Syllis khronii Ehlers 1864

Syllis khronii Ehlers, 1864

Figure 7

Syllis krohnii Ehlers, 1864: 233, pl. 10, figs 1–4. San Martín 2003: 386, figs 211, 212. Typosyllis (Syllis) krohnii. Langerhans 1879: 529, fig. 2.

Typosyllis krohnii. Langerhans 1881: 102. Campoy 1982: 430, pls 53, 54. Typosyllis krohni. Licher 1999: 205, pl. 87.

Syllis (Typosyllis) krohnii. Fauvel 1923: 259, figs 96 a–e.

Typosyllis (Typosyllis) krohni. Hartmann-Schröder 1991: 28 (in part).

Material examined. AUSTRALIA, QUEENSLAND: Heron Island, North Reef, coralline sand, 4 February 1976, coll. and id. G. Hartmann-Schröder, HZM P-21006, 13 specimens.

Additional material. 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, 18 May 2011, AM W.42886, 7 specimens. SPAIN. Nerja, Málaga, calcareous algae, 14 June 1983, MNCN 16.01 /8180, 1 specimen.

Description. Longest Australian specimen, complete, 25 mm long, 1.5 mm wide, with 84 chaetigers. Body robust, large; without colour in examined Australian specimens. Prostomium oval; 4 eyes in trapezoidal arrangement. Palps robust, slightly longer than prostomium (Fig. 7 A). Median antenna arising slightly in front of posterior eyes, with about 25 articles, slightly longer than combined length of prostomium and palps; lateral antennae about 2/3 the length of median one, with about 18 articles. Peristomium slightly shorter than subsequent segments (Fig. 7 A). Dorsal tentacular cirri similar in length to median antenna, with about 25 articles; ventral tentacular cirri about 2/3 as long as dorsal ones. Dorsal parapodial cirri of anterior segments alternating long, thick, inflated, with numerous short articles, and shorter, not inflated, with fewer articles (Fig. 7 A); dorsal parapodial cirri of chaetigers 1, 3, 6 markedly inflated, with about 50, 35, and 33 articles respectively. Anterior non inflated dorsal parapodial cirri shorter than body width, with 20–25 articles. Remaining dorsal parapodial cirri relatively short, alternating longer and shorter. Ventral parapodial cirri digitiform. Compound chaetae heterogomph falcigers, slightly bidentate anteriorly (Fig. 7 B), becoming almost unidentate progressively in midbody (Fig. 7 C) and clearly unidentate in posterior parapodia (Fig. 7 D); shafts gradually thicker as more posterior, with a more pronounced “spur”, especially in ventral ones (Fig. 7 B–D). Anterior parapodia each with 18 compound chaetae, blades 36 µm long above, 26 µm long below (Fig. 7 B); midbody parapodia with 12 compound chaetae each, blades 33 µm long above, 28 µm long below (Fig. 7 C); posterior parapodia with 9–10 compound chaetae each, with blades 32 µm above, 27 µm below (Fig. 7 D). Dorsal and ventral simple chaetae not seen. Each anterior parapodium with 6–7 aciculae (Fig. 7 E), number diminishing progressively backwards to 4 in midbody (Fig. 7 F), and 2 in posteriormost parapodia, one acute and the other distally blunt (Fig. 7 G). Pharynx wide, extending through about 7 segments; large pharyngeal tooth near anterior margin of pharynx (Fig. 7 A). Proventricle through 9–10 segments, with about 32–36 muscle cell rows. Pygidium with 2 anal cirri, and a median stylus.

Remarks. This species is characterized by having long, inflated dorsal cirri alternating with normal, noninflated, dorsal cirri on anterior segments, posterior compound chaetae unidentate (occasionally some slightly bidentate) and somewhat hooked, with enlarged shafts; and a distinct colour pattern of transversal red bands on anterior segments (Fauvel 1923; San Martín 2003), not seen in Australian specimens. Colour can be easily lost after fixation and so, we confirm Hartmann-Schröder’s report of this species in Australia (except for one of the specimens, see Álvarez-Campos et al. 2015a).

The most similar species in the Pacific is Syllis setoensis (Imajima, 1966), from Japan, Indonesia, New Zealand and Australia, but this species has posterior compound chaetae bidentate, and a few with unidentate blades (see Álvarez-Campos et al. 2015a).

Habitat. Widely distributed in different habitats: algae, seaweeds, coralline crustose algae, sand, from intertidal to sublittoral.

Distribution. North Atlantic Ocean, from the North Sea to South Africa. Mediterranean Sea. Also reported from the Red Sea, Indian Ocean, NE Australia, New Zealand.

Scale bars: A: 0.4 mm. B–G: 20 µm.