Oligobregma brasierae, Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019

Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Annelida: Capitellidae, Opheliidae, Scalibregmatidae, and Travisiidae, ZooKeys 883, pp. 1-82 : 1

Oligobregma brasierae sp. nov. Figs 24 A–J , 25 A–C

Material examined.

NHM_032 NHMUK ANEA 2019.7150, coll. 09 Oct. 2013, 13°50.232N, 116°33.506W, 4336 m http://data.nhm.ac.uk/object/43545746-b8ad-43a8-92b7-53637dd131d6; NHM_404 NHMUK ANEA 2019.7151, coll. 20 Oct. 2013, 13°51.797N, 116°32.931W, 4050 m http://data.nhm.ac.uk/object/5fda0cac-0a77-4ec7-a2fa-5cd529548a19; NHM_684 (paratype) NHMUK ANEA 2019.7152, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/d84c37ed-138e-4064-a11d-a11a2470dfdf; NHM_823 (holotype) NHMUK ANEA 2019.7153, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/74781dbb-1f65-4839-a766-24d6cde63ed0; NHM_1423 (paratype) NHMUK ANEA 2019.7154, coll. 03 Mar. 2015, 12°27.26N, 116°36.77W, 4137 m http://data.nhm.ac.uk/object/d949e987-6e03-4092-8492-c51dd7fcf4d7; NHM_1895 NHMUK ANEA 2019.7155, coll. 13 Mar. 2015, 12°02.49N, 117°13.03W, 4094 m, http://data.nhm.ac.uk/object/02aaa9c0-837a-4836-8b34-5e68296c958e.

Type locality.

Pacific Ocean, CCZ, 12°32.23N, 116°36.25W, depth 4425 m, in mud between polymetallic nodules.

Description.

Small species, represented by six specimens. Holotype posteriorly incomplete, but otherwise in good condition, 9 mm long and 1 mm wide at the widest point for 24 chaetigers; paratypes complete, 6.0-6.5 mm long and 0.5-0.7 mm wide for 26 chaetigers. Body most expanded (inflated) through chaetigers 5-9, thereafter narrowing to posterior end. Colour in alcohol creamy white, without body pigment ( Fig. 24A ); live specimens translucent ( Fig. 25 )

Anterior body segments smooth, no obvious annulation of raised pads detected (even after staining) ( Fig. 24B ); annulation becomes most distinct in narrow, posterior part of the body, where segments quadriannulate ( Fig. 24C ). Venter with prominent ventral midline from chaetiger 2 composed of a row of large pads within a groove ( Fig. 24D ). Branchiae absent.

Prostomium broadly rounded anteriorly, weakly expanded laterally, narrowing posteriorly; with two short, rounded lobes (horns) emerging anterolaterally from anterior prostomial margin ( Figs 24B , 25C ). Eyes absent. Proboscis observed as a soft, smooth sac-like structure ( Fig. 24E ). Peristomium forming a smooth large ring around prostomium dorso-laterally, interrupted middorsally ( Figs 24B , 25C ), ventrally obscured by extended proboscis in holotype.

Parapodia biramous; inconspicuous in chaetigers 1-7, becoming longer posteriorly and prominent from around chaetiger 14. Tiny dorsal cirri detectable from chaetigers 14 in holotype, whereas ventral cirri occur from chaetiger 15 where well developed; both cirri large on subsequent segments; conical with broad base ( Fig. 24F ); without pigmentation; both dorsal and ventral cirri with detectable gold-pigmented internal glands ( Fig. 24G ). Interramal papilla present, inconspicuous in anterior parapodia (only observed upon staining), well developed in posterior parapodia Fig. 24F ).

Curved acicular spines present in notopodia and neuropodia on chaetigers 1-4 ( Fig. 24H ). Notopodia with about 20 spines arranged in two rows in chaetigers 1 and 2, and with about 10 spines arranged in one row in chaetigers 3 and 4, spines accompanied posteriorly by single row of capillaries; neuropodial spines fewer in numbers arranged irregularly. Spines slightly curved, narrowing to slender elongated tip ( Fig. 24H ). Short spinous chaetae anterior to spines not observed. Subsequent chaetigers with long thin capillaries in both rami. Lyrate chaetae from chaetiger 5, in both rami, positioned anteriorly to capillaries. Lyrate chaetae short, with unequal tynes bearing short bristles ( Fig. 24I ), numbering two or three per noto- and neuropodium in anterior segments and up to six in posterior segments.

Single achaetigerous ring subsequent to the last chaetiger. Pygidium missing in holotype, but observed in paratypes; broad, triannulated, distally broadly rounded lobe; with few terminal, short anal cirri still attached in paratype NHM_684 ( Fig. 24J ).

Morphological variation: Some variability was noticed between different sized specimens. In the slightly bigger holotype (NHM_823) the spines can be observed on chaetigers 1-4 in both rami, and the dorsal cirri can be detected from chaetiger 14. In the smaller paratype (NHM_684), the spines cannot be unambiguously confirmed in ch. 4, particularly in neuropodia and dorsal cirrus can be detected from chaetiger 13.

Genetic data.

GenBank MN217422-MN217427 for 16S, MN217498 for 18S and MN217517 for COI. This species is genetically identical or very similar to sequences published in Janssen et al. (2015), with K2P values ranging from 0.0-0.003 between O. brasierae and the already published sequences with accession numbers KJ736359-KJ736363. The three Oligobregma species in this study form a well-supported clade in our phylogenetic analyses, with Oligobregma brasierae sp. nov. as sister to Oligobregma tani sp. nov. ( Fig. 32 ).

Remarks.

Currently, there are nine valid species assigned to the genus Oligobregma ( Read and Fauchald 2018b), with O. blakei Schüller & Hilbig, 2007 considered a nomen dubium. All three Oligobregma species from the ABYSSLINE material can be easily distinguished from those that have acicular spines in two ( O. pseudocollare Schüller & Hilbig, 2007, O. oculata Kudenov & Blake, 1978) or three ( O. mucronata Blake, 2015, O. aciculata (Hartman, 1965), O. collare (Levenstein, 1975), O. notiale Blake, 1981) anterior chaetigers only.

More specifically, Oligobregma simplex Kudenov & Blake, 1978, O. lonchochaeta Detinova, 1985 and O. quadrispinosa Schüller & Hilbig, 2007 share the presence of spines in chaetigers 1-4 with O. brasieri sp. nov., as well as having relatively large posterior dorsal and ventral cirri. Oligobregma simplex is a shallow water species (Western Port, Victoria, Australia, 11 m) and, while similar in size (5 mm long), it has a greater number of chaetigers (43 versus 26 in UKSR species) and more posterior appearance of dorsal and ventral cirri (on ch. 20-22 versus ch. 13-15). Oligobregma lonchochaeta has been described from a single, incomplete specimen from the abyssal North Atlantic, but its description is brief, not including the observation on the appearance of dorsal and ventral cirri, and there are no DNA data. Detinova (1985) differentiated her species from O. simplex by having first four chaetigers triannulate rather than uniannulate. However, there appears to be a typographical mistake in description of O. simplex by Kudenov and Blake (1978), as the authors state: "Body segments are annulated as follows: chaetigers 1-12 are uniannulate; 3-4 biannulate; 5-12 (? or 15) quadriannulate." It is likely that chaetigers 1 and 2 not 1 to 12 are uniannulate. Oligobregma quadrispinosa has been described from the lower bathyal and abyssal Southern Ocean (Scotia and Weddell Seas, in 2258-4069 m) and is most similar to UKSR species in possessing similar number of chaetigers (n = 28) and podial cirri can be also detected from around chaetiger 13 and 14 [(estimated from the drawing provided in the original description by Schüller and Hilbig (2007)]. However, the new species possess spines in both rami of chaetigers 1-4, while O. quadrispinosa has spines in notopodia only according to Schüller and Hilbig (2007).

Ecology.

Found in polymetallic nodule province of the eastern CCZ.

Etymology.

Named in honor of Madeleine Brasier, member of the science party of the ABYSSLINE AB02 cruise onboard the RV Thomas G. Thompson.

Figures

Figure 24. Oligobregma brasierae sp. nov. A Lab image, whole specimen (holotype [specimen NHM _ 823], pre-staining) B Lab image, dorsal anterior (holotype, faded stain, h = prostomial horns, pe = peristomial ring) C Lab image, dorsal segments, quadriannulate chaetigers (holotype, faded stain) D Lab image, ventral segments (holotype, faded stain, vm = ventral midline) E Lab image, ventral anterior, (holotype, pre-staining) F Lab image, mid-body parapodia (holotype, shirlastained, dc = dorsal cirrus, vc = ventral cirrus, ip = interramal papilla) G Lab image, detail of dorsal cirrus (paratype NHM _ 684, ig = internal gland) H Lab image, detail of hirstute notopodial spines on chaetiger 1 (paratype NHM _ 684, ig = internal gland) I Lab image, detail of capillary and lyrate chaetae (paratype NHM _ 684) J Lab images, posterior (paratype NHM _ 684, [bottom-left panel], ac = anal cirri, ig = internal gland). Morphological features in plates B-D, F, G, H have been outlined with a fine white or black line to improve clarity of those features. Scale bars: 1 mm (A, E); 50 μm (G); 25 μm (H, I); 100 μm (J).

Figure 25. Oligobregma brasierae sp. nov. A Live image, whole specimen, ventral view (holotype [specimen NHM _ 823]) B Live image, whole specimen, dorsal view (paratype NHM _ 684) C Live image, dorsal anterior, with prostomial features outlined in a fine white line (paratype NHM _ 684, h = prostomial horns, pe = peristomial ring).

Figure 32. Phylogenetic analysis of Scalibregmatidae and Travisiidae. 50 % majority rule tree from the Bayesian analyses using 18 S and 16 S, with posterior probability values on nodes. Twenty taxa from GenBank were included, and Opheliidae was chosen as outgroup following the annelid phylogeny of Weigert and Bleidorn (2016).