Cyclochlamys plectofilum, P. G. Oliver & Holmes, 2004

Oliver, P. Graham & Holmes, Anna, 2004, Cryptic bivalves with descriptions of new species from the Rodrigues lagoon, Journal of Natural History 38 (23), pp. 3175-3227 : 3191

Cyclochlamys plectofilum n. sp.

( figures 60–65 )

HOLOTYPE: 1 rv from Grand Pate´ , off Port Mathurin, shell gravel, 17 m 19 ‡ 39.307 ’ S, 63 ‡ 24.950 ’ E ( SEM stub), NMW.Z.2001.061.00018.

PARATYPES: 6 lv and 3 rv as holotype, NMW .Z.2001.061.00019.

Measurements (mm, L 6 H). Holotype: 1.42 6 1.35. Paratypes: 1.36 6 1.39, 1.18 6 1.23, 1.46 6 1.46, 1.23 6 1.21, 1.07 6 1.08, 1.40 6 1.47, 1.03 6 0.98, 1.16 6 1.15, 1.41 6 1.34.

Description. Shell minute to 2 mm in height. Very thin, fragile, hyaline. Inequivalve, rv with a deep byssal notch, lv entire. Outline roughly subcircular, slightly oblique, with a long straight dorsal margin. Shell is cream, translucent and shiny.

Left valve ( figure 63 ): less oblique than rv, anterior and posterior margins more equally curved, byssal notch shallow, auricles subequal with anterior a little larger. Sculpture of numerous narrow radial, slightly nodulose, riblets with similar, secondary riblets in interspaces at margins, totalling around 60 in number. Riblets beginning at margin of prodissoconch. Prodissoconch large, 330 M m across the dorsal margin, apex raised, peaked, sculptured with a web-like pattern of raised tracery ( figure 64 ).

Right valve ( figure 62 ): posterior margin gently curved, almost straight, becoming rounded towards the ventral margin. Anterior margin narrowly very curved into deep byssal notch. Anterior auricle prominent, wing-like. Sculpture similar to lv but there is a wide area beyond the prodissoconch that lacks radial riblets. Prodissoconch as lv but apex not raised ( figure 65 ).

Derivation of name. Latin plecto ‘interwoven’ and Latin fila ‘a thread’, pertaining to the sculpture on the prodissoconch.

Comparisons. Cyclochlamys species are few and mostly restricted to the southern oceans (South Australia, New Zealand and Subantarctic) with only C. favus (Hedley, 1902) , C. incubata ( Hayami and Kase, 1993) and C. tenuissima ( Hayami and Kase, 1993) extending into tropical seas ( Hayami and Kase, 1993). Dijkstra (1995) redescribed C. favus (Hedley, 1902) and noted the concentric sculpture and relatively small, 240 M m in diameter, prodissoconch. In contrast, the Rodrigues shells have a distinct radial sculpture and the prodissoconch has a web-like tracery. These characters are also found in one of the cavernicolous species described by Hayami and Kase (1993) as Chlamydella incubata . That species lacks radial sculpture on the right valve and the left valve sculpture is strongly reticulate rather than radial. Cyclochlamys incubata and C. plectofilum are similar and we thank Henk Dijkstra for confirming their separate identity.

Figures

FIGS. 60–65. Cyclochlamys plectofilum n. sp., holotype, NMW.Z.2001.061.00018: (60, 61) external left and right valves (MontageTM); (62–65) external left and right valves (SEM).