Ammotrypanella keenani, 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

Ammotrypanella keenani sp. nov. Fig. 6 A–J

Material examined.

NHM_1166C NHMUK ANEA 2019.7109, coll. 26 Feb. 2015, 12°06.93N, 117°09.87W, 4100 m http://data.nhm.ac.uk/object/483c6faa-0338-4cf5-a21d-6f448c72f4aa; NHM_1250 (holotype) NHMUK ANEA 2019.7110, coll. 01 Mar. 2015, 12°15.44N, 117°18.13W, 4302 m http://data.nhm.ac.uk/object1514d25d-b485-4b90-8981-3e84381bf250; NHM_1871 (paratype) NHMUK ANEA 2019.7111, coll. 13 Mar. 2015, 12°02.49N, 117°13.03W, 4094 m http://data.nhm.ac.uk/object/d93680b5-a3a3-4623-afc4-17062e1a1a58; NHM_1949 NHMUK ANEA 2019.7112, coll. 14 Mar. 2015, 12°11.406N, 117°22.282W, 4182 m http://data.nhm.ac.uk/object/cff2696d-06ab-42a1-843e-6ef894872f32.

Type locality.

Pacific Ocean, CCZ, 12°15.44N, 117°18.13W, depth 4302 m, in mud between polymetallic nodules.

Description.

This is a small to medium-sized species (6-16 mm long), represented by four specimens. NHM_1250 and NHM_1871 are complete specimens in good condition 12 mm long and 0.8 mm wide for 38 chaetigers and 16 mm long and about 1 mm wide respectively for 38 chaetigers. NHM_1166C and NHM_1949 are complete, but much smaller specimens in poor condition, 6-7mm long, with mid-body region twisted and damaged, therefore the exact number of chaetigers cannot be established, but at least 34 chaetigers observed in both specimens.

Body cylindrical, iridescent and smooth, no annulation detectable. Ventral groove along the entire body length. Preserved specimen pale yellow in ethanol ( Fig. 6A ). Live specimens translucent with orange gut ( Fig. 6B ). First 5-8 and posterior (branchial and 7 postbranchial) chaetigers crowded, chaetigers in midbody elongated.

Prostomium conical with distinct, slightly elongated palpode (NHM_1871, NHM_1166C) ( Fig. 6C, H ) or broad with short, button-like palpode ( Fig. 6D, E ). (NHM_1250, NHM_1949). Nuchal organs everted in NHM_1871, not pigmented ( Fig. 6C, H ).

Branchiae present, but limited to posterior region only, where at least 10 or 11 pairs present in chaetigers 22(23)-32, but only seven pairs were observed in smaller specimens (NHM_1166C and NHM_1949). All branchiae cirriform; first two pairs observed in NHM_1781 reduced in size, with the first pair (ch. 22) smallest ( Fig. 6F ); first (ch. 23) and last pair observed in NHM_1250 reduced in size ( Fig. 6G ); all branchiae of similar size in NHM_1166C and NHM_1949.

Parapodia distinct, biramous; observed as broad lobes in chaetigers 1-5 ( Fig. 6H ), becoming smaller in subsequent chaetigers; parapodia embedded in distinct lateral grooves. Chaetae are capillaries ( Fig. 6I ), anterior 5-8 crowded chaetigers with numerous chaetae in bundles, fewer chaetae in following chaetigers; chaetae longest in the anterior crowded chaetigers.

Anal tube the length of about half of the length of abranchiate posterior region, elongated, cylindrical; distal end with circlet of about four tightly packed cushion-like pads and thickened ventral pad observed in specimen NHM_1250 (damaged in other specimens) ( Fig. 6J ), ventral cirrus not observed.

Genetic data.

GenBank MN217408-MN217411 for 16S, MN217491 for 18S and MN217513-MN217514 for COI. This species is genetically identical or very similar to COI sequences attributed to " Opheliidae sp. 2" in Janssen et al. (2015) collected in the German and French exploration contract areas, with K2P values ranging from 0.0-0.008 between A. keenani sp. nov. and specimens with accession numbers KJ736399-KJ736403. In our phylogenetic analyses A. keenani sp. nov. is basal in a well-supported clade containing the three other Ammotrypanella species from this study.

Remarks.

Posterior distribution of branchiae and variously preserved cylindrical tube was observed in all specimens examined, irrespective of their size. These specimens represent one of several species consistent with genus Ammotrypanella recognized from the UKSR material. This species is most similar to Ammotrypanella sp. NHM_1653 in the relatively small body size and possession of an elongated (cylindrical) anal tube. This species can be distinguished from other Ammotrypanella material in this study and known Ammotrypanella species in having an anal tube distally with 4 or 5 cushion-like pads rather than distinct cirri, although this observation is based on only single specimen.

Ecology.

Found in the eastern part of polymetallic nodule province in the CCZ.

Etymology.

Named in honor of Edward Keenan, boatswain onboard RV Melville on the AB01 ABYSSLINE cruise in 2013.

Figures

Figure 6. Ammotrypanella keenani sp. nov. A Lab images, whole specimens (holotype [specimen NHM _ 1250], post-staining, faded stain [left], paratype NHM _ 1871, unstained [right]) B Live images, whole specimens (holotype [left], paratype NHM _ 1871 [right]) C Lab image, prostomium (paratype NHM _ 1871, damaged, no = everted nuchal organ) D Lab image, prostomium (holotype, p = palpode) E Lab image, detail of palpode (holotype) F Lab image, posterior branchiae (paratype NHM _ 1871, br = branchiae) G Lab image, posterior branchiae (holotype, br = branchiae) H Live image, anterior (paratype NHM _ 1871, pp = parapodia, no = nuchal organ) I Lab image, detail of capillary chaetae (holotype) J Lab image, detail of anal funnel, ventro-distal (left) and latero-distal (right) views (holotype, stained, cp = cushioned pad, vc = ventral cirrus). Morphological features in plates C-H, J have been outlined with a fine white line to improve clarity of those features. Scale bars: 1 mm (A, F, G); 100 μm (E, I).