Minnivola Iredale, 1939

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 : 294

Minnivola Iredale, 1939

Minnivola Iredale, 1939: 363 . Type species (by original designation): Minnivola isomeres Iredale, 1939 (= Ostrea pyxidata Born, 1778 ); Recent, Queensland.

Diagnosis. Moderate-sized Mimachlamydini with a somewhat concave left valve and convex right valve, mimicking the appearance of Pecten ; semi-circular, with auricles slightly unequal in size, byssal notch moderately deep, functional ctenolium present, radial macrosculpture present, shallowly pitted microsculpture on pre-radial area of left valve, reticulate “pseudo-shagreen” microsculpture on left valve at least in early ontogeny, weak commarginal microsculpture on right valve, and on left valve in late ontogeny. Internal rib carinae moderately prominent around ventral margin. Hinge teeth weak.

Distribution. Miocene–Recent (Hayami, 1989: 16). Indo-West Pacific, living in the littoral zone on soft sediment.

Discussion. Hertlein (1969: N371) placed Minnivola in the Pecten (Patinopecten) subgroup, merely based on the reticulate microsculpture of the left valve. Other morphological characters are similar to those of Pecten , although it is now clear that this is another confusing convergence resulting from similarity in life habit rather than from close phylogentic relationship. Patinopecten is currently placed in Pedinae , tribe Fortipectinini (see Kafanov, 1986; Waller, 1991, 2006a).

The molecular phylogeny by Mahidol et al. (2007: fig. 3) placed Minnivola in the same clade as several Mimachlamys species. T. R. Waller (USNM, pers. comm. 1 July 2017) has advised us that both Minnivola and Volachlamys species have a shallowly pitted pre-radial area on the left valve, as in Mimachlamys . They also share a unique form of “pseudoshagreen” microsculpture, in which the individual cells are not closed over the outer surface to form a secondary shell surface, as occurs in true shagreen microsculpture in Pedini . In both Minnivola and Volachlamys , the internal rib carinae are weaker than in Mimachlamys species , suggesting that they occupy a primitive position in Mimachlamydini . A position within Mimachlamydini was also suggested for Volachlamys by the molecular phylogeny of Matsumoto (2003: fig. 2) and is clearly implied by the molecular phylogeny of Feng et al. (2011: figs 1–3). T. R. Waller has therefore concluded that both Minnivola and Volachlamys likely belong in Mimachlamydini , and we follow his opinon here. We have not rearranged the plates to follow this conclusion.