Syllis
Creators: name: Aguado, Teresa
name: Martín, Guillermo San
name: Ten, Harry A.
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Polychaeta
Phyllodocida
Syllidae
Syllis

description: Syllis sp. 2
Fig. 20
Material examined. 1 spec. ZMA V.Pol. 1986.01 (as S. brachychaeta), Indonesia, 5º56.7´N 126º25´E, 0–36 m, Siboga Expedition, Sta. 133, 25/ 27 July 1899.
Comparative material examined. Syllis gracilis. 1 syntype MPW395, Mediterranean Sea, Adriatic Sea; several spec. MNCN 16.01/ 8927, 8928, 8936, 8938, 8948, Spain, Málaga, Nerja, 36º44’28.85’’N 3º52’47.15’’W, Dec. 1982 - Aug. 1983. (identified by San Martín, 2003).
Syllis armillaris. Several spec. MNCN 16.01/7906-07, Spain, Almería, Cabo de Gata, 2 m, 36º46’49.11’’N 2º14’25.31’’W, Jan. 1987. (Identified by San Martín, 2003).
Description. Complete specimen 6.5 mm long, 0.5 mm wide, with 96 segments. Strongly pigmented red. Prostomium wider than long, with two pairs of eyes in trapezoidal arrangement, anterior ones slightly larger than posterior. Median antenna inserted on middle of prostomium, similar in length to combined length of prostomium and palps, with 19 articles; lateral antennae shorter, inserted on anterior margin of prostomium, with 11 articles. Palps triangular, longer than prostomium, fused at base, with distinct median groove (Fig. 20 A). Peristomium shorter than subsequent segments, with two pairs of tentacular cirri. Dorsal tentacular cirri longer than lateral antennae, with 17 articles, ventral ones with 10–11 articles. Dorsal cirri of most anterior segments with 25–26 articles. Midbody and posterior dorsal cirri shorter than anterior ones, varying slightly in length, alternately with 10 and 8 articles (Fig. 20 A). Ventral cirri digitiform, inserted proximally to parapodia, not extending beyond parapodial lobes (Fig. 20 K). Anterior parapodia with ten compound, heterogomph chaetae, distal part of shafts provided with spines. Blades bidentate, decreasing in length (ca. 23 µm dorsal-most, ca. 18 µm ventral-most), long spines on edge (Fig. 20 B). Midbody parapodia with five compound chaetae, blades bidentate, shorter than those of anterior chaetigers (ca. 15–13 µm), gradually decreasing in length posteriorly (ca. 11–9 µm), and shafts becoming thicker (Fig. 20 D). Spines on margin short, decreasing posteriorly in number, proximal tooth also decreasing in size to become almost unidentate (Fig. 20 D). Posterior chaetigers with three to four compound unidentate chaetae, blades short with distal end curved and proximal edge large, more developed than those of anterior chaetigers, short and thin spines on edge (Fig. 20 F). Shafts large and strong, distal end curved. Blades and shafts on posterior chaetae in close contact but not fused (Fig. 20 F); dorsal-most blade smallest, and more clearly separated from shaft than ventral-most (Fig. 20 F). Posterior chaetigers with one dorsal simple chaeta, straight and weakly bidentate (Fig. 20 G), and one ventral simple bidentate chaeta, slightly curved distally (Fig. 15 H). Two acuminate aciculae per parapodium (Figs 20 C, E, I). Pygidium conical, two anal cirri with 18 articles (Fig. 20 J). Pharynx extending through eight segments; conical tooth on anterior margin. Proventricle extending through nine segments, cell-rows difficult to distinguish (Fig. 20 A).
Remarks. Syllis sp. 2 is principally characterized by the shape of the posterior compound chaetae, considerably shorter than the anterior ones, tending to an ypsiloid condition, although blades are never fused with the shafts. Syllis sp. 2 is similar to Syllis gracilis and other species having ypsiloid chaetae in midbody to posterior parapodia, originating from enlarged shafts fused with blades, and having short, spindle-shaped dorsal cirri. Syllis gracilis has only two large ypsiloid chaetae (with fused blades) on midbody to posterior parapodia. In addition, the posterior compound chaetae of Syllis sp. 2 have an unusual inverse gradation in length, the dorsal blades being more slender and shorter than the ventral ones (Figs 20 F, K). Syllis armillaris presents in midbody to posterior parapodia compound chaetae with short, unidentate blades never fused. Syllis mayeri is another similar species, but its anterior dorsal cirri are longer, the spines of the blades in anterior chaetae are shorter and one of the two midbody aciculae is larger (Musco & Giangrande, 2005). Also the compound chaetae exhibit the common condition of gradation in size and length with longer blades dorsally, shorter ones ventrally. Other similar species are S. magellanica, which presents ypsiloid chaetae together with compound chaetae, and S. ypsiloides n. sp. (see remarks of that species in this study).
The specimen is a complete adult, and is different from other species of the genus. Syllid species with simple chaetae formed from a fusion process between shaft and blade occur in different body regions. We cannot exclude the possibility that a specimen may undergo such a fusion process only later in life. Thus not knowing the possible range of variation in this case, we are of the opinion that this single specimen better should not be formally named as a new species unless additional material is found.
Distribution. Indonesia.
description: Published as part of Aguado, Teresa, Martín, Guillermo San & Ten, Harry A., 2008, Syllidae (Annelida: Polychaeta) from Indonesia collected by the Siboga (1899 – 1900) and Snellius II (1984) expeditions, pp. 1-48 in Zootaxa 1673 on pages 41-43, DOI: 10.5281/zenodo.180233