Pruvotaplysia, ENGEL, 1936

SUBGENUS PRUVOTAPLYSIA ENGEL, 1936 View in CoL

Engel (1936) introduced the subgenus Pruvotaplysia for species of Aplysia characterized by having a large mantle foramen, even in adult specimens, a strongly arched shell and narrow parapodia. Engel (1936) included in Pruvotaplysia the nominal species Aplysia punctata and A. parvula and their synonyms, including six subspecies in A. parvula . Medina et al. (2001) using molecular evidence recovered Pruvotaplysia as monophyletic and sister to the rest of Aplysia , providing further support for the validity of this subgenus.

The molecular phylogenies presented here also recover a well-supported clade containing individual specimens identified as Aplysia parvula and A. punctate , and therefore corroborates the results of Medina et al. (2001) and the validity of the subgenus Pruvotaplysia . However, because of a much larger sample size, our phylogenetic analysis recovers additional subclades in Pruvotaplysia . Below we describe these subclades and assign them names (and synonyms) based on a review of the literature and morphological comparisons. Because some of the newly recognized species are cryptic or pseudocryptic, we will arrange such species into species complexes, meaning groups of closely related, but genetically distinct, species that are indistinguishable morphologically.

SPECIES COMPLEX 1

THE APLYSIA PARVULA–ATROMARGINATA SPECIES COMPLEX

( FIGS 6–9)

Diagnosis

External anatomy: Animal robust, elongate, wider in visceral region, narrowing gradually toward head and tail ( Fig. 6); visceral hump large, oval, not clearly differentiated from rest of body, occupying ~1/4–1/3 of body length; mantle foramen relatively small, circular, elevated (resembling a volcano), located near centre of visceral hump; parapodia narrow, fused posteriorly, typically joined anteriorly, forming a single, narrow, conspicuous fold mid-length; rhinophores and oral tentacles elongate, enrolled, with several projections in oral tentacles; siphon wide, elongate, clearly protruding above parapodia. Colour cream to brownish red, completely covered with white pigment, often aggregated in dense concentrations; parapodia edged in white, typically with submarginal bluish band (sometime absent), not interrupted with white spots; rhinophores and oral tentacles with dark tips; mantle foramen with conspicuous dark inner edge and series of radial white lines ( Fig. 6).

Internal anatomy: Shell elongated, narrow, widest near posterior end; posterior left side regularly curved, posterior right side conspicuously concave adjacent to protoconch ( Fig. 7); rachidian tooth with robust, triangular central cusp bearing multiple sharp denticles, 2–3 lateral cusps on each side of central cusp, lacking denticles ( Figs. 8A, 8D, 8G); lateral teeth with haplotypes as indicated in scale. Dashed lines separate haplotypes belonging to different species recognized in this study. A, species complex 1: Aplysia parvula – atromarginata species complex. B, species complex 2. C, A. japonica . D, species complex 3: A. elongata – nigrocincta species complex. E, A. punctata .

central cusp denticulated on both sides, larger tooth or secondary cusp near base; up to seven simple outer teeth ( Figs. 8B, 8E, 8H); jaw with cylindrical, elongated elements with 2–4 cusps at tips ( Figs. 8C, 8F, 8I). Penis elongate, narrow, simple, with two retractor muscles, papillae absent ( Fig. 9).

Remarks

The Aplysia parvula View in CoL – atromarginata View in CoL species complex is well supported in the mtDNA analyses and includes three genetically distinct species that correspond to the haplogroups recovered in the haplotype network analysis ( Fig. 3A). Although the species delimitation analysis did not recover these groups as distinct species, because of the geographic distance and the absence of shared haplotypes between them, we regard them as different species. The name A. parvula View in CoL is here retained for the north-western Atlantic species represented by specimens collected in the Virgin Islands (the type locality of this species), Honduras and northern Brazil (see remarks for A. parvula View in CoL ). The name A. atromarginata Bergh, 1905 View in CoL (originally described from Indonesia) is resurrected for a tropical Indo-Pacific species, including representatives from Papua New Guinea and Vanuatu. The third species is recorded only from the remote island of St. Helena in the central South Atlantic and not described herein. Externally, species in this complex are distinguishable from other species of Aplysia parvula View in CoL s.l. in several regards, but particularly by their robust and elongate body, with a large, oval visceral hump not clearly differentiated from the rest of the body and the presence of a relatively small, circular, elevated mantle foramen, resembling a volcano, located near centre of visceral hump. The sample size is limited, but examination of photos and specimens did not allow a determination of the presence of morphologically useful traits to differentiate among these three species. Internally, species in the Aplysia parvula View in CoL – atromarginata View in CoL species complex have simple, elongate penises, lacking papillae, and the radulae appear to have more outer simple teeth than other species of Aplysia parvula View in CoL s.l. The shell is narrow and elongate with a conspicuous concavity on the posterior right side.