Bathyeliasona mariaae, Bonifácio & Menot, 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 : 583-585

BATHYELIASONA MARIAAE SP. NOV.

( FIG. 7A–J; TABLES 1, 2)

Type material: Holotype, MNHN-IA-TYPE 1815 ( IFR107 ), complete, length 9.86 mm, width 1.88 mm, 17 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, BGR license area, station 50, collected 26 March 2015, epibenthic sledge supra-net, start 11°49.592′N, 117°30.786′W, end 11°49.756′N, 117°29.574′W, 4360– 4328 m depth, 2469 m trawling distance . Paratype, MNHN-IA-TYPE 1816 ( IFR666-4 ), complete, length 2.90 mm, width 0.44 mm, 15 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 , station 197, collected 22 April 2015, epibenthic sledge epi-net, start 18°48.659′N, 128°22.753′W, end 18°49.088′N, 128°21.289′W, 4805–4823 m depth, 2529 m trawling distance .

Description (based on holotype and paratype): Holotype complete, 9.86 mm long and 1.88 mm wide for 17 segments (including tentacular segment), dorsoventrally slightly flattened, not tapering posteriorly; live specimen iridescent, purplish in colour dorso-anteriorly, prostomium whitish ( Fig. 7A, B); ethanol-preserved specimen pale yellow, prostomium whitish; golden aciculae.

Prostomium bilobed, about as wide as long, lobes pronounced, anteriorly extending into slender, long frontal filaments; median notch between prostomial lobes moderately wide and deep; eyes absent; a pair of comma-shaped, pigmented nuchal organs in a slight depression present on mid anterior prostomial lobes ( Fig. 7B, C). Median antenna present, lateral antennae absent; ceratophore of median antenna cylindrical, long (not surpassing anterior end of frontal filaments), inserted in median notch, style missing. Palps smooth, tapering, very long (reaching to segment 8; Fig. 7C). Facial tubercle absent.

Tentacular segment with elongate acicular lobe, inserted laterally and slightly ventral to prostomium; with acicula not penetrating epidermis, with chaetae; tentaculophores small, cylindrical, equal sized, insertion arranged horizontally, inserted distally; tentacular styles papillated, tapering, long (reaching segment 5), thin; dorsal tentacular style (innermost, now lost in holotype) slightly longer than ventral (outermost) tentacular style ( Fig. 7C). Pharynx not everted in holotype; dissected in paratype (MNHN-IA- TYPE 1816 ) with nine pairs of subtriangular, equalsized distal papillae; two pairs of jaws, each with main fang, margin smooth ( Fig. 7D). Second segment with elytrophores, subbiramous parapodia, chaetae and ventral cirri .

Eight pairs of distinct, knob-like elytrophores present on segments 2, 4, 5, 7, 9, 11, 13 and 15 (all elytra missing).

Cirrigerous segments with distinct, cylindrical dorsal cirrophores ( Fig. 7F), inserted subdistally on notopodia; styles missing; dorsal tubercles absent.

Ventral cirri smooth, tapering, present from segment 2 to last segment; inserted basally on neuropodia of segment 2, style short (much shorter than tip of neuroacicular lobe); in subsequent segments inserted subdistally on neuropodia ( Fig. 7F), styles short (approaching tip of neuroacicular lobe); in last segment, style longer than in preceding segments.

Parapodia subbiramous; notopodia shorter than neuropodia ( Fig. 7F). Notopodia arising from the dorsum, as two thickened ridges; notopodia 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. The last pair of parapodia similar to preceding ones. Notochaetae of two types: (1) very few (four observed), short, stout, slightly curved with distinct spinous rows on convex side, with blunt tips ( Fig. 7G); and (2) moderate in number (12 observed), long to very long, slender, slightly curved with distinct, well-developed, clear spinous rows, occasionally one of those notochaetae can be stouter and straight ( Fig. 7H), with blunt tips; notochaetae stouter and narrower than neurochaetae. Neurochaetae of two types: (1) upper group, variable in number (three to 19 observed), long, distally very wide, flattened, serrated along both margins, with pointed tips ( Fig. 7I); and (2) middle and lower group, numerous (12–35 observed), long to short, distally wide, flattened, serrated along both margins, with pointed tips ( Fig. 7J), with a kind of central rib distally present on some specimens ( Fig. 7J).

Nephridial papillae absent. Pygidium ventrally bilobed, lobes subconical; enclosed by last segment; with dorsal anus ( Fig. 7A, E). Anal cirri lost, scars not seen.

Morphological variation: The specimens found in the CCFZ are morphologically very similar, having 15 and 17 segments. The common morphological characters included: shape of prostomium and form of prostomial appendages, shape of parapodia and types of chaetae. However, the specimen with 15 segments showed some differences probably related to growth: seven pairs of elytrophores, median notch less prominent, longer ventral cirri, longer palps, pygidium not clearly bilobed and not enclosed by the last parapodia.

R e m a r k s: O n l y t h r e e s p e c i e s b e l o n g i n g t o Bathyeliasona are known: Bathyeliasona kirkegaardi ( Uschakov, 1971) , Bathyeliasona abyssicola ( Fauvel, 1913) and Bathyeliasona nigra Hartman, 1967 . These species were reviewed by Pettibone (1976), who separated them using characters such as the number of segments, type of notochaetae and development of notopodia/neuropodia in the last segments. Although not mentioned by Pettibone (1976), differences in the shape of pygidium can be highlighted from her drawings, which can also be used to separate species. The species Bathyeliasona abyssicola and Bathyeliasona nigra have 18 segments (including tentacular segment), whereas Bathyeliasona kirkegaardi has 17 segments, like Bathyeliasona mariaae sp. nov. Additional similarities between the latter two species are: shape of jaws, shape of pygidium and notopodial lobes shorter than neuropodia on the last segments. However, while Bathyeliasona mariaae sp. nov. has prostomial lobes anteriorly extending into long frontal filaments that reach the distal end of the ceratophore of the median antenna, in Bathyeliasona kirkegaardi the prostomial lobes are anteriorly rounded and the frontal filaments are minute and filiform, shorter than the ceratophore of the median antenna. Furthermore, in Bathyeliasona kirkegaardi , Bathyeliasona abyssicola and Bathyeliasona nigra the length of the ventral cirri is much shorter than the neuroacicular tip and the notochaetae are of one type only (stout with distinct spinous rows), whereas in Bathyeliasona mariaae sp. nov. the length of the ventral cirri is approaching the neuroacicula tip and the notochaetae are of two types (stouter with distinct spinous rows and slender with developed spinous rows). Pettibone (1976) described all the Bathyeliasona species with notochaetae more slender than neurochaetae, but in Bathyeliasona mariaae sp. nov. one notochaeta per notopodium can be stouter (and always narrower) than the neurochaetae. Furthermore, in Bathyeliasona mariaae sp. nov. the middle and lower neurochaetae show a kind of central rib distally that gives the neurochaetae a bilimbate appearance.

Etymology: This species is dedicated to Maria Silva, mother of P.B., for her love.

Genetic data: DNA sequencing for this species was successful for COI, 16S and 18S, with all three genes sharing 100% of genetic material between the specimens. The average K2P distance for intraspecific variation was 0.0% for both COI and 16S.

Distribution: Based on the material examined (two specimens), this species has a wide distribution within the Clarion-Clipperton Fracture Zone, being sampled in BGR license (type locality) and APEI#3 areas.