Syllidia amaralae, Rizzo, Alexandra E. & Salazar-Vallejo, Sergio I., 2014

Rizzo, Alexandra E. & Salazar-Vallejo, Sergio I., 2014, Hesionidae Grube, 1850 (Annelida: Polychaeta) from South-Southeastern Brazil, with descriptions of four new species, Zootaxa 3856 (2), pp. 267-291 : 273-276

Syllidia amaralae n. sp.

( Figs 2 , 3 )

Type material. holotype, MZUSP 506, 24°07.637' S 45°51.895' W, between Ilha Grande Bay, off Rio de Janeiro State to Santos, off São Paulo State, Sta. 6661, subtidal, 147 m depth, 09.i.1998; paratypes, MZUSP 504 (1), MZUSP 505 (2), 23°32.765' S 44°44.380' W, off Ubatuba, SP, Sta. 36I, subtidal, 43.8 m depth, 10.vi.2001; paratypes, MZUSP 507 (2), 24°07.637' S 45°51.895' W, between Ilha Grande Bay, off Rio de Janeiro State to Santos, off São Paulo State, Sta. 6661, subtidal, 147 m depth, 09.i.1998.

Additional material. Argentina. 8 specimens ( UERJ 3878), R.V. Mejillon I, Sta. 15bis, 37°10' S 56°14' W, off Pinamar, 30 m depth. One specimen ( UERJ 3879), Mar del Plata, Escollera Norte, 3 m depth, 16 Aug. 1968. 15 anterior fragments ( UERJ 3880), Mar del Plata, Escollera Norte, 3 m depth, 26 Aug. 1965, Bulla, coll. Two specimens ( UERJ 3881), Puerto, Mar del Plata, Costanera Norte, 14 Jan. 1968.

Description. Holotype complete, 3.3 mm long, 0.5 mm wide, 31 chaetigers. Three paratypes complete 1.6–6.0 mm long, 0.3–0.7 mm wide, 19–35 chaetigers. Other two paratypes incomplete with 9 and 15 chaetigers. Body subcylindrical, wider anteriorly, on pharyngeal region ( Fig. 2 A), whitish to dark-yellow; brownish ventrally from median to posterior region ( Fig. 2 B), sometimes extending to anterior region. Complete specimens with some brownish pigment prostomium, mainly on its posterior margin.

Prostomium slightly oval; posterior margin slightly rounded to straight ( Fig. 2 A). Lateral antennae digitiform, distally slender, about as long as palps, lost in most specimens (lateral antennae present only in paratype MZUSP504). Palps biarticulate, latero-frontal, outer to lateral antennae ( Fig. 2 A). Palpophores short, robust; palpostyle digitiform, distally blunt, almost as long as palpophores. Two pairs of reddish dorso-lateral eyes in trapezoidal arrange (absent in one paratype); anterior eyes larger, reniform, with lenses; posterior eyes rounded. Nuchal organs distinct, on prostomial postero-lateral margins.

Pharynx (everted in holotype), short, smooth, with 10 short, blunt papillae ( Fig. 2 A). Pharyngeal region muscular, occupying first nine chaetigers. Jaws black, each with 7–10 denticles, posterior outer projection curved, tapered, separated by wide open space from straighter inner projection ( Fig. 2 C–D, 3A–F), and a ventral stylet dark brown, blunt, in the pharynx internal surface. Ventral stylet roughly prismatic or deltoid, with a rather smooth surface. Denticulate margin with a series of teeth, blunt, subconical, pointing dorsally, and their relative size decrease ventrally.

First three segments fused, dorsally reduced. Six pairs of tentacular cirri; cirrophore short, robust, cirrostyle moniliform, longer, reaching up to chaetiger 12 when complete. First pair of tentacular cirri dorsal; second dorsolateral, third latero-ventral; most tentacular cirri lost or distally truncated.

Parapodia sub-biramous ( Fig. 2 E–F). One or two notoaciculae, slender, straight, not protruding. Notochaetae absent. Most dorsal cirri lost or distally truncated; cirrophore short, cirrostyle longer, moniliform; anterior ones extending for about six chaetigers. One or two neuroacicula distally straight, not protruding. Neuropodial prechaetal lobe liguliform; postchaetal lobe subtriangular to rounded, shorter than prechaetal one ( Fig. 2 E–F). Ventral cirri digitiform, distally slender, shorter than parapodial lobe on anterior chaetigers, longer on posterior ones, inserted basally and centrally on parapodial lobe; easily lost.

Neurochaetae of a single type, about 40–50 heterogomph falcigers per bundle; shaft long, blade long or mediumsized, bidentate, marginally serrate; superior neurochaetae ( Fig. 2 G) slightly longer than ventral ones ( Fig. 2 H).

Anal cirri filiform, as long as last six chaetigers. A mature female paratype packed with oocytes, each one 0.1 mm in diameter; eyes, parapodia and chaetae well-developed (MZUSP 504).

Remarks. As stated above, the jaws could provide useful information to separate similar species as shown in the key below. Each jaw rests on the muscular limit, with a wide, curved outer projection that extends into the pharyngeal cavity as a denticulate rostrum, and a perpendicular inner projection ( Fig. 3 A–C). The ventral stylet seems to be more denticles in larger specimens ( Fig. 3 D–F), and the dorsalmost tooth is less pigmented than the other teeth along each series. However, more specimens must be studied before finding out any trend between these features.

Syllidia armata sensu Day, 1967 , may be different from S. armata de Quatrefages, 1866. Syllidia amaralae n. sp. resembles more closely S. armata sensu Day because both have annulated or moniliform dorsal and tentacular cirri. Their jaws differ as indicated in the key above. However, S. amaralae n. sp. specimens differ from Day’s ones by having a quadrangular prostomium, by the relative size and arrangement of eyes, and by a reduced number of chaetae which are disposed in two bundles. These features are consistent and do not change during ontogeny or sexual maturity.

Etymology. This species is named after A. Cecília Z. Amaral, for her contributions to the study of polychaetes from Brazil.

Distribution. Brazil, from Ilha Grande Bay, off Rio de Janeiro State to Northern Argentina, in 43.8–147.0 m in Brazilian waters and in 3–30 m in Argentinean ones.

Figures

FIGURE 2. Syllidia amaralae new species. A. Holotype MZUSP 506 with pharynx everted, dorsal view; B. Same, ventral view; C. Same, jaws; D. Position of jaws and stylet on proboscis; E. Paratype MZUSP 505, parapodium 4, posterior view; F. Same, parapodium 12, anterior view; G. Supra-acicular heterogomph falciger neurochaetae; H. Sub-acicular heterogomph falciger neurochaetae.

FIGURE 3. Syllidia amaralae new species, non-type specimens’ pharynx and jaws. A. Pharynx, distal portion (UERJ 3880), cross-section showing some marginal papillae, jaws and ventral stylet, frontal view. B. Same, close-up, green hue is after methyl green staining (IP: inner projection; OP: outer projection; VS: ventral stylet). C. Another specimen (UERJ 3880), damaged, with integument pulled-out, frontal view, left jaw seen from inside, right jaw seen from the outside, and ventral stylet (same abbreviations as in C). Denticulate margins of progressively larger jaws, D – E. UERJ 3880. F. UERJ 3878. Scale bars. - A: 0.17 mm, B: 0.07 mm, C: 0.09 mm, D: 28 µm, E: 25 µm, F 22 µm.