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1 October 2011 Reinstatement of the Fissurellid Subfamily Hemitominae, with the Description of New Genera, and Proposed Evolutionary Lineage, Based on Morphological Characters of Shell and Radula (Gastropoda: Vetigastropoda)
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Abstract
The fissurellid subfamily Hemitominae Kuroda, Habe & Oyama, 1971, has been synonymized under the subfamily Emarginulinae by recent authors. Here it is redefined and characterized by a shell with either a short slit and selenizone, or a small notch without selenizone, and a radula synapomorphy, in which the rachidian and adjacent lateral teeth are of nearly the same size, the central field partitioned by a “transverse ridge.” A generic review treating nine genera, including three new genera, is provided.Three new genera — Hemimarginula, Octomarginula, and Variegemarginula — are considered basal, differing from the Mesozoic stem genus Emarginula Lamarck, 1801, in lower profile and by the shorter slit and radula synapomorphy. The genus Montfortula Iredale, 1915, is also basal, having a selenizone and notch visible in anterior view. The earliest basal member of the hemitomine lineage is the extinct Loxotoma Fischer, 1885, which arose in the Late Jurassic. Derived genera are Montfortia Récluz, 1843; Montfortista Iredale, 1929; and Hemitoma Swainson, 1840, which lack the slit and selenizone but have a notch in anterior view. Montfortulana Habe, 1961, and Clypidina Gray, 1847, are further derived, with the transverse ridge replaced by clumped pustules.Instead of progressing to a shell form with an excurrent foramen at the apex (as in the derived emarginuline genera Puncturella Lowe, 1827, and Diodora Gray, 1821), this lineage reduces the prominence of the slit and leads to an imperforate shell that resembles the shell of other limpet groups.My concept of the Hemitominae differs from that of the recent molecular phylogeny of Fissurellidae (Aptikis et al., 2011), which was poorly resolved, principally because it sequenced species of four rather than nine genera here determined as Hemitominae.
and James H. McLean "Reinstatement of the Fissurellid Subfamily Hemitominae, with the Description of New Genera, and Proposed Evolutionary Lineage, Based on Morphological Characters of Shell and Radula (Gastropoda: Vetigastropoda)," Malacologia 54(2), (1 October 2011). https://doi.org/10.4002/040.054.0111
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