Syllis setoensis ( Imajima, 1966 )

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 : 321-324

Syllis setoensis ( Imajima, 1966)

Figures 12 , 13

Typosyllis setoensis Imajima, 1966: 284 , Fig. 62 A–L.— Licher 1999: 124, Fig. 56 A–F. Syllis setoensis Aguado et al., 2008: 33 .

Material examined. Non-type material. AUSTRALIA. WESTERN AUSTRALIA. Woodside Kimberley Survey, 2009–2010: Cassini Island, lower mid-littoral reef platform, 13°57'06"S, 125°37'27"E, 3 m depth, 18 Oct 2010, 1 specimen mounted for SEM (AM W41605.001); Montgomery Reef, mid-littoral lower terrace, 16°01'14"S, 124°09'33"E, coral rubble with Sargassum sp., intertidal, 23 Oct 2009, 1 specimen (AM W42462); Long Reef, mid-littoral lower terrace, 13°49'11"S, 125°46'48"E, coral rubble and algae, intertidal, 23 Oct 2010, 1 specimen (AM W42528); Adele Island, sublittoral fore-reef slope, 15°34'49"S, 123°09'26"E, coral and algae, 12.6 m depth, 18 Oct 2009, 1 specimen (AM W42529). Bush Bay, 30 km south of Carnarvon, 25°10'S, 113°39'E, in algal lumps on shallow sand flats, intertidal, 6 Jan 1984, 1 specimen, (AM W46283). Off south end of Long Island, 28°28'48"S, 113°46'18"E, dead coral and algae, 4–5 m depth, 25 May 1994, 1 specimen (AM W46287). PHILIPPINES. LUZON ISLAND. “Koala Point”, Balayan Bay, 13º41'51"N, 120º49'45"E, coral rubble, 5–16 m depth, 5 Dec 2010, 1 specimen ( MCZ 25418); “Sepok Wall”, between Balayan Bay and Batangas Bay, 13º41'02"N, 120º53'45"E, coral rubble, 6–13 m depth, 10 Dec 2010, 1 specimen ( MNCN 16.01/16870).

Morphologically similar species. Syllis krohni : SPAIN. Nerja, Málaga, calcareous algae, 14 Jun 1983, 1 specimen ( MNCN 16.01/8180). Typosyllis (Typosyllis) krohnii . AUSTRALIA. QUEENSLAND. Heron Island, North Reef, coralline sand, 4 Feb 1976, coll. and id. G. Hartmann-Schröder, 13 specimens ( HZM P- 21006), NEW ZEALAND. Kermadec Biodiscovery Expedition, 2011: Kermadec Islands, Raoul Island, “Fishing Rock” landing, 29°15'03"S, 177°54'12"W, algal turf, 1 m depth, 18 May 2011, 7 specimens (AM W42886).

Description. Longest examined specimen incomplete, 6 mm long, 0.8 mm wide, with 60 chaetigers. Body relatively robust anteriorly, slender from midbody, without colour pattern ( Figs 12 A, 13A–B). Prostomium oval, wider than long, with two pairs of red eyes in trapezoidal arrangement and 2 anterior eyespots ( Figs 12 A, 13A–B). Median antenna inserted on middle of prostomium, between anterior pair of eyes, longer than combined length of prostomium and palps, with 30–32 articles ( Figs 12 A, 13B); lateral antennae shorter, inserted at anterior margin of prostomium, with 25–27 articles (small specimens with fewer articles in antennae and cirri, Fig. 12 A). Palps triangular, longer than prostomium ( Fig. 12 A). Nuchal organs not seen. Peristomium shorter than subsequent segments ( Fig. 12 A), in larger specimens forming a small lobe partly covering posterior part of prostomium ( Fig. 13 B). Dorsal tentacular cirri similar in length to median antenna, with 32–34 articles, ventral ones shorter with 24– 26 articles ( Fig. 12 A). Dorsal cirri of chaetigers 1, 4, 6, 9, 11 distinctly thickened ( Figs 12 A, 13A–C); midbody dorsal cirri alternating long (longer than body width) and short (shorter than body width); long dorsal cirri slightly thicker than short dorsal cirri ( Fig. 12 A). Anterior dorsal cirri (except those of anteriormost chaetigers) with 30–33 articles. Midbody and posterior dorsal cirri shorter, with 23–25 articles. Antennae and tentacular cirri spindleshaped, thicker than dorsal cirri. Anterior and midbody parapodia each with 8–10 bidentate, falciger chaetae. Blades bidentate, with proximal tooth smaller than distal one, with dorsoventral gradation in length (34–21µm on anterior parapodia; 30–20 µm on midbody parapodia), short spines on edge, shafts with short distal spines ( Figs 12 B–C, 13D–E). Posterior parapodia with 8–9 compound chaetae; blades hooked, bidentate, shorter than those of anterior parapodia, almost all similar in length (22 µm dorsalmost, to 20 µm ventralmost), with acute distal tooth, small proximal tooth, and short spines on edge ( Figs 12 D–E, 13F–G); ventralmost chaetae short, some unidentate ( Fig. 12 F–G); shafts of ventralmost posterior compound chaetae smooth, with a marked spur ( Figs 12 E, 13F–G). Four aciculae in each anterior parapodium, one straight, one distally curved and two distally blunt ( Fig. 12 F), decreasing in number to three aciculae in each midbody parapodium, one distally knobbed, one curved at tip and one larger, straight acicula ( Fig. 12 G); posterior parapodia with 1–2 aciculae each, distally pointed, tip slightly oblique ( Fig. 12 H). Pharynx longer than proventricle, extending through 11 segments; conical tooth located on anterior margin. Proventricle through 7 segments with about 57 muscle cell rows ( Fig. 12 A).

Remarks. The morphology of our specimens agreed with that of Licher’s (1999) redescribed paratype material, except for the length of the specimens (up to 26.4 mm long, 110 chaetigers) and the number of aciculae in each anterior parapodium (3 in the specimens revised by Licher (1999), 4 in our study). The most similar species to Syllis setoensis is S. krohni Ehlers 1864 , which has been reported worldwide. Both species are characterized by having distinctly thickened dorsal cirri in some of the anterior segments, and posterior compound chaetae with distinctly enlarged shafts, distally curved spurs, and short, hooked blades. The two species are distinguished by the form of their compound chaetae, mostly unidentate in S. krohni and mostly bidentate in S. setoensis . Furthermore, while S. setoensis lacks any colour pattern, S. krohni has a distinctive colour pattern (see Fauvel 1923; San Martín 2003).

Habitat. Coral rubble, algae.

Distribution. Japan, New Zealand, Australia (Queensland, Western Australia).

Figures

FIGURE 12. Syllis setoensis (Imajima, 1966) (AM W 46287). A, anterior end, dorsal view. B, falciger chaetae, anterior parapodium; C, falciger chaetae, midbody parapodium; D, dorsalmost falciger chaetae, posterior parapodium. E, ventralmost falciger chaetae, posterior parapodium; F, aciculae, anterior parapodium; G, midbody aciculae; H, aciculae, posterior parapodium. Scale: A, 0.2 mm. B – H, 20 µm.

FIGURE 13. Syllis setoensis (AM W 41605). A, anterior end, dorsal view; B. prostomium, dorsal view. Scanning Electron Micrographs: C, anterior end, dorsal view; D, falciger chaetae, anterior parapodium; E, falciger chaetae, midbody parapodium; F, falciger chaetae, posterior parapodium; G, ventralmost falciger chaetae, posterior parapodium.