Oligobregma whaleyi, 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 whaleyi sp. nov. Fig. 27 A–I

Material examined.

NHM_822 (holotype) NHMUK ANEA 2019.7160, coll. 20 Feb. 2015, 12°32.23N, 116°36.25W, 4425 m http://data.nhm.ac.uk/object/dde1c8f9-f87a-430b-be9d-5e34685772bb.

Type locality.

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

Description.

Large species, represented by a single, posteriorly incomplete specimen, with 26 chaetigers, 16 mm long and about 2 mm wide at widest (inflated) region (first eight chaetigers, particularly chaetigers 3-8), with another widening of the body in chaetigers 23-26, likely due to sediment ingestion. Colour in alcohol creamy white, without body pigment, live specimens semi-translucent ( Fig. 27A ). Anterior body segments appear smooth, without distinct annulation, chaetigers 1-5 with three transverse rows of weakly developed lobes; subsequent segments quadriannulated until the end of the fragment (chaetiger 26) ( Fig. 27B, C ). Ventral midline on venter prominent, from chaetiger 2, composed of a row of large pads within a groove ( Fig. 27C ). Branchiae absent.

Prostomium broadly rounded anteriorly, weakly expanded laterally, narrowing posteriorly; with two well-developed, anterior rounded lobes (horns) emerging from anterior prostomial margin ( Fig. 27D ). Eyes absent. Proboscis observed as a soft, smooth sac-like structure. Peristomium forming smooth figure-of-8-like loops laterally to prostomium ( Fig. 27D ), dorsally interrupted, ventrally obscured by extended proboscis; with faint light-brown pigmentation.

Parapodia biramous; conspicuous even in anterior-most segments ( Fig. 27E ), becoming longer and prominent from around chaetiger 10. Dorsal and ventral cirri appear abruptly from chaetiger 14, where similar to those on subsequent segment; relatively small (about 1/2 the size of associated podial lobes) in posterior chaetiger; all conical with broad base ( Fig. 27E ), without pigmentation; some dorsal and ventral cirri with gold-pigmented internal glands, now bluish upon uptake of Shirlastain ( Fig. 27F ). Interramal papilla present, inconspicuous in anterior parapodia, well developed from chaetiger 10 ( Fig. 27E ).

Curved acicular spines present in notopodia and neuropodia on chaetigers 1‒4. Notopodia with about 15 spines arranged in irregular row, accompanied posteriorly by single row of capillaries; neuropodial spines fewer in numbers arranged irregularly. Spines slightly curved, narrowing to slender elongated tip ( Fig. 27G ). Short spinous chaetae anterior to spines not observed. Subsequent chaetigers with long thin capillaries in both rami ( Fig. 27H ). Lyrate chaetae at least from chaetiger 11, in both rami, positioned anteriorly to capillaries. Lyrate chaetae short, with unequal tynes bearing short bristles ( Fig. 27I ), numbering 12-20 per noto- and neuropodium. The rest of the body and pygidium unknown.

Genetic data.

GenBank MN217432 for 16S and MN217500 for 18S. The three Oligobregma species in this study form a well-supported clade. Oligobregma whaleyi sp. nov. is sister to a clade consisting of Oligobregma tani sp. nov. and Oligobregma brasierae sp. nov. in our phylogenetic analyses ( Fig. 32 ).

Remarks.

The UKSR-collected species O. whaleyi sp. nov. differs from other Oligobregma species bearing spines on the first four chaetigers in having a peristomial ring forming a figure-of-8 loops laterally to prostomium and in furcate chaetae appearing more posteriorly (first observed on chaetiger 11 although due to its large size the specimen was difficult to manipulate and removal of several parapodia would have damaged the single specimen significantly), while in other species the furcate chaetae are present from chaetiger 6. In O. lonchochaeta Detinova (1985) described the furcate chaetae as occurring only in mid- and posterior chaetigers but without specifically stating on which chaetiger they were first observed. Therefore, the newly described species can be distinguished from O. lonchochaeta by having the anterior chaetigers smooth, rather than triannulated. For further comparison see Table 3 .

Ecology.

Found in polymetallic nodule province of the eastern CCZ.

Etymology.

Named in honor of Jeremy Whaley, Able Seaman onboard RV Melville on the ABYSSLINE cruise AB01 in 2013.

Figures

Figure 27. Oligobregma whaleyi sp. nov. holotype (specimen NHM _ 822). A Lab (upper) and live (lower) images, whole specimens [lab image] B Lab image, mid-body segments and annulation C Lab image, ventral midbody (vm = ventral midline) D Live (left) and lab (right) images of prostomium (pe = peristomial ring, h = prostomial horns) E Lab images, midbody and posterior parapodia, chaetigers 15 (left) and 24 (right) (dc = dorsal cirrus, vc = ventral cirrus, ip = interramal papilla) F Lab image, detail of dorsal cirrus and internal gland (dc = dorsal cirrus, ig = internal gland) G Lab image, detail of notopodial spines on chaetiger 1 H Lab image, detail of capillary chaetae (lc = lyrate chaetae) I Lab image, detail of lyrate chaetae. 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); 100 μm (F-H); 50 μm (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).