginal lirae (sometimes nearly lacking) with irregularly arranged nodules (also lacking) commence at c. 0.8 from the umbonal margin, more widely spaced on the central part (c. 0.2 mm) of the disc than near the ventral margin (c. 0.1 mm). Auricles gradually modulated into disc.

Right valve disc and ventral half of posterior auricle with outer layer of commarginally elongate, hexagonal prisms that form broad, flexible ventral apron. Anterior auricle with 1-3 weak nodulifer radial threads. Byssal notch moderately deep.

Dimensions of holotype: H 1.7 mm, W 1.5 mm, D 0.8 mm.

REMARKS

Many specimens are strongly deformed, perhaps due to their life in microcavities, made possible by their very small adult size.

Cyclochlamys australensis n. sp. differs from Cyclochlamys favus ( Hedley, 1902) , from the South-West Pacific ( Dijkstra 1995a: 40), by having a smaller size ( C. australensis n. sp. 1.8 mm, C. favus 4.0 mm in height), a more prominent commarginal sculpture on the left valve (commarginal lirae with nodules in C. australensis n. sp., smooth or a few commarginal growth lines in C. favus ).

Cyclochlamys australensis n. sp. also differs from Cyclochlamys obliqua ( Hedley, 1902) , from the same geographical range as C. favus ( Dijkstra 1995a: 40) , by having a smaller size ( C. obliqua is 4.6 mm in height), a more widely spaced commarginal sculpture and a weaker and more closely spaced irregular intercalated radial sculpture.

Cyclochlamys incubata ( Hayami & Kase, 1993) , from southern Japan, also has nodules on the commarginal lirae of the left valve, but these are only placed on the intersections of the commarginal and radial sculpture (irregularly arranged in C. australensis n. sp.). Moreover, this radial sculpture is much more prominent than in C. australensis n. sp.

Recently Dijkstra & Marshall (2008) named several new Cyclochlamys species from the New Zealand region. A few species have a similar size and shape, but all differ from C. australensis n. sp. by the sculpture of the left valve.

Figures

FIG. 3. — A-D, Cyclochlamys australense n. sp.; A, holotype, external view of the left valve;B, holotype,external view of the right valve; C, idem (SEM); D, details of the right valve; E, prodissoconch and auricle (SEM); F-K, Lamellipecten aduncus n. sp.; F, G, holotype, external and internal views of the left valve; H, I, holotype, external and internal views of the right valve; J, prodissoconch and early stage of the left valve (SEM); K, details of the left valve (SEM); L, M, Pascahinnites pasca (Dall,1908); L, external view of the left valve; M, details of the left valve. Scale bars: C, 200 μm; D, 50 μm; E, J, 100 μm; K, M, 1 mm.