Paradiopatra acirrata Paxton & Budaeva, 2013, n. sp.

Paradiopatra acirrata n. sp.

Figures 1, 2; Table 2

Material examined. Type material—SLOPE 53: holotype (MV F192516); 4 paratypes (MV F192517); 1 paratype (AM W43548); 1 paratype, mounted for SEM (AM W43548.001).

Type locality. Pacific Ocean, off eastern Australia, S of Sydney, NSW: 34º54.72’S, 151º15.04’E, 996 m.

Diagnosis. Ovoid frontal lips; ceratophores without lateral projections; peristomial cirri absent; first three pairs of parapodia with pseudocompound bidentate falcigers with moderately long pointed hoods, shafts with spines in rows and scattered, appendages with scattered spines; subacicular hooks subequal, starting from chaetiger 9; branchiae single filaments, starting from chaetigers 16–21, present for short region; moderately-sized protomandibles.

Description. All examined specimens lacking posterior ends. Length of holotype 15 mm for 34 chaetigers, width 0.9 mm (at chaetiger 10, excluding parapodia); paratypes ranging from 6–15 mm long (19–27 chaetigers), 0.6–1.2 mm wide. Alcohol stored specimens overall cream-coloured, lacking colour pattern.

Prostomium very short, only half as long as wide, with paired, closely spaced ovoid frontal lips, directed anteroventrally (Fig. 1 A–C). Palps of holotype reaching peristomium (paratypes: peristomium–chaetiger 1); lateral antennae reaching chaetiger 3 (chaetigers 2–4); median antenna reaching chaetiger 1 (chaetiger 1). Ceratophores with well developed annulation, lacking lateral projections; ceratophores of lateral antennae with 5 (4–5) rings, median antenna with 4 (3–5) rings; distal ring twice as long as proximal ones. Nuchal grooves with wide middorsal separation, laterally curved towards lateral antennae. Eyes absent. Peristomium slightly shorter than first chaetiger. Peristomial cirri absent (Fig. 1 C).

First three pairs of parapodia modified, projecting anterolaterally, directed slightly ventrally (Fig. 1 D). Prechaetal lobes rounded on all parapodia; postchaetal lobes triangular to subulate in first four chaetigers, decreasing rapidly in size, absent from chaetiger 9 (7–9). Dorsal cirri well developed and subulate in anterior parapodia, becoming smaller and cirriform in median region. Ventral cirri subulate on first three chaetigers, third one shorter with blunt end in smaller paratypes, replaced by ovoid ventral glandular pads from chaetiger 4 (Fig. 1 B).

Parapodia supported by 2–3 aciculae projecting less than half as far as falcigers and limbate chaetae from prechaetal lobes (Fig. 2 A, B). First three pairs of parapodia with dorsal fascicle of 1–2 simple limbate chaetae and ventral fascicle of 3–4 bidentate pseudocompound falcigers with moderately long pointed hoods (Fig. 2 C); shafts of falcigers with scattered spines and two rows of spines, appendages with scattered spines (Fig. 1 E). Two fascicles of simple limbate chaetae starting from chaetiger 4. Ventral fascicle of limbate chaetae replaced by paired bidentate subacicular hooks from chaetiger 9, hooks unequal, upper one thicker and longer than lower one (Fig. 2 D). Pectinate chaetae (Fig. 1 F) with wide shafts, combs slightly oblique with 16–18 teeth.

Branchiae present as single filaments over short region, consisting in holotype of two segments on right side (chaetiger 21–22), four segments on left side (chaetiger 19–22). In larger paratypes (width 0.9–1.2 mm) branchiae starting on chaetigers 16–20, present until end of fragments (chaetiger 20–27), when best developed branchial filament about twice as long as dorsal cirrus (Fig. 2 D); two smallest paratypes (width 0.6 mm) without branchiae. Posterior end of worms and tubes unknown.

Mandibles (Fig. 2 E) slender, moderately sized protomandibles; examined paratype lacking calcareous cutting plate. Maxillae (Fig. 2 F) lightly sclerotised, with distally slender forceps. Maxillary formula (based on one paratype): MI = 1 + 1; MII = 8 + 8; MIII = 7 + 0; MIV = 7 + 9; MV = 1 + 1.

Remarks. Paradiopatra acirrata n. sp. is the fourth species in the genus lacking peristomial cirri. It differs from P. antarctica (Monro, 1930) and P. abyssalis (Imajima, 1999) in having branchiae (vs. lacking). The third species, P. gracilis Imajima, 2009, has branchiae with up to three filaments and starting from chaetiger 8–10, whereas P. acirrata n. sp., has single-filament branchiae starting after chaetiger 16.

Etymology. The specific name acirrata refers to the lack of peristomial cirri.

Distribution. Paradiopatra acirrata n. sp. was collected only in one station: 54 km ESE of Nowra, NSW, in 990– 996 m.