Pleurolucina Dall, 1901

Glover, Emily A. & Taylor, John D., 2016, Pleurolucina from the western Atlantic and eastern Pacific Oceans: a new intertidal species from Curacao with unusual shell microstructure (Mollusca, Bivalvia, Lucinidae), ZooKeys 620, pp. 1-19 : 2-3

Taxon classification Animalia Lucinida Lucinidae

Pleurolucina Dall, 1901

Dallucina Olsson & Harbison, 1953. Type species, by original designation, Lucina (Here) amabilis Dall, 1898. Pliocene, Florida. Gender feminine.

Type species.

Lucina leucocyma Dall, 1886, by original designation. Recent, western Atlantic Ocean. Gender feminine.

Diagnosis.

Shell small, L to 27 mm ( Pleurolucina sombrerensis usually less than 10 mm), subcircular to ovate, generally higher than long, inflated to highly inflated. Sculpture of 4-6 broad radial ribs separated by broad sulci, sometimes absent in adult shells, crossed by closely-spaced, often terraced, commarginal lamellae. Lunule deeply excavated to shallow. Ventral margin finely beaded. Hinge: RV with two cardinal teeth, posterior-most sometimes bifid, anterior and posterior lateral teeth present; LV with two cardinal teeth, anterior smaller, with anterior and posterior lateral teeth. Anterior adductor muscle scar relatively short, broad, separate from pallial line for about ½ to 2/3 of length, pallial line entire.

Included species.

Western Atlantic: Pleurolucina leucocyma (Dall, 1886), Pleurolucina hendersoni Britton, 1972, Pleurolucina sombrerensis (Dall, 1886). Eastern Pacific: Pleurolucina leucocymoides (Lowe, 1935), Pleurolucina taylori Coan & Valentich-Scott, 2012, Pleurolucina undata (Carpenter, 1865).

Distribution.

Western Atlantic: northern Florida to Brazil ( Pleurolucina sombrerensis Espirito Santo, Rios 1994). East Pacific: Baja California Mexico to Ecuador, Galapagos Islands ( Coan and Valentich-Scott 2012).

Geological range.

Early Oligocene to Recent. Pleurolucina amabilis (Dall, 1898) is a distinctive, laterally compressed species from the Late Pliocene to mid-Pleistocene of Florida. It was made type species of the new genus Dallucina by Olsson and Harbison (1954) but other than the lateral compression it is similar in most characters to Pleurolucina leucocyma . From Miocene deposits of Ecuador Olsson (1964) described Paslucina with Lucina (Paslucina) follis Olsson, 1964 as type species. This has the shape and radial folds typical of Pleurolucina species and may be an antecedent.

Pleurolucina quadricostata (Dall, 1903) from the Pliocene Bowden Formation of Jamaica ( Woodring 1925: 121, pl. 16, figs 4-6) resembles the living Pleurolucina leucocyma . From the same deposit, Phacoides (Linga) tithonis (Dall, 1903) ( Woodring 1925: 120, pl. 16, figs 2, 3) is similar to Pleurolucina sombrerensis . A species described as Lucina (Cavilinga) triloba ( Dockery 1982, pl. 19, fig 4) from the Early Oligocene, Vicksburg Group, Mississippi, USA, has characters of Pleurolucina but with only two radial folds. From the same deposits, Lucina (Cavilinga) imbricolamella Dockery (1982 pl. 20, figs 11-12) resembles the Recent Pleurolucina sombrerensis .

Relationships.

From morphological characters of the shells, Pleurolucina species are usually regarded as being related to Lucina s.s. or Cavilinga ( Britton 1972, Bretsky 1976). Pleurolucina harperae below is the only member of the genus yet to be included in molecular analyses and results ( Taylor et al. submitted) show that it groups within the Lucininae, close to Cavilinga blanda , in a subclade of Lucina and Divalinga species.

Remarks.

In the absence of molecular evidence, other than for Pleurolucina harperae , our concept of Pleurolucina embraces a range of shell morphologies from species like Pleurolucina leucocyma , Pleurolucina undata and Pleurolucina taylori that have prominent radial ribs, through the less ribbed Pleurolucina hendersoni and Pleurolucina leucocymoides , to the small Pleurolucina sombrerenis that has a rounded shell lacking radial ribs. Nevertheless, they are all rather inflated with similar dentition, anterior adductor muscle scars and beaded inner margins.