Rugalucina, 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 gen. nov.

Type species.

Lucina (Codakia) angela Melvill, 1899. Here designated.

Diagnosis.

Small L to 15 mm, sub-circular, sculpture of fine, commarginal lamellae crossed by strong radial ribs more prominent to anterior and posterior, with overall crinkled appearance, ligament largely internal, obliquely inset, anterior adductor muscle scar ventrally detached from pallial line for half of length, inner shell margin crenulate.

Etymology.

From Latin ruga for wrinkle or crease and Lucina, feminine.

Included species.

Lucina (Codakia) angela Melvill, 1899, Pillucina vietnamica Zorina, 1978, Lucina (Codakia) munda A. Adams, 1856. Tentatively included: Divaricella cypselis Melvill, 1918 and Lucina concinna H. Adams, 1871.

Comparison with other genera.

Rugalucina is part of the broader Loripes group within the Lucininae, all having an obliquely inset internal ligament. Other genera within the group are Pillucina , Pusillolucina Wallucina , Lucinella , Chavania , and Keletistes . Of these only Pillucina , Pusillolucina , and Rugalucina have prominent radial sculpture. In shell characters Rugalucina differs from Pillucina in the more strongly divergent radial sculpture, the longer anterior adductor muscle scar and the more coarsely crenulate inner shell margin.

In molecular analyses members of the Loripes group form a monophyletic subclade of Lucininae. Seven species of putative Pillucina have been included in analyses ( Taylor et al. 2016), P. pisidium , P. symbolica , P. australis , P. profusa , P. pacifica , ' P. ' pusilla , and ' P. ' vietnamica , the latter from Thailand, Abu Dhabi, and Queensland. Although the type species P. hawaiiensis has not yet been included, P. pacifica is similar in morphology and could be regarded as a proxy. The Pillucina species are not monophyletic in published trees or in the mitochondrial cytochrome b gene tree ( Fig. 1 ), with those identified as P. vietnamica and P. pusilla separated from the other species and now classified herein into two new genera with distinct morphological characters. Note: we use the cyt b gene in the analysis of the Loripes group shown in Fig. 1 as this best reflects species level relationships within clades of the subfamily Lucininae as shown by previous analyses using three genes ( Taylor et al. 2011, 2016).

Previously, we regarded Pillucina vietnamica as a wide-ranging species in the northern Indian Ocean through south east Asia to southern China ( Glover and Taylor 2001), the name replacing the earlier but preoccupied Lucina fischeriana Issel, 1869, with P. angela as an possible phenotype from the northern Arabian Sea. Although more comprehensive sampling across the whole range is desirable, evidence from analysis of the cytochrome b gene ( Fig. 1 ) shows that specimens from Tin Can Bay and Moreton Bay, Qld, Australia differ from samples from Kungkraben Bay, Thailand and Abu Dhabi supporting a species level separation. Our evidence suggests that Pillucina ' vietnamica ' from Arabia, Thailand and Queensland are distinct. After further study of type material, we use the name R. angela for the northern Indian Ocean species, P. vietnamica for the southeast Asian species, and P. munda for the northern Australian species.

Lucina concinna H. Adams, 1871 previously placed in the synonymy of P. vietnamica by Glover and Taylor (2001) is now recognised as having distinct morphological characters and renamed because the original species name is preoccupied. We also resurrect Divaricella cypselis Melvill, 1918 from the synonymy of R. angela and recognise it as another morphologically distinct species, from the Arabian Sea and southern India.

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).