Paradiopatra variabilis, Paxton, Hannelore & Budaeva, Nataliya, 2013

Paxton, Hannelore & Budaeva, Nataliya, 2013, Paradiopatra (Annelida: Onuphidae) from eastern Australian waters, with the description of six new species, Zootaxa 3686 (2), pp. 140-164 : 157-160

Paradiopatra variabilis , n. sp.

Figures 12 –14; table 2

Material examined. Type material—SLOPE 32: holotype (MV F189440); 4 paratypes (MV F189441); 2 paratypes (AM W43549, W43550); 1 paratype mounted for SEM on 2 stubs (AM W43555.001); SLOPE 33: 5 paratypes (MV F189442); SLOPE 34: 1 paratype mounted for SEM (AM W43554.001).

Non-type material—SLOPE 34: 2 specimens (MV F189443); SLOPE 45: 5 specimens (MV F189444); SLOPE 47: 1 specimen (MV F189445).

Type locality. Pacific Ocean, Bass Strait, off eastern Victoria, 38º21.90’S 149º20.0’E, 1000 m.

Diagnosis. Ovoid frontal lips; ceratophores without lateral projections; peristomial cirri present; first three pairs of parapodia with pseudocompound, uni- to 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 16–25, present over short region or completely absent; moderately-sized protomandibles.

Description. All examined specimens lacking posterior ends. Length of holotype 12.0 mm for 28 chaetigers, width 1.1 mm (at chaetiger 10, excluding parapodia); paratypes ranging from 8–25 mm long (25–54 chaetigers), 0.8–1.0 mm wide. Non-type material ranging from 0.5–0.9 mm wide. All specimens stored in alcohol overall cream-coloured, lacking colour pattern.

Prostomium anteriorly rounded, wider than long, with paired ovoid frontal lips, separated by small gap, directed anteroventrally ( Fig. 12 A–C). Palps of holotype reaching chaetiger 1 (paratypes: chaetiger 1); lateral antennae reaching chaetiger 4 (chaetigers 2–7); median antenna reaching chaetiger 2 (chaetigers 2–4). Ceratophores with well developed annulation, lacking lateral projections; ceratophores of lateral antennae with 5 (5–6) rings, median antennae with 5 (4–5) rings; distal ring twice as long as proximal ones. Nuchal grooves slightly curved, medially widely separated. Eyes absent. Peristomium slightly shorter than first chaetiger. Peristomial cirri short and tapering, about half as long as peristomium, inserted subdistally.

First three pairs of parapodia modified, projecting anterolaterally, directed slightly ventrally ( Fig. 13 B).

Prechaetal lobes rounded on all parapodia; postchaetal lobes triangular to subulate in first chaetigers, decreasing rapidly in size, absent from chaetiger 9 (8–9). Dorsal cirri well developed and subulate with slightly inflated bases in anterior parapodia ( Fig. 13 A, B), becoming smaller and digitiform in median region. Ventral cirri subulate on first three chaetigers, third one shorter than first two, replaced by ovoid pads from chaetiger 4 ( Fig. 12 B).

Parapodia supported by two aciculae, with only filiform tips projecting from prechaetal lobe ( Figs 12 D, 13A, B). First three pairs of parapodia with dorsal fascicle of 1–2 dorsal limbate chaetae and ventral fascicle of 4–5 unito bidentate pseudocompound falcigers with moderately long pointed hoods ( Fig. 13 C–E); shafts with spines in rows and scattered, appendages with scattered spines ( Fig. 12 E). Two fascicles of simple limbate chaetae starting from chaetiger 4. Ventral fascicle of limbate chaetae replaced by paired bidentate subacicular hooks ( Fig. 13 F) from chaetiger 9; hooks unequal, upper one thicker and longer than lower one. Pectinate chaetae ( Fig. 12 F) slightly oblique with 17–20 teeth.

Branchiae present over short body region, consisting of single filaments or absent. Branchiae in holotype starting on chaetiger 20 on left side, chaetiger 21 on right side, present until end of fragment (chaetiger 28), in paratypes starting from chaetigers 17–25, absent from chaetigers 24–33, giving branchiate regions of 2–16 chaetigers. Branchiae short and delicate, about size of dorsal cirri ( Fig. 12 G). Posterior end and tubes unknown.

Mandibles ( Fig. 13 G) robust, strongly calcified, appearing white except for small sclerotised areas such as protomandibles and lateral edges of cutting plates, distal part of each cutting plate with one subcentral indentation and high triangular lateral part. Maxillae ( Fig. 13 H) lightly sclerotised, with large carriers and distally slender forceps. Maxillary formula (based on two paratypes): MII = 1 + 1; MII = 7 + 7; MIII = 7 + 0; MIV = 5 + 5; MV = 1 + 1.

Variation. The distal ends of the falcigers are variable within and between specimens, ranging from unidentate to weakly and clearly bidentate. The holotype and some paratypes have mainly clearly bidentate ( Fig. 13 C) and a few weakly bidentate ( Fig. 13 D) falcigers, while other paratypes have varying proportions of clearly bidentate, weakly bidentate and unidentate falcigers ( Fig. 13 E).

The presence/absence of branchiae is shown in Fig. 14A in relation to body width (n = 22, all studied specimens). Specimens less than 0.7 mm wide lack branchiae; this can be attributed to their juvenile condition. Specimens of width 0.7 mm are mostly abranchiate specimens; those of width 0.8 mm include one branchiate and one abranchiate. All four specimens of 0.9 mm width had branchiae, but three 1.0 mm wide specimens lacked branchiae. Two of these consisted of only 24 and 26 chaetigers and the branchiae may have started later, but one specimen consisted of 52 chaetigers and had no sign of branchiae. The appearance of the first branchiae in relation to body width (Fig. 14B), is weakly size-dependent.

FIGURE 14. Graphs illustrating branchial development in Paradiopatra variabilis n. sp. A, Presence/absence of branchiae in relation to body width (n = 22); B, relationship between body width of specimens (n = 10) and origin of branchiae (y = 8.44x + 12.82, R2 = 0.084).

Remarks. Since P. variabilis n. sp., occurs with or without branchiae, we are comparing it here separately with similar branchiate/abranchiate species. The new species resembles P. crassa Imajima, 1999 and P. s i m p l e x Imajima, 1999 in having branchiae with a relatively late origin. Paradiopatra variabilis n. sp., differs from P. crassa in having single branchial filaments restricted to a short region rather than bifid filaments continuing to the posterior end, subacicular hooks from chaetiger 9 rather than 10–11, and lacking eyes. Although P. variabilis n. sp., shares the possession of simple branchiae restricted to a short region with P. simplex , it differs in having three parapodia with uni- to bidentate falcigers rather than four with bi- to tridentate falcigers, and pectinate chaetae with 17–20 rather than 12–17 teeth.

The abranchiate individuals of Paradiopatra variabilis n. sp., are here compared to the abranchiate P. fragosa , P. piccola , P. imajimai and P. okai . The first two species can be distinguished from P. variabilis , n. sp., by having globular rather than ovoid frontal lips and distinctive tubes with attached foreign objects. Paradiopatra okai differs from P. variabilis , n. sp., in having two pairs of eyes (vs. no eyes) and five anterior pairs of parapodia with postchaetal lobes (vs. 7–8). Paradiopatra imajimai has slender mandibles with very large protomandibles and pectinate chaetae with 13–15 teeth, whilst P. variabilis , n. sp., has robust mandibles with moderately sized protomandibles and pectinate chaetae with 17–20 teeth.

Etymology. The specific name variabilis refers to the variability of the dentation of the falcigers and presence/ absence of branchiae of the new species.

Distribution. Paradiopatra variabilis n. sp., was collected in two transects: off eastern Victoria in Bass Strait and off Freycinet Peninsula, eastern Tasmania, in 400– 720 m.

Figures

FIGURE 12. SEM images of Paradiopatra variabilis n. sp. (AM W 43554.001, A, F, G; B – E; AM W 43555.001). A, Anterior end, dorsal view; B, same, ventral view; C, same, enlarged, ventral view; D, parapodium 1, anterior view; E, pseudocompound falciger from chaetiger 3; F, pectinate and limbate chaetae from median parapodium; G, median parapodium, showing simple branchia.

FIGURE 13. Line drawings of Paradiopatra variabilis n. sp. (AM W 43549, A, B, E – H; holotype MV F 189440, C, D). A, Parapodium 2, anterior view; B, parapodium 3, anterior view; C, bidentate pseudocompound falciger from chaetiger 1; D, weakly bidentate pseudocompound falciger from chaetiger 1; E, unidentate pseudocompound falciger from chaetiger 1; F, subacicular hook from chaetiger 23; G, mandibles; H, maxillae.