Mesopeplum Iredale, 1929

Dijkstra, Henk H. & Beu, Alan G., 2018, Living Scallops of Australia and Adjacent Waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae), Records of the Australian Museum (Rec. Aust. Mus.) 70 (2), pp. 113-330 : 173

Mesopeplum Iredale, 1929

Mesopeplum Iredale, 1929: 162 . Type species (by original designation): Mesopeplum caroli Iredale, 1929 (= Chlamys fenestrata Hedley, 1901 ); Recent, New South Wales, Australia.

Dendopecten Hertlein, 1936: 26 . Type species (by original designation): Pecten dendyi Hutton, 1902 ; early Pliocene , Momoe-a-toa Shellbed, Chatham Island, New Zealand.

Diagnosis. Mesopeplini with weakly subdivided radial plicae or costae on large radial plicae (five plicae in many species); left valve flat to weakly convex, right valve strongly convex; pre-radial dissoconch with reticulate commarginal and antimarginal microsculpture; radially sculptured area of disc with widely spaced commarginal lamellae; internal rib carinae prominent near ventral margin; resilial teeth prominent early in ontogeny but weak or absent in late ontogeny; ctenolium obsolete or almost so in late ontogeny in some species, functional in others.

Distribution. Late Eocene–Recent. New Zealand, temperate Western Australia, South Australia, Tasmania, New South Wales and southern Queensland, living in the littoral to bathyal zones on soft sediment.

For fossil records see Beu & Maxwell (1990), Beu (1995) and Beu & Darragh (2001). The holotype of Mesopeplum polymorphoides ( Zittel, 1865) (Beu et al., 2012: fig. 11B) from Glen Massey Formation at Waikato South Head, southwest Auckland, is early Whaingaroan in age, and so late Eocene (Priabonian). Also, a specimen of a typical Mesopeplum species collected by Prof. T. Kotaka from the Point Elizabeth section, north of Greymouth, Westland (IGPS96853) is Kaiatan or Runangan in age (Bartonian– Priabonian). Mesopeplum definitely occurs in late Eocene rocks in New Zealand, although suitable facies for it apparently are rare.

Discussion. Hertlein (1969, p. N366) treated Mesopeplum and its supposed junior synonym Notochlamys Cotton, 1930 as a subgenus of Semipallium Jousseaume in Lamy, 1928, placed in the Decatopecten group. Currently Mesopeplum and Notochlamys are considered to be valid genera ( Waller, 1991) with different ancestries. Mesopeplum was placed in Mesopeplini by Waller (2006a) whereas Notochlamys is retained in Pedini .

Figure 28. Distribution of Mesopeplum fenestratum (Hedley) .