Oligobregma tani, 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 tani sp. nov. Fig. 26 A–J

Material examined.

NHM_773A (paratype) NHMUK ANEA 2019.7156, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/4b673a6a-9090-4c24-a4eb-231190507b60; NHM_1454 (holotype) NHMUK ANEA 2019.7157, coll. 03 Mar. 2015, 12°27.26N, 116°36.77W, 4137 m http://data.nhm.ac.uk/object/67d3f58a-9c13-423e-93b7-3ddcf98a361e; NHM_1480J NHMUK ANEA 2019.7158, coll. 03 Mar. 2015, 12°27.26N, 116°36.77W, 4137 m http://data.nhm.ac.uk/object/d47f17aa-c0c1-44f0-a448-d3f3c395fc47; NHM_1665 (paratype) NHMUK ANEA 2019.7159, coll. 10 Mar. 2015, 12°21.81N, 116°40.86W, 4233 m http://data.nhm.ac.uk/object/eca166ae-3fe0-4367-860f-08c7410165dd.

Type locality.

Pacific Ocean, CCZ, 12°27.26N, 116°36.77W, depth 4137 m, in mud between polymetallic nodules.

Description.

Small species, represented by four posteriorly incomplete specimens, 4-4.5 mm long and 0.4-0.7 mm wide. Holotype posteriorly incomplete, but otherwise in good condition, 4.5 mm long and 0.7 mm wide at the widest point for 18 chaetigers long fragment. Colour in alcohol creamy white, without body pigment ( Fig. 26A ); live specimens semi-translucent ( Fig. 26B ). Anterior body segments appears smooth, annulation of raised pads detected best upon staining ( Fig. 26 C–E ) revealing chaetigers 1-4 with two transverse rows of relatively large lobes; subsequent chaetigers may be tri-annulate, but epithelium with mostly with wrinkled appearance till end of fragment (chaetiger 18) ( Fig. 26 B–E ).Ventral midline on venter not too prominent, from chaetiger 2, composed of a row of large pads within a groove ( Fig. 26E ). Branchiae absent.

Prostomium broad (wider than long), nearly oval; with two very prominent, distinctly rounded lobes (horns) emerging from anterior prostomial margin ( Fig. 26C, D ). Eyes absent. Peristomium forming a large smooth ring around prostomium dorso-laterally, with narrow interruption middorsally ( Fig. 26C, D ). Mouth obscured by everted proboscis in holotype, which is observed as soft inflated sac ( Fig. 26E ).

Parapodia biramous; inconspicuous in chaetigers 1-14, becoming conical and prominent from around chaetiger 15. Tiny dorsal cirri detectable from chaetiger 13 in holotype, whereas ventral cirri occur from chaetiger 15; both cirri best developed from chaetigers 16 and 17, remaining small and conical (less than 1/2 the size of corresponding podial lobes) ( Fig. 26F ); without pigmentation; internal glands not detected in few cirri present ( Fig. 26G ). Interramal papilla present, well developed from chaetiger 15 ( Fig. 26 ).

Curved acicular spines present in notopodia only on chaetigers 1‒4 ( Fig. 26H ); spines in chaetiger 4 transitional between distinct spines and capillaries. Notopodia with about 14 spines arranged in two rows in chaetigers 1and 2 and with about five spines arranged in one row in chaetigers 3 and 4; spines accompanied posteriorly by single row of capillaries. Spines in chaetigers 1-3 curved, straw-coloured, with hirsute shaft, narrowing to slender, elongated and hirsute tip ( Fig. 26H ); spines in chaetiger 4 transitional, more slender and straighter than in chaetigers 1-3, but with hirsute shafts and shorter unlike accompanying capillaries. Short spinous chaetae anterior to spines not observed. Subsequent chaetigers with long thin capillaries in both rami, but very few present ( Fig. 26I ). Lyrate chaetae likely from chaetiger 5 in both rami, where very short and difficult to observe; best observed from chaetiger 8; accompanied by very few capillaries. Lyrate chaetae initially short but becoming longer and very prominent from around chaetiger 8; with unequal tynes bearing short bristles ( Fig. 26I, J ), numbering up to 5 or 6 in each ramus. The rest of the body and pygidium unknown.

Genetic data.

GenBank MN217428-MN217431 for 16S, MN217499 for 18S and MN217518-MN217519 for COI. This species is genetically very similar to one sequence published in Janssen et al. (2015), with a K2P value of 0.008 between O. tani and the already published sequence with accession number KJ736365. The three Oligobregma species in this study form a well-supported clade, with Oligobregma tani sp. nov. as sister to Oligobregma brasierae sp. nov. in our phylogenetic analyses ( Fig. 32 ).

Remarks.

The UKSR-collected species is most similar to Oligobregma quadrispinosa described from abyssal Southern Ocean ( Schüller and Hilbig 2007) in having the first four notopodia with acicular spines, lyrate chaetae from chaetiger 5 and podial cirri arising from around chaetiger 13-15. However, O. quadrispinosa differs in the following characters; spines in chaetiger 4 are prominent, stout and not hirstue, while the median and posterior chaetigers bear much larger ventral cirri. The UKSR species also has very prominent round "Mickey Mouse"-like anterior prostomial lobes (observed in all four specimens examined). For comparison with other Oligobregma species see Table 3 .

Ecology.

Found in polymetallic nodule province of the eastern CCZ.

Etymology.

Named in honor of Koh Siang Tan, member of the science party of the ABYSSLINE AB02 cruise onboard the RV Thomas G. Thompson.

Figures

Figure 26. Oligobregma tani sp. nov. holotype (specimen NHM _ 1454). A Lab image, whole specimen (pre-stain,) B Live image, whole specimen C Lab image, dorsal anterior, (stained, h = prostomial horns, pe = peristomial ring) D Lab image, lateral anterior, (stained, h = prostomial horns, pe = peristomial ring) E Lab image, ventral anterior, (stained, vm = ventral midline) F Lab image, mid-body parapodia (faded stain, dc = dorsal cirrus, vc = ventral cirrus, ip = interramal papilla) G Lab image, detail of dorsal cirrus, with no internal gland visible (dc = dorsal cirrus) H Lab image, detail of hirsute spines on notopodia on chaetiger 1 ([left panel]) I Lab image, detail of capillary and lyrate chaetae on chaetiger 12 J Lab image, detail lyrate chaetae. Morphological features in plates F, G have been outlined with a fine white line to improve clarity of those features. Scale bars: 0.5 mm (A, C, E); 50 μm (G-I).

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).