Figure 19

Material examined. AUSTRALIA, NEW SOUTH WALES: MI NSW3427, north east of Kurnell, “Anchor Reef”, 34° 00’ 33” S, 151° 13’ 51” E, coll. 16 Mar 2009, 17.6 m, coarse-medium shelly sediment with echinoid spines, holotype AM W.53916, paratypes, AM W.53917, 2 specimens.

Additional material examined: NEW SOUTH WALES: Maroubra Beach, 33° 57’ S, 151° 15’ E, coll. 21 Apr 2005, 0.5 m, M. Capa, algae Corallina and Udotea in intertidal pools, AM W.53915, 2 specimens.

Diagnosis. Single, slender, transverse reddish band on posterior part of each segment and two spots on bases of cirrophores. Dorsal cirri long, alternating in length in midbody. Compound chaetae bidentate falcigers. Posterior aciculae distally rounded, with apparently hollow tips. Pharynx and proventricle of similar length.

Description. Holotype, complete specimen, 5 mm long, 0.4 mm wide, with 55 chaetigers. Body wide, orangeyellowish, with a slender transverse reddish band on the posterior margins of each segment and a lateral spot on bases of each cirrophore (Fig. 19A). Prostomium almost pentagonal; four eyes in open trapezoidal arrangement and two anterior eyespots. Palps similar in length to prostomium. Median antenna arising in center of prostomium, with about 33–35 articles, distinctly longer than combined length of prostomium and palps; lateral antennae shorter than median one, with about 22–23 articles (Fig. 19A). Peristomium markedly shorter than subsequent segments (Fig. 19A). Dorsal tentacular cirri longer than median antenna, with about 38–40 articles; ventral tentacular cirri distinctly shorter than dorsal ones, with about 15 articles. Dorsal parapodial cirri long, those of anterior chaetigers longer than subsequent ones with 40–42/30/34/40/25 articles on first five chaetigers; remaining dorsal cirri alternating long, longer than body width, and short, similar to body width, with 28–30/20 articles respectively (Fig. 19A). Parapodia distally slightly bilobed. Ventral parapodial cirri digitiform. Compound chaetae all markedly bidentate falcigers, with proximal teeth similar or larger than distal teeth (Fig. 19B–D) and short to moderate straight spines on margin, diminishing in length from basal to distal parts; shafts of posterior chaetae somewhat larger and more strongly bidentate than those of anterior parapodia. Anterior parapodia each with 10–12 compound chaetae, blades with dorso-ventral gradation, 25 μm long above, 13 μm long below (Fig. 19B); midbody parapodia each with about 6–8 compound chaetae, with less marked dorso-ventral gradation in length than those of anterior parapodia and blades strongly bidentate, less marked dorso-ventral gradation in length of blades, about 22 μm long above, 12 μm long below (Fig. 19C); posterior parapodia each with six compound chaetae, strongly bidentate blades, similar in length to those on midbody. Dorsal simple chaetae on midbody and posterior parapodia, distally bifid, with minute spines on margin (Fig. 19F). Ventral simple chaetae on far posterior segments, slender, smooth, bidentate, (Fig. 19G). Aciculae distally rounded, apparently hollow on tips (Fig. 19H–J), two on each anterior parapodium, and solitary on each midbody and posterior parapodia. Pharynx extending through about eight segments; pharyngeal tooth daggershaped, located close to anterior margin (Fig. 19A). Proventricle through about seven segments, with about 32 muscle cell rows. Pygidium with two anal cirri, and median stylus.

Remarks. Syllis thylacine n. sp. is similar to the Australian species S. busseltonensis Hartmann-Schröder, 1982, described above, and S. prolifera Krohn, 1852, an apparently world- wide species, but these species lack any colour pattern, the dorsal cirri are not as long as in S. thylacine n.sp. and there are some small differences in the details of the chaetae, although similar in all these species. These species have slender aciculae, ending in a rounded tip, apparently hollow. There are only a few other species of Syllis with this type of aciculae, such as S. vivipara Krohn, 1869; S. prolixa Ehlers, 1901, from Southern Chile and Argentina, as well as Antarctica; S. rubicunda Aguado, San Martín & Nishi, 2006, from Japan; S. antoniae Salcedo-Oropeza, San Martín & Solís-Weiss, 2012, from the Pacific coast of México; S. zahri Sedick & Simon, 2019, and S. unzima Simon, San Martín & Robinson, 2014, both from South Africa; S. escribanoi San Martín, Lucas & Westheide, 2021, from China; and the above described species S. similisunizima. Syllis vivipara and S. unzima are viviparous species (see Krohn, 1869; Goodrich, 1900; San Martín, 2003; Simon et al. 2014), with almost unidentate blades; S. vivipara lacks any colour pattern and S. unzima has a different colour pattern to S. thylacine n. sp., with two slender dark bands on each segment. Also S. escribanoi, S. antoniae; and S. prolixa, lack colour patterns and the chaetae are unidentate or with small proximal teeth (Ehlers 1901; Salcedo-Oropeza et al. 2012; San Martín et al. 2021). Syllis rubicunda has broad dorsal cirri and a red or orange uniform colour pattern (Aguado et al. 2006). Syllis zahri is light pink to light brown, with two dark brown bars across dorsum on anterior and posterior margins of anterior segments, and the chaetae are not as strongly bidentate as in S. thylacine n. sp.

Syllis malaquini Ribeiro. Ponz-Segrells, Helm, Egger & Aguado, 2020, has a similar colour pattern, but the body is slender, the dorsal cirri are much shorter, the pharynx and proventricle are much longer and the aciculae are acuminate.

Haswell (1886) described from the same area the species Gnathosyllis zonata, which is considered by Licher (1999) as synonym of S. prolifera. It was described based on a single, incomplete specimen; the chaetae seem to be similar to those of S. thylacine n. sp., but the colour pattern is different, with two transverse bands on the dorsum of each segment and purple rings on dorsal cirri, so we consider them as different species. Unfortunately, the type is lost so the status of this species cannot be confirmed unless additional material is collected and a neotype designated.

Etymology. The species is named after the Tasmanian Wolf (Thylacinus cynocephalus), an extinct carnivorous marsupial, which also had distinctive stripes on its back.

Habitat. Shelly sediments with echinoid spines, from intertidal to 11.8 m depth.

Distribution. Australia (NSW).