Magadis, MELVILL & STANDEN, 1899

Fukumori, Hiroaki, Yahagi, Takuya, Warén, Anders & Kano, Yasunori, 2019, Amended generic classification of the marine gastropod family Phenacolepadidae: transitions from snails to limpets and shallow-water to deep-sea hydrothermal vents and cold seeps, Zoological Journal of the Linnean Society 185, pp. 636-655 : 649

MAGADIS MELVILL & STANDEN, 1899

Magadis Melvill & Standen, 1899: 174 . Type species: Magadis eumerintha Melvill & Standen, 1899: 179 ; pl. 10, fig. 8 (Torres Strait; holotype BMNH 1899.2.23.14), by monotypy.

Semineritina Cossmann, 1925: 215 . Type species: Nerita mammaria Lamarck, 1804: 94 (Eocene, France; a syntype MNHN.F.A66899), by original designation.

Seminerita (Cossmann) : Wenz, 1938: 421 (incorrect subsequent spelling: ICZN Article 33.3).

Remarks: Magadis Melvill & Standen, 1899 has been left as the most enigmatic of living genera of the superfamily Neritoidea ( Holthuis, 1995) . The type and sole extant representative of the genus, M. eumerintha , is known from a single empty shell from ‘channels between reefs’ in Mér Island of the Torres Strait, Northern Australia ( Melvill & Standen, 1899: pl. 10, fig. 8). This colourless, hemispherical coiled shell resembles those of some Vanikoro Quoy & Gaimard, 1832 in the caenogastropod family Vanikoridae in sharing strong axial lamellae and fine spirals. However, the flat deck of the apertural inner lip warrants its current position in the Neritimorpha. The original and succeeding authors have unanimously, but often with a question mark, placed the genus in the family Neritidae based on the coiled shell ( Melvill & Standen, 1899; Wenz, 1938; Knight et al., 1960; Holthuis, 1995).

Surprisingly, M. eumerintha is almost identical with ‘ Nerita ’ mammaria Lamarck, 1804 , the type species of the Eocene genus Semineritina Cossmann, 1925 , in shell shape and sculpture despite their> 30 Myr gap (see Cossmann & Pissarro, 1910 –1913: pl. 5, fig. 38-8). The two species have protoconch and teleoconch characteristics that are suggestive not only of their congeneric status, but also of their phylogenetic position in the subfamily Phenacolepadinae rather than in the family Neritidae (Y. Kano, personal observation; see Bandel, 2001: figs 297, 300). Feminine.