Macellicephala parvafauces, 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 : 604-607

MACELLICEPHALA PARVAFAUCES SP. NOV.

( FIG. 15A–I; TABLES 1, 2, 4)

Type material: Holotype, MNHN-IA-TYPE 1830 ( IFR602 ), complete, length 11.82 mm, width 1.50 mm, 18 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 nodules, station 189, collected 20–21 April 2015, ROV Kiel 6000, biobox, start 18°47.80′N, 128°18.53′W, end 18°48.13′N, 128°18.20′W, 4933–4964 m depth . Paratype, MNHN-IA-TYPE 1831 ( IFR403 ), complete, length 8.02 mm, width 1.05 mm, 18 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, GSR license area, station 131, collected 9–10 April 2015, ROV Kiel 6000, biobox, start 13°52.39′N, 123°15.03′W , end 13°52.44′N, 123°14.88′W, 4478 m depth.

Description (based on holotype and paratype): Holotype complete, 11.82 mm long and 1.50 mm wide for 18 segments, slightly dorsoventrally flattened, not tapering posteriorly; live specimen whitish anteriorly and slightly brownish posteriorly; ethanol-preserved specimen pale yellow throughout ( Fig. 15A, C). Body surface smooth.

Prostomium bilobed, about as wide as long, lobes pronounced anteriorly, truncated; small, oval frontal filaments present, inserted at innermost margin of prostomial lobes; median notch between prostomial lobes moderately wide and deep ( Fig. 15D); eyes absent. Median antenna present, lateral antennae absent; ceratophore of median antenna large, cylindrical, short (shorter than anterior margin of prostomial lobes), inserted near median notch, style missing. Palps smooth, tapering, short (reaching segment 4; Fig. 15D). Trilobed facial tubercle present, median tubercle larger than lateral ones ( Fig. 15B, D).

Tentacular segment with short lobes, inserted laterally and slightly ventral to prostomium; without acicula or chaetae; tentaculophores large, cylindrical,

References for species are provided in Table 2. The descriptions of the valid species Macellicephala alia and Macellicephala tricornis were not included (see Taxa selection for detail). ‘?’ indicates uncertain information.

equal sized ( Fig. 15D); styles missing. Pharynx not everted in holotype; dissected in paratype (MNHN-IA- TYPE 1831), with nine pairs of rounded to subtriangular, equal-sized distal papillae; two pairs of small jaws with main fang, margin smooth ( Fig. 15E). Second segment with elytrophores, subbiramous parapodia, chaetae and ventral cirri.

Nine pairs of large, bulbous elytrophores present on segments 2, 4, 5, 7, 9, 11, 13, 15 and 17; elytron dropped from segment 13 but still attached on segment 15, both elytra in poor condition; moderately large (partly covering preceding segment and subsequent two segments), surface smooth; posterior margin papillated, with large, short papillae.

Cirrigerous segments with large, bulbous dorsal cirrophores, inserted subdistally on notopodia; style smooth, tapering, long (reaching three or four subsequent segments, much longer than tip of neuroacicular lobe); dorsal tubercles distinct, conical, small ( Fig. 15D).

Ventral cirri smooth, tapering, present from segment 2 to last segment; inserted basally on neuropodia of segment 2, style long (longer than tip of neuroacicular lobe); in subsequent segments inserted medially on neuropodia (in middle body slightly subdistally on neuropodia), style short (shorter than tip of neuroacicular lobe), style longer than neuropodia lobe in last segment.

Parapodia subbiramous; notopodia shorter than neuropodia ( Fig. 15F). Dorsal ridges absent. Notopodia subtriangular, tapering into long acicular lobe, tip of notoacicula not penetrating epidermis. Neuropodia large, subtriangular, tapering into long acicular lobe, tip of neuroacicula not penetrating epidermis. Notochaetae moderate in number (15–20 observed), short to long, distally straight to slightly curved, with very faint spinous rows, with pointed tips ( Fig. 15G); some with slightly hooked tip; notochaetae as stout as neurochaetae. Neurochaetae of two types: (1) upper group, moderate in number (~20 observed), long to very long, distally flattened to concave, with very faint spinous rows along both margins, with pointed tips ( Fig. 15H), laterally appearing with hooked tips; and (2) middle and lower groups, moderate in number (~20 observed) long to short, distally flattened to concave with very faint spinous rows on both sides but distally not touching the margins, with minute hooked tips ( Fig. 15I).

Nephridial papillae on segments 10, 11 and 12, small, bulbous ( Fig. 15C). In last segment, notopodia and neuropodia of similar size. Pygidium rounded, not enclosed by last segment; with dorsal anus ( Fig. 15A). Anal cirri lost, scars not seen.

Morphological variation: The specimens found in the CCFZ are highly similar. The only difference between them concerns the chaetae. In the holotype, the chaetae are slightly wilted, giving an impression of flatness, whereas in the paratype the chaetae have the usual appearance. This could be an artefact of the fixation/ conservation process .

Remarks: Macellicephala parvafauces sp. nov. is closer to Macellicephala violacea ( Levinsen, 1886) and Macellicephala australis Wu & Wang, 1987 , having a smooth body surface and neurochaetae with hooked tips ( Table 4). However, the styles of the dorsal cirri in Macellicephala violacea are shorter than the tip of neuropodial lobe, whereas in Macellicephala australis they are longer, as in Macellicephala parvafauces sp. nov. This new species also has prostomial lobes anteriorly truncated and conical dorsal tubercles, whereas Macellicephala australis has prostomial lobes anteriorly rounded and no dorsal tubercles.

Etymology: The species name came from the Latin ‘ parvă fauces ’ meaning ‘small jaws’. It refers to the relatively smaller jaws of this species.

Genetic data: DNA sequencing for this species was successful for COI, 16S and 18S. The holotype and paratype shared 98.6% of genetic material in COI and 100% in 16S or 18S. The average K2P distance for intraspecific variation was 1.4% for COI and 0.0% for 16S.

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

Ecological notes: The holotype was extracted from a sponge, Corbitella discasterosa Tabachnick & Lévi, 2004 ( Kersken et al., 2018), indicating a commensal life mode with this sponge.