Elisesione mezianei, Salazar-Vallejo, Sergio I., 2016

Salazar-Vallejo, Sergio I., 2016, Elisesione, a new name for Wesenbergia Hartman, 1955, and the description of a new species (Annelida, Hesionidae), ZooKeys 632, pp. 1-12 : 5-8

Taxon classification Animalia Phyllodocida Hesionidae

Elisesione mezianei sp. n. Figs 1, 2

Type material.

Holotype (MNHN 1777), Musorstom Expedition 7, Wallis & Futuna Islands, Sta. 536 (12°30.8'S, 176°41'W), Waren Dredge, Waterwitch Bank, 128 km NW off Wallis Island, 27-37 m, coralline rocks, crinoids, crabs, 16 May 1992, B. Richer, coll.

Etymology.

This species is named to honor Dr. Tarik Meziane, Curator of Polychaeta in the Muséum National d'Histoire Naturelle, Paris, as an appreciation of his efforts and support to my research activities during many years. The epithet is a noun in apposition.

Description.

Holotype (MNHN 1777) complete, subcylindrical, slightly damaged, bent ventrally, many neurochaetal blades broken; 28 mm long, 3 mm wide, 16 chaetigers (right parapodium of chaetiger 7 removed for observation, now kept in plastic vial with holotype).

Body with parallel sides (Fig. 1A), barely tapered posteriorly; pigmentation brownish, with abundant irregular spots variably fused into transverse or longitudinal lines, leaving a mid-dorsal, irregular, wider than long pale area in each segment (Fig. 1B); pigment intensity and definition progressively reduced posteriorly. Lateral and ventral surfaces pale.

Prostomium slightly wider than long, anterior margin with a shallow depression, lateral margins rounded, wider medially, posterior margin with a shallow depression, as long as 1/6 prostomial length. Antennae digitate, longer than interocular distance. Palps simple, blunt, 2/3 as long as antennae, positioned at the same level, external to antennae. Eyes blackish, anterior ones half-moon shaped, three times as large as posterior rounded ones (Fig. 2A, B).

Enlarged cirri long, thick, longest one reaches chaetiger 5. Lateral cushions low, projected anteriorly, slightly projected laterally, undivided.

Parapodia with chaetal lobes cylindrical, truncate, longer than wide; dorsal cirri thick with cirrophores cylindrical, 4-5 times longer than wide (Fig. 2C), cirrostyle basally cylindrical, smooth, medially annulated, distally articulated, shorter than body width (without parapodia). Ventral cirri basally smooth, rugose medially and distally, surpassing chaetal lobes.

Acicula black, tapered; acicular lobe double, each lobe blunt, of similar size, barely visible because of chaetal lobe contraction (Fig. 2C, inset). Neurochaetae about 30 per bundle, handle and blade brownish, blade unidentate but some chaetae with subdistal tooth remains, probably eroded; guards not seen (Fig. 2D).

Posterior end tapered into a blunt cone (Fig. 1C); prepygydial segment with asymmetrical cirri, dorsal ones over 10 times longer than ventral ones; pygidium smooth, depressed (Fig. 1D); anus dorso-terminal, open, about 9 anal papillae.

Pharynx not exposed. Oocytes not seen.

Remarks.

As indicated in the key above, Elisesione mezianei sp. n. differs from both the Icelandic and the Japanese Elisesione problematica in parapodial and chaetal features. In Elisesione mezianei dorsal ceratophores are long (4 –5× longer than wide), the acicular lobe is double, and neurochaetal blades are short (1-3 times longer than wide), whereas in Elisesione problematica dorsal ceratophores are short (2 × longer than wide), the acicular lobe is single, and neurochaetal blades are long (8 –12× longer than wide). Based upon the observation of other similar hesionid specimens, it is clear that these morphological differences are not the result of preservation methods, or prolonged storage in ethanol.

On the contrary, pigmentation patterns can be modified by dissolution in ethanol, because of photo-oxidation, or both, and despite the striking contrast between the two species, they could not be employed as diagnostic features. The pigmentation of Elisesione mezianei is long-lasting since it has been in ethanol for at least 16 years, when it was initially sorted-out as part of the Musorstom materials ( Salazar-Vallejo 1999). Although they might be regarded of as having a little diagnostic relevance, the dorsal anastomosing thin brownish lines together with the shape and large size of the anterior eyes, are quite remarkable and unique for the genus, and, it must be added, not apparent in any Hesione species.

Distribution.

Elisesione mezianei sp. n. is the second species in a previous monotypic genus and it is apparently rare along its distribution in rocky, shallow water substrates (35 m) in the Southwestern Pacific. The distribution for the genus is rather interesting and difficult to explain. The type species, Elisesione problematica (Wesenberg-Lund, 1950) thrives in very cold waters in Iceland, and was also recorded in Japan in sediments at 150-320 m depth ( Imajima 2003), whereas the new species, Elisesione mezianei , was found in shallow environments in a single locality in the tropical Pacific.