Scalibregmatidae sp. (NHM_2308)

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

Scalibregmatidae sp. (NHM_2308) Fig. 28 A–F

Material examined.

NHM_2308 NHMUK ANEA 2019.7161, coll. 01 Mar. 2015, 12°15.44N, 117°18.13W, 4302 m http://data.nhm.ac.uk/object/7b9d4ab8-4b7b-45c4-9cf4-6fd6b1229f48.

Description.

This species is represented by a single, small, posteriorly incomplete specimen, 2.5 mm long and 0.4 mm wide for about 12 chaetigers, in poor condition. Colour of preserved specimen creamy yellow ( Fig. 28A ). Anterior part of the body rugose, chaetigers 1-4 dorsally with two? (some damaged) transverse rows of tightly packed squarish lobes; subsequent chaetigers with three such row or damaged ( Fig. 28B ). Venter with prominent ventral midline from chaetiger 2 composed of a row of large pads within a groove ( Fig. 28C ).

Prostomium small, broadly rounded anteriorly, weakly expanded laterally, narrowing posteriorly; with two short, rounded lobes (horns) emerging anterolaterally from anterior prostomial margin ( Fig. 28D ). Eyes absent. Branchiae absent.

Heavily curved acicular spines present in notopodia only on chaetigers 1 and 2 ( Fig. 28D ). Notopodia of chaetigers 1, bearing 10 very prominent spines arranged in two rows, accompanied posteriorly by single row of capillaries; notopodia of chaetiger 2 with five spines arranged in a single row, accompanied posteriorly by single row of capillaries. Spines relatively straight, stout, straw-coloured, distally narrowing to slender, elongated and somewhat hairy tip ( Fig. 28E ). Short spinous chaetae anterior to heavy spines not observed. Neuropodia of chaetiger 1 and 2 with long slender capillaries; subsequent chaetigers with long thin capillaries in both rami. Lyrate chaetae from chaetiger 3 in both rami, positioned anteriorly to capillaries. Lyrate chaetae short, with unequal tynes bearing short bristles ( Fig. 28F ), around 4 or 5 per ramus.

Parapodia biramous, podial lobes not developed in 12 chaetigers long fragment. Dorsal and ventral cirri not observed in 12 chaetiger long fragment. Rest of the body unknown.

Genetic data.

GenBank MN217467 for 16S. Scalibregmatidae (NHM_2308) does not cluster convincingly with any other Scalibregmatidae species available on GenBank ( Fig. 32 ).

Remarks.

Poor preservation of mid body and missing posterior part prevents reliable identification to genus level. Observations from the anterior part (the absence of branchiae and presence of acicular spines) suggest that this may be yet another representative of genus Oligobregma in the UKSR-collected material. It can be distinguished from other scalibregmatid species in this study by having spines in notopodia of chaetigers 1 and 2 only.

Figures

Figure 28. Scalibregmatidae sp. NHM _ 2308 (specimen NHM _ 2308). A Lab image, whole specimen, dorsal view (pre-stain) B Lab image, dorsal anterior (stained) C Lab image, ventral anterior, (shirla stained, vm = ventral midline) D Lab image, detail of hirsute spines on chaetigers 1 and 2 E Lab image, detail of hirsute spine tips F Lab image, detail of lyrate chaeta. Scale bars: 1 mm (A-C); 100 μm (D); 50 μm (E); 10 μm (F).

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).