Bylgides samueli, Ogawa & Miranda & Rizzo, 2025

Bylgides samueli sp. nov.

( Figures 1–4)

Type Material.

Holotype: UERJ — Pol 0327 Brazil: Santos Port Channel , São Paulo state ( 23º 59'07.07"S, 46º 17'17.04"W) at 10 meters depth.; 9 Oct 2006. GoogleMaps

Measurement: Complete specimen, 35 segments; 8 mm in length, 2 mm in width (excluding chaetae).

Description: Body flattened dorsoventrally, tapering slightly anteriorly and posteriorly. Fifteen pairs of elytra present on segments 2, 4, 5, alternating from segments 7 to 23, and on segments 26, 29, 32. Reniform elytra covering completely dorsum, attached to prominent elytrophores ( Fig. 1C, D). Elytra without scattered tubercles, microtubercles absent, dorsal surface, lateral and posterior margins with long, filamentous papillae with blunt tips ( Figs 1D; 2D). Dorsal cirri on cylindrical cirrophores on posterior surface of notopodium, extending beyond neurochaetae, with some small clavate papillae scattered over its surface ( Fig. 1C). Nodular dorsal tubercles on nonelytrigerous segments ( Figs 1C; 3A).

Prostomium bilobed with small rounded anterior margins small, inconspicuous, cephalic peaks, lateral margins projecting below anterior pair of eyes. Two pairs of eyes, with anterior pair on larger portion of prostomium, larger than posterior pair, which is on posteriormost projection of prostomium; eyespots located just after anterior pair of eyes. Median antenna long and smooth on a large, bulbous ceratophore inserted in anterior median notch ( Fig. 1C). Lateral antennae short, subulate, with mamilliform papillae on inner face ( Fig. 1F); ceratophores short, rounded, ventrally to median antennae. Palps robust, conical, with small papillae scattered on its surface. Tentaculophores lateral to the prostomium, supported by a projecting acicula; a single saberlike, smooth notochaeta on the inner face of tentaculophore ( Fig. 1E). Two pairs of tentacular cirri, tapered, with mamilliform papillae up to posterior third, apical region smooth; dorsal cirri longer than ventral ones (approximately 30% longer) ( Fig. 1C); facial tubercle absent.

Second segment with dorsal nuchal lobe. First pair of elytrophores prominent. Parapodia biramous with rami subequal in length. Ventral buccal cirri lateral to mouth, longer than parapodia, tapering, smooth, similar to those in following segments, but twice as larger. Pharynx not everted, prolonging from the 5 th to the 14 th segments, two pairs of amber coloured jaws on its anterior border.

Parapodia prominent, biramous, gradually increasing in size to median region, decreasing in last segments. Notopodium small (three times smaller than neuropodium), with conical acicular lobe, acicular tip projecting from epidermis ( Fig. 2C). Neuropodium with subconical pre-chaetal lobe, acicula projecting form epidermis, and small acicular knob above; postchaetal lobe rounded. Notochaetae more robust than neurochaetae, organized in three fascicles: dorsalmost short and curved ( Fig. 3B), intermediate fascicle straight, smooth with rounded tip ( Fig. 3C), and ventral fascicle longer, straight, with acuminate tips ( Fig. 3D). Neurochaetae organized in three fascicles: dorsal neurochaetae long, barbed capillary chaetae with two rows of lateral spines on the distal region ( Fig. 3H–J); intermediate neurochaetae lanceolate, with one or two rows of small spines on subdistal region, tips recurvated ( Fig. 3E, F); ventral neurochaetae, shorter than upper subacicular, with smooth surface ( Fig. 3G). Ventral cirri subulate and smooth on globular ceratophores.

Pygidium rectangular, with length equal to previous segments. Anus dorsal. Pygidial cirri longer than dorsal cirri, surface smooth, tapering to acuminate tips ( Fig. 2A). Short and bulbous nephridial papillae between parapodia, starting on segment 12 and continuing to last segment.

Green fluorescence present under ultraviolet light and red fluorescence present under green light across entire body except on elytral papillae ( Fig. 4A, D).

Etymology. The species name Bylgides samueli is in honor of our friend and polychaetologist M.Sc. Samuel Lucas Delgado da Silva Mendes.

Geographic and Bathymetric Distribution. Known only from the type locality, Brazil: Santos Port Channel , São Paulo, at 10 meters depth .

Remarks. Bylgides samueli sp. nov. is compared to other species in the genus in Table 1. The new species is morphologically similar to B. acutisetis and B. annenkovae as these are the only species presenting a nuchal lobe. However, the new species differs from the later in having smooth median antenna and ventral cirri, in contrast to the papillated condition observed in the other species. Bylgides samueli sp. nov. differs from B. acutisetis in possessing a pigmented prostomium. Bylgides samueli sp. nov. has very small, rather inconspicuous, cephalic peaks, while they are well developed in B. acutisetis and B. annenkovae . Notochaetae also can be used the distinguish the three species, Bylgides samueli sp. nov. has smooth notochaetae, in contrast to spinous notochaetae observed in the other two species.

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The characters described above, and also the type and distribution of papillae on the lateral antennae, the position of the first nephridial papillae, and the number of fascicles of notochaetae, are useful to distinguish Bylgides samueli sp. nov. from its congeners.

In relation to B. cinthyae sp. nov., Bylgides samueli sp. nov. is distinguished based on the presence of the nuchal lobe, the smooth median antenna, unpigmented prostomium, three fascicles of notochaetae all smooth, and middle fascicle of neurochaetae with hooked tips.

Fluorescence has not previously been documented in any other species of Bylgides . Expanding studies on the occurrence of this trait within the genus, and across the family, may not only increase the number of known cases but also provide a useful taxonomic character. Bylgides samueli sp. nov. exhibits a strong green fluorescence under violet illumination and a weaker red fluorescence under green light. This makes B. samueli sp. nov. the first species of the genus reported to display fluorescence.