Phyllodoce thalia Oliveira & Magalhães & Lana 2021, sp. nov.

Phyllodoce thalia sp. nov.

urn:lsid:zoobank.org:act: 2EEFCC1D-0E28-486E-9781-F51C143D3223

Figures 29–30

Holotype. Continental slope in Campos Basin in Campos Basin, Rio de Janeiro, Brazil, Hab 03 G10 R1, 22º7`18.3”S 39º44’23.9”W, 1,924.5 m, 12 May 2008 (ZUEC–POL 16331).

Paratypes. A total of 3 specimens, length 18.3± 16.1 mm and 63.89± 33.6 segments. Continental slope in Campos Basin: Hab 1 Drag 27B, 22°36’19.1”S 40°42’17.5”W, 103.1 m, 13 Apr 2008 (2 paratypes, ZUEC–POL 16337); Hab 7 H07 B3, 21°41’11.7 “S 40°2’20.3”W, 700 m, 7 Jul 2008 (1 paratype, ZUEC–POL 16428), Brazil.

Diagnosis. Prostomium with M–shaped posterior margin, where the nuchal papilla is located. Proximal part of proboscis with oval-shaped papillae irregularly distributed on each side, separated by non-papillated median-dorsal and median-ventral areas.

Description. Holotype incomplete, 35 mm long, 2.0 mm wide at median part of body, including parapodia and excluding chaetae, for 116 segments. Body long, dorso-ventrally flattened and tapered posteriorly. Prostomium elongated and distinctly cordiform, M-shaped posterior margin, and incised with nuchal papilla and pair of lateral nuchal organs (Fig. 29A). Paired frontal antennae and palps conical, long and of similar lengths. Antennae and palps 1/4 of prostomial length (Fig. 29 A–B). One pair of brown subepidermal eyes with lenses. Proboscis basally with oval papillae irregularly distributed on each side, separated by horizontal row of median-dorsal papillae and non-papillated median-ventral region (Fig. 29C, E). Distal region with six longitudinal rows of prominent tubercles (rugged papillae). Terminal ring with 17 oval papillae distally acute (Fig. 29 B–D). Segment 1 not visible dorsally. Four pairs of cylindrical tentacular cirri, biarticulated, with ringed cirrophores and long cirrostyles, situated on first three segments; cirrophores basally ringed. Tentacular cirri of segment 1, reaching segment 5. Dorsal and ventral tentacular cirri of segment 2 reaching segments 8 and 3, respectively. Dorsal tentacular cirri of segment 3 extending to segment 7. Neuropodia and ventral cirri from segment 3. Dorsal cirri with developed cirrophores and dorsal extensions on median parapodia. Dorsal cirri asymmetrical, foliaceous anteriorly and sub-rectangular with rounded edges on median segments. Parapodial lobes shorter than dorsal and ventral cirri with light-brown aciculae and bundles of chaetae. Prechaetal lobes asymmetrical and rounded. Postchaetal lobes rounded. Ventral cirri from segment 3, horizontally oriented in relation to lobes, asymmetrical and dorso–ventrally flattened; ventral cirri of anterior segments rounded and medially more elongated than anterior ones (Fig. 30 A–D). Compound spinigerous chaetae uniform and from segment 4. Rostrum of chaetal shaft surrounded by irregularly distributed conical denticles; articles with serrated outer edges (Fig. 30 E–G). Pygidium not observed.

Colour. The pigmentation is in general light brown with traces of green pigment in the median-dorsal part of the body. In some preserved specimens, the pigmentation disappears from the antennae and prostomium.

Habitat. Muddy substrate dominated by silt, between 103–1,925 m.

Distribution. Atlantic Ocean, Brazil: Margin of continental shelf and slope in Campos Basin.

Etymology. The species name is derived from the Greek words Thalia (flower button). The epithet refers to the distribution of denticles on the rostrum of the chaetal shaft, shaped as flower buds.

Remarks. Phyllodoce thalia sp. nov. resembles P. cf. madeirensis in the presence of a cordiform prostomium and morphology of the tentacular cirri with ringed cirrophores. However, they differ in the distribution of papillae in the proximal part of the proboscis, which in P. thalia sp. nov. are irregularly distributed on each side, separated by a horizontal row of median-dorsal papillae and median-ventral non-papillated area, and in P. cf. madeirensis with a row of median-dorsal papillae and six regular rows on each side. In addition, the parapodial cirri are sub-rectangular in median segments with rounded edges in P. thalia sp. nov. and lanceolate in P. madeirensis.

Phyllodoce thalia sp. nov. may be separated from other morphologically similar species (P. longipes, P. tamoya sp. nov., P. cf. madeirensis , P. erythrophylla, P. medipapillata, P. tupana sp. nov., Phyllodoce sp. A., and P. brasiliensis sp. nov.) by the shape of the posterior part of the prostomium (M–shaped), distribution of proboscidial papillae, and a distinct chaetal distribution. It also differs from P. rosea, P. colorata sp. nov., P. concava sp. nov., and Phyllodoce sp. B. because these present cuspidate papillae with oblique rows (Pleijel 1993; Blake 2001). P. concava sp. nov., P. lamella sp. nov., P. ovalis sp. nov., and Phyllodoce sp. B. are separated from P. thalia sp. nov. by the presence of eyes and morphology of the dorsal cirri.