Bradabyssa sachalina Salazar-Vallejo 2017, n. comb.

Bradabyssa sachalina (Annenkova-Chlopina, 1922) n. comb.

Figure 11

Brada sachalina Annenkova-Chlopina 1922: 39.— Ushakov 1955: 310 (1965: 287), Figs 115K–L.— Levenstein 1966: 46.— Jirkov & Filippova 2001: 355, Fig. 1.

Type material. Northwestern Pacific Ocean. Holotype (ZIRAS 26659), off northern tip of Sakhalin Island, Baikal Gulf, Okhotsk Sea, R.V. Lieutenant Dydymov, Sta. 380 (53°42'30" N, 141°41' E), 27–32 m, 28 Jul. (10 Aug.) 1913, V.K. Solgamov, coll.

Additional material. Northwestern Pacific Ocean. One specimen (ZIRAS 26661), Okhotsk Sea, R.V. Lebet, Sta. 259, 39 m, 5 Nov. 1938, K. Troiskaya, coll. (31 mm long, 6 mm wide, cephalic cage 2.5 mm (chaetiger 2 notochaetae 4 mm long), 23 chaetigers, gonopodial lobes in chaetiger 5; sand crust detached in several parts, dorsal papillae low, hardly detectable, present an elevated ridge, especially in posterior chaetigers, arranged in two diffuse transverse rows). One specimen (ZIRAS 26662), off southern Sakhalin Island, Okhotsk Sea, R.V. Toporok, Sta. 168 (49°03.1' N, 144°17.3' E), 16.5 m, 2 Oct. 1949, Skalkin, coll. (28 mm long, 5 mm wide, cephalic cage 3 mm, 26 chaetigers; nephridial lobes in chaetiger 5; sand crust complete, with a transverse furrow in most median chaetigers). Bering Sea. Four specimens (CAS 19105), Alaskan Outer Continental Shelf Environmental Assessment Program, Sta. G 20-70 (57°01.9' N, 169°30.4' W), 67 m, M. Freeman, coll. (complete, variously damaged, 32–39 mm long, 5.5–7.0 mm wide, cephalic cage 5–6 mm long, 23–24 chaetigers, gonopodial lobes in chaetiger 5). Two specimens (USNM 23266), US Signal Service Point Barrow Expedition, Cape Smyth, Alaska, 4.6 m, Autumn 1883 (complete 45 mm long, 6 mm wide, cephalic cage 3.5 mm long, 26 chaetigers; gonopodial lobes in chaetiger 5).

Description. Holotype of Brada sachalina (ZIRAS 26659) pale, partly dehydrated, slightly damaged, most tunic and sediment cover missing (Fig. 11A); non-type specimens better preserved (CAS 19105, Fig. 11C). Holotype with body blunt, tapered posteriorly; 38 mm long, 8.5 mm wide, cephalic cage chaetae all broken, 21 chaetigers. Body oval in cross section, incurved, with several parapodia previously removed, dissected anteroventrally previously (Fig. 11B). Dorsal papillae large, globular, in 1–2 transverse irregular series per chaetiger, ventral papillar series poorly marked, eroded, in posterior chaetigers more noticeable due to dehydration; without thick tunic, sediment grains adherent to papillae and body integument forming single transverse ridges per segment.

Cephalic hood not exposed in holotype, previously dissected. Anterior end exposed in non-type specimen (CAS 19105, Fig. 11D). Prostomium rounded elevated cone, eyes colorless. Caruncle extended posteriorly, separating branchial plate, median keel and lateral ridges converging posteriorly. Palps large, pale, corrugated; palps keels rounded, low. Branchiae cirriform, sessile on branchial plate, arranged into two lateral group, each with filaments in concentric series, about 130 filaments per group. Lips darker; lateral ones wide, thick; dorsal lip reduced, ventral lip short, rounded (largest paratype with ventral pharyngeal organ exposed, muscular Y-shaped opening. Nephridial lobes not seen.

Cephalic cage chaetae broken in holotype, chaetigers 4–5 with notochaetae (2.0– 3.5 mm long); chaetal basis arranged in short lateral series, chaetigers 1–2 with about 12 notochaetae, chaetiger 1 with 8 neurochaetae; cephalic cage better preserved in non-type specimens (CAS 19105). Chaetae as long as 1/8 body length, or slightly shorter than body width; arranged in short lateral series, 10–12 notochaetae and 8–10 neurochaetae per side.

Anterior dorsal margin of first chaetiger rounded, completely covered by sand-grain crust. Anterior chaetigers without especially long papillae. Chaetigers 1–3 of similar length. Chaetal transition from cephalic cage to body chaetae abrupt; aristate neurospines present from chaetiger 2. Gonopodial lobes pale, distally eroded, short, in chaetiger 5 (Fig. 11B).

Parapodia well developed, lateral. Median neuropodia ventrolateral. Notopodia and neuropodia close to each other. Notopodia short, low rounded lobes, without long papillae. Neuropodia larger rounded lobe, with about 4 anterior and 4 posterior papillae, either covered by sediment or eroded.

Median notochaetae arranged in short transverse series; all notochaetae multiarticulate capillaries, most broken, few remaining ones very long, distally curled (straight in non-type specimens), most with short articles basally, medium-sized medially and longer distally (Fig. 11E); thinner notochaetae with long articles, progressively longer medially and distally, about 5 per bundle, one left in chaetiger 9 about as long as ½ body width. Neurochaetae multiarticulate capillaries in chaetiger 1, aristate neurospines from chaetiger 2, most broken, arranged in oblique series, mostly 5 per bundle, rarely 6 (Fig. 11F); a single remaining neurospine (left neuropodia 4) with short rings basally and medially, tapering distally, yellowish, tip broken.

Posterior end tapered into rounded lobe, partly dehydrated, pygidium with anus terminal, opening vertically, anal cirri absent.

Variation. Adults 31–45 mm long, 5–7 mm wide, cephalic cage 2.5–6.0 mm long, 23–26 chaetigers.

Remarks. Bradabyssa sachalina (Annenkova-Chlopina, 1922) n. comb. has a continuous sandy ridge per segment, which may appear to be in two transverse series. This feature separates it from any other species in this genus, together with the presence of a well developed cephalic cage. These features are more or less shared with Brada granosa, B. granulosa, and B. incrustata which all show a tendency to accumulate sediment, forming dorsal tubercles that are restricteddorsolaterally, even forming a rough double sediment ridge per segment. These species, however, belong in Brada as they have few branchial filaments and distally falcate neurochaetae, suggesting that the formation of a sediment crust is a convergent character.

The appearance of the dorsal sandy ridge or tuberculate transverse series has been confusing, after the illustration by Ushakov (1955, 1965, Fig. 115K), based upon the holotype in left lateral view. Indeed, the holotype possesses two transverse series of papillae, but they fix sediment forming a singledorsal sandy ridge; however, the holotype is variously eroded, especially on the left side, so that the distal portions of the papillae are exposed, and thus giving the appearanceof two separate series. It seems that following the original description, he chose to illustrate this. However, these series of papillae are completely covered by sediment in less eroded areas, and in better preserved specimens, and are less evident as independent series on the right side because they are covered by a sand-grain crust, and this formation is a unique feature for the species. This feature is confirmed in other specimens collected near the type locality. Other northeast Pacific specimens that have been identified as B. sachalina, but which possess a sandy cover that does not obscure their papillae profile, should be regarded as a different species and are B. tenebricosa (Berkeley, 1968) n. comb., n. status (see below, this paper).

As indicated in the key above, B. sachalina (Annenkova-Chlopina, 1922) n. comb. differs from B. minuta (Amoureux, 1986) n. comb. because particles of different sizes adhere to the tunic, and by the number of chaetae in chaetiger 1 - in B. sachalina there are small sediment particles adhering to the tunic and about 20 chaetae in chaetiger 1, whereas in B. minuta there are large sediment particles and about 10 chaetae in chaetiger 1.

Distribution. Northwestern to northeastern Pacific Ocean, 5–39 m depth.