Syllis narranuk Martín & Lucas & Hutchings 2023, n. sp.

Syllis narranuk n. sp.

Figures 7, 8

Material examined. AUSTRALIA, WESTERN AUSTRALIA: St. 115, Kimberleys, Shirley Island, 16° 17’ S, 123° 26’ E, coll. 20 July 1988, by P. Hutchings, Holotype, AM W.53791.

Diagnosis. Body slender. Dorsal cirri slender, alternating long and short on midbody. Two kinds of spiniger-like chaetae, one with longer blades, both unidentate, with short spines on margin basally, apparently smooth distally; falcigers slender, slightly bidentate, with long and fine spines on margin. Posterior aciculae acuminate.

Description. Holotype complete specimen, 6 mm long, 0.28 mm wide, with 80 chaetigers. Body relatively small, slender, filiform, without colour pattern. Prostomium oval; four small eyes in trapezoidal arrangement and pair of anterior minute eyespots. Palps broad, slightly longer than prostomium (Fig. 7A). Median antenna arising between posterior eyes, with about 16 articles, somewhat longer than combined length of prostomium and palps together; lateral antennae shorter than median one, with about 12 articles. Peristomium dorsally distinctly shorter than subsequent segments (Fig. 7A). Dorsal tentacular cirri similar in length or shorter than median antenna; ventral tentacular cirri about half the length of dorsal ones. Dorsal parapodial cirri of chaetigers 1 and 4 longer than remaining, with about 19 articles, those of chaetiger 2 and 3 shorter, with 10–11 articles, remaining dorsal cirri alternating long and short; in midbody, long ones with about 14 articles; short ones with nine articles, all shorter than body width (Fig. 7B). Parapodia conical. Ventral parapodial cirri digitiform, shorter than parapodial lobes. Compound chaetae of each parapodium with long pseudospinigers (Fig. 8A, E, I), short pseudospinigers (Fig. 8B, F, J) and falcigers (Fig. 8C, G, K); all types of chaetae with slender shafts and elongated, thin blades, with moderate to long, very thin spines on margin. Spiniger-like chaetae unidentate and apparently smooth distally; falcigers slightly bidentate, with a minute proximal tooth. Anterior parapodia with 2–3 long spiniger-like chaetae (Fig. 8A), with long blades, about 88 µm, 3–4 short spiniger-like chaetae (Fig. 8B), 30 µm long, and about 8 falcigers (Fig. 8C), 20–9 µm long; midbody segments with two long spinger-like chaetae (Fig. 8E), 140 μm long, two short spiniger-like chaetae (Fig. 8F), 35 μm long, and five falcigers (Fig. 8G), 20–13 μm long; posterior parapodia with single long spiniger-like chaeta (Fig. 8I), blade 110 µm long, one short spiniger-like (Fig. 8J), 33 µm long, and 2–3 falcigers (Fig. 8K), 19–12 µm long. Dorsal simple chaetae only present in some posterior parapodia, relatively thick, smooth, distally markedly bidentate (Fig. 8L). Ventral simple chaetae only on most posterior segments, slender, smooth, weakly bidentate (Fig. 8M). Anterior parapodia with 3–4 slender aciculae each, distally pointed (Fig. 8D), reducing to single in midbody and posterior parapodia, slender and acuminate (Fig. 8H, N). Pharynx long, everted, extending through about 8–9 segments (occupying probably 11 when retracted); pharyngeal tooth conical, on anterior margin of pharynx (Fig. 7A). Proventricle shorter than pharynx, through seven segments, with about 28 muscle cell rows. Pygidium with two anal cirri, and a median stylus.

Remarks. Syllis narranuk n. sp. is characterized by having two kinds of spiniger-like chaetae on each parapodium, some with very long blades and others shorter, and also some falcigers, with slightly bidentate blades and moderate to long, very thin spines on margin. None of the described species of this genus have similar chaetae, and so we have described this as a new species, although we found only a single specimen.

There are some other Australian species with spiniger-like compound chaetae, but they are very different to S. narranuk n. sp. Syllis broomensis (Hartmann-Schröder, 1979) has a single kind of spiniger-like chaetae, with spines on margin up the tip, more markedly bidentate falcigers, with longer spines on margin (Hartmann-Schröder 1979, Álvarez-Campos et al. 2015a). Syllis boggemanni San Martín, Álvarez-Campos & Hutchings, 2017 has bidentate spiniger-like chaetae with short spines, except distally, and the falcigers are longer than those of S. narranuk n. sp., distinctly bidentate (San Martín et al. 2017). Syllis rosea (Langerhans, 1879) has very different compound chaetae, the dorsal simple chaeta is truncated and the posterior aciculae are “foot-like” (San Martín et al. 2017) instead of acuminate as found in S. narranuk n. sp. Finally, Syllis yallingupensis (Hartmann-Schröder 1982) has much longer antennae, tentacular and dorsal cirri, the spiniger-like chaetae are spinulated on the margin up the distal part, the falcigers are markedly bidentate, with proximal tooth longer than distal one, and the distal spines are long (Hartmann-Schröder, 1982, San Martín et al. 2017).

Etymology. The specific name “narranuk” is an aboriginal name to “hair”, in reference to the long, slender chaetae, appearing as long hairs in the parapodia.

Habitat. Intertidal on sand/mudflats in front of extensive stands of mangroves.

Distribution. Only known from the Kimberley region, Western Australia.