Mesopeplini Waller, 2006

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 : 172

Mesopeplini Waller, 2006

Diagnosis. Palliolinae with radial costae clustered into broad radial plicae, posterior auricle with a distinctive posterior margin (at least in primitive members of the tribe), prominent widely spaced commarginal ridges in costal interspaces, with internal rib carinae in most taxa, and with byssal notch reduced in depth.

Remarks. Waller (2006a: 20–21) stated that the tribe Mesopeplini was established “to contain a phylogenetically closely knit group of five palliolinine genera and one subgenus … all of which are endemic to New Zealand and Australia …: Mesopeplum (Mesopeplum) Iredale, 1929 , … Mesopeplum (Borehamia) Beu, 1978 , … Sectipecten Marwick, 1928 , … Phialopecten Marwick, 1928 , … Kaparachlamys Boreham, 1965 , … and Towaipecten Beu, 1995 , … Collectively, this group displays a higher level of variation in ribbing patterns and shell shapes than almost any other group of Pectinidae . What ties these genera together are demonstrations of morphological transitions in carefully collected stratigraphic sequences.” Waller (2006a) established the tribe in part because of their demonstrated phylogeny and geographical restriction, but also because they are the only Palliolinae with obvious commarginal ridges throughout ontogeny (limited to the early pre-radial disc in other Palliolinae ), as well as the only Palliolinae that develop internal rib carinae. Further study of the New Zealand fossils has demonstrated that almost all of them develop internal rib carinae, including Kaparachlamys (which distinguishes it from the morphologically similar genus Placopecten Verrill, 1897 ). These genera were discussed by Beu (1995) and Beu & Darragh (2001).

Waller (2006a: 32) indicated that the relationship of Mesopeplum to the Palliolini needs to be re-evaluated, implying that he thought it possible that Mesopeplini represents a subfamily separate from Palliolinae . The molecular phylogeny by Sherratt et al. (2016: fig. 2) and Serb et al. (2017) placed Mesopeplum as almost the most basal of Pectinidae , separating Camptonectinae from Chlamydinae (i.e., Pedinae ) plus Pectininae, and distinct from Palliolinae . This needs confirmation from further comparisons. Only a single species of this tribe remains in Australia at present, along with one other living species in New Zealand, although Mesopeplum has a fossil record from Oligocene time onwards in Australia and from late Eocene time onwards in New Zealand. A further Australian fossil genus is possibly represented by Mesopeplum (?) contrainflatum Beu & Darragh (2001: 163, fig. 58A–D; late Miocene, eastern Victoria).A radiation of genera and species from Mesopeplum in New Zealand late Miocene–Pliocene rocks (the genera listed above, citing Waller) was described by Beu (1995).