Condylocuna, Iredale, 1930

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 : 3214-3216

Condylocuna io ( Bartsch, 1915)

( figures 135–140 )

Rochefortia io Bartsch, 1915: 201, pl. 39 figure 5 , pl. 53 figures 5, 6 .

Condylocuna tricosa Middelfart, 2002: 63–65 , figures 19, 23 .

Material examined. Two specimens and one specimen (gold-coated) from Gravier (2000, Stns 9Az34), NMW .Z.2000.086.00030; one from Petite Butte, NMW.Z.2000.086.00031.

Measurements (mm, H 6 L). 0.80 6 0.72, 0.78 6 0.70, 0.72 6 0.70, 0.75 6 0.71.

Description of Rodrigues material. Shell to 0.8 mm in height. Equivalve. Outline rounded trigonal, somewhat oblique; anterior-dorsal margin straight, longer and less angled than straight posterior-dorsal margin; ventral curved; posterior ventral junction subacute; anterior ventral junction rounded. External sculpture of deep, wide, concentric ridges, which become tighter and lamellose towards the posterior. Hinge with elongate laterals and tuberculate cardinals ( figures 136, 137 ); rv with a long, anterior, marginal lateral and socket, posterior lateral as a marginal extension, anterior cardinal tubercle and posterior cardinal socket; lv ( figure 139 ) a mirror image of rv. Ligament internal, between the cardinal teeth. Prodissoconch I, 175 M m in diameter, with a pattern with three wide triangular dents ( figure 138 ). Prodissoconch II, 358 M m in diameter, with a pattern of concentric lines and closely packed radial lines. Shell colour white.

Anatomy ( figure 140 ): the adductor muscles are unequal, the anterior a little larger than the posterior. The mantle margins appear to be unfused but may be so along the posterior ventral area where the ventral edge of the ctenidium is closely adhered. The ctenidium is of single demibranchs consisting of eight filaments each. The labial palps are very small and their structure was not observed. The foot is relatively large, hatchet-shaped with poorly developed heel and toe. The digestive gland is large and contained many crystalline granules. A single larva, about 350 M m in diameter, lay in the left mantle cavity between the foot and mantle and ventral to the ctenidium.

Comparisons. The Rodrigues specimens have been compared with C. tricosa Middelfart, 2002 described from eastern Australia and found to be conspecific (P. Middelfart, personal communication). Middelfart (2002) believed that Rochefortia io Bartsch, 1915 was very close to his C. tricosa but because of the vast geographical separation deemed it unlikely that they were conspecific. Middelfart, however, mentions a possible record from Rottnest Island in Western Australia and in combination with our discovery on Rodrigues undermines his argument and we consider the Rodrigues material to be conspecific with that from South Africa and eastern Australia.

Figures

FIGS. 135–139. Condylocuna io, NMW.Z.2000.086.00030 (SEM): (135) external left valve; (136, 137) internal right and left valves; (138) prodissoconch view; (139) hinge view.

FIGS. 140. Condylocuna io, NMW.Z.2000.086.00030, line drawing of anatomy.

FIGS. 1–7. (1–5) Acar marsupialis n. sp. (1, 2) Holotype, NMW.Z.2001.061.00004: (1) external (MontageTM); (2) internal (SEM). (3–5) Paratype, NMW.Z.2001.061.00005 (SEM): (3) external; (4) internal; (5) prodissoconch. (6, 7) Acar plicata Rodrigues, NMW.Z.2000.086.00034 (SEM): (6) external left valve; (7) prodissoconch.

FIGS. 17–26. (17–20) Barbatia pyrrhotus. (17) Holotype, NMW.Z.2001.061.00011, external (MontageTM). (18–20) Paratype, NMW.Z.20001.061.00012: (18) external (MontageTM); (19) internal (MontageTM); (20) prodissoconch (SEM). (21–23) Barbatia sculpturata, NMW.Z.2000.083.03215 (SEM): (21) external; (22) external; (23) prodissoconch. (24–26) Barbatia sp. from Réunion, NMW.Z.2001.061.00047 (SEM): (24) external; (25) internal; (26) prodissoconch.