Syllis pharynxcircunfusata Martín & Lucas & Hutchings 2023, n. comb.

Figure 14

Typosyllis (Typosyllis) pharynxcircunfusata Hartmann-Schröder, 1979: 94, Figs 88–90. Typosyllis pharynxcircunfusata.— Licher 1999: 156, fig. 69.

Material examined. AUSTRALIA. WESTERN AUSTRALIA: Broome, cavity in calcareous crust, intertidal, Hartmann-Schröder leg. id., ZHM P-15471, holotype.

Diagnosis. Body slender. Dorsal cirri short. Compound chaetae with slightly bidentate blades. Dorsal simple chaetae truncate. Posterior aciculae distally bent in right angle. Pharynx long and proventricle short. Anterior part of pharynx surrounded by a transparent, spherical structure with double wall and a longitudinal line.

Description. Small size, 8–9 mm long incomplete and partially damaged specimen, 0.16 mm wide, 69 segments. Body colourless, slender, with segments not well marked. Prostomium oval, with four small eyes in open trapezoidal arrangement (Fig. 14A). Palps slightly longer than prostomium. Median antenna arising between anterior pair of eyes, similar in length to prostomium and palps together, with about 15 articles; lateral antennae shorter than median one, inserted in front of anterior eyes, with about nine articles. Peristomium shorter than subsequent segments; dorsal tentacular cirri similar in length to median antenna, with about 14 articles; ventral tentacular cirri about half of length of dorsal ones, with about 10 articles. Dorsal cirri relatively short, fusiform, mostly broken; dorsal cirri of first chaetiger longer than subsequent ones, with about 19–22 articles; midbody dorsal cirri with about 12 articles (Fig. 14B). Articles of dorsal cirri with numerous convoluted inclusions (Fig. 14A, B). Parapodia conical, slightly bilobed distally. Ventral cirri conical, shorter than parapodial lobes. Anterior parapodia with about 10 compound, heterogomph chaetae, reducing progressively to 6–8 on midbody-posterior parapodia. Blades of compound chaetae bidentate, with proximal tooth slender and slightly shorter than distal one and fine, short spines on margin; marked dorso-ventral gradation in size, 25 µm above, 10 µm below, in midbody (Fig. 14C). Shafts smooth, with small and fine spines on margin of most dorsal chaetae. Dorsal simple chaetae on most posterior parapodia, truncate, with minute subdistal spines (Fig. 14D). Ventral simple chaetae not seen. Aciculae solitary on all parapodia except most anterior ones, with two aciculae, slender, stout, distally slightly bent at right angle (Fig. 14E). Pharynx long, slender, through eight segments; pharyngeal tooth located on anterior margin, surrounded by a crown of 10 soft papillae; anterior part of pharynx surrounded by a transparent, spherical to ovate, probably a chitinous structure, with a double wall and a median, longitudinal line (Fig. 14A). Proventricle shorter than pharynx, through four segments, with around 30 muscle cell rows.

Remarks. Syllis pharynxcicunfusata belongs to the group of species with truncate dorsal simple chaetae and aciculae bent in right angle. This species is very similar to Syllis erikae (Hartmann-Schröder, 1981), also from Western Australia, but the proventricle is shorter (through 2–3 segments), the dorsal cirri are not fusiform, as in S. pharynxcircunfusata, and the blades of compound chaetae are shorter. Other species of this group in Australia are Syllis albanyensis (Hartmann-Schröder, 1984), Syllis rosea (Langerhans, 1879), Syllis edensis (Hartmann-Schröder, 1989), and Syllis augeneri Haswell, 1920, but clearly differ in several characters such as proventricle length, dorsal cirri and chaetae (see Álvarez-Campos et al. 2015a; San Martín et al. 2017). None of the described species of Syllis have the characteristic hyaline, structure surrounding the pharynx, of unknown function, of S. pharynxcircunfusata. Although we have examined a large number of species and specimens of the genus Syllis from samples all around Australia, we have not seen any specimen with such a structure nor any other specimen of that species; perhaps it is simply an artifact, but since this species also differs from other species, we are maintaining S. pharyxcircunfusata as a valid species.

Habitat. Inside crevices in calcareous concretions, intertidal.

Distribution. Only known from the type-locality, Broome, Western Australia.