Pleurolidiidae Burn 1966

Family Pleurolidiidae Burn, 1966 (Figs 1, 2; Table 4) Protoaeolidiellidae Odhner in Franc 1968: 882. Diagnosis: Body narrow. Notal edge present, narrow. Ceratal rows branched, numerous non-elevated cerata per row. Rhinophores smooth. Anus pleuroproctic. Masticatory edges of the jaws moderately denticulated with single row of denticles. Radula formula 0.1.0. Central teeth arc-shaped, pectinate. Distal or proximal receptaculum seminis. Vas deferens short, prostate indistinct. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Pleurolidia Burn, 1966 and Protaeolidiella Baba, 1955. Remarks: The family Pleurolidiidae and the following family Babakinidae are interesting cases because they represent either a relatively defined, or partly reduced, notal edge, which is a definite ancestral feature for all Nudibranchia [see Korshunova and Martynov (2020) for the character states’ discussion], and, respectively, remain within the few families of the superfamily Aeolidioidea. The presence of a notal edge in families within Aeolidioidea, otherwise a superfamily with a completely reduced notal edge, in combination with the ancestral-confirmed placement of a pleuroproctic anus (see: Korshunova and Martynov 2020) in both Pleurolidiidae and Babakinidae is illustrated in the phyloperiodic approach, in which quasiperiodic, ontogeny-based ancestral phylotypic features can be expected to be found in every higher level taxon such as family- and order-group. [See Martynov and Korshunova (2022) for discussion and presentation in this study of Phyloperiodic Tables, which align the three major aeolidacean oligoserial, triseral, and uniserial radular patterns with the results of molecular phylogenetic analysis (Figs 1, 2; Tables 1, 2)]. Therefore, while the well-defined notal edge (continuous or in various degree reduced or modified) is characteristic of the superfamily Flabellinoidea (see Synopsis below), its presence in reduced form in a few families of the superfamily Aeolidioidea, highlights the reliability of the Phyloperiodic Tables to explicitly present ancestrally preserved features, based on phylotypic periods confirmed by evolutionary development biology (e.g. Love 2024) for various disparate animal phyla. The ancestral notal area of non-aeolidacean nudibranchs possesses a well-defined, ample notal edge (Korshunova and Martynov 2020), and, therefore, this feature is an ontogenetically conserved character and persists in various forms, even in such crown-groups of the suborder Aeolidacea (Korshunova et al. 2017a, present study; Figs 1, 2). It must also be noted that both Pleurolidiidae and Babakinidae either comprise only two genera or are monotypic, but in this case the separate status of these families, for some non-scientific reasons is ‘allowed’, whereas the fundamentally similar cases of describing various finely differentiated families of the superfamily Fionoidea instead causes a strong ‘revision-shock’ lumping reaction [see details in Korshunova et al. (2022) and Discussion].