Anguillosyllis Day 1963

Anguillosyllis sp.

(Figure 9g –j)

Material examined. St. 16: 1 individual.

Description. Specimen complete, 2 mm long and 0.17 mm wide for 14 chaetigers (Fig. 9g). Prostomium ovate, broader than long, difficultly distinguishable from palps; palps distally acute, completely fused, without traces of longitudinal furrow. Eyes absent, lateral antennae short, papilliform; median antenna almost as long as the prostomium, digitiform, backwards directed. One pair of very long, thin cirri on peristomium. Segments becoming wider towards posterior part of body. Parapodia rectangular, elongated, dorsal cirri not seen, with 6–9 long chaetae. Dorsal simple chaeta very long and thin, with rounded tip and a well-developed subdistal spine (Fig. 9h); compound chaetae with smooth shafts, strong dorso-ventral gradation in the size of blades, from approximately 80 µm most dorsal to 12 µm most ventral. All blades unidentate, with smooth edge and blunt tip, longer blades slightly sinuous, shorter blades straight (Fig. 9i). One robust acicula, with briskly crooked tip, forming a ca. 90° angle (Fig. 9j). Pygidium rounded, wide, anal cirri not seen. Pharynx and proventricle difficult to distinguish; pharynx narrow, through three segments, without pharyngeal tooth; proventricle barrel-shaped, through two chaetigers, with 12–15 muscle cell rows.

Distribution. Sardinian Slope, at 2100 m depth.

Remarks. The low number of body segments, along with the pharynx without tooth, the small size of antennae and the completely fused palps allow to assign the examined individual to the genus Anguillosyllis Day, 1963 (Aguado & San Martín 2008). The morphology of the examined specimen, however, does not correspond to any of the four known species of Anguillosyllis. The entirely fused palps resemble those in A. lanai Barroso, Paiva, Nogueira & Fukuda, 2017 and A. pupa (Hartman, 1965), while the shape of antennae and the number of proventricle cell rows resemble those of A. lanai (Barroso et al. 2017). However, it differs from the latter in having the blades of compound chaetae up to 80 µm long (up to 170 µm in A. lanai), up to 8 compound chaetae (up to 15 in A. lanai) and the parapodial glands absent (present in A. lanai). Our specimen shows 14 chaetigers (10 or 11 in all known Anguillosyllis species), thin elongate tentacular cirri (papilliform in the other species) and a crooked acicula (unknown in the other species). Overall, our specimen seems to belong to an undescribed species. However, we consider our single individual in poor preservation status (most appendages are lacking) as not enough to formally describe it as a new species. Nonetheless, it represents the first Mediterranean record of the genus.