Elysia azorica, Martín-Hervás & Carmona & Jensen & Krug & Vitale & Cervera, 2024

Martín-Hervás, M. Rosario, Carmona, Leila, Jensen, Kathe R., Krug, Patrick J., Vitale, Fabio & Cervera, Juan Lucas, 2024, A global phylogeny of Elysia Risso, 1818 (Gastropoda: Heterobranchia): molecular systematic insights focusing on European taxa and description of a new species, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 200 (3), pp. 670-689 : 680-682

Elysia azorica sp.nov.

( Figs 6A , 7A )

urn:lsid:zoobank.org:pub:C01F2876-A12F-4B37-8841-3D19D8FC617D .

References:

Elysia flava (non Verrill, 1901): Malaquias et al. (2009).

Material examined:

Holotype: MNCN15.05 /47823 one specimen, dissected, 6 mm length alive, Praia de Porto Pim , (38°31ʹ27.2ʹʹN, 28°37ʹ32.4ʹʹW), Ilha do Faial, the Azores, August 2007 . Paratypes: MNCN15.05 /47823A, one specimen, 3.5 mm preserved length, Praia de Porto Pim , (38°31ʹ27.2ʹʹN, 28°37ʹ32.4ʹʹW), Ilha do Faial, the Azores, August 2007 ; MNCN15.05 /47823B, one specimen, 3 mm preserved length, Praia de Porto Pim , (38°31ʹ27.2ʹʹN 28°37ʹ32.4ʹʹW), Ilha do Faial, the Azores, August 2007. All specimens were collected by Manuel Malaquias in the infralittoral zone at 6 m depth .

External morphology:

Adults with total length about 6 mm (present study). Overall coloration orangish, with opaque white papillae on edges of parapodia ( Fig. 6A ). Some scattered white dots also present on head and sides of parapodia. Digestive gland visible through skin as a dark-green pigment. Body relatively short and wide. Small eyes located behind the rhinophores. Rhinophores relatively long, rolled and uniform with body colour.

Renopericardial prominence small with bright white spots. Branching of dorsal ‘vessels’ not evident on preserved specimens. Large parapodia extend to posterior end of body, with undulated edges. Foot sole not distinctly demarcated and the posterior end of body blunt-ended.

Internal anatomy:

Pharynx elongated and very small.Oesophagus with a small pouch. Radula with 17 teeth (MNCN15.05/47823), seven in ascending limb and 10 in descending limb. Ascus lost during preparation. Leading tooth wide, with a slightly curving cusp tip, bearing a fine, blunt denticulation on cusp and one smooth lateral edge ( Fig. 7A ). Housing depression for interlocking teeth extending half total tooth length. Base of tooth approximately half total tooth length.

Reproductive system triaulic ( Fig. 8 ) with a robust and cone-shaped penis, devoid of stylet, and with a long and thin vas deferens. Female gland complex consisted of different arrangements of glandular tissue, where the mucous gland constituted the largest portion. Hermaphroditic follicles densely distributed throughout parapodia. Rounded ampulla present and a small, spherical genital receptacle under female gland complex.Albumen gland formed by a branched system whose connections were diffuse in some sections.

Etymology:

The species name azorica refers to the collection site from which specimens were found (Ihla do Faial, the Azores) and is a Latin feminine adjective in the nominative case, in gender agreement with the genus.

Type locality: Praia de Porto Pim, Ilha do Faial, the Azores.

Geographical distribution:

Species only known from the eastern Atlantic, Praia de Porto Pim, Ihla do Faial , the Azores (present study).

Remarks:

Elysia azorica sp. nov. is easily recognizable alive by its bright and translucent orange colour, which allows the digestive gland to be observed through the skin, and the presence of opaque white rounded papillae along the edge of the parapodia. Externally this species resembles the Atlantic E. flava and the Pacific species E. obtusa Baba, 1938 , but they mainly differ in the external coloration. Aforementioned species have an overall translucent paleyellow body colour with a greenish inner surface and white spots on the tips of the rhinophores, unlike the uniformly orangeyellow rhinophores of E. azorica sp. nov. In addition, E. flava and E. obtusa have a broader bright white line on the margins of the parapodia formed by white papillae, which may also be found in small clusters on the pericardial swelling. Also, white patches may appear scattered on the outer side of the parapodia of both species, not visible in E. azorica sp. nov.

The radula in E. azorica sp. nov. has shorter and wider bladelike teeth than those of E. flava and E. obtusa . Both E. azorica sp. nov. and E. flava show short denticulations on the cutting edge but differ in a lateral smooth edge present in E. flava . Likewise, E. obtusa possesses a different tooth shape with smooth edges without denticles or ‘serrulations’ (according to its original description).

Our molecular phylogenetic analyses confirm that E. obtusa from Indo-Pacific and Atlantic specimens of E. flava are genetically distinct in accordance with the analysis by Krug et al. (2016), and both species are different from E. azorica sp. nov. ( Fig. 1 ). Indeed, the minimum uncorrected p -distances for COI between E. azorica sp. nov. and the sister-species E. flava were 10.6% (see Table 1 ) and 10.2% between E. azorica sp. nov. and E. obtusa (not shown).

Figures

Figure 1. Molecular phylogeny of worldwide Elysia species rooted on genus Bosellia (not shown). Topology is based on Bayesian inference analysis of concatenated dataset (H3 + COI + 16S + 28S). Only one specimen per species is shown according to species delimitation analyses. Bold red species names indicate the species sequenced in this study that are present in European waters.Significant support values are given as ML bootstrap percentages (BS, below branch) and BI posterior probabilities (PP, above branch). Asterisks indicate complete support (PP = 1.0, BS = 100%). Vertical grey bars indicate specimens grouped as species entities by ABGD, GMYC and bPTP methods based on the COI gene.Unfilled vertical bars indicate the specimens grouped as species based on the 16S gene.

Figure 6. Living individuals of four Elysia species from European waters used in this study. A, Elysia azorica sp.nov.(MNCN15.05/47823); B, E.flava (MNCN15.05/90931); C, E.rubeni (MNCN15.05/200080); D, E. timida (MNCN15.05/90934). Photos taken by Manuel Malaquías (A); Jakov Prkic (B); Fabio Vitale (C) and Giulia Furfaro (D). Scale bars = 1 mm.

Figure 7. Scanning electron micrographs of Elysia spp. radular teeth. A, E.azorica sp. nov. (MNCN15.05/47823); B, E.rubeni (MNCN15.05/200080); C, D, E.viridis: C, MNCN15.05/90903; D, MNCN15.05/90912; E, E.flava (MNCN15.05/90929); F, E. timida (MNCN15.05/90933); G, E.gordanae (MNCN15.05/90843); H, E. gordanae (MNCN15.05/90836); I, J, K, E.margaritae: I, J, MNCN15.05/90817; K, MNCN15.05/94854; L, E.evelinae (MNCN15.05/90924). Scale bars = 10 μm.

Figure 8. Elysia azorica sp. nov. reproductive system (MNCN 15.05/47823), scale bar = 100 μm. Abbreviations: ag, albumen gland; am, ampulla; fmgc, female gland complex; fp, female pore; hf, hermaphroditic follicle; gr, genital receptacle; p, penis; sr, seminal receptacle; vd, vas deferens.