Laetmonice paxtonae, Flaxman & Kupriyanova, 2024

Laetmonice paxtonae View in CoL sp. nov.

urn:lsid:zoobank.org:act:9972720B-ECA3-48E0-BFC9-360169DD585A

Figs. 3d View Figure 3 , 4d View Figure 4

Material examined. Holotype: AM W.53419, Christmas Island NW, 463 m, 8 July 2021 . Paratypes: AM W. 54522, 463 m, 8 July 2021 ; AM W. 54523, 463 m, 8 July 2021 .

Description. Holotype ( Fig. 3d View Figure 3 ), with 33 segments, length 34 mm, maximum width 24 mm (including chaetae) and 12 mm (excluding chaetae). Body ovate to elongate, dorsoventrally flattened, dorsal felt absent. Ventral surface cream-coloured, covered with fine papillae.

Prostomium rounded and small (one fifth of body width at its widest point), with a small pair of anterolateral cylindrical ocular peduncles, one third length of prostomium, a gap between them and with two pairs of eyes. Ceratophore of median antenna elongated, located behind ocular peduncles ( Fig. 4d View Figure 4 ); style missing. Palps missing. Nuchal flaps present ( Fig. 4d View Figure 4 ). Facial tubercle located below ocular peduncles with long papillae.

Elytra 15 pairs, attached to elytrophores on segments 2, 4, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 28 and 31, completely covering dorsum; elytra large, rounded, smooth, semitranslucent white, without tubercles or papillae on surface and margins. Dorsal cirri present on segments without elytra; cirrophores large, styles missing.

First segment elongated conical uniramous parapodia, basally papillated, with four tufts of fine, pale golden acicular chaetae, extending from dorsal and ventral margins of parapodia, two anterior and two posterior. Each parapodia with a pair of long dorsal and ventral tentacular cirri, with large cirrophores and extending laterally (styles missing).

Following segments with biramous parapodia. Segments 2–4 notopodia with pointed aciculum and segment 2 with row of approximately 30 long acicular chaetae running dorsoventrally along the anterior margin. Neuropodium conical, with two tiers of neurochaetae; lower tier with numerous golden bipinnate neurochaetae, upper tier with one to two neurochaetae, with basal spur and distal fringe of hairs. Neuropodia from segment 5 to posterior end elongated, cylindrical with inflated base; three to four golden yellow neurochaetae with basal spur and distal fringe of hairs. Ventral cirri appear absent or missing from all specimens, however there are apparent scars on the middle of some neuropodia.

Elytrigerous notopodia with tuft of approximately 20 translucent acicular notochaetae, tapering with fine, pointed tip, posterio-laterally oriented from triangular acicular lobe. Lateral to acicular notochaetae, up to 12 harpoon notochaetae, with very fine tubercles and three to four fangs. Approximately 10 very fine, short acicular chaetae directly anterior of harpoon chaetae.

Cirrigerous notopodia elongated, with pointed acicular lobe and four tufts of notochaetae; two tufts (one dorsal, one ventral) of ~40 long golden acicular chaetae with fine pointed tips, then ~10 long stiff acicular chaetae posterior to aciculum, and ~60 short, fine chaetae fanning along posterior margin. Elongated cirrophore and aciculum located on posterior margin, oriented posterior-laterally.

Variation. Specimens range from 32 to 36 mm in body length, number of segments from 33 to 35 and number of elytra pairs from 14 to 15.

Diagnosis. As for the genus; with a combination of: 33–35 segments, 14–15 elytra pairs, presence of prostomial nuchal flaps, two pairs of eyes, facial tubercle with long papillae, up to 12 harpoon chaetae per notopodium, with finely tuberculate shafts and three to four fangs, long acicular notochaetae equal in length to body width. Most similar to Laetmonice wonda .

Etymology. This species is named after Dr Hannelore Paxton (Macquarie University andAustralian Museum), an expert in taxonomy of polychaetes, who has made numerous important contributions to taxonomy of polychaetes, especially those of the family Onuphidae .

Distribution. Only known from off the Northwest corner of Christmas Island seamount in 463 m.