Melanochlamys, CHEESEMAN, 1881

Zamora-Silva, Andrea & Malaquias, Manuel António E., 2018, Molecular phylogeny of the Aglajidae head-shield sea slugs (Heterobranchia: Cephalaspidea): new evolutionary lineages revealed and proposal of a new classification, Zoological Journal of the Linnean Society 183, pp. 1-51 : 44

THE GENUS MELANOCHLAMYS CHEESEMAN, 1881

Thirteen valid species of Melanochlamys are recognized as valid in current literature ( Bouchet, 2015; Table 4) and eight of them are represented in the present study including the type species M. cylindrica from New Zealand. Melanochlamys was paraphyletic in the molecular phylogenetic analysis by Anthes & Michiels (2007), but Camacho-García et al. (2014) retrieved high support for the monophyly of the genus, which is corroborated by our analysis (PP/BS = 0.98/76; Fig. 2A, B). This group is morphologically distinct from other lineages of Aglajidae and is characterized by the presence of a cylindrical body with a single pair of sensory mounds on the head, sunken eyes, reduced caudal lobes, spoon-shaped with an inward spiral shell ( Fig. 5F), a tubular fused capsule and albumen gland, a bilobed mucous gland and a espermatic bulb lying alongside the prostate in some species ( Cheeseman, 1881; Rudman, 1972b; Gosliner, 1980).

THE GENUS NAKAMIGAWAIA KURODA & HABE, 1961 AND ITS SYNONYM MIGAYA ORTEA, CABALLER & ESPINOSA, 2014

Kuroda & Habe (1961) (in Baba, 1985) described the genus Nakamigawaia in the family Aglajidae with the single species N. spiralis from Mukaishima, Japan, characterized by a unique shell type among the Aglajidae (spiral; Figs 5C, 6C), frontal eyes inserted in unpigmented periocular areas, reduced parapodia, reduced and eversible buccal bulb, and a small oval body with rounded symmetrical caudal lobes. Neither Rudman (1978) nor Gosliner (1980) considered this taxon in their subsequent works on the systematics of aglajids. Yet, Baba (1985) discussed the anatomical similarities between Nakamigawaia and other genera of the family, such as Melanochlamys , and suggested its inclusion in Aglajidae , a view followed by all subsequent works (e.g. Burn & Thompson, 1998; Camacho-García et al., 2014; Zamora-Silva & Malaquias, 2016).

The results obtained by Camacho-García et al. (2014) and the current work confirm the monophyly of Nakamigawaia and its inclusion in Aglajidae (PP/BS = 1/100; Fig. 2A, B). Our analyses revealed the presence of three distinct lineages – one WA ( N. felis ) and two from the western Pacific ( N. spiralis , Nakamigawaia sp. ).

The generic assignment of the WA ‘ Aglaja ’ felis (type locality Curaçao) described by Marcus & Marcus (1970) has been a matter of disagreement. Because of external similarities with N. spiralis , some authors have included it in Nakamigawaia ( Camacho-García et al., 2014; Zamora-Silva & Malaquias, 2016), whereas others have maintained the species in Aglaja ( Valdés et al., 2006) . Ortea et al. (2014) presumed that differences between the shells of ‘ A.’ felis (convex, dilated, with an open whorl; Fig. 6B) and the type species N. spiralis (spiral shell; Fig. 6C) warranted a different generic assignment and, therefore, introduced the new genus name Migaya for the Atlantic lineage.

The shell is an important character in the systematics of Aglajidae both to characterize species and genera. There are five genera with unique types of shell ( Noalda , Fig. 5A; Niparaya , Fig. 5D; Melanochlamys , Fig. 5F, Odontoglaja , Fig. 5H; Camachoaglaja , Fig. 5J), but there are also shell types present in more than one genus, such as in Nakamigawaia ( Figs 5B, C, 6B, C).

Furthermore, the diagnosis of Migaya ( Ortea et al., 2014) is based on characters shared by some other aglajid genera; for example ‘ head bearing sensorial bristles ’ – is in fact a diagnostic feature of the family ( Rudman, 1974; Gosliner, 1980, 2015); ‘ internal shell simple with a wing on the upper edge, teleoconch vestigial, reduced to an arched and narrow plate attached to the protoconch’ – are features present in Aglaja , Philinopsis and Navanax ( Rudman, 1972a, Rudman, 1974; Gosliner, 1980) and a ‘ protoconch smooth, strong, and proportionally big on the right side of the animal ’ – are features present at least in Odontoglaja ( Rudman, 1978) . Therefore, the genus Migaya is here considered to be a junior synonym of Nakamigawaia .