Bradabyssa jirkovi, Salazar-Vallejo, 2017

Salazar-Vallejo, Sergio I., 2017, Revision of Brada Stimpson, 1853, and Bradabyssa Hartman, 1967 (Annelida, Flabelligeridae), Zootaxa 4343 (1), pp. 1-98 : 71-72

Bradabyssa jirkovi n. sp.

Figure 36

Type material. Northeastern Pacific Ocean, Aleutian Trench. Holotype (SIORAS 6085), and 6 paratypes (SIORAS 6085a, ECOSUR 186), R.V. Vitjaz, Sta. 6085 (50°48.6' N, 173°29.0' W), 6965–7000 m, Sigsbee trawl, 1 May 1969 (complete paratypes 15–21 mm long, 2.0– 3.5 mm wide, cephalic cage chaetae 1.0 mm long, 22–34 chaetigers; gonopodial lobes in chaetigers 5; 9–11 transverse series of dorsal papillae).

Description. Holotype (SIORAS 6085) complete, slightly dehydrated, soft, pale (greenish after Methyl green stain), some chaetae broken. Body elongate, anterior end wider, slightly fusiform ( Fig. 36A ); 30 mm long, 3 mm wide, cephalic cage 1.0 mm long, 33 chaetigers. Papillae abundant, filiform, slightly capitate, with fine looselyadhered sediment particles forming globose masses, more or less collapsed with each other during preservation. Removal of sediment reveals papillae filiform, thicker basally, about 8–9 transverse series per chaetiger. Papillae of posterior body region decreasing in size towards pygidium.

Anterior end features observed in paratype (ECOSUR 186). Prostomium low cone, pale. Eyes not seen. Caruncle poorly developed, median keel low, lateral ridges low, continued posteriorly, not reaching posterior margin of branchial membrane. Palps thick, very short after contraction, darker dorsally; palp keels rounded, low. Lateral lips well developed; ventral and dorsal lips reduced.

Branchiae cirriform, most pale, sessile on branchial plate, arranged in lateral groups ( Fig. 36D ); about 50 filaments per group, marginal filaments largest, basal and central ones smaller. Longest filaments about half as long as palps. Nephridial lobes in branchial plate not seen.

Cephalic cage reduced, chaetae as long as 1/30 body length, or about half body width. Chaetiger 1 involved in cephalic cage; chaetae arranged in short dorsoventral series; 2 notochaetae and 3 neurochaetae per fascicle; first neuropodia not projecting or swollen.

Anterior dorsal margin of first chaetiger papillated, rounded ( Fig. 36B ). Chaetal transition from cephalic cage to body chaetae abrupt; large aristate neurospines present from chaetiger 2. Ventral gonopodial lobes in chaetiger 5, each short, slightly darker than surrounding area, basally swollen, tip rounded; visible only after brushing off the sediment ( Fig. 36C, E ).

Parapodia poorly developed, chaetae emerge from body wall. Parapodia lateral; median neuropodia ventrolateral. Notopodia and neuropodia close to each other; notopodia short, low conical lobes, neuropodia larger.

Median notochaetae in short series, two per fascicle, all multiarticulate capillaries, but articles restricted to distal chaetal half, articles very long, decreasing in size distally ( Fig. 36F ), but terminal article long; chaetae (chaetiger 11) about as long as 2/3 body width. Neurochaetae multiarticulate capillaries in chaetiger 1; aristate neurospines from chaetiger 2, small, becoming larger in median neuropodia, decrease in size posteriorly, 3–4 neurochaetae in anterior chaetigers, 4–5 in median chaetigers, only 1–2 in posterior ones, most broken off. Neurospines with very short rings basally and medially, distally hyaline, curved, aristate ( Fig. 36G ).

Posterior end tapered into rounded cone ( Fig. 36A ); pygidium with anus terminal, provided with dark muscular ring; anal cirri absent.

Variation. Paratypes 15–21 mm long, 2.0– 3.5 mm wide, cephalic cage chaetae 1.0 mm long, 22–34 chaetigers.

Remarks. Bradabyssa jirkovi n. sp. is very similar to B. hartmanae n. sp. as both possess multiarticulate notochaetae with articles restricted to the distal half or third. However, whereas in B. jirkovi the articles are very long throughout the articulated region, in B. hartmanae the articles are medium-sized, becoming slightly longer distally. Most other species have a single superior notochaeta with long articles and the rest of the notochaetae with shorter articles.

Etymology. This species is named after Dr. Igor A. Jirkov, a hard-working specialist of terebellomorph polychaetes, from the Moscow State University, in recognition of his many contributions dealing with Arctic and Subarctic polychaetes.

Distribution. Aleutian trench, Northeastern Pacific Ocean, in about 7000 m depth.

Figures

FIGURE 36. Bradabyssa jirkovi n. sp., holotype (SIORAS 6085). A. Dorsal view. B. Anterior end, dorsal view. C. Same, ventral view (arrow points to gonopodial lobes, neurochaetae removed). Paratypes (ECOSUR 186): D. Head, frontal view, palps removed, branchiae on site. E. Same, close-up, right neuropodia from chaetigers 4 – 7 (arrow points to gonopodial lobe, most papillae brushed off). F. Chaetiger 14, right parapodium, notochaetal basal, subdistal and distal regions. G. Same, neurochaetal basal, medial and distal regions. Scale bars. A: 1.5 mm, B: 0.9 mm, C: 0.6 mm, D: 0.3 mm, E: 0.2 mm, F: 40 µm, G: 80 µm.