Prosphaerosyllis danovaroi Langeneck, Musco & Castelli, 2018

Langeneck, Joachim, Musco, Luigi, Busoni, Giulio, Conese, Ilaria, Aliani, Stefano & Castelli, Alberto, 2018, Syllidae (Annelida: Phyllodocida) from the deep Mediterranean Sea, with the description of three new species, Zootaxa 4369 (2), pp. 197-220 : 207

Prosphaerosyllis danovaroi Langeneck, Musco & Castelli n. sp.

( Figure 6 )

Material examined. Holotype ( MSNP: P/253/V): St. 11, Sardinian Slope, 600 m depth. Paratypes: St. 8: 2 individuals ( MSNP: P/239/V); St. 11: 3 individuals ( MSNP: P/237/V; P/3887; P/3888); St. 13: 1 individual ( MSNP: P/3889).

Description. All individuals lack pygidium. Holotype 2 mm long for 28 chaetigers, 0.16 mm maximum width. Body elongated, thread-like; anterior segments short, more elongated after proventricle, giving a moniliform appearance ( Fig. 6a ). Dorsal papillae small, scattered, not very conspicuous. Prostomium small, oval, fused with palps, with a small, pointed median antenna; lateral antennae smaller than median antenna, with rounded tip. Four small eyes in open trapezoidal arrangement, only seen in two paratypes ( Fig. 6g ). Palps entirely fused, covered by several, distinct papillae. Peristomial and dorsal cirri very small, papilliform, becoming slightly more elongated posteriorly.

Parapodia well-developed, conical, each with single dorsal simple chaeta, ventral simple chaeta and up to seven compound chaetae on anterior parapodia, diminishing progressively to five posteriorly. Compound chaetae hemigomph, with both hinges of shafts almost of same length ( Fig. 6c ); blades approximately 5 µm long, short, slightly hooked, unidentate, smooth. Dorsal simple chaetae slightly hooked, slightly spinulated subdistally ( Fig. 6d ); ventral simple chaetae similar in shape, distinctly thinner, smooth ( Fig. 6e ). Aciculae robust, thick, with widened subdistal region and slightly deviated tip ( Fig. 6f ). Pharynx relatively short and wide, through three chaetigers. Small, triangular, thin tooth, located close to pharyngeal opening ( Fig. 6g ), not seen in holotype and other paratypes. Proventricle long and wide, barrel-shaped, through four chaetigers ( Fig. 6a ), with 20–23 cell rows.

Etymology. The new species is dedicated to Prof. Roberto Danovaro, in recognition of his important scientific contributions to the knowledge of the Mediterranean deep-sea.

Distribution. Western Mediterranean Sea: Sea of Sardinia (type locality), Tyrrhenian Sea.

Remarks: One of the paratypes is a mature female, with very large intra-coelomic oocytes from chaetiger 10 to chaetiger 27. Individuals from the shallowest station (St. 8) show four very small, black eyes in trapezoidal arrangement. Prosphaerosyllis danovaroi n. sp. resembles Prosphaerosyllis giandoi ( Somaschini & San Martín 1994) in the extremely small size of antennae and cirri, as well as the hemigomph articulation of compound chaetae and the moniliform body. However, it differs in the absence of eyes (which may be present but being very small) and eyespots (four very large eyes and two eyespots in P. giandoi ), in the blades of compound chaetae (5 µm in P. danovaroi n. sp. for 9–10 µm in P. giandoi ), in the body size (0.16 mm width, 28 chaetigers an incomplete individual of P. danovaroi n. sp. for 0.12 mm width, 23 chaetigers a complete individual of P. giandoi ) and in the bathymetric distribution, circalittoral to bathyal (110–1200 m depth) in P. danovaroi n. sp. vs. shallow waters (0– 30 m depth) for P. giandoi ( Somaschini & San Martín 1994; Olivier et al. 2012). Prosphaerosyllis adelae San Martín, 1984b is also characterised by falcigers with hemigomph articulation and by papilliform cirri, but in this species the prostomium is usually retracted under the peristomium, and aciculae show a subdistal crown of spines. Also Prosphaerosyllis opisthoculata ( Hartmann-Schröder, 1979) is characterised by hemigomph falcigers, but dorsal cirri are distinctly larger, and this species is provided with well-developed eyes hidden by the dorsal part of the peristomium. All remaining species of the genus Prosphaerosyllis are characterised by heterogomph articulation of falcigers and larger dorsal cirri and therefore can be readily distinguished from P. danovaroi n. sp. ( San Martín 2005; Ding and Westheide 2008; Fukuda et al. 2009; Çinar et al. 2011; Olivier et al. 2012; Salcedo et al. 2016).

Figures

FIGURE 6. Prosphaerosyllis danovaroi n. sp. Holotype (MSNP: P/253/V): a) anterior end in dorsal view; b) close-up of the prostomium, dorsal view; c) compound chaetae; d) dorsal simple chaeta; e) ventral simple chaeta; f) acicula.Paratype (MSNP: P/239/V): g) anterior end in dorsal view. Scale-bar:a, g: 0.10 mm; b: 60 µm; c‒f: 6 µm.