Syllis terraeignium Soto & Martín & Lucas 2020, new species

Syllis terraeignium new species

Figures 5, 6

Material examined. Holotype (MNCN 16.01 /18726). Station 36, 1 Paratype (MNCN 16.01 /18727) and 2 specimens (SEM). St. 36, 2 specimens (LBUV 003 /2020). St. 50, 3 specimens (LBUV 004 /2020). Dates of collections: 5 November 2010 (St. 36) and 8 November 2010 (St. 50). Coordinates: St. 36 54º57´30.9” S 70º44´41.0” W, St. 50 55º08´39.4” S 68º49´34.0” W.

Description. Body elongated, robust, with wide, well-marked segments anteriorly (Figs 5A; 6A, B), abruptly tapered from midbody backwards, white to yellowish, without color pattern (Fig. 6A, B). Holotype complete, 10 mm long, 0.9 mm wide, 77 chaetigers. Prostomium almost circular, with two pairs of small eyes in open trapezoidal arrangement; median antenna longer than prostomium and palps together, inserted between posterior eyes, near posterior margin of prostomium, with about 24 articles; lateral antennae inserted in front of anterior eyes, near anterior margin of prostomium (Figs 5A; 6 A–D), shorter than median antenna, with 15 articles. Peristomium distinctly shorter than subsequent segments (Figs 5A; 6D); dorsal tentacular cirri similar in length to median antenna, with 24 articles; ventral tentacular cirri shorter than dorsal ones, with 11 articles. Dorsal cirri shorter than body width, more or less fusiform on anterior segments, elongated from midbody (Figs 5A, B; 6C, D); anterior dorsal cirri somewhat longer than remaining, with about 27-13-22-18-17 articles, on first five chaetigers; dorsal cirri of proventricular segments with 23–16 articles; midbody dorsal cirri elongated, alternating long ones with 25 and shorter ones, with 15 articles (Fig. 5B). Parapodia conical, distally slightly bilobed; ventral cirri digitiform. Compound chaetae heterogomph falcigers with elongated, slender bidentate blades, proximal teeth small, distinctly smaller than distal ones, and short spines on margin, similar throughout, with slight antero-posterior gradation and marked dorsoventral gradation in length, more marked on anterior segments.Anterior parapodia each with 10–12 compound chaetae, blades 57–58 µm above, 26–27 µm below (Fig. 5C); midbody parapodia each with 8–10 compound chaetae, blades similar to those of anterior segments but more distinctly bidentate (Figs 5D; 6E); posterior parapodia each with six compound chaetae, blades 26 µm above, 24 µm below (Fig. 5E), finely bidentate. Solitary dorsal capillary chaetae on posterior parapodia, slender, minutely bidentate, with minute subdistal serrations (Figs 5F; 6F); ventral simple capillary chaetae on far posterior segments, more distinctly bidentate than dorsal one (Fig. 5G). Anterior parapodia with four slender, pointed aciculae (Fig. 5H), two on midbody parapodia, distinctly thicker (Fig. 5I), and single in posterior parapodia, thicker than anterior and midbody ones, distally pointed (Fig. 5J). Pharynx through 11 segments; pharyngeal tooth conical, on anterior margin (Fig. 5A). Proventricle longer than pharynx, through 15 segments, with 43–45 muscle cell rows, without midline (Fig. 5A). Pygidium small, with two short anal cirri, with 11–17 articles.

Distribution. Only known from Chilean Patagonia. Concepción channel, Drumond Hay island, Ballenero channel: Magellan Strait and Ponsonby sound, Beagle channel (Fig. 1).

Habitat. Inside tubes (non-empty and empty) of Chaetopterus cf. variopedatus, from boulders and sediment bottoms and associated to M. pyrifera holdfasts in fjords, islands and channels from Chilean Patagonia. Salinity: from 30.2 to 35 PSU, temperature: from 8.5 to 8.9°C. Shallow subtidal, between 14 and 30 meters depth.

Type locality. Concepción channel, Drumond Hay island, southern Chile (Patagonia).

Remarks. Syllis terraeignium n.sp. is characterized by its robust body, with short dorsal cirri, compound chaetae with elongated, slightly bidentate blades, and pointed, straight acicula on posterior parapodia. Syllis albanyensis (Hartmann-Schröder 1984) from Australia, has similar body and elongated blades, but the posterior acicula are bent at right angle and the dorsal simple chaetae are truncated (Hartmann-Schröder 1984; San Martín et al. 2017b). Syllis lunaris (Imajima 1966), from the Pacific Ocean, occurying from Japan to Australia, has similar chaetae and acicula, but the dorsal cirri are much longer and the proventricle is much shorter (Imajima 1966; San Martín et al. 2017b). Syllis crassicirrata (Treadwell 1925) also has a robust body with long proventricle, but the dorsal cirri are much thicker and longer, the chaetae are more distinctly bidentate and the acicula protrudes out from the parapodial lobes; furthermore, it is a brightly colored species (Álvarez-Campos et al. 2015b; Ba-Akdah et al. 2018). The compound chaetae of Syllis terraignium n. sp. are very similar to those of Syllis pallida Verrill, 1875, but the proventricle is shorter and the posterior aciculae are acuminate (San Martín 1992). Syllis antarctica (Averincev 1972), from Antarctica and deep areas in the Pacific Ocean, has very similar compound chaetae, but the dorsal cirri are shorter, the body is pigmented with a brown-chocolate color, and the aciculae protrudes out from parapodial lobes (San Martín 2004). Syllis nigricirris Grube, 1863 from Mediterranean and Madeira also has similar compound chaetae, but the dorsal cirri are longer and pigmented, and the aciculae protrude out from parapodial lobes (Licher 1999). Finally, Syllis alternata Moore, 1908, an apparently worldwide distributed species, has also similar compound chaetae, and straight, pointed aciculae, but it is a much longer species, with dorsal cirri very long and the aciculae protrude out from parapodial lobes (Licher 1999; San Martín 2003).

Etymology. This species is named after “Tierra del Fuego’’ island, from Latin Terra (land) and Ignis (fire). Syllis terraeignium was mainly found in shallow waters of Magellan Strait and Beagle Channel that surround this island, which is located in the South America southern point.