Syllis gracilis Grube, 1840

Álvarez-Campos, Patricia, Riesgo, Ana, Hutchings, Pat & Martín, Guillermo San, 2015, The genus Syllis Savigny in Lamarck, 1818 (Annelida, Syllidae) from Australia. Molecular analysis and re-description of some poorly-known species, Zootaxa 4052 (2), pp. 297-331 : 315-317

Syllis gracilis Grube, 1840

Figures 9 A, B, F1, F2, 10A–E

Syllis gracilis Grube 1840: 77 . Langerhans 1879: 540, figs. 8a–c. Fauvel 1923: 259, figs. 96 f–i. Campoy 1982: 368, pl. 31, figs. a–l. Hartmann-Schröder 1996: 150, fig. 65 a–d.

Syllis (Syllis) gracilis Day 1967: 241 , fig. 12.I. m–p. Ben-Eliahu 1977: 7.

Material examined. Non-type specimens. AUSTRALIA. QUEENSLAND. Lizard Island, MacGillivray Reef, 14°38'52"S, 145°29'12"E, 10 m depth, 31 Aug 2010, 1 specimen (AM W41691); Lizard Island, south of Mermaid Cove, 14°38'53"S, 145°27'00"E, 14.5 m depth, 1 Sep 2010, 1 specimen (AM W41701); South of Smoky Cape, Black Rocks, 30°56'59"S, 153°04'29"E, reef rock encrusted with red and green algal turf, 10.3 m depth, 10 Feb 2002, 1 specimen mounted for SEM (AM W33281.001); Cassini Island, fore-reef slope, 13°56'59"S, 125°37'15"E, 11 m depth, 17 Oct 2010, 1 specimen mounted for SEM (AM W41619.001). WESTERN AUSTRALIA. Cassini Island, fore-reef slope, 13°56’01”S, 125°37’09”E, hard coals, encrusting soft corals and hydroids, 12 m depth, 16 Oct 2010, 1 specimen (AM W41533); Ningaloo Reef, 22°45'24"S, 113°39'00"E, epifauna under rock, 15 m depth, 17 May 2009, 1 specimen (AM W41633). MEDITERRANEAN SEA. Spain, Málaga, Nerja, 36°44’28.85’’N 3°52’47.15’’W, Dec. 1982 - Aug. 1983, id. San Martín, 2003, several specimens ( MNCN 16.01/ 8927, 8928, 8936, 8938, 8948).

Morphologically similar species. Syllis ypsiloides Aguado , San Martín & Ten Hove, 2008. Indonesia, NE coast of Sumba, 09°57'S 120°48'E, sandy bottom, sponges and gorgonians, 50 m, 1.2 m Agassiz trawl, Snellius II, Sta. 4.068, 16 Sept. 1984, 1 paratype mounted for SEM ( ZMA V.Pol. 5266). Syllis picta n. comb. (see material studied below).

Description. Longest examined specimen incomplete, 20 mm long, 0.6 mm wide, with 66 chaetigers. Body robust, anterior segments pigmented with two thin black lines ( Fig. 9 A). Prostomium oval, wider than long, with two pairs of red eyes in trapezoidal arrangement ( Figs 9 A, 10A). Median antenna inserted on middle of prostomium, between anterior pair of eyes, with 15–16 articles ( Figs 9 A, 10A); lateral antennae shorter, inserted at anterior margin of prostomium, with 13–14 articles ( Figs 9 A, 10A). Palps triangular, longer than prostomium. Nuchal organs not seen. Peristomium shorter than subsequent segments ( Fig. 10 A). Dorsal tentacular cirri similar in length to median antenna, with 17–18 articles, ventral ones shorter with 14–15 articles ( Figs 9 A, 10A). Anterior dorsal cirri with 12–14 articles ( Figs 9 A, 10A); midbody and posterior dorsal cirri spindle-shape, shorter than anterior ones, with 6–8 articles ( Figs 9 B, F1). Small vesicles observed in some midbody cirri ( Fig. 9 F1). Anterior and midbody parapodia each with 6–8 bidentate, falciger chaetae. Bidentate blades with both teeth similar in length, and several spines on margin. Blades of dorsalmost falcigers longer than of ventralmost ones in anterior parapodia ( Fig. 10 B, C); spines of blades of midbody falcigers slightly larger than those of anterior falcigers ( Fig. 10 B–D). Midbody and posterior parapodia with 2–3 ypsiloid chaetae each, originating from fusion of blade and shaft, fusion line only distinguishable in some chaetae ( Figs 9 F2, 10E); some parapodia with one falcigerous chaetae with short unidentate blade. Four aciculae in each anterior parapodia, all of them distally curved; midbody with 2–3 aciculae per parapodium, one straight, one distally curved and one distally pointed; only one acicula in each posterior parapodia, straight or slightly curved at tip. Pharynx similar in length to proventricle, extending through 10–11 segments; conical tooth located on anterior margin. Proventricle through 12 segments with about 45 muscle cell rows.

Remarks. The most similar species to Syllis gracilis , are Syllis ypsiloides Aguado , San Martín & Ten Hove, 2008 and Syllis picta n. comb. Both S. ypsiloides and Syllis picta n. comb. differ from S. gracilis in the number per parapodium and shape of ypsiloid chaetae, since they only present one thin ypsiloid chaetae, with a clearly discernible fusion line (see Figs 9 F4, 10H–I, and Aguado et al. 2008), whereas S. gracilis presents two thick and well-fused ypsiloid chaetae ( Figs 9 F2, 10E). In addition, Syllis picta n. comb. differs from S. gracilis in body width, colour pattern and length of pharynx and proventricle (see description below and Figs 9–10 ). Syllis gracilis and S. picta n. comb present thick and short dorsal cirri on midbody segments, instead those from S. ypsiloides that are short and slender. Syllis gracilis and S. ypsiloides present two chaetae in midbody parapodia, but they both are ypsiloid in the former, whereas S. ypsiloides only has one ypsiloid chaetae and the other falcigerous. Syllis picta n. comb. always present three chaetae on midbody parapodia, two falcigerous and one ypsiloid.

Habitat. Coral rubble, algae.

Distribution. Apparently worldwide distributed. Australia (New South Wales, Queensland, Western Australia).

Figures

FIGURE 9. Syllis gracilis Grube 1840. A, anterior end, dorsal view. B, midbody segments, dorsal view. Syllis picta (Kinberg, 1866) n. comb. C, anterior end, dorsal view. D, midbody segments, dorsal view. E, posterior segments, dorsal view. F (1), S. gracilis mid-posterior parapodium. (2) mid-posterior ypsiloid chaetae. (3), S. picta midbody parapodium. (4) Midbody ypsiloid chaetae and two falciger chaetae.

FIGURE 10. Scanning Electron Micrographs: Syllis gracilis Grube 1840. A, anterior end, dorsal view. B, dorsalmost falciger chaeta, anterior parapodium. C, ventralmost falciger chaetae, anterior parapodium. D, falciger chaetae, midbody parapodium. E, ypsiloid chaetae, mid-posterior parapodium. Syllis picta (Kinberg, 1866) n. comb. F, anterior end, dorsal view. G, falciger chaetae, anterior parapodium; H, ypsiloid and falciger chaetae, midbody parapodium. I, ypsiloid and falciger chaetae, posterior parapodium.