Hesionella problematica Wesenberg-Lund, 1950, by monotypy.

The name is a combination of the first name of the late Elise Wesenberg-Lund, and Hesione, which is the type genus for the family, but in order to make it more euphonic, the first two letters of the genus-group name are suppressed; the new name emphasizes the similarities between these two genera. Gender feminine.

(emended).Hesionini with two antennae; palps simple, lateral to antennae. Eight pairs of tentacular cirri. Dorsal cirri with short or long cirrophores. Notochaetae absent. Aciculae colorless or blackish. Acicular lobes single or double. Neurochaetae with blades bidentate, guards approaching subdistal tooth, or absent. Prepygidial segment with dorsal cirri about 10 times longer than ventral cirri.

Wesenbergia Kryger, 1943 was proposed for a group of chalcid hymenopterans, but the name was overlooked by Hartman (1955) when she proposed the same genus-group name for hesionid polychaetes. Despite Wesenbergia Kryger, 1943 being considered a synonym of Macromesus Walker, 1848 within Hymenoptera, the name still cannot be made available (ICZN 1999, Art. 23, Principle of Priority).

Homonymies are not allowed in Zoological Nomenclature (ICZN 1999, Chap. 12) and junior homonyms must be replaced (Art. 60). Further, the Code of Ethics includes (ICZN 1999, Point 3) a recommendation for the procedure, especially if the author(s) involved are alive. There are no junior synonyms available and this explains why a new name must be proposed, and both authors involved are deceased.

As indicated above, Wesenbergia Hartman, 1955 is a junior homonym and must be replaced, even though the senior homonym is regarded as a junior synonym (Heqvist 1960). In naming Wesenbergia, Hartman used the first word in the compound last name of Elise Wesenberg-Lund. Using this same principle, the new name, Elisesione, is derived from the first name of the author.

Elisesione nom. n. is closely related to Hesione as shown by Ruta et al. (2007). They differ, however, not only by the presence of simple palps in the former, but because the body is more or less cylindrical, not widened medially or posteriorly as in Hesione species. In fact, the lateral cushions, which are typically divided into 2-3 sections and can vary on their degree of lateral expansion in Hesione, are rather solid, undivided and projected anteriorly in Elisesione nom. n. This feature was noted in the original description when the body was characterized as scolopendriform (Wesenberg-Lund 1950: 14). Further, the anterior eyes of Wesenbergia (only recorded for the shallow water species), are half-moon shaped and about three times larger than posterior ones; this is another feature not recorded for any Hesione species.

Savigny (1822: 39) included four anterior appendages in the generic diagnosis of Hesione, but because they were not included in the description (Savigny 1822: 40), nor in the corresponding illustration (his plate 3, figure 3), they were regarded as a mistake. Grube (1867: 65) corrected this and later Chamberlin (1919: 185) used this in his key to genera. However, by regarding Hesione as having four antennae and eight pairs of tentacular cirri, de Quatrefages (1866) proposed Fallacia for species having two antennae: H. pantherina Risso, 1826 and H. proctochona Schmarda, 1861, whereas Claparède (1868: 541) proposed Telamone for species having two antennae and six pairs of tentacular cirri with H. sicula delle Chiaje, 1822 as its only species. Fallacia and Telamone are junior synonyms of Hesione (Fauvel 1911: 374, Chamberlin 1919: 186, Pleijel 1998: 107), and H. sicula and H. pantherina have been regarded as synonyms (Fauvel 1923: 233).

The two known species in the genus have been found in different ecological conditions and geographical regions. The type species, E. problematica, was found in the North Atlantic, off Iceland, in sediments taken at 550 m depth, and the new species, E. mezianei sp. n., was collected in the Western South Pacific, in hard substrates in shallow water (35 m), in the Wallis and Futuna Islands. Another species, previously recorded as E. problematica from Japan (Imajima 2003) differs from the nominal form in several features. For example, in the Japanese specimens palps are half as long as antennae (rather than about equal-sized), and ventral cirri extend beyond chaetal lobe (rather than short of it); pigmentation also differs because the Japanese specimens are brownish with dorsal cirrostyles banded, whereas the Icelandic specimens are pale yellowish.

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.

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.

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.

Figure 1. 

Elisesione mezianei sp. n. Holotype (MNHN 1777). A Anterior region, dorsal view B Anterior end, dorsal view C Posterior region, slightly oblique dorsal view D Pygidium. Scale bars A 1.6 mm, B 0.5 mm, C 1.2 mm, D 0.4 mm.

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).

Figure 2. 

Elisesione mezianei sp. n. Holotype (MNHN 1777). A Prostomium, dorsal view B Same, after methyl-green staining C Chaetiger 7, right parapodium, anterior view, dorsal cirrostyle removed, only base left on cirrophore (inset: close-up showing tips of double acicular lobe) D Chaetiger 7, neurochaetal blades, variably eroded; the one on the right has a wider handle due to optical interference, not really wider than the others. Scale bars A, B 0.27 mm, C 0.3 mm, D 20 µm.

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.

As indicated in the key above, Elisesione mezianei sp. n. differs from both the Icelandic and the Japanese E. problematica in parapodial and chaetal features. In E. 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 E. 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 E. 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.

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, E. 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, E. mezianei, was found in shallow environments in a single locality in the tropical Pacific.