Exogone sophiae Langeneck & Musco & Busoni & Conese & Aliani & Castelli 2018, n. sp.

Exogone sophiae Langeneck, Musco & Castelli n. sp.

(Figures 3–4)

Material examined. Holotype (MSNP: P/3879): St. 8, Northern Tyrrhenian Sea, 110 m. Paratypes: St. 8: 1 individual (MSNP: P/001/SEM); St. 10: 2 individuals (MSNP: P/242/V; P/246/V). Additional material: St. 8: 1 individual.

Description. Holotype complete specimen, 6 mm long for 47 chaetigers, 0.30 mm wide. All paratypes incomplete. Prostomium short, rectangular, distinctly broader than long, with four rounded, small eyes in trapezoidal arrangement, reddish, sometimes difficult to distinguish in preserved material. Antennae absent in all examined individuals (Fig. 4a). Palps long, broad, fused for their total length, with barely noticeable distal notch. Dorsal cirri very small, oval, slightly longer in the posterior region, lacking at chaetiger 2 (Fig. 3a). First four parapodia with 2 compound spiniger-like chaetae and 3–4 falcigers, after chaetiger 5 only 1 spiniger-like and 3 falcigers (Fig. 4c). Anterior spiniger-like compound chaetae with thick, distally spinulous shaft (Figs 3c, 4d), and thin, elongated blades 25–35 µm long; blades sometimes slightly curved with several long teeth on basal part (Figs 3c, 4d), difficult to see with the light microscope. Posterior spinigers-like chaetae similar but shorter and thinner, 15–20 µm long blades. Anterior falcigers with 7.5–10 µm long blade, with very small distal tooth, massive, strong proximal tooth, and relatively short, coarse serration along ventral edge (Figs 3d, 4e). Posterior falcigers shorter, blades 3.8–5 µm long, with thicker basal part. Anterior dorsal simple chaetae unidentate, smooth; posterior dorsal simple chaetae become distinctly thicker, with a subdistal notch (Fig. 3e). Ventral simple chaetae absent. Pharynx long, relatively wide, extending through six chaetigers, with a large, triangular distal tooth. Proventricle barrelshaped, as long as pharynx, with 20–23 muscle cell rows. Pygidium sub-triangular with two very long, tapering anal cirri (Fig. 3b).

Etymology. This species is dedicated to Sophie Langeneck, sister of the first author.

Distribution. Tyrrhenian Sea, at a depth between 100 and 110 m.

Remarks. Exogone sophiae n. sp. is chiefly characterised by the absence of antennae; albeit preservation may cause the loss of antennae in some syllid species, we believe that this character is not a preservation artefact, as all the sampled individuals do not show any trace of antennae, nor of scars indicating the lost of antennae. Moreover, dorsal cirri are perfectly preserved, suggesting that preservation should not have altered the soft appendages of the collected specimens. Until now two species of Exogone without prostomial antennae have been described, namely Exogone acerata San Martín & Parapar, 1990, and Exogone oculata (Hartman & Fauchald, 1971) (San Martín, 1991). E. sophiae differs from E. acerata in the absence of dorsal cirri at chaetiger 2 (present in E. acerata), in the less pronounced spinulation on shafts of spiniger-like chaetae and in the longer spines on blades of spiniger-like chaetae (San Martín & Parapar, 1990). Exogone sophiae appears closer to E. oculata, as both species lack the dorsal cirrus at chaetiger 2, but E. oculata lacks spiniger-like chaetae on the first four chaetigers. Moreover, both species are provided of ventral simple chaetae, that are absent in all examined individuals of the new species.

Among Mediterranean species, E. sophiae appears particularly close to Exogone verugera (Claparède, 1868) and Exogone dispar (Webster, 1879) in size and overall body shape and number of proventricle cell rows. Apart from the absence of antennae, this species differs from E. verugera as E. sophiae has smaller, non-coalescent eyes, longer blades of falciger chaetae, with a higher number of marginal teeth, and slightly shorter blades of spinigerlike chaetae with a more pronounced spinulation along the ventral edge; moreover E. sophiae lacks ventral simple chaetae. Exogone dispar has similar blades of falciger chaetae, and a more pronounced spinulation along the ventral edge of spiniger-like blades (San Martín, 2003); however, in E. sophiae such spinulation is even more pronounced (Fig. 3d). Moreover, E. dispar has dorsal cirri at the second chaetiger. Lastly, E. sophiae might resemble Exogone lopezi San Martín, Ceberio & Aguirrezabalaga, 1996, since this last species apparently lacks ventral simple chaetae, and has very small antennae that are difficult to see. However, E. lopezi has falciger chaetae with long, thread-like marginal teeth that outgrow the chaetal tip, whereas in E. sophiae the marginal serration of falcigers is coarser and less developed.