Calmidae Iredale and O'Donoghue 1923

Family Calmidae Iredale and O’Donoghue, 1923 (Figs 1, 2; Table 4) Iredale and O’Donoghue 1923: 200. Family Calmidae confirmed: Korshunova et al. 2017c: 9, 14, 17, 18. Korshunova et al. 2017a: 73–8, supplementary materials. Diagnosis: Body wide. Notal edge completely reduced. Ceratal rowssimple, numerousnon-elevatedcerataperrow.Rhinophores smooth. Anus absent (unique among members of the entire suborder Aeolidacea) in adult state. Masticatory edges of jaws commonly bear single row of simple denticles. Central teeth without distinct cusp and denticles, individual teeth are mostly fused in a highly peculiar band-like structure, also unique within Aeolidacea, and within a majority of the order Nudibranchia. Distal receptaculum seminis. Vas deferens long, prostate indistinct. Supplementary gland present, inserts into vas deferens. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Calma Alder and Hancock, 1855. Remarks: Whilst all the above-mentioned families of the superfamily Fionoidea possess a unique set of both external and internal characters, the family Calmidae remarkably stands apart even compared to the other otherwise unique families. This is because the family Calmidae possesses two more unique features in both its external and internal morphology: the complete absence of an anus and a very special, mostly fused, radular ribbon comprised of former teeth. This case leaves no room for doubt about the absolute advantage of fine-scale taxonomic differentiation, since if the family Calmidae was lumped into ‘Fionidae’, then the diagnosis of ‘ Fionidae sensu superlatissimo ’ would include characters barely known even within disparate classes of the phylum Mollusca, and common in a completely different distantly related phylum, Plathyhelminthes, whereas the highly modified, fused radula of Calmidae has very little similarity even to a majority of members of the class Gastropoda. At the same time, phylogenetically Calmidae are sister to the family Cuthonellidae, and, therefore, it is completely impossible to leave the profoundly unique family Calmidae alone and lump all other families into the putative family ‘Fionidae’. Therefore, by this and all previously presented cases (Korshunova et al. 2017 a,c, 2018, 2021, 2022) of the morphologically highly disparate fionoidean families (Figs 1, 2; Synopsis), we conclude that any further attempts to merge the evolutionary-fuelled diversity of the superfamily Fionoidea into a ‘single putative family’ must end.