Scintilla lynchae, 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 : 3204-3205

Scintilla lynchae n. sp.

( figures 81 , 90 , 97 )

HOLOTYPE: one specimen, Petite Butte, 19 ‡ 45.066 ’ S, 63 ‡ 23.802 ’ E. NMW.Z.2000.086.00011.

PARATYPES: eight specimens, Petite Butte, under rocks lying on sand, NMW .Z.2000.086.00010.

Other material examined. Nine specimens, Stn 33, Plaine Mapou/ Pointe Palmiste , NMW . Z.2000.086.00023; west Rodrigues ; five specimens, Stn 38, Ile Hermitage, south Rodrigues, NMW . Z.2000.086.00024; one specimen, Stn 26, north of Port Mathurin , NMW . Z.2000.086.00025; two specimens, Stn 39, NE end of Ile Gombrani, south Rodrigues , NMW . Z.2000.086.00026; five specimens, Stn 15, Plaine Mapou, NMW .Z.2000.086.00027.

Measurements (mm, L 6 H). Holotype: 8.98 6 6.16. Paratypes: 8.21 6 5.77, 7.44 6 5.38, 8.02 6 6.01, 5.99 6 4.72, 9.78 6 6.88, 7.88 6 5.83, 6.97 6 4.73, 7.57 6 5.90.

Description. Shell small to 10 mm in length. Fragile. Opaque. Equivalve. Somewhat inflated with narrow anterior and posterior gapes. Equilateral. Outline subelliptical but posterior broader than anterior; dorsal margins dipping into umbos which project beyond the summits of the dorsal margins; posterior margin straight sloping to rounded posterior-ventral junction, anterior margin as posterior but shorter and anterior ventral junction more narrowly rounded; ventral margin straight. External surface highly polished, may be slightly undulating and sculptured with growth lines and weak concentric lines. Hinge plate short, teeth weak ( figure 90 ). Right valve with a single, large, projecting cardinal below the beak and fused with a laminar extension of the dorsal margin. Posterior teeth as two, oblique, diverging ridges with a median socket. Left valve with a similar arrangement but posterior teeth are smaller and the upper one almost obsolete. The large, projecting, anterior tooth is accompanied by a small, oblique ridge. Ligament mostly internal, as an oblique, posteriorly directed resilium separating the anterior and posterior teeth. External ligament as a thin layer over hinge plate. Prodissoconchs weakly defined, total diameter 258 M m, marginal sculpure of concentric lines.

The extended mantle displays an array of long slender tentacles, all of which are white in colour ( figure 97 ). The most prominent are the single medially placed anal and cephalic tentacles, which have a wrinkled appearance in contrast to the smooth form of the other tentacles. Of the latter the longest are three pairs which are adjacent to the inhalant aperture, the remainder are slender and pointed. The anterior mantle can extend well beyond the shell margin and the posterior exhalant aperture takes the form of a short siphon.

Derivation of name. Named for Tara Lynch, field centre manager of Shoals Rodrigues.

Habitat. Small colonies were found under coral rubble blocks and volcanic rocks lying on sand in the lagoon at very shallow depths of a few centimetres to 1 m. There was no obvious association except that large fireworms ( Polychaeta: Amphinomidae ) were frequently found.

Remarks. Many of the species described by Deshayes and Sowerby can be attributed to Amphilepida as they are elongate oblong in outline, others can be attributed to a thicker-shelled group similar in form to S. pisum (illustrated here) and possibly referable to Scintillula . Thin-shelled forms with depressed beaks are few but careful attention was paid to S. hydrophana Deshayes, 1856 ( BM (NH) 196 780), S. semiclausa Sowerby, 1865 (not verified as type), S. candida Deshayes, 1856 ( BM (NH) 196 774) and S. philippinensis Deshayes, 1856 ( BM (NH) 196 745). The distinctive feature of S. lynchae is the sloping-shouldered appearance of the dorso-lateral margins, with all of the other species being generally more rounded.

Figures

FIGS. 81–88. (81) Scintilla lynchi, NMW.Z.2000.086.00011 [8.98 mm]. (82) Scintilla vitrea, NMW.Z.2000.086.00004 [7.37 mm]. (83) Scintilla larcombei, NMW.Z.2001.061.00028 [3.29 mm]. (84) Scintilla anomala, NMW.Z.2000.086.00007 [9.2mm]. (85) Scintilla pisum, NMW.Z.2001.061.00025 [8.5 mm]. (86) Amphilepida aurantia, NMW.Z.1999.073.00004 [10.1 mm]. (87) Scintilla sp. A, NMW.Z.2000.086.00012 [2.62 mm]. (88) Scintilla sp. B, NMW.Z.2000.086.00013 [14.91 mm]. All external (MontageTM).

FIGS. 89–94. (89) Scintilla larcombei, NMW.Z.2001.061.00028. (90) Scintilla lynchi, NMW.Z.2000.086.00011. (91), Scintilla anomala, NMW.Z.2000.086.00007. (92) Scintilla vitrea, NMW.Z.2000.086.00004. (93) Scintilla pisum, NMW.Z.2001.061. 00025. (94) Amphilepida aurantia, NMW.Z.1999.073.00004. All hinge views (SEM).

FIGS. 95–98. Line drawings of live Scintilla showing tentacles. (95) S. pisum, NMW.Z.2001.061.00025. (96) S. anomala, NMW.Z.2000.086.00007. (97) S. lynchi, NMW.Z.2000.086.00011. (98) S. vitrea, NMW.Z.2000.086.00004.