Bradabyssa minuta ( Amoureux, 1986 ) 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 : 24-26

Bradabyssa minuta ( Amoureux, 1986) n. comb.

Figure 10

Buskiella minuta Amoureux 1986: 607 –608, Fig. 2 .

Type material. Northeastern Atlantic Ocean. Syntypes in two lots ( MNHN 834), one with 158 specimens, R.V. Cryos, from several stations: 2 (37°18' N, 15°33' – 15°38' W), 4200–4500 m, 17–18 May 1981 ; 5 (34°48' N, 21°19' W → 35°00' N, 21°28' W), 5100–5160 m, 21–22 May 1981; 6 (32°02' N, 21°59' W → 33°01' N, 22°00' W), 5230–5250 m, 23–24 May 1981, 8 (34°04' N, 17°04' W → 34°01' N, 17°07' W), 4260–4270 m, 30 May 1981, 9 (39°55' N, 14°56' W → 40°00' N, 15°06' W), 5270–5320 m, 10–11 Jun. 1981, 10 (42°44' N, 15°53' W → 42°51' N, 15°57' W), 4190–4480 m, 10–11 Jun. 1981; 11 (42°57' N, 13°59' W → 43°00' N, 14°08' W), 5260–5280 m, 12–13 Jun. 1981. The other one ( MNHN 834b) includes 69 specimens, R.V. Jean Charcot, Sta. 12 (44°39' N, 17°48' W → 44°31' N, 18°01' W), 4990 m, 20–21 Jul. 1981 .

Additional material. Southeastern Atlantic Ocean. One anterior fragment ( SMF 15328), Angola Basin, R.V. Meteor, Cruise 48/1, Sta. 324-KG9 (19°58.291' S, 02°59.682' E), 5494 m, 13 Jul. 2000 (2 mm long, 0.8 mm wide, cephalic cage 2 mm long, 8 chaetigers; most fine sediment particles removed from the cuticle). Seventeen specimens ( SMF 15331), damaged, Angola Basin, R.V. Meteor cruise 48/1, Sta. 340-EBS (18°17.3' S, 04°41.2' E → 18°19.3' S, 04°41.8' E), 5419–5443 m, 23 Jul. 2000 . Anterior fragment ( SMF 15329), Angola Basin, R.V. Meteor, Cruise 48/1, Sta. 330-KG3 (19°08.275' S, 03°50.988' E), 5469 m, 17 Jul. 2000 (2.3 mm long, 1 mm wide, cephalic cage 3 mm long, 8 chaetigers).

Description. Nine syntypes, anterior fragments only, posteriorly incomplete (MNHN 834, now separated); 2–3 mm long, 1.0– 1.5 mm wide, cephalic cage 2–3 mm long, 8–10 chaetigers. Body globose, tunic papillated, thin; papillae digitate or capitate, mostly eroded ( Fig. 10A ), tunic with large sediment particles and foraminiferans, closely fitting to each other ( Fig. 10B ).

Cephalic hood not exposed. Anterior end not studied because of poorly preserved condition of syntypes. Cephalic cage present, notochaetae 2–3 times longer than body width, neurochaetae shorter. Chaetiger 1 involved in the cephalic cage; notochaetae arranged in short dorsal series, neurochaetae ventral; 1–2 notochaetae, 5–6 neurochaetae. Notochaetae with very short articles; neurochaetae with longer articles.

Anterior dorsal margin of first chaetiger truncate, papillate, two long capitate papillae. Anterior chaetigers without especially long papillae. Chaetigers 1–3 of similar length. Chaetal transition from cephalic cage to body chaetae abrupt; chaetiger 2 with aristate neurospines. Gonopodial lobes not seen.

Parapodia poorly developed; chaetae emerge from body wall (when the outer cover is removed, parapodia rounded projected lobes with long papillae). Parapodia lateral; median neuropodia ventrolateral. Notopodia and neuropodia close to each other, each with single capitate postchaetal papilla.

Median notochaetae arranged in short transverse series; all notochaetae multiarticulate capillaries, 3–4 per bundle, longest twice as long as body width. Neurochaetae multiarticulate capillaries in chaetiger 1; aristate neurospines from chaetiger 2, arranged in transverse series, 3–4 per bundle ( Fig. 10C ).

Posterior end unknown.

Variation. Anterior fragments 2.0– 2.3 mm long, 0.8–1.0 mm wide, cephalic cage 2–3 mm long, 8 chaetigers.

Remarks. The type material comes from 4200–5320 m depth from a series of stations (32°02' – 44°39' N, 13°59' – 21°59' W), and the Angola Basin specimens fit the original description, extending the depth and geographical range.

This species may possibly have more papillae than are apparent, but after dredging and sieving, many may have been eroded, with only those partly protected by chaetae or larger particles remaining in better condition.

Amoureux (1986) lumped all of his organisms into two vials; in the first one he grouped specimens from 7 stations, and left those of a single station (St. 12) in another vial. From the first one he took one specimen, removed the outer cover, and selected it as the holotype, but it was not separated and deposited as such, rendering all specimens syntypes. However, because all specimens are anterior fragments, variously damaged, no lectotype is being designated and the redescription is based on some of the better preserved specimens.

This species does not belong in Buskiella McIntosh, 1885 , which has been revised elsewhere ( Salazar-Vallejo & Zhadan 2007), because it is not pelagic, it lacks the hyaline outer cover (free from sediment particles), and lacks the very long neurochaetae with long articles. It is included, with some hesitation, as a member of Bradabyssa pending the study of branchiae. The specimens are in poor shape and those that had been dissected show very few filaments, in comparison to most species in the genus. However, because they were collected in very deep water and the body is delicate, this apparently low number of branchial filaments is enigmatic.

Bradabyssa minuta ( Amoureux, 1986) n. comb., differs from other species in the genus because of its small size and because it has very few long papillae along its body. As indicated in the key above, B. minuta differs from B. sachalina ( Annenkova-Chlopina, 1922) n. comb. because large sediment particles (foraminiferan tests) adhere to its tunic and it has about 10 chaetae in chaetiger 1, whereas B. sachalina has small sediment particles adhering to papillae and it has about 20 chaetae in chaetiger 1. A similar species, represented by a poorly preserved specimen from the Gulf of California, is still undescribed; however, they differ because in B. minuta the anterior margin of chaetiger 1 is truncate, whereas in the undescribed species there is a large rounded projection.

Distribution. Northeastern Atlantic Ocean, Southern Atlantic Ocean, in 4200–5500 m depth.

Figures

FIGURE 2. Brada granosa Stimpson, 1853. A. Neotype (USNM 1422407), lateral view, anterior end to the right (inset: small paratype, lower right in Fig. 3 A). B. Same, anterior end, ventral view (arrows point to gonopodial lobes). C. Non-type specimen (USNM 22851), head dissected, branchiae and palps removed (Br: branchial scar, PS: palp scar). Scale bars: A: 1.7 mm, B: 1.3 mm, C: 0.4 mm.

FIGURE 10. Bradabyssa minuta (Amoureux, 1986) n. comb., syntypes (MNHN 834). A. Five syntypes, mostly without globose foraminiferans. B. Three syntypes with globose foraminiferans on tunic. C. Median chaetiger, right parapodium (insets: notochaetal basal regions, neurochaetal tips). Scale bars: A: 0.4 mm, B: 0.3 mm, C: 65 µm.