A review of Moerchia A. Adams, 1860 and Microthyca A. Adams, 1863 from the Indo-West Pacific, with the description of a new subfamily, Moerchiinae subfam. nov. (Gastropoda: Pyramidellidae)

The shells of Moerchia A. Adams, 1860 are unique pyramidellids with a planispiral shell that have a shoulder and keel and the aperture at an angle of up to 90° from the vertical axis. In their monography on the genus, Rubio & Rolán (2014) discussed three previously described species: Mo. obvoluta A. Adams, 1860, Mo. morleti P. Fischer, 1877 andMo. introspecta Hedley, 1907 to which they added Mo. deformata and Mo. perforata, all from the Indo-West Pacific. They overlooked Mo. biplicata P. Fischer, 1877 and Mo. mariae Jousseaume, 1898 (which were never figured) and Mo. intermedia (Thiele, 1925) and did not review the type material of Mo. morleti. Herein all these species are discussed. The present study concludes that Mo. deformata is a junior synonym of Mo. Morleti, that Mo. perforata is a junior synonym of Mo. biplicata, and that Moerchia mariae is a ‘’nomen dubium’’. A neotype is assigned for Mo. biplicata. The rows of nodules on shoulder and keel show the genus Microthyca A. Adams, 1863 to be closely related, albeit that these shells are globose with an about vertical aperture. Two species were known: Microthyca crenellifera (A. Adams, 1862) and Mi. laevis Thiele, 1925, the latter of which was never recorded after its description. Marshall (in Marshall et al., 2023) concluded Lissotesta aupouria A. W. B. Powell, 1937 also to be a Microthyca, which is herein confirmed. For the present review numerous lots from various museums and private collections were studied, besides literature and type specimens, showing both genera to be more speciose and to have a much wider distribution than thus far known, comprising many undescribed species. Moerchia arabica, Mo. corrugata, Mo. philippinensis, Mo. zuluensis, Microthyca aotearoa, Mi. australiana, Mi. corrugata, Mi. foliata, Mi. magna, Mi. marshalli and Mi. norfolkensis are described as new species, bringing the total number of species within Moerchia to 9 and in Microthyca to 10. These two genera are interpreted to represent a single clade within the Pyramidellidae. Based on their unique features a new subfamily is herein defined: Moerchiinae subfam. nov.