Odontosyllis brevichaetosa sp. n.

Figures 8–11; Table 1

Material examined. Project ' BioPol-NE'. State of Paraíba, Mataraca, Barra de Camaratuba (6°36.196'S 34°57.867'W), intertidal: 1 specimen (MZUSP 2817), coll. 12 August 2010. Baía da Traição, Praia do Farol (6°41.331'S 34°55.803'W), intertidal: 66 specimens (MZUSP 2813), coll. 0 9 August 2010. Rio Tinto, Barra de Mamanguape (6°46.140'S 34°55.025'W), intertidal: 47 specimens (MZUSP 2812), coll. 11 August 2010. João Pessoa, Cabo Branco (7°8.815'S 34°47.773'W), intertidal: 5 specimens (MZUSP 2811), coll. 0 2 February 2010. Conde, Praia de Jacumã (7°16.535'S 34°47.969'W), intertidal: 1 specimen (MZUSP 2818), coll. 29 January 2010. State of Pernambuco, Goiana, Praia de Pontas de Pedra (7°36.927'S 34°48.296'W), intertidal: 91 specimens (MZUSP 2819), coll. 13 December 2012. Ilha de Itamaracá, Ponta do Jaguaribe (7°4.243'S 34°49.291'W), intertidal: 7 specimens (MZUSP 2821), coll. 11 December 2012.

Type series. All specimens collected by the Project ' BioPol-NE '. State of Pernambuco, Goiana, Praia de Pontas de Pedra (7°36.927'S 34°48.296'W), intertidal: Holotype (MZUSP 2806), Paratype 1 (MZUSP 2807) and Paratype 7 (ZUEC-POL17003) collected 13 December 2012. State of Paraíba, Baía da Traição, Praia do Farol (6°41.331'S 34°55.803'W), intertidal: Paratype 2 (MZUSP 2808), Paratype 3 (MZUSP 2809), Paratype 4 (MZUSP 2810), Paratype 5 (ZUEC-POL17004), Paratype 6 (ZUEC-POL17005) and Paratype 8 (MNCN 16.01/16550), coll. 0 9 August 2010; Rio Tinto, Barra de Mamanguape (6°46.140'S 34°55.025'W), intertidal: Paratype 9 (MNCN 16.01/ 16551), coll. 11 August 2010.

Additional material examined. Odontosyllis australiensis Hartmann-Schröder, 1979 . Australia, Western Australia, Kimberley region: Lafontaine Is. (14°10'S 125°47'E), 15 m: 1 specimen (AM W28933), coll. P.A. Hutchings, 19 July 1988; reef south of Lucas Is., Brunswick Bay (15°16'S 124°29'E), 2 m; 1 specimen (AM W28932), coll P.A. Hutchings, 24 July 1988; Calliope R., Gladstone (23°51'S 151°10'E), silty sand, 5.6 m: 1 specimen (AM W198074), coll. P. Saenger, October 1980.

Description. Small to medium-sized body, largest specimen incomplete, 10.2 mm long, 0.8 mm wide, with 58 segments (Table 1). Live specimens without pigmentation, body beige after preservation. Palps distally rounded, basally fused (Fig. 8 A–D). Prostomium ovate with two pairs of eyes in rectangular to trapezoidal arrangement, anterior eyespots absent (Fig. 9 A); lateral antennae inserted on anterior margin of prostomium, about twice as long as combined length of palps and prostomium; median antenna inserted on middle of prostomium, between eyes, 1.5 times length of lateral antennae (Figs 8 A–F; 9A); nuchal organs as a broad semi-circular rows of cilia, from bases of lateral antennae to lateral borders of prostomium (Figs 8 D–F; 9A), bordering posterior margin of prostomium (Fig. 8 D, F). Peristomium dorsally reduced, with semi-circular occipital flap covering middorsal area of posterior prostomium (Figs 8 A–B, D–F; 9A), occipital flap with fringe of cilia on anterior boarder (Fig. 8 A–B, D, F); dorsal peristomial cirri slightly longer than median antenna, ventral peristomial cirri about same length as median antenna, inserted ventro-lateraly, close to mouth (Fig. 8 C). Chaetiger 1 with transverse row of cilia extending dorsally for short extension from bases of dorsal cirri (Fig. 8 A); midbody with lateral constrictions between chaetigers, with tufts of cilia ventrally at bases of cirrophores (Fig. 10 O) and a tuft of cilia in either side, anterior and posterior, of parapodial lobes (Fig. 8 G–H). Dorsal cirri of chaetiger 1 slighly longer than dorsal peristomial cirri (Fig. 8 B); dorsal cirri of chaetigers 2 and 3 ca. 1/2 and 2/3 as long as dorsal cirri 1, respectively; remaining dorsal cirri slightly shorter than dorsal cirri 2 (Fig. 8 A). Antennae, peristomial and dorsal cirri throughout with short cirrophores (Figs 8 A–G; 9A; 10A), cirrostyles distally tapering, alternating between long, similar in length to body width or slightly shorter, and short, ca. 2/3 as long as longer cirri. Ventral cirri rounded to ovate, slightly shorter than parapodial lobes (Fig. 8 C). Parapodial lobes conical, bilobed distally (Fig. 8 G). Anterior parapodia with 17–22 falcigers each (Fig. 10 C), midbody with 5–16, posterior parapodia with 8–14 falcigers each (Table 1); shafts of falcigers subdistally spinulated, with straight tips in anterior parapodia and in dorsalmost falcigers of each fascicle throughout; from midbody onwards, shafts of ventralmost falcigers subdistally inflated, sigmoid, with short, forward directed tips (Figs 9 C, E, I; 10B, D, F–G, J, M–N); ligament between shafts and blades spinulated, especially on mid- and posterior body chaetigers (Figs 9 C, E, I; 10G, J); blades of falcigers spinulated and bidentate, teeth of similar size on anterior and midbody parapodia, falcigers of posterior parapodia with subdistal tooth shorter, difference in length of teeth more conspicuous in ventral chaetae (Figs 9 C, E, I; 10B, D–L); blades with inverted dorso-ventral gradation in length, 6–17 µm long on anterior chaetigers, 5–16 µm long on midbody, 8–14 µm long on posterior chaetigers (Table 1). Dorsal simple chaetae beginning on chaetigers 2–24 (Table 1), thin, ca. 1/3 as thick as shafts of falcigers, slightly sigmoid, subdistally spinulated (Figs 9 G; 10B) with rounded tips; ventral simple chaetae only present in last chaetigers (Table 1), sigmoid, bidentate, subdistal tooth triangular, sligtly smaller than distal tooth, subdistally spinulated, about 1/2 as thick as shafts of falcigers (Figs 9 H; 10O). Anterior parapodia with 2–3 aciculae each, midbody with 1–2, each posterior parapodium with single acicula; aciculae subdistally enlarged, with collar of spines, and short, acute tip (Fig. 9 B, D, F). Pygidium not seen. Pharynx through 2–3 segments (Fig. 9 A; Table 1), trepan with six teeth and two lateral plates (Fig. 11 C); proventricle through 6–8 segments, with ca. 60 muscle cell rows (Figs. 9 A; 11A–B; Table 1).

Remarks. Odontosyllis brevichaetosa sp. n. is characterized by having short, bidentate falciger blades with inverted dorso-ventral gradation in length, and shafts of ventralmost falcigers from midbody parapodia onwards subdistally inflated, with sigmoid tip. At first glance, the pharynx of O. brevichaetosa sp. n. seems to lack denticles. In fact, they are very difficult to see, even after dissection, because they are covered by an opaque hood (Fig. 11 A–B).

Odontosyllis australiensis Hartmann-Schröder, 1979, from Australia, closely resembles O. brevichaetosa sp. n., in having an occipital flap of similar size, dorsal cirri with a similar pattern of alternation between long and short cirri along the body, falcigers with short, bidentate blades, with heavily spinulated ligament between shafts and blades, dorsal and ventral simple chaetae morphologically similar, same number of aciculae per parapodium throughout, and pharynx and proventricle of similar length. However, O. australiensis has one transverse row of cilia dorsally on each chaetiger, extending to parapodial lobes, falcigers with all shafts similar in shape and blades with teeth about same size throughout, and trepan with five teeth (San Martín & Huchings 2006). On the other hand, O. brevichaetosa sp. n. has a fringe of cilia on anterior border of peristomium and, except for chaetiger 1, dorsal rows of cilia are absent on chaetigers; falcigers with more sigmoid, subdistaly inflated shafts ventralwards, blades with distal tooth larger than subdistal one on posterior parapodia; and a trepan with six teeth.

Odontosyllis polycera (Schmarda, 1861) a widely reported species, with type locality in Table Bay, South Africa, resembles O. brevichaetosa sp. n. in the morphology of the falcigers and dorsal simple chaetae.

Nevertheless, it is a larger species, with proportionally larger occipital flap, covering most of the prostomium, and has up to 50 falcigers per parapodium on anterior body, blades of falcigers 23–15 µm long, and ventral simple chaetae with short subdistal tooth (San Martín & Huchings 2006). In contrast, O. brevichaetosa sp. n. has shorter occipital flap, 17–22 falcigers per parapodium on anterior body, blades of falcigers 5–16 µm long, and ventral simple chaetae with large subdistal tooth.

Odontosyllis brevichaetosa sp. n. differs from the other species of this genus occurring in Brazilian waters except for O. cf. fulgurans sensu Fukuda & Nogueira, 2006 in lacking dorsal colour patterns. However, Odontosyllis cf. fulgurans, has falcigers with longer, bidentate blades throughout, with teeth of similar size.

In addition to the presence of color patterns, O. guarauensis has longer and ciliate palps; shorter and proportionally stouter antennae and dorsal cirri throughout; roughly rectangular occipital flap, almost as wide as the prostomium, covering posterior and, sometimes, the anterior pairs of eyes; shafts of dorsalmost falcigers with subdistal, nearly triangular enlargement and thin, straight tip (see Fukuda et al. 2013, Figs 4 C–D; 7E, G); aciculae irregularly enlarged distally; and trepan with nine teeth (Fukuda et al. 2013). Odontosyllis aracaensis has a characteristic distribution of body ciliation, shafts of falcigers with straight tips and thinner and elongated blades, and characteristic aciculae, subdistally enlarged and slightly spinulated, sometimes with short, acute tip (Fukuda et. al. 2013); Odontosyllis guillermoi has 28 and 20 falcigers on each anterior and midbody parapodium, respectively, falcigers with sharp and slightly shorter subdistal tooth on anterior chaetigers, much shorter from midbody onwards, and a pharynx extending for 9–10 chaetigers.

Distribution. Atlantic Ocean: only know from off the northern coast of Paraíba, northeastern Brazil.

Etymology. The species epithet refers to the characteristic short size of the blades of falcigers.