Petta alissoni Nogueira & Ribeiro & Carrerette & Hutchings 2019, n. sp.

Petta alissoni n. sp.

(Figs 8–12, Table 2)

Material examined. Holotype (ZUEC Pol 7891): coll. state of São Paulo, 24°21'S 44°10'W, 10 Jan 1998, 258 m. Paratype 1 (ZUEC Pol 7880): coll. state of Rio de Janeiro, 23°09'36”S 40°57'00”W, 01 Mar 1998, 257 m. Paratypes 2–5 (ZUEC Pol 7882 and 21341–21343): coll. state of Rio de Janeiro, 23°36'30”S 42°10'00”W, 16 Feb 1998, 187 m; paratype 2 (ZUEC Pol 21343) mounted on SEM stub, paratype 5 (ZUEC Pol 21342) dissected, some notochaetae and uncini mounted on microscope slide. Paratype 6 (ZUEC Pol 7892): coll. state of São Paulo, 24°07'36”S 45°52'00”W, 09 Jan 1998, 147 m. Paratype 7 (ZUEC Pol 7890): coll. state of São Paulo, 24°07'18”S 44°42'00”W, 09 Jan 1998, 101 m. Morphological variation within the type series is shown in Table 2.

Comparative material examined. Petta pusilla Malmgren, 1 866, NRM 104108: coll. Sweden, Bohuslän, Koster area, Kostergrund, 3 specs in excellent state of preservation.

Description. Tubes not studied, as all specimens examined lacked tubes. Conical body, 5–18 mm long and 1– 2 mm wide, pale creamy in color. Operculum with smooth marginal lobe low all around; 10–12 pairs of long golden paleae, distally tapering to blunt tips, slightly curved dorsalwards (Figs 8 A–C, E–G; 9A; 10A, B; 11A; 12A; Table 2). Cephalic veil completely free from operculum, with few short, pointed buccal tentacles; distal margin of cephalic veil smooth, except for medial triangular cirrus, distally entire or bifid (Figs 8 A–C; 9A; 10B); cephalic veil terminating by rounded flaring lobe at each side, each ending by spherical papilla. Tentacular cirri of segments 1 and 2 of similar length, both thin and elongate, distally blunt; tentacular cirri of segment 1 ventrally aligned to those of segment 2 (Figs 8 A–C, E–G; 9A, C; 10A, B). Segments 2–6 distinctly raised ventrally, as ventral crests; first crest, on segment 2, with pair of low ventral lobes interrupted mid-ventrally, each side reaching mid-ventral line, with 5–7 marginal cirri; segment 3 with ventrolateral crests interrupted mid-ventrally by pair of large spherical papillae (Figs 8 A–C, E, G; 9A–C; 10B, C; Table 2). Two pairs of small pectinate stalked branchiae, on segments 3 and 4, each pair consisting of loose, flat and smooth rounded lamellae, almost circular, first pair slightly larger, inserted laterally, second pair inserted dorso-laterally (Figs 8 E–G; 9C; 10A, E). Notopodia beginning on segment 5, extending until segment 21, first 3 pairs shorter; neuropodia beginning on segment 8, extending until segment 21; last segment before scaphe with biramous parapodia (Fig. 12H). Notochaetae of two types, those of anterior row with narrow limbation from base, terminating by serrated alimbate blade, much wider at base, triangular, with smooth edge and coarse striations on sides, edge serrated from immediately after base of blade; chaetae of posterior row narrowly-winged throughout (Figs 10D; 11 B–C; 12B–E, H). Neurochaetae as avicular uncini, with clearly defined main fang, with 2–3 transverse rows of progressively shorter secondary teeth on top, short triangular heel, slightly curved base and rounded basal peg, composed of many densely packed denticles as seen under SEM (Figs 11D; 12F, G). Scaphe consisting on five fused posterior segments, not clearly separated from segment 21; scaphe oval in shape, flattened and arched ventrally, lateral margins with 6 pairs of lamellae, anal flaps distinctly short, shorter than lateral papillae, with long anal cirrus inbetween dorsally (Figs 8D, H–J; 9D, E; 10A, F); 5–8 pairs of brown, dorso-lateral scaphal hooks distally blunt, slightly arched posteriorwards (Figs 10F; 11E; 12 H–J; Table 2).

Variation. Intraspecific variation among the specimens of the type series is given in Table 2. Observed variation in the numbers of pairs of paleae, scaphal hooks and cirri on ventral lobes of segment 2 is size-related (Table 2).

Remarks. Members of P. pusilla differ from specimens of P. alissoni n. sp. in having distally trifid medial extension of cephalic veil, fewer pairs of cirri on lobes of segment 2, with wider mid-ventral gap, larger midventral lobes on segment 3, and distinctly shorter scaphal medial cirrus, about as long as lateral papillae. Members of P. alissoni n. sp., in contrast, have distally entire or bifid medial extension of cephalic veil (paratype 7 with bifid extension, entire in all other specimens) and scaphal cirrus about 5 times as long as lateral papillae.

Members of P. pellucida (Ehlers, 1887) differ from individuals of P. alissoni n. sp. in having distally entire and blunt medial extension of cephalic veil, lobes of segment 2 with pair of ventralmost cirri distinctly longer than other cirri, longer mid-ventral lobes on segment 3, cylindrical and distally rounded. Among members of P. alissoni n. sp., the medial extension of the cephalic veil is distally pointed, cirri of lobes of segment 2 are all of even length, and the mid-ventral lobes of segment 3 are spherical.

Petta assimilis McIntosh, 1885 was described based on material from the Kerguelen Islands, Indian Ocean, and the type material is lost, according to Alexander Muir (personal communication). According to the original description, the holotype of P. assimilis differed from specimens of P. alissoni n. sp. in having triangular, distally entire cephalic veil; lobes of segment 2 with 4–5 pairs of cirri, the ventralmost pair distinctly shorter; entire lobe on segment 3, extending across ventral surface of segment without mid-ventral gap, distally cirrate throughout; scaphe with distinctly larger anal flaps, fused to each other in a foliaceous process, with minute terminal cirrus; and notochaetae without specialization at base of blade. In contrast, members of P. alissoni n. sp. have an almost circular cephalic veil, with entire or bifid medial extension; 5–7 pairs of cirri on lobes of segment 2, all of similar length; smooth ventrolateral crests on segment 3, with pair of mid-ventral spherical lobes; scaphe with minute anal flaps, rounded, and distinctly longer terminal cirrus; and their notochaetae have a foliaceous process at base of blade.

Members of P. tenuis Caullery, 1944, according to the original description, have ventro-lateral lobes of segment 2 with 4 pairs of triangular cirri, U-shaped ventral lobe on segment 3, and uncini with 3 teeth only, main fang and 2 secondary teeth. In contrast, members of P. alissoni n. sp. have 5–7 pairs of cirri on lobes of segment 2, segment 3 without a ventral lobe, with a pair of spherical papillae instead, and uncini with more secondary teeth, main fang and 2–3 transverse rows of progressively shorter secondary teeth.

Type locality. The holotype comes from off the state of São Paulo, southeastern Brazil, southwestern Atlantic. The type series includes material from the northern coast of São Paulo and southern coast of Rio de Janeiro. Etymology. This species is dedicated to Alisson Ricardo da Silva for his friendship with JMMN.