Orbinia sagitta Leão & Santos, 2016, n. sp.

Orbinia sagitta n. sp.

Figures 2 A–B; 3 A–F

Type material. Total: 11 specimens. Holotype: Hab. 6; CANAC 6; Repl. 2; Stratum 2–5 (MNRJ /P769), 21º 50′S 40º 5″W. Depth: 400 m. Paratypes: Hab. 6; CANAC 6; Repl. 2; Stratum 2–5 (10 spec., MNRJ /P770), 21º 50′S 40º 5″W. Depth: 400 m.

Diagnosis. Prostomium short and conical; 13–17 thoracic chaetigers. Branchiae from chaetiger 5. Abdominal neuropodia bilobate. Translucent spine in abdominal notopodia. Furcated chaetae absent.

Description. Complete specimens ranging from 11 to 24 mm in total length with 39 to 67 chaetigers. Holotype complete, with 52 chaetigers, total length 20 mm. Prostomium short and conical (Fig. 2 A), 0.15 in width and 0.1 in height. Peristomium with one achaetous ring. Chaetigers 1–3 22 mm in length. First abdominal chaetiger 3 mm wide.

Thorax depressed dorsoventrally, subcylindrical, with 16 chaetigers. Branchiae ligulate from chaetiger 5 (Figs 2 A; 3A). Thoracic post-chaetal notopodial lobe elongate, conspicuous from chaetiger 1 (Fig. 3B); one post-chaetal neuropodial thoracic lobe visible from chaetiger 1 (Fig. 3B). Abdomen cylindrical. Abdominal notopodia with one post-chaetal lobe (Fig. 3C); abdominal neuropodia bilobate, dorsal lobe longer than ventral lobe (Fig. 3C).

Thoracic notochaetae with crenulated capillaries (15–20 per bundle); abdominal notochaetae crenulated capillaries (6–8 per bundle), with one translucent spine in alternate parapodia, showing a central channel (Fig. 3D). Thoracic neurochaetae with four rows of uncinate spines accompanied by crenulated capillaries (5–7); abdominal neurochaetae crenulated capillaries (4–5) and one smooth acicular spine. Pygidium bilobed with two cirriform appendages.

Etymology. The species name “ sagitta ” refers to the long, translucent spine in the abdominal notopodia.

Occurrence. Southeast Brazil. Depth: 400 m.

Remarks. The long and translucent spine present in alternate thoracic parapodia distinguishes O. sagitta n.sp. from all other Orbinia species. However, the presence of branchiae from chaetiger 5 is similar to Orbinia latreilli (Audouin & Milne Edwards 1833), reported from La Rochelle (Western France), the Gulf of Naples (Southwestern coast of Italy) and also recorded in Brazil (Southeastern coast). Nevertheless, O. latreilli exhibits a lateral flange and furcate chaetae, both lacking in O. sagitta n.sp. Orbinia sagitta n.sp. was found at a depth of 400 m and Orbinia latreilli at shallow depths and intertidal regions (Fauvel, 1927; Parapar et al., 1993). According to Blake (1996), most species of Orbinia are either intertidal or from shallow waters and have not been recorded from greater depths as observed for Orbinia sagitta n. sp. and O. camposiensis.