Bradabyssa irenaia (Chamberlin, 1919) n. comb.

Figure 24

Brada irenaia Chamberlin, 1919: 400 –401, Pl. 68, Figs 7–9, Pl. 69, Figs 1–3.

Type material. Eastern Tropical Pacific. Holotype of Brada irenaia (USNM 19340), R.V. Albatross Tropical Pacific Expedition, off southern Panama, Sta. 3382 (06°21' N, 80°41' W), 3281 m, green mud, 7 Mar. 1891.

Description. Holotype (USNM 19340) damaged, broken in two portions, partly dehydrated, body dark, slightly fusiform (Fig. 24A); 43(27+16) mm long, 5.5 mm wide, cephalic cage chaetae broken, 41 (23+18) chaetigers. Tunic papillated, dorsal papillae larger, globular, in 4–5 alternating series per chaetiger (Fig. 24B), ventral papillae smaller, arranged in 8–9 alternating series per chaetiger, each with smaller or larger papillae; without thick tunic, sediment grains adherent to papillae, not forming large tubercles.

Anterior end exposed, mostly eroded (Fig. 24C, D). Prostomium eroded. Caruncle eroded posteriorly, separating branchial plate, median keel and lateral ridges eroded, probably converging posteriorly. Palps large, one missing, remaining one with tip partially eroded, not corrugated; palp keels low, rounded.

Branchiae missing, branchial scars arranged into two lateral groups, each with filaments in radiating series, about 110 scars per group. Individual lips not discernable, smashed and eroded (ventral pharyngeal bulb slightly exposed). Nephridial lobe scars in lower half of branchial plate, each as rounded darker lobes.

Cephalic cage probably present (notochaetae in chaetiger 4 very long), chaetae as long as 1/8 body length, or slightly shorter than body width. Chaetal lobes of chaetiger 1 with chaetal bases arranged in short lateral series, chaetal number unknown.

Anterior dorsal margin of first chaetiger rounded, papillated. Anterior chaetigers with anteroventral filaments, probably epizoans. Chaetigers 1–3 of similar length. Chaetal transition from cephalic cage to body chaetae abrupt; aristate neurospines present from chaetiger 2 (most broken, bases remain). Gonopodial lobes dark, rounded, short lobes in chaetiger 5 (Fig. 24D).

Parapodia well developed, lateral. Notopodia and neuropodia close to each other. Median neuropodia ventrolateral. Notopodia short low rounded lobes, with 3–4 long papillae. Neuropodia larger rounded lobe, 8–10 marginal papillae (mostly eroded), each with globular base.

Median notochaetae arranged in short transverse series; all notochaetae multiarticulate capillaries, articles short basally and medially, distally long (Fig. 24E); 6–8 per bundle, as long as 1/3 body width. Chaetiger 1 neurochaetae missing, aristate neurospines from chaetiger 2, most eroded, few smaller ones with tips aristate, tapered, slightly curved (Fig. 24F); 7–8 per bundle, arranged in È-shaped patterns; each neurospine with rings short, decreasing in length medially and distally, penetrating aristal basis, tip hyaline, recurved.

Posterior end tapered into rounded lobe (Fig. 24G); pygidium with anus dorso-terminal, round opening; anal cirri absent.

Remarks. Bradabyssa irenaia (Chamberlin, 1919) n. comb. differs from B. verrucosa (Chamberlin, 1919) n. comb., both coming from abyssal sediments in the Eastern Pacific, by the relative size of the larger dorsal papillae. In B. irenaia there is no large epi-notopodial papillae, whereas there is one in B. verrucosa, another difference being that there are 8–9 ventral transverse series of papillae in B. irenaia whereas there are only 2–3 ventral transverse series in the latter.

Chamberlin (1919:401) regarded B. irenaia as closely resembling B. villosa (Rathke, 1843), and separated them by the relative chaetal size. The type and number of papillae provide more striking differences; most papillae in B. villosa are of similar size and slightly swollen basally, whereas in B. irenaia dorsal papillae are of two markedly different sizes. Thus, B. irenaia resembles those species that possess dorsal papillae arranged in alternating size and position, but it differs from these by the number of transverse series of papillae, as stated in the key above.

However, as indicated above, Bradabyssa irenaia (Chamberlin, 1919) n. comb. also resembles B. abyssalis (Fauchald, 1972) n. comb. by having about 5 series of dorsal tubercles. They differ because in B. irenaia neurochaetae are tapered and integument is dark, whereas in B. abyssalis neurochaetae are medially cleft and integument is pale. Furthermore, in B. irenaia notochaetae have short rings basally and medially, whereas in B. abyssalis they are present only basally.

Distribution. Pacific Ocean, off Panama, in sediments deeper than 3200 m water depth.