Abronicidae Korshunova et al. , 2017

Family Abronicidae Korshunova et al., 2017 View in CoL

( Figs 1, 2; Table 4)

Korshunova et al. 2017a: 72–4, supplementary materials.

Diagnosis: Body narrow. Notal edge completely reduced. Cerata non-elevated, few per row. Ceratal rows simple. Rhinophores smooth. Anus acleioproctic. Masticatory edges of jaws commonly bear single row of denticles. Radula formula 0.1.0. Central teeth usually with distinct cusp not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens usually short, prostate indistinct. Supplementary gland present, inserts to penis. Massive external permanent penial collar absent. Penis internal, narrow, armed with a hollow, well-defined stylet.

Genera included: Abronica Cella et al., 2016 .

Remarks: The family Abronicidae invariably represents an earlier off-shoot of Fionoidea evolutionary radiation, and is placed even more basally than the triserial Eubranchidae , as sister to all other families of the superfamily Fionoidea , according to the molecular phylogenetic data ( Figs 1, 2). However, at the morphological level, the family Abronicidae is similar to the distantly related family, Trinchesiidae , in having a uniserial radula and a reduced slender body with a fewer number of ceratal rows. Such a remarkable mosaicism at different organismal levels is an indispensable feature of biological evolution. All the substantial diversity caused by many various processes, including the reduction of some characters, as well as the progressive development of other features (see details in: Korshunova et al. 2021, Martynov et al. 2022), forms an astonishingly diverse perspective of the organism, which must be correspondingly reflected in a taxonomic system, instead of greatly obscured by pan-lumping incorrectly named ‘intermediate forms’ and ‘variations’.