Abyssarya, 2019

Bonifácio, Paulo & Menot, Lénaïck, 2019, New genera and species from the Equatorial Pacific provide phylogenetic insights into deep-sea Polynoidae (Annelida), Zoological Journal of the Linnean Society 185, pp. 555-635 : 577-580

ABYSSARYA ACUS GEN. NOV., SP. NOV.

( FIG. 5A–Q; TABLES 1, 2)

Type material: Holotype, MNHN-IA-TYPE 1811 ( IFR632- 2 ), complete, length 4.77 mm, width 0.40 mm, 18 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 seamount, station 212, collected 24 April 2015, ROV Kiel 6000, biobox, start 18°32.83′N, 128°44.88′W, end 18°32.57′N, 128°44.93′W, 1853– 1713 m depth . Paratype 1, MNHN-IA-TYPE 1812 ( IFR632-5 ), complete, length 3.50 mm, width 0.36 mm, 18 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 seamount, station 212, collected 24 April 2015, ROV Kiel 6000, biobox, start 18°32.83′N, 128°44.88′W, end 18°32.57′N, 128°44.93′W, 1853– 1713 m depth . Paratype 2, MNHN-IA-TYPE 1813 ( IFR632-1 ), complete, length 4.64 mm, width 0.53 mm, 18 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 seamount, station 212, collected 24 April 2015, ROV Kiel 6000, biobox, start 18°32.83′N, 128°44.88′W, end 18°32.57′N, 128°44.93′W, 1853– 1713 m depth . Paratype 3, NHMUK 2018.25346 ( IFR632-3 ), posterior fragment, used for molecular analysis and SEM, Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone , APEI#3 seamount, station 212, collected 24 April 2015, ROV Kiel 6000, biobox, start 18°32.83′N, 128°44.88′W, end 18°32.57′N, 128°44.93′W, 1853– 1713 m depth .

Additional material: P.B. 's collection ( IFR632-4 ), complete, length 2.77 mm, width 0.29 mm, 16 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 seamount, station 212, collected 24 April 2015, ROV Kiel 6000, biobox, start 18°32.83′N, 128°44.88′W, end 18°32.57′N, 128°44.93′W, 1853– 1713 m depth .

Description (based on holotype and paratypes): Holotype complete, 4.77 mm long and 0.40 mm wide for 18 segments (including tentacular segment), dorsoventrally flattened, slightly tapering posteriorly ( Fig. 5A); colour of live animal not known; ethanolpreserved specimen pale white.

Prostomium bilobed, about as wide as long, lobes moderately pronounced, anteriorly extending as oval projections, ventrally directed; small, oval frontal filaments present, inserted at innermost margin of prostomial lobes, between lobes and oval projections; median notch between prostomial lobes moderately wide and deep ( Fig. 5A, H, I); eyes absent. Median antenna present, lateral antennae absent; ceratophore of median antenna bulbous, large, inserted anteromedially on prostomium (in the notch); style smooth, tapering into thin tips, long (reaching segment 4). Palps smooth, tapering, short (reaching around segment 2), ventrally directed, shorter than all tentacular appendages ( Fig. 5I). Facial tubercle absent.

Tentacular segment fused to prostomium, with short lobe, inserted laterally and slightly ventral to prostomium; achaetous; tentaculophores large, cylindrical, equal sized; tentacular styles smooth, tapering, long, dorsal tentacular style (reaching segment 6) longer than ventral style ( Fig. 5H). Pharynx not everted on holotype, dissected in paratype (MNHN-IA-TYPE 1812); the pharyngeal papillae could not be counted; two pairs of jaws, each with main fang, margin smooth ( Fig. 5J). Second segment with elytrophores, subbiramous parapodia, chaetae and ventral cirri.

Nine pairs of large, bulbous elytrophores, on segments 2, 4, 5, 7, 9, 11, 13, 15 and 17; elytra large (covering dorsum and parapodia; the largest overlapping about four to five segments), thin, translucent, rounded ( Fig. 5H); margin smooth; surface covered uniformly, moderate number of rounded microtubercles ( Fig. 5K).

Cirrigerous segments with large, bulbous dorsal cirrophores ( Fig. 5L), inserted subdistally on notopodia; styles smooth, tapering to thin tips, long (longer than neuropodial pre-chaetal lobe); dorsal tubercles absent ( Fig. 5L).

Ventral cirri smooth, tapering, present from segment 2 to last segment; inserted basally on neuropodia of segment 2, style long (as long as neuropodial pre-chaetal lobe); in subsequent segments inserted medially on neuropodia ( Fig. 5L, M), style short (much shorter than distal neuropodial pre-chaetal lobe).

Parapodia subbiramous; notopodia reduced, much shorter than neuropodia ( Fig. 5L). Dorsal ridges with one to three folds in all segments. Notopodia reduced, subtriangular, tapering into long acicular lobe, tip of notoacicula not penetrating epidermis. Neuropodia large, rectangular to subtriangular, tapering into long acicular lobe, tip of neuroacicula not penetrating epidermis, neuroacicula reaching midway of pre-chaetal lobe; pre-chaetal lobe expanded, lanceolate (usually approaching the end of neurochaetae in length); postchaetal lobe poorly developed, short, pointed; ventral lobe, oval, small ( Fig. 5L, M). Notochaetae very few (one or two observed), short, slightly curved, distally with distinct, faint spinous rows on convex side, with blunt tips ( Fig. 5B, C, N); notochaetae more slender than neurochaetae. Neurochaetae of two types: (1) upper and middle groups, moderate in number (24 observed), long, slightly curved, distally, with distinct, faint spinous rows on convex side, with slightly bent blunt tip (occasionally presenting a very small secondary apical tooth; Fig. 5D, E, O); and (2) lower group, few (eight to ten observed), short, distally falcate, with faint spinous rows ( Fig. 5F, G, P, Q); on segment 2, the lower group with strongly bent tips ( Fig. 5Q); on segments 17 and 18 slightly more bent than on preceding segments.

Nephridial papillae present from segment 5 to end of body, small, bulbous ( Fig. 5M); slightly enlarged, digitiform in mid body. Pygidium rounded, inflated dorsally, not enclosed by last segment; with terminal anus

( Fig. 5A). In paratype (MNHN-IA-TYPE 1812) anal cirri observed, smooth, tapering to thin tips, very long (reaching segment 9).

Morphological variation: The specimens differing in number of segments (16 and 18) otherwise showed great morphological similarities, including: size of appendages, form of prostomium and its appendages, first occurrence of nephridial papillae, form of parapodia and type of chaetae. However, animals with 16 segments had eight pairs of elytrophores instead of nine pairs, probably related to size.

Remarks: No other genera of Macellicephalinae show neuropodia with lanceolate pre-chaetal lobes and falcate neurochaetae differing between segment 2 and subsequent segments. In Uncopolynoinae the species Uncopolynoe corallicola likewise shows strongly curved hooks present in anterior segments ( Wehe, 2006). This character might be linked to the life history of these worms, which are always found living on alcyonarian corals. Furthermore, Parahololepidella greeffi (Augener, 1918) is commensal on antipatharians ( Britayev et al., 2014) and shows neurochaetae rather similar to Abyssarya acus gen. nov., sp. nov. This evidence reinforces a possible commensal relationship between Abyssarya acus gen. nov., sp. nov. and corals recovered from the same sampling biobox.

Etymology: The species name came from Latin ‘ ăcŭs ’ meaning ‘needle’. It refers to modified neurochaetae present on segment 2 similar to a ‘crochet needle’.

Genetic data: DNA sequencing for this species was successful for COI, 16S and 18S, respectively sharing at least 99.1, 99.8 and 100% of genetic material between the specimens. The average K2P distance for intraspecific variation was 0.5% for COI and 0.1% for 16S.

Distribution: Only five specimens were sampled and all at a single station within the Clarion-Clipperton Fracture Zone in APEI#3 seamount area (type locality).

Ecological notes: These worms were found in the water sieved from the ROV biobox at station 212, which contained sponges ( Hexactinellidae ), alcyonaceans, antipatharians and pennatulacean corals, in addition to ophiuroids. Abyssarya acus gen. nov., sp. nov. is likely to be commensal with one of these taxa, and more studies in the area are needed to identify the host.