Pusillolucina, 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

Pusillolucina gen. nov.

Type species.

Pillucina pusilla Glover & Taylor, 2016. Here designated. Philippines.

Diagnosis.

Very small, L to 3 mm, sub-circular, higher than long. Umbones prominent. Sculpture of thin commarginal lamellae, elevated to anterior and posterior, crossed by radial ribs that are more prominent to anterior and posterior. Lunule broadly lanceolate, concave. Ligament short, largely internal. Hinge: RV with single cardinal tooth, large anterior lateral tooth and a complex multi-cuspate posterior lateral tooth consisting of up to ten cusps; LV with two cardinal teeth, the anterior larger, posterior lateral tooth formed of sockets for projecting cusps of the right valve. Anterior adductor scar very short, barely detached from pallial line, pallial line irregularly discontinuous. Inner shell margin crenulate.

Etymology.

Derived from Latin pusilla meaning very small and Lucina. Feminine

Comparison with other genera.

Pusillolucina is similar in many external characters including shape and sculpture to some Pillucina (type species Pillucina spaldingi Pilsbry, 1921 = Pillucina hawaiiensis (Smith, 1885)). By comparison no Pillucina species possess the unusual multi-cuspate posterior dentition. Moreover, Pusillolucina pusilla is distinct in molecular analyses ( Fig. 1 and Taylor et al. 2016) from most Pillucina including five common shallow water Indo-West Pacific species but aligns with ' Pillucina vietnamica '. This latter is now placed in a separate genus, Rugalucina (see below), whose species are larger and, significantly, even in minute juveniles, lack the multi-cuspate posterior lateral teeth of P. pusilla and its congeners.

Included species.

Pillucina pusilla , Pillucina denticula Glover & Taylor, 2001, Pusillolucina africana sp. nov., Pusillolucina arabica sp. nov., Pusillolucina biritika sp. nov. These species differ mainly in characters of the dentition.

Distribution.

Indo-West Pacific, low intertidal to 70 m.

Figures

Figure 1. Single gene tree for the Loripes group of genera and species based on cytochrome b gene sequences, using Bayesian inference as implemented by MrBayes. Support values are posterior probabilities. Methods as in Taylor et al. (2011, 2016). GenBank numbers are attached to names. Newly sequenced species: Wallucina fijiensis Kavieng, Papua New Guinea (MNHN IM- IM- 2013 - 54066), Pillucina pacifica, Kavieng, KAV 1 (MNHN IM- IM- 2013 - 54743), KAV 2 (MNHN IM- 2013 - 51690), Pillucina sp. Kavieng, PNG (MNHN IM- 2013 - 54590), Rugalucina munda North Stradbroke Island, Moreton Bay, Qld, Australia (NHMUK 20191069), R. munda Tin Can Bay, Qld, Australia (NHMUK 20191070).