Syllis similisunzima, Martín & Lucas & Hutchings, 2023

Martín, Guillermo San, Lucas, Yolanda & Hutchings, Pat, 2023, The genus Syllis Savigny in Lamarck, 1881 (Annelida: Syllidae: Syllinae) from Australia (Part 3): new species and redescription of previously described species, Zootaxa 5230 (3), pp. 251-295 : 282-285

Syllis similisunzima n. sp.

Figures 17 , 18

Material examined. AUSTRALIA. NEW SOUTH WALES: NSW 3382 , Pittwater, pontoon 400 m east of The Basin, 33° 36’ 09” S, 151° 17’ 49” E, coll. 4 May 2009, 11.9 m, hand collected on SCUBA, scraping of pontoon, Holotype AM. W.35404; Sydney Harbour , White Bay Berth 3, 33° 51’ 47” S, 151° 11’ 00” E, coll. 5 March 2009, 11.8 m, hand collected on SCUBA, scraping of wharf, AM W.53806, 5 paratypes.

Diagnosis. Single transversal, purple to brown, band on anterior segments; double band from segments anterior to proventricle backwards. Dorsal cirri long and slender, alternating in length in midbody. Compound chaetae bidentate falcigers, with small proximal tooth and short spines on margin. Posterior aciculae distally rounded, apparently hollow on tips. Pharyngeal tooth located back from anterior margin of pharynx.

Description. Longest complete paratype, broken into two pieces, 7 mm long, 0.47 mm wide, 61 chaetigers. Holotype smaller, an anterior part with regenerating posterior end, 4.2 mm long, 31 chaetigers. Body of medium size, elongate, cylindrical, with a distinctive colour pattern, anterior segments dorsally dark, each segment with a purple to brown or reddish band, anteriorly less marked; from proventricle onwards two slender transverse bands, anterior larger and less marked, posteriorly thin and darker; from midbody, only one thin transverse band, present just before intersegmental furrow, and some scattered spots of pigment dorsally on segments ( Fig. 17A ), or forming two rows, anterior light and posterior darker; some scattered pigment on prostomium. Prostomium oval, with two pairs of red eyes in trapezoidal arrangement and pair of anterior eyespots ( Fig. 17A ). Palps triangular, as long as prostomium. Antennae, tentacular and dorsal cirri slender and distinctly articulated ( Fig. 17A, B ). Median antenna much longer than prostomium and palps together, with about 37 articles, arising between posterior pair of eyes; lateral antennae distinctly shorter than median one, about half the length, with about 30–32 articles, originating in front of anterior pair of eyes ( Fig. 17A ). Peristomium shorter than subsequent segments; dorsal tentacular cirri similar to median antenna, with about 30 articles, ventral pair shorter, with about 18 articles. Dorsal cirri longer than body width, longer on anterior segments, with about 40, 15, 34, 37 articles on first four segments, and alternating in length in midbody and posteriorly, with about 36 articles longer, 20 articles shorter ones ( Fig. 17B ), diminishing in length posteriorly. Ventral cirri short, digitiform, not extending beyond parapodial lobes. Parapodial lobes distally bilobed ( Fig. 17A ). All falcigers heterogomph, bidentate with proximal tooth small, distally hooked, with long, thin spines on margin, numbering 7–8 per parapodium throughout; slight dorso-ventral gradation on anterior parapodia ( Fig. 18A ), 40 µm above, 25 µm below; compound chaetae of midbody all similar ( Fig. 18B ), broader than those of anterior segments, 33 µm above, 25 µm below; posterior compound chaetae ( Fig. 18C ) with smaller blades, 23–16 µm. Dorsal simple chaeta on posterior chaetigers, slender, subdistally spinulated, finely bidentate ( Fig. 18D ); ventral simple chaetae thin, sinuous, finely bidentate ( Fig. 18E ). Three aciculae in each anterior parapodium, distally rounded, difficult to see ( Fig. 18F ), two in midbody, distally rounded and hollow ( Fig. 18G ) and solitary in midposterior and posterior parapodia, distally hollow ( Fig. 18H ). Pharynx long, extending through 8–10 segments; large, conical tooth distinctly distant to anterior margin ( Fig. 17A ). Proventricle similar in length to pharynx, extending through 6–8 segments, with about 40–48 muscle cell rows, with midline ( Fig. 17A ). Pygidium rounded, with a digitiform median stylus and two long anal cirri, with about 40 articles.

Remarks. Syllis similisunzima n. sp. is very similar to Syllis unzima Simon, San Martín & Robinson, 2014 , from South Africa; both have similar colour pattern, size, shape of dorsal cirri, bilobed parapodial lobes, long and distinct pharyngeal tooth located distally from anterior margin of pharynx, and compound chaetae with slightly hooked blades. However, S. similisunzima n. sp. has darker pigmentation on anterior segments, the transverse row of pigment on midbody and posterior segments is just in front of the subsequent intersegmental furrow, not after, as happens in S. unzima , the blades of compound chaetae in S. similisunzima are bidentate (although the proximal tooth is small), whereas they are unidentate in S. unzima , the anterior chaetae in S. similisunzima are longer than those of S. unzima , the compound chaetae of S. unzima have longer spines on the margin than those of S. similisunzima , and finally, S. similisunzima has a longer proventricle than S. unzima , with more muscle cell rows and a marked midline, which is lacking in S. unzima .

Furthermore, S. unzima is a viviparous species living associated with sea cucumbers of the genus Holothuria ; none of the specimens of S. similisunzima shows any sign of viviparity, and they are free living.

Etymology. The species is named after its similarity to Syllis unzima Simon, Robinson & San Martín, 2014 ; similis is a latin word that means “similar to”.

Habitat. Scrapings of pylons in 12 m depth.

Distribution. Australia (NSW).

Figures

FIGURE 17. Syllis similisunzima n. sp. Holotype, AM. W.35404. A, anterior end, dorsal view. B, midbody long and short dorsal cirri. Scale. 0.2 mm

FIGURE 18. Syllis similisunzima n. sp. Holotype, AM. W.35404. A, falcigers, anterior parapodium. B, falcigers, midbody parapodium. C, falcigers, posterior parapodium. D, dorsal simple chaeta. E, ventral simple chaeta. F, aciculae, anterior parapodium. G, aciculae, midbody parapodium. H, acicula, posterior parapodium. Scale. 20 µm.