'Rugalucina' cracentis, Taylor, John D. & Glover, Emily A., 2019

Taylor, John D. & Glover, Emily A., 2019, Unloved, paraphyletic or misplaced: new genera and species of small to minute lucinid bivalves and their relationships (Bivalvia, Lucinidae), ZooKeys 899, pp. 109-140 : 109

'Rugalucina' cracentis sp. nov. (replacement name) Figs 3 , 7

Lucina concinna H. Adams, 1871: 791, pl. 48, fig. 13 (non Lucina concinna Deshayes, 1857 an Eocene fossil).

Loripes concinnus : Lamy 1916: 15.

? Pillucina concinna : Oliver 1992: 98, pl 20, figs 5a, b.

Pillucina cypselis (Melvill, 1918): Dekker and Orlin 2000: 11.

Pillucina vietnamica : Zuschin and Oliver 2003: pl. 24, figs 24.8-24-13.

Type material.

Holotype of Lucina concinna UMZC I.100470 Gulf of Suez, Red Sea. L 9.2 mm.

Etymology.

cracentis Latin, genitive singular of cracens meaning neat, graceful. Adjective.

Diagnosis.

Ovoid shape, slightly higher than long, diverging radial ribs, ligament short, largely internal, hinge with ventral flexure, right valve with single large cardinal tooth, anterior adductor muscle scar short.

Description.

Small, L to 9 mm. ovoid, slightly higher than long (H/L 1.01), inflated, umbones prominent, rounded. Colour white or yellowish. Sculpture of diverging radial ribs, coarser and more widely spaced to anterior and posterior, ribs finer and more subdued in middle parts of shell. Ribs crossed by fine, low, closely spaced, commarginal lamellae. Lunule short, heart shaped. Ligament short, obliquely inset. Hinge line with ventral flexure ( Fig. 7R, S ), right valve with single, relatively large cardinal tooth and small anterior and posterior lateral teeth, left valve with two cardinal teeth the anterior larger and a central socket, small anterior and posterior lateral teeth. Anterior adductor muscle scar short with lobate posterior dorsal edge, ventrally detached from pallial line for 15% of length; posterior scar ovate. Pallial line largely entire, irregularly lobate. Pallial blood vessel trace visible. Inner shell margin crenulate, more coarsely to anterior and posterior.

Distribution.

Red Sea: Egypt: Gulf of Suez (ZMC), Port Safaga (Dekker colln), Ras Baghdadi (Dekker colln), Sharm el Naga (Dekker colln), Makadi Bay (Dekker colln), Gulf of Aqaba: Dahab (Blatterer colln), Yemen -al Durayhimi (Dekker colln), Aden (NHMUK 1902.12.30.749). Arabian Gulf: Kuwait (NHMUK), Saudi Arabia, Tarut Bay (NHMUK 20191076).

Remarks.

Dekker and Orlin (2000) used Pillucina cypselis as a synonym of the preoccupied Lucina concinna but, as shown above, the species differ in external morphology. Although Glover and Taylor (2001) included this species in the synonymy of Pillucina vietnamica (NW Indian Ocean forms now Rugalucina angela ) we consider it distinct. Externally, it is similar to Rugalucina angela but differs in the ovoid shape, the finer radial ribs, the much shorter anterior adductor scar, the ventral flexure of the hinge line and large cardinal tooth in the right valve.

The ovoid shape and flexured hinge line with the large cardinal tooth in the right valve are features of Pillucina s. s. but Pillucina species usually have less prominent radial ribbing ( Glover and Taylor 2001, 2016). Molecular data are needed to determine placement in either Pillucina or Rugalucina .

Figures

Figure 3. Internal drawings of left valves of Rugalucina and Pusillolucina species. Not to scale.

Figure 7. ' Rugalucina ' cracentis sp. nov. A-E Lucina concinna Holotype (ZMC I. 100470) Gulf of Suez, exterior and interior of right and left valves and dorsal view, L 9.2 mm F-H ' Rugalucina cracentis ' exterior of right valve and interior of right and left valves Egypt, Dahab, Gulf of Aqaba, Red Sea. H. Blatterer colln, L 6.7 mm I, J R. cracentis exterior and interior of right valve Dahab, Gulf of Aqaba, Red Sea, H. Blatterer colln, L 8.5 mm K, L R cracentis exterior and interior of left valve Egypt, 4 km north of Port Safaga, H. Dekker colln 6930, L 8.3 mm M interior of right valve, L 8.8 mm N, O exterior and interior left valve Egypt, 4 km north of Port Safaga, H. Dekker colln 6930, L 7.1 mm P, Q interiors of right and left valves, H. Dekker colln 6930, L 8.7 mm R, S hinge details of P and Q.