Syllis ypsiloides, Aguado, Teresa, Martín, Guillermo San & Ten, Harry A., 2008

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, Zootaxa 1673, pp. 1-48 : 36-39

Syllis ypsiloides n. sp.

Figs 16–18

Material examined. Holotype ZMA V.Pol. 5265, Indonesia, Teluk Ambon, near Tawiri, 03°42'S 128°07'E, sandy bottom with Acropora and sponges, 1–5 m, Snellius II, Sta. 4.010, 6 Sept. 1984; paratype (mounted for SEM) ZMA V.Pol. 5266, 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; 2 Paratypes ZMA V.Pol. 1988.01, 1988.02 (as Syllis gracilis ), Indonesia, Lesser Sunda Isl., Bay of Bima, near south fort, trawl, dredge, muddy bottom with coral sand, 55 m, Siboga Expedition, Sta. 47, 8/ 12 April 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).

Description. Holotype incomplete 17 mm long, 0.5 mm wide, with 113 segments; best preserved paratype incomplete 43 mm long, 0.3 mm wide, with 56 segments. Prostomium wider than long, with two pairs of eyes in trapezoidal arrangement, anterior ones larger than posterior pair. Median antenna with 17 articles, inserted on middle of prostomium, slightly longer than combined length of prostomium and palps; shorter lateral antennae with 11 articles, inserted on anterior margin of prostomium. Palps triangular, similar in length to prostomium ( Figs 16 A, 17A, B), fused at base, with distinct median groove. Peristomium shorter than subsequent segments, with two pairs of tentacular cirri. Nuchal organs not seen. Dorsal tentacular cirri longer than lateral antennae, with 18 articles, ventral ones with 13 articles. Anterior-most dorsal cirri with 10– 13 articles ( Fig. 16 A). Midbody and posterior dorsal cirri segments spindle shaped, shorter than anterior ones, with six to eight articles ( Fig. 18 B). Ventral cirri short, globular, inserted proximally on parapodia, not extending beyond parapodial lobes ( Fig. 16 G). Anterior parapodia each with six compound, heterogomph chaetae, distal part of shafts provided with spines. Bidentate blades, dorsoventrally decreasing in length (ca. 30 µm dorsal-most, ca. 18 µm ventral-most), moderate long spines on edge of blade ( Figs 16 B, 17D–F, 18A). Midbody chaetigers with four to five compound chaetae. Blades bidentate, shorter than those present on anterior chaetigers (ca. 25–12 µm), decreasing towards posterior chaetigers. Spines short, gradually decreasing in number and length posteriorly, proximal tooth also decreasing in size becoming almost unidentate. Midbody to posterior chaetigers with two chaetae, one dorsal, ypsiloid simple chaeta originated from fusion of blade and shaft, fusion line barely distinguishable; and one compound ventral chaeta with short unidentate blade (ca. 14 µm), smooth on edge ( Figs 16 E, 18B–D). Posterior-most chaetigers with only one ypsiloid simple chaeta, fusion line barely visible ( Fig. 16 H). Two acuminate aciculae per parapodium ( Figs 16 C, D, 17D). Pygidium conical ( Fig. 16 F), two anal cirri with eight articles (in paratype). Pharynx similar in length to proventricle; tooth on anterior margin. Proventricle extending through nine segments, with about 40 cellrows, median longitudinal line visible ( Fig. 16 A).

Remarks. There are several species sharing these morphological characters such as spindle shaped, short (less than body width) dorsal cirri and bidentate compound chaetae on anterior chaetigers, which change in shape and length towards the posterior part of the body. Syllis gracilis and S. magellanica both too have ypsiloid simple chaetae from midbody to posterior parapodia. Syllis ypsiloides n. sp., has one ypsiloid simple chaeta and one compound ventral chaeta, whereas two ypsiloids are present in S. gracilis . Besides, the ypsiloid simple chaetae of S. gracilis do not show a fusion line, which is always present in S. ypsiloides n. sp. This line reveals that the simple (not-compound) chaetae evolved from a fusion process between the blade and shaft, in a similar way as was proposed for the simple chaetae present in Haplosyllis anthogorgicola Utinomi, 1939 (Martin et al., 2002) and in H. loboi Paola, San Martín & Martin 2006 ( Paola et al., 2006) . Syllis magellanica has several compound and ypsiloid chaetae on each posterior parapodia, the latter also showing a fusion line. Another similar taxon is S. gracilis australiensis Hartmann-Schröder, 1979 , described from Western Australia and New South Wales. It was later synonymised with S. gracilis by Licher (1999) but we consider that this species might be a valid taxon that should be re-described. Syllis gracilis australiensis is similar to S. ypsiloides n. sp. in having only one ypsyloid chaeta in addition to one compound on posterior chaetigers ( Hartmann-Schröder, 1979). However, it is different principally because the ypsiloid chaetae has spines on the verge while they are completely smooth in S. ypsiloides n. sp., and the anterior compound chaetae have a longer and thinner proximal tooth.

The simple chaetae of S. ypsiloides n. sp. may be related to the habitat in which the species occurs (sponges and corals), as several authors have suggested that acquisition of simple chaetae may be an adaptation to such a symbiotic way of life, as these stout blades could be useful for attachment to the host ( Martin & Britayev, 1998). However, such an eco-morphological relationship between shape and function seems difficult to establish without additional research ( Musco & Giangrande, 2005).

Distribution. Indonesia.

Etymology. The specific name refers to the ypsiloid chaetae present in the posterior parapodia.

Figures

FIGURE 16. Syllis ypsiloides n. sp. Holotype ZMA V. Pol. 5265. A: Anterior part, dorsal view; B: Anterior chaetae; C: Anterior aciculae; D: Posterior aciculae; E: Posterior chaetae; F: Posterior part, dorsal view; G: Posterior parapodium, anterior view; H: Most posterior chaeta. Scale A, F: 0.2 mm; B: 5 µm; C – E, H: 20 µm; G: 48 µm.

FIGURE 17. Syllis ypsiloides n. sp. Paratype ZMA V. Pol. 5266. SEM. A: Anterior part, dorsal view; B: Prostomium, dorsal view; C: Posterior part, dorsal view; D: Anterior parapodia, dorsal view; E; F: Anterior chaetae.

FIGURE 18. Syllis ypsiloides n. sp. Paratype ZMA V. Pol. 5266. SEM. A: Anterior chaeta; B: Posterior parapodia, dorsal view. C, D: Posterior chaetae.