Rugalucina angela (Melvill, 1899)

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 angela (Melvill, 1899) Figs 2 , 3

Lucina fischeriana Issel, 1869: 83-84, pl. 1, fig. 8 (non L. fischeriana d’Orbigny, 1845: Jurassic fossil).

Lucina (Codakia) angela Melvill, 1899: 98, pl. 2, fig. 8.

Loripes fischeriana : Lamy 1916: 151.

Pillucina fischeriana : Oliver 1992: 98, pl. 20, fig. 4.

Pillucina fischeriana : Oliver 1995: 236, fig. 1026.

Pillucina angela : Oliver 1995: 236, fig. 1025.

Pillucina vietnamica (part): Glover and Taylor 2001: 273.

Pillucina angela : Glover and Taylor 2001: 279, figs 9 h, i.

Pillucina angela (part): Huber 2015: 422, figs p. 76.

Type material.

Lucina fischeriana 5 syntypes (MCG), type locality: Suez, Egypt.

L. angela two syntypes NHMUK1899.12.18.20-21; L 7.9 mm and 6.1 mm; 1 syntype NMW 1955.158.684.

Type locality.

Gwadur, Pakistan, 8 fathoms (15 m).

Description.

Small (L to 15 mm), subcircular, inflated. Colour white, yellow or orange. Waxy appearance. Sculpture of strong diverging radial ribs, broader and more widely spaced to the anterior and posterior. Ribs crossed by fine, closely spaced, commarginal lamellae which curve over ribs producing a roughly scabrous appearance. Central parts of shell generally without ribs. Lunule large, broadly lanceolate, smooth. Ligament internal, obliquely inset. Hinge: RV with single large cardinal tooth and short anterior and posterior lateral teeth, LV with two cardinal teeth, lateral teeth consisting of small sockets. Anterior adductor scar narrow, elongate, detached from pallial line for ca. half of length. Pallial line irregularly lobate, or slightly divided. Inner shell margin coarsely crenulate to anterior and posterior.

Distribution.

Red Sea: Great Bitter Lake (Hoffman et al. 2006), Suez Canal, El Ballah (NHMUK 1950.11.10.1), Suez (NHMUK 1968.5.29.2), Safaga, Dongonab Bay (NHMUK), Oreste Point, Yemen (Dekker colln), Aden (NHMUK 1963340). Arabian Gulf: Kuwait (NHMUK), Tarut Bay, Qatar (NHMUK), Abu Dhabi (NHMUK), Ras al Khaimah (NHMUK). Arabian Sea: Khor Kalba, Sharjah (NHMUK), Karachi, dredged (NHMUK 1953.1.30.85). Oman: Masirah Island (NHMUK). Indian Ocean: South India: Chennai (Madras) (NHMUK 1953.1.30.169-73), Krusadai Island (NHMUK 1953.1.30.110), Kundugal Point, Krusadai Island (NHMUK1953.1.30.175-181), Tuticorin (NHMUK 1953.1.30.99-101). Sri Lanka: Trincomalee (NHMUK 1910.9.28.175-178).

Rugalucina angela (as Pillucina vietnamica ) is recorded as an invasive species off Israel in the eastern Mediterranean ( Steger et al. 2018).

Remarks.

Rugalucina angela shows variation in shell morphology between various localities around the Arabian Peninsula and Red Sea. For example, shells from the Arabian Gulf are usually smaller, while those from the northern Red Sea as on Gulf of Suez shores are generally larger, and the marginal crenulations stronger. We regard these differences as ecophenotypic probably associated with the extreme environmental conditions such as the very high salinities experienced in the southern Arabian Gulf, usually more than 40 psu but in shallow lagoons as high as 52-55 psu ( Price 1982) and approximately 40-46 psu at Safaga in the northern Red Sea ( Zuschin and Oliver 2003) and probably higher for the habitats occupied by Rugalucina .

Rugalucina angela is closely similar in shell morphology to R. vietnamica and R. munda . The differences are subtle; externally they share diverging radial ribs that are stronger to anterior and posterior, and the fine commarginal lamellae. Rugalucina angela has a shorter anterior dorsal area, larger hinge plate and teeth, and a slightly more divergent anterior adductor scar. Rugalucina vietnamica is higher, with a longer anterior dorsal area. Rugalucina munda is similar but the radial sculpture is much less pronounced with finer margin denticulations and subdued commarginal sculpture.

Figures

Figure 2. Rugalucina angela (Melvill, 1899). A-C Syntype of Lucina (Codakia) angela Melvill, 1899 (NHMUK 1899.12.18.20), exterior of left valve and interiors of right and left valves. Gwadur, Pakistan, L 8.1 mm D-F L. (C.) angela syntype (NHMUK 1899.12.18.20), exterior of left valve and interiors of right and left valves, L 6.1 mm G-M Rugalucina angela Ras al Khaimah, Arabian Gulf, (NHMUK 20191071) G exterior SEM of right valve, L 5.0 mm H, I interior SEM of right and left valves, L 7.7 mm J dorsal view, L 5.9 mm K exterior of left valve, L 7.9 mm L, M exterior of left valve, interior of right valve, L 7.6 mm N, O R. angela exterior and interior of left valve, Gulf of Suez (NHMUK 1868.5.29.2), L 13.7 mm P R. angela exterior of right valve and interior of right and left valves, Egypt, 7 km south of Hurgada, H Dekker colln 4569, L 12.8 mm Q interior of left and right valves, Egypt, Port Safaga, H Dekker colln 3263, L 9.4 mm R, S detail of hinge teeth of Q. T R. angela exterior of left valve. Red Sea, Yemen, Orestes Point, N of Midi, H Dekker colln 4553, L 9.8 mm U R. angela exterior of right and interior of left valves, Aden (NHMUK 1963340), L 10.6 mm V R. angela exterior and interior of right valve, Krusadai, India, (NHMUK 1953.1.30.69 - 76), L 8.4 mm.

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