Elisesione problematica ( Wesenberg-Lund, 1950 )

Jimi, Naoto, Eibye-Jacobsen, Danny & Salazar-Vallejo, Sergio I., 2018, Description of Elisesione imajimai sp. nov. From Japan (Annelida: Hesionidae) and A Redescription of E. problematica (Wesenberg-Lund, 1950) and Its Confirmation Within Hesionini, Zoological Studies 57 (8), pp. 1-9 : 6-8

Elisesione problematica ( Wesenberg-Lund, 1950)

( Figs 3-4 )

Hesionella problematica Wesenberg-Lund, 1950: 14-15 , fig. 15.

Wesenbergia problematica: Hartman 1955: 41 .

Wesenbergia problematica: Pleijel 1998: 112-113 , fig. 9.

Elisesione problematica: Salazar-Vallejo 2016: 3-5 .

Description: Holotype about 50 mm long, 8 mm wide, 16 chaetigers. Body cylindrical, tapered in posterior region ( Figs. 3A, B ), brownish in ethanol, dorsal integument annulated, with 13- 15 transverse wrinkles per segment ( Figs. 3A, B, C ). Tentacular cirri, dorsal cirri and parapodial lobes whitish. Pigmentation of holotype unknown (specimens in ethanol for over 55 years before description; now darker).

Prostomium wider than long, median line with a shallow depression, lateral margins rounded, wider medially ( Fig. 3C ). Eyes not seen. Palps and antennae present, damaged; palps ventral, slightly more lateral than antennae; left antenna present, tip damaged; right antenna missing (in the original illustration, palps and antennae tapered, of similar length). Tentacular cirri long, thick. Lateral cushions low, slightly projected laterally, divided in 2-3 parts ( Figs. 3A, C ).

Parapodia with chaetal lobes cylindrical, truncate, longer than wide ( Fig. 4A ); dorsal cirrophores cylindrical, smooth, about 4 / 5 times as long as wide ( Fig. 4B ). Ventral cirrophore cylindrical, smooth, as long as wide ( Fig. 4C ). Ventral cirri smooth, not reaching tip of neurochaetal lobe (as indicated in original illustration).

Acicula black, tapered; acicular lobe single, blunt, digitate. About 25 neurochaetae per bundle ( Fig. 4D ), shaft and blade pale brownish, blade 8-12 times as long as wide, with subdistal tooth as long as apical tooth, guard approaching apical tooth ( Fig. 4E ).

Posterior region tapered into a blunt cone; body wall macerated ( Fig. 3B ). Cirri of prepygydial segment broken; pygidium smooth, depressed; anus dorso-terminal, open, with two pairs of lateral anal cirri.

Pharynx smooth, partially everted, basal ring barely exposed, dorsal papilla not exposed, terminal papillae absent ( Figs. 3A, C ).

Type material: Holotype (ZMUC-POL-480), sex unknown. Southwest off Iceland (555 m depth, 64°18'N, 27°00'W).

Distribution: Only known from the type locality, southwest off Iceland, 555 m depth.

Phylogenetic analysis

In the resulting tree, Elisesione , Hesione , and Leocrates are reciprocally monophyletic, with high support value (86% bootstrap support [BS]). Elisesione is sister to Leocrates , although they comprise a poorly supported clade (52% BS) ( Fig. 5 ).

In a previous morphological study, Elisesione , Hesione , and Leocrates were monophyletic and regarded as tribe Hesionini ( Pleijel 1998) . Our results based on four genes also supported the tribe as monophyletic. In Pleijel’s paper, Elisesione is sister to Hesione ; this is not in agreement with our results. However, the BS value of the clade is poor (52% BS); hence, additional study is needed to clarify the position of Elisesione in the clade Hesionini .

Figures

Fig. 3. Elisesione problematica (Wesenberg-Lund, 1950), holotype (ZMUC-POL-480). (A) anterior end, dorsal view; (B) posterior end, dorsal view; (C) head, dorsal view. Scale bars: A-C= 1 mm.

Fig. 4. Elisesione problematica (Wesenberg-Lund, 1950), holotype (ZMUC-POL-480). (A) chaetiger 5, right parapodium, posterior view (chaetae omitted); (B) same, dorsal cirrophore; (C) same, ventral cirrophore; (D) same, neurochaetae; (E) same, tip of ventral neurochaetal blade. Scale bars: A = 0.5 mm; B-D = 0.2 mm; E = 20 µm.

Fig. 5. Phylogenetic tree of Hesionidae based on COI, 16S, 18S and 28S sequences. Dysponetus caecus and Nereis pelagica were used as an ‘outgroup’. Nodal support values (Maximum-likelihood (ML) bootstrap support [BS] value) are indicated on each branch.