Paracoryphella Miller, 1971

Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017, Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda), ZooKeys 717, pp. 1-139 : 12-13

Paracoryphella Miller, 1971 Figs 2, 7, 8, 9, 10

Type species.

Coryphella islandica Odhner, 1937

Diagnosis.

Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled, shorter than or similar in size to oral tentacles. Anterior foot corners present. Anus pleuroproctic under the notal edge. Rachidian teeth with strong cusp; lateral denticles not clearly delineated from cusp. Lateral teeth weakly denticulated without attenuated process basally. Reduced additional rows of of small lateral teeth may present. Single distal receptaculum seminis. Long vas deferens without separate granulated prostate. Penis not internal, permanently attached externally.

Species included.

Paracoryphella ignicrystalla sp. n. (Fig. 8), P. islandica (Odhner, 1937) (Fig. 9) (original description in Odhner 1937), Paracoryphella parva (Hadfield, 1963), comb. n. (original description in Hadfield 1963) (Fig. 10).

Remarks.

The genus Paracoryphella and the family Paracoryphellidae were initially proposed by Miller (1971) because of the putative presence of a second asymmetrical row of lateral teeth in the original description of the species " Coryphella " islandica (see Odhner 1937). However, the latter character is not very evident compared to the true unique feature of the genus Paracoryphella , a non-retractable, permanently external penis, which is attached directly to the body wall and does not possesses any penial sheath (Figs 8J, 9M, 10C). Importantly, all three known species of this genus invariably possess this feature. This character is unique not only within traditional flabellinids, but also within the majority of Aeolidacea . Only a single species of the family Notaeolidiidae also has such an external penis ( Wägele 1990). Furthermore, several members of the notaspid family Pleurobranchidae with an internal shell ( Martynov and Schrödl 2008) and very basal Acteonidae with an external solid shell also possess an external penis. Therefore, this character within the genus Paracoryphella may be either a basal plesiomorphy, or an ontogenetic reversion to the basal plesiomorphy. Molecular data shows that in either case it occurs within one of the most basal clades of the traditional flabellinids. Additionally, analysis of the light microscopy images of the radula of both the type species P. islandica and the new species confirm the possible presence of 1-3 very reduced, asymmetrically placed, additional rows of lateral teeth (Figs 8F, 9K). During preparation for the SEM study these apparently reduced additional teeth became fully indistinguishable. Their correspondence to the normal lateral teeth needs to be further investigated.

Coryphella parva , only known from its original description from Swedish waters ( Hadfield 1963), was described as having a permanent external penis and therefore is included here in the genus Paracoryphella . Here, for the first time, we have studied type material of C. parva from the Natural History Museum of Denmark (NHMD-91476) (Fig. 10) and confirmed that it possesses a non-retractable external penis (Fig. 10C) and other external features that align with the diagnosis of the genus Paracoryphella . The drawings of the radula (Fig. 10D, E) and reproductive systems (Fig. 10F) in the original description of P. parva in Hadfield (1963) are also very consistent with two other species of the genus Paracoryphella . Remarkably, even though the length of living specimens of P. parva do not exceed 3.5 mm (fixed not more than 2 mm, Fig. 10A, B), the animals at that size were fully mature and produced egg masses ( Hadfield 1963). Because both P. ignicrystalla sp. n. and the type species of the genus P. islandica reach mature size in specimens at least three times larger than P. parva , the latter species thus is clearly a separate one and may represent an example of a partial paedomorphosis. According to the molecular phylogenetic analysis, the genus Paracoryphella is the sister of the Chlamylla clade (Figs 1, 2, 7). We retain the genus Paracoryphella as separate because of unique morphological characteristics including a permanent external penis and also the apparent presence of additional rudimentary lateral teeth rows.