Odontosyllis gymnocephala Hartmann-Schröder, 1965

Verdes, Aida, Pleijel, Fredrik & Aguado, Teresa, 2011, A new species of Odontosyllis Claparède, 1863 (Annelida, Syllidae) with re-descriptions of O. liniata Hartmann-Schröder, 1962 and O. gymnocephala Hartmann-Schröder, 1965, Zootaxa 3095, pp. 27-38 : 29-30

Odontosyllis gymnocephala Hartmann-Schröder, 1965

( Fig. 1 A–C)

Odontosyllis gymnocephala Hartmann-Schröder, 1965: 115 , figs. 43–45.

Material examined. American Samoa: holotype ( ZMH P- 14756). Tutuila, Matuu Bay; seagrass; 22 Oct 1959. Coll. G. Hartmann-Schröder.

Description. Holotype complete specimen, about 3 mm long, 0.3 mm wide, with 44 chaetigers; arched dorsally and flattened ventrally; without colour pattern, yellowish in alcohol. Prostomium rounded; four eyes in open trapezoidal arrangement. Antennae smooth, originating near anterior prostomial margin, close to each other, median antenna inserted slightly posterior to lateral ones, distinctly longer than combined length of prostomium and palps; lateral antennae shorter than central one. Palps shorter than prostomium, ventrally folded. First segment reduced dorsally. Occipital flap distinct, small, covering posterior margin of prostomium. Dorsal tentacular cirri smooth, elongated, similar to median antenna, ventral tentacular cirri shorter than dorsal ones. Dorsal cirri smooth and tapered distally, those of first chaetiger long, distinctly longer than body width, those of second and third chaetiger similar in length to body width, from fourth chaetiger onwards, shorter than body width. Ventral cirri oval, shorter than parapodial lobes. Parapodial lobes conical, with two small, distal pre- and postchaetal parapodial lobes. Chaetal fascicle with about 10–13 compound chaetae. Compound chaetae heterogomph, shafts with distal spines, blades short, bidentate, distal tooth larger than proximal one ( Fig. 1 A); blades of chaetae within fascicle slightly decreasing in length from dorsal to ventral blades; dorsal blades about 12 Μm length, ventral blades about 9.5 Μm long. Dorsal simple chaetae on posterior parapodia, slender, with thin spines on edge ( Fig. 1 B). Ventral simple chaetae not observed. Aciculae distally knobbed, ending with short terminal process ( Fig.1 C). Pharynx short, through four segments, number of teeth unknown (the holotype could not be dissected and the original description does not describe the structure of the pharynx). Proventricle short, through about five segments, muscle cell rows not visible through body wall. Pygidium lost.

Remarks. Specimen poorly preserved. Odontosyllis gymnocephala chaetae and aciculae are similar to those of O. australiensis , but this species has bidentate chaetae with both teeth of similar size, while O. gymnocephala has the distal tooth larger than the proximal one. Additionally, O. australiensis differs from O. gymnocephala in having a longer proventricle, through about eight segments. Odontosyllis gymnocephala chaetae and aciculae also resemble those of O. polycera ( Schmarda, 1861) , although in the latter species the blades are narrower and the distal tooth is larger. Furthermore, O. polycera has a long proventricle, through nine to ten segments, while O. gymnocephala has a short proventricle, through about five segments. Another species with similar chaetae is O. detecta . However, this species differs from O. gymnocephala in having distally rounded aciculae and lacking occipital flap.

Figures

FIGURE 1. Odontosyllis gymnocephala Hartmann-Schröder, 1965. Holotype ZMH P- 14756. A: Compound chaetae, midbody chaetiger (chaetae arranged dorso-ventrally from left to right); B: Dorsal simple chaeta, posterior chaetiger. C: Acicula, midbody chaetiger. Scale A – C 14 µm.