MONITILORINAE, Taylor & Glover & Smith & Dyal & Williams, 2011

Taylor, John D., Glover, Emily A., Smith, Lisa, Dyal, Patricia & Williams, Suzanne T., 2011, Molecular phylogeny and classification of the chemosymbiotic bivalve family Lucinidae (Mollusca: Bivalvia), Zoological Journal of the Linnean Society 163 (1), pp. 15-49 : 34-35

MONITILORINAE NEW SUBFAMILY

Living Monitilora are known from eastern Australia, the type species Monitilora ramsayi (Smith, 1885) , and two unnamed species from South-East Asia. The single species included in the molecular analysis, Monitilora ramsayi ( Fig. 6G), forms a separate branch with an unstable position, but never aligns ·

within any other of the major clades. In the BEAST chronogram ( Fig. 5 ) it forms a sister branch to the combined Codakiinae and Lucininae . Chavan (1969) placed Monitilora within the Myrteinae , but our analysis shows that Monitilora is distinct from Myrteinae , and in view of its phylogenetic position on a separate branch we propose a new subfamily Monitilorinae for this distinctive and long-lived clade. In shell characters Monitilora species are subcircular, moderately inflated, with regularly spaced, low, commarginal lamellae that have fine radial folds in the interspaces. The lunule is large and asymmetrical, the cardinal teeth are small, and there is an anterior lateral tooth in the right valve only.

Apart from Monitilora ramsayi , the species from southern Australia that have been classified as Monitilora (e.g. Lamprell & Whitehead, 1992) should be placed in other genera. ‘ Monitilora ’ adelaidiana Cotton & Godfrey, 1938 is similar to Callucina , whereas ‘ Monitilora ’ paupera (Tate, 1892) probably belongs with the Myrtea group. Another little-studied genus, Prophetilora (type species Prophetilora arizela Iredale, 1930 = Lucina simplex Reeve, 1850 ), has been classified as a subgenus of Monitilora ( Lamprell & Whitehead, 1992) , but no specimens were available for molecular analysis, and its position is uncertain.

Shells with characters very similar to the living Monitilora ramsayi can be recognized up to the early Palaeocene (Danian), for example, Monitilora duponti (Cossmann, 1908) ( Fig. 6F) from the Calcaire de Mons, Belgium, was previously classified in the genus by Chavan (1937 –1938). Our analysis suggests that Monitilorinae split from other lucinids at least by the mid-Cretaceous ( Fig. 5 ). Some Monitilora -like bivalves were present in the Mesozoic, but have been placed in the genus Mesomiltha Chavan, 1952 (type species Lucina pulchra Zittel & Goubert, 1861 , Jurassic, Oxfordian): an example being Mesomiltha cf. fallax (Forbes, 1846), from the Cretaceous (Cenomanian) of India ( Kendrick & Vartak, 2007: fig. 13I–M), but a more detailed study of these species is needed.

Figures

Figure 5. Chronogram generated by BEAST for species of Lucinidae, and calibrated using ten fossil records. The position of each calibration point is indicated by the numbers in circles (see the Material and methods and Discussion sections for details about the fossils). Error bars for node ages are the 95% highest posterior density intervals; clades with less than 50% support have no error bars; the root node has node bar trimmed by 50% for clarity. New subfamily divisions are shown on the right-hand side, with details presented in Table 3.