Bylgides cinthyae, Ogawa & Miranda & Rizzo, 2025

Bylgides cinthyae sp. nov.

( Figures 5–7)

Type Material.

Holotype: UERJ — Pol 8751 Brazil: Piauí-Real Complex , Sergipe state ( 11º 24'47.89"S, 37º 24'44.55"W) at 1–27 meters depth.; 22 Feb 1991. GoogleMaps

Paratype ( 2 specimens): UERJ — Pol 8850 ; UERJ — Pol 8851 Brazil: Piauí-Real Complex , Sergipe state ( 11º 24'47.89"S, 37º 24'44.55"W) at 1–27 meters depth; 22 Feb 1991 GoogleMaps .

Measurements: All specimens complete. Holotype 8 mm long, 2 mm width for 29 segments. Paratypes 3–8 mm long, 2 mm width for 14–28 segments.

Description: Body flattened dorsoventrally, tapering slightly posteriorly. Fifteen pairs of elytra present on segments 2, 4, 5, alternating from segments 7 to 23, and on segments 24, 25, and 27. Elytra partially covering the dorsum, attached to prominent elytrophores ( Figs 6A; 7A), last two segments with dorsal cirri. Elytra rounded on anteriormost segments, oval on middle and posterior segments; smooth, brown pigmentation forming a crescent shaped on the internal margin of elytra, and a round spot present on the elytral insertion. Dorsal cirri, smooth, tapering, on cylindrical cirrophores attached on the posterior surface of the notopodium, extending beyond the neurochaetae ( Fig. 7A). Nodular dorsal tubercles near the basis of cirrophores and elytrophores, less prominent on posteriormost segments.

Prostomium bilobed, with sulcus reaching middle of cephalic region, small rounded cephalic peaks present on anterior border. Two opaque spots located on anterior half of prostomium. Two pairs of sessile eyes, small, black, and rounded; anterior pair larger than posterior one and placed on widest part of prostomium; posterior pair at posterior margin, near nuchal slit. Median antenna bulbous and tapering, twice as long as lateral antennae, insertion on prostomial anterior notch; style with scattered, clavate papillae ( Fig. 7A). Ceratophores of lateral antennae short, rounded, fused latero-ventrally to median antenna; styles short, subulate, with scattered, clavate papillae over its surface ( Fig. 7A). Palps long and smooth ( Fig. 7A). Tentaculophores lateral to prostomium with a small projecting aciculum, and a small curved notochaeta on its inner face ( Fig. 5A). Tentacular cirri tapering ( Fig. 6B), with clavate papillae over its surface, densely arranged at basis and smoother in subdistal region, dorsal pair about 1/3 longer than ventral cirri.

Second segment without dorsal nuchal fold. First pair of elytrophores prominent. Parapodia biramous, notopodium half the lenght of neuropodium. Ventral buccal cirri lateral to mouth, longer than parapodia, tapering, smooth, similar to those in following segments, but three time larger. Pharynx not everted, prolonging from the 5 th to 12 th segments, two pair of amber coloured jaws on its anterior border, viewed by transparency.

Notopodium conical, with projecting acicular lobe, half the lenght of neuropodium. Notochaeta organized into two bundles, the dorsalmost are shorter than the lower bundle, both groups of notochaetae are curved, stout, with row of spines on the convex surface. Neuropodia conical, neurochaetae similar throughout, all are lanceolate in shape, thin, straight, with spiny structures along the inner surface. Pharynx not everted and not examined.

Parapodia prominent, gradually increasing in length up to the middle of the body and decreasing towards the posterior region; biramous, notopodia half the length of neuropodia. Notopodia conical with prominent acicular lobe. Notochaetae more robust than neurochaetae, organized in two fascicles: dorsal fascicle more robust, shorter, curved, with rows of spines on the outer convex margin ( Fig. 7B); ventral fascicle longer, sabrelike, with rows of spines on convex margin ( Figs 6C; 7C). Neuropodia with a subconical post-chaetal lobe and a longer acicular pre-chaetal lobe with a digitiform supra-acicular projection. Neurochaetae lanceolate, with entire tips ( Fig. 7D); supra-acicular chaetae barbed, with rows of spines on both sides ( Fig. 7E), sub acicular chaetae with a single row of lateral spines ( Fig. 7F). Ventral cirri subulate and smooth.

Pygidium with anal cirri similar in shape to the dorsal cirri. Nephridial papillae short and bulbous located laterally between the parapodia, starting on segment 12 and presenting through remaining segments.

Fluorescence observed only under green illumination, by exhibiting a faint red light under this spectrum. Under UV illumination no excitation was observed.

Etymology. The species name Bylgides cinthyae sp. nov. is after the polychaetologist Dra. Cinthya Simone Gomes Santos, for her contribution to the study of the polychaetes, particularly nereidids, and to celebrate our friendship.

Geographic and Bathymetric Distribution. Brazil: estuary of the Piauí River, Sergipe state at 1–27 meters depth.

Remarks. The new species is also compared with other congeners in Table 1. Bylgides cinthyae sp. nov. is unique in having smooth palps, elytra and dorsal cirri, and inconspicuous dorsal tubercles on posteriormost segments.

Bylgides cinthyae sp. nov. resembles B. acutisetis in having a pigmented prostomium, the former has brown spots covering almost all the prostomium, while the latter has black pigments on the anterior half only. Both species can be differentiated based on presence of smooth palps, elytra and dorsal cirri, on B. cinthyae , whereas B. acutisetis present these structures ornamented. Both species also differ in the segmental origin of the nephridial papillae.

The crescent-shaped pigmentation pattern presented in preserved specimens of Bylgides cinthyae sp. nov. is shared only with two congeners, B. elegans and B. macrolepidus . However, B. elegans has smooth elytra, in contrast to the papillated condition observed in B. macrolepidus . The three species can also be differentiated by the ventral cirri: smooth in B. cinthyae sp. nov., but papillated in the other two species. In addition, the absence of middle neurochaetae with hooked tips, in Bylgides cinthyae sp. nov., further separates it from both B. elegans and B. macrolepidus .