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

Paradiopatra piccola n. sp.

Figures 8, 9; Table 2

Material examined. Type material—SLOPE 56: holotype (MV F195957); 17 paratypes and 2 posterior fragments in tubes (MV F195958); 2 paratypes (AM W43552); 1 paratype, mounted for SEM (AM W43552.001).

Non-type material—SLOPE 40: 4 specimens (MV F195959); SLOPE 48: 3 specimens (MV F195960); RV Tangaroa Sta. BSS 167, Eastern Bass Strait, 63 km W of North Point Flinders Island (39º44.8’S, 148º40.6’E), 124 m, muddy sand, coll. R. Wilson, 14 Nov 1981; 1 specimen (MV F195961).

Type locality. Pacific Ocean, off eastern Australia, S of Sydney, NSW: 34º55.79’S, 151º08.06’E, 429 m.

Diagnosis. Globular frontal lips; ceratophores without lateral projections; peristomial cirri present; first three pairs of parapodia with pseudocompound, uni- to weakly 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 absent; protomandibles not visible; symmetrical maxillae in all three specimens dissected.

Description. All examined specimens lacking posterior ends. Length of holotype 8 mm long for 39 chaetigers, width 0.5 mm (at chaetiger 10, excluding parapodia); paratypes ranging from 4–13 mm long (smallest paratype consisting of 24 chaetigers, largest partially in tube, number of chaetigers unknown, next to largest paratype without tube 9 mm for 44 chaetigers), width 0.4–0.5 mm. Non-type material ranging from 0.2–0.5 mm in width. Alcohol stored specimens overall cream-coloured, lacking colour pattern.

Prostomium anteriorly rounded, wider than long with paired globular frontal lips situated closely together (Fig. 8 A–C). Palps of holotype reaching chaetiger 1 (paratypes: peristomium–chaetiger 1); lateral antennae reaching chaetiger 5 (chaetigers 5–7); median antenna reaching chaetiger 4 (chaetigers 3–5). Ceratophores with well developed annulation, lacking lateral projections, ceratophores of lateral antennae with 4 (4–5) rings, median antenna with 4 (4–5) rings; terminal ring as long as two lower ones combined. Nuchal grooves could not be made out. Relatively large eyespot or fusion of 2–3 small ones slightly below and between lateral antennae and palps. Peristomium slightly longer than first chaetiger. Peristomial cirri present, short and thick, inserted subdistally.

First three pairs of parapodia modified, projecting anterolaterally, directed slightly ventrally (Fig. 8 B), following ones directed laterally. Prechaetal lobes rounded on all parapodia; postchaetal lobes triangular to subulate in first chaetigers decreasing rapidly in size, absent from chaetiger 7–8. Dorsal cirri subulate on first three chaetigers (Figs 8 D, 9A), becoming gradually shorter and digitate. Ventral cirri subulate on first three chaetigers, third one shorter than first two, replaced by ventral lateral pads from chaetiger 4 (Fig. 8 B).

Parapodia supported by two aciculae projecting less than half as far as falcigers and limbate chaetae from prechaetal lobe (Fig. 9 A). First two pairs of parapodia with dorsal fascicle of 1–2 dorsal simple limbate chaetae and ventral fascicle of 4–5 unidentate (Fig. 9 B) and bidentate falcigers with very small subterminal tooth (Fig. 9 C) and moderately long pointed hoods; shafts of falcigers with small scattered spines and two rows of spines, appendages with scattered spines (Fig. 8 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; by chaetiger 12–14 superior hook surpassing inferior one in thickness and length, remaining so to end of fragments (Fig. 9 D). Pectinate chaetae slightly oblique with 14–16 teeth (Fig. 9 E). Branchiae absent. Posterior end unknown. Tube cylindrical, with inner soft secreted layer and outer layer of grey mud and sand with foreign objects such as shell fragments, sea urchin spines and sponge spicules attached at right angle in similar fashion to Diopatra tubes (Fig. 8 A).

Mandibles (Fig. 9 G) slender, with very high calcareous cutting plates with central distal indentation, protomandibles not visible through calcareous cutting plate. Maxillae delicate, hardly sclerotised. Of three sets of maxillae dissected, all displaying symmetry, i.e. both left and right MII and MIII present (Fig. 9 G). Maxillary formula: MI = 1 + 1; MII = 7 + 7; MIII = 8 + 8; MIV = 5 + 4; MV = 1 + 1.

Remarks. Paradiopatra piccola is most similar to P. fragosa Ehlers, 1887 from the western North Atlantic and P. okai Imajima, 1999 from the Pacific off Japan. It shares with these species the small size, having three pairs of modified parapodia, the origin of subacicular hooks from chaetiger 9, and the lack of branchiae. The new species shares with P. fragosa the possession of tubes with attached foreign objects, while those of P. o k a i lack these decorations, and is similar to P. okai in having eyes which are absent in P. fragosa. However, P. piccola differs from both species in having uni- to weakly bidentate instead of clearly bidentate falcigers and that its paired subacicular hooks differ distinctly in size. Furthermore, the dissected maxillary apparatuses of three paratypes were symmetrical, having identical left and right elements, with the MIII present on both sides. This is a case of symmetry variation, the result of a mutation. Due to the small size of the specimens and scarce amount of material we cannot further investigate the extent to which the mutation has become fixed in the population. In the case of Diopatra dexiognatha Paxton & Bailey-Brock from Hawaii, out of 41 specimens 27 were symmetrical, 14 had a right but no left MIII, and none displayed the ‘normal’ asymmetry with only left MIII present (Paxton & Bailey- Brock 1986).

Etymology. Paradiopatra piccola is one of the smallest species in the genus, which is reflected in its specific name.

Distribution. Paradiopatra piccola n. sp., was collected in all three transects: south of Sydney, NSW, off eastern Victoria in Bass Strait, and off Freycinet Peninsula, eastern Tasmania, in 400–500 m, as well as off Flinders Island, Bass Strait, during previous sampling, in 124 m.