Nothria digitata, Paxton & Budaeva & Gunton, 2023

Paxton, Hannelore, Budaeva, Nataliya & Gunton, Laetitia M., 2023, Amazing Diversity of Nothria (Annelida, Onuphidae) in the Australian Deep Sea, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 215-247 : 227-229

Nothria digitata sp. nov.

urn:lsid:zoobank.org:act:02457FA3-9067-4E97-B6EE-94AB977859D0

Figs 1 , 9–11 , Tables 2 , S 1

Holotype. SAMA E8969 , IN2015 _C02_174; 8 Dec 2015; Australia, Southern Ocean , Great Australian Bight, 34.25– 34.24°S 132.62°E; 400 m depth . Paratypes (3): SAMA E8970 , IN2015 _C02_174 (1); AM W.49953, IN2015 _ C02_174 (1, anterior part on SEM pin, posterior part wet specimen); AM W.49954, IN2015 _C02_174 (1).

Description. All specimens lacking posterior ends. Length of holotype 18 mm for 22 chaetigers, width 2.3 mm; paratypes 9–19 mm (13–24 chaetigers) long, 2.2–2.3 mm wide.

Alcohol-stored specimens overall whitish without any pigmentation. Prostomium anteriorly rounded, wider than long, with 2 ovoid frontal lips separated by small space ( Fig. 9A,B ). Palpo- and antennophores with 3–4 proximal rings and longer distal ring. Palpostyles tapering, extending to chaetiger 1, antennostyles tapering gradually, lateral antennostyles extending to chaetiger 8 (7–8), median antennostyle generally longest, extending to chaetiger 9 (7–9); slightly shorter one in W.49953 ( Fig. 9A ) atypical. Nuchal grooves straight, with small middorsal separation. Small anterior eyespots on anterior part of prostomium between palps and lateral antennae (only left one visible in holotype), large posterior eyes between bases of palps and lateral antennae next to peristomium. Ventral upper lip squared with median section, lower lip subtriangular ( Fig. 9B ). Peristomium short, peristomial cirri inserted subdistally on peristomium, about twice as long as peristomium ( Fig. 9A ).

First chaetiger enlarged, slightly more than twice as long as peristomium, chaetiger 3 similar in length to following chaetigers. Anterior three pairs of parapodia modified ( Fig. 9A,B ). First pair greatly enlarged, directed forward, extending beyond anterior margin of prostomium, with large auricular prechaetal lobes and subulate postchaetal lobes. Parapodia 2 and 3 similar but smaller, with smaller prechaetal lobes. Third pair similar to subsequent parapodia, with small tongue-like prechaetal lobes present into posterior region, last postchaetal lobes on chaetiger 12 (11–12). Ventral cirri of first two chaetigers subulate, becoming rounded on chaetiger 3 as transitioning to glandular pads ( Fig. 9B ). Dorsal cirri subulate from chaetiger 1, becoming cirriform, gradually thinner and shorter. Branchiae starting from chaetiger 9, 10 (9–10) as short filament ( Fig. 9C ), increasing to length of dorsal cirrus by chaetiger 12–14 ( Fig. 9D ); branchiae retaining length, dorsal cirrus becoming smaller and slenderer, by chaetiger 22–24 (end of largest types) branchia about 2–3 times as long as dorsal cirrus.

First pair of parapodia with 2 robust bidentate simple ( Fig. 10A ) and 1–2 very slender bidentate pseudocompound hooks ( Fig. 10B ). Second pair of parapodia with 2 slender ( Fig. 10C ) and 1–2 very slender bidentate pseudocompound hooks ( Fig. 10D ). Third pair of parapodia with 2–3 upper limbate chaetae, 3–5 scoop-shaped pectinate chaetae with 14–16 teeth, and 2–3 bidentate pseudocompound to compound hooks ( Fig. 10E ). Anterior hooks absent from chaetiger 4, upper and lower limbate chaetae and pectinate chaetae present to end of fragments (presumably end of body). Subacicular hooks present singly from chaetiger 11 (10–11), as pairs from chaetiger 13 (11–13). Pygidium unknown.

Mandibles ( Fig. 10F ) highly calcified, white, except for short darkly sclerotized protomandibles; shafts long and slender, cutting plates high with weakly defined median and large distal tooth. Maxillae ( Fig. 10G ) overall whitish, fangs and teeth light brown, ligaments and attachment lamellae more sclerotized, appearing dark brown. Maxillary formula (based on holotype): MI = 1+1, MII = 9+10; MIII = 10+0, MIV = 8+9, MV = 2+2. Ratio of mandibles/maxillae = 1.2. Flattened tube, lining transparent, covered with pieces of shells (often larger than width of worm), laterally filled in with foraminiferans and other small fragments ( Fig. 11A ) .

Remarks. Nothria digitata sp. nov. resembles N. otsuchiensis in having eyes, long branchiae from chaetiger 9–10 and subacicular hooks from chaetiger 10 ( Table 2 ). The two species differ in that N. digitata sp. nov. has digitate rather than flat branchial filaments, 11–12 postchaetal lobes rather than 14–17, pseudocompound hooks on chaetiger 2 rather than simple and pseudocompound hooks. Furthermore, the new species displays no pigmentation pattern while N. otsuchiensis has a brown spot on each segment.

Etymology. The name of the new species is suggested by its long, digitate branchiae.

Distribution. Nothria digitata sp. nov. was collected from the GAB, in 400 m depth ( Fig. 11B ).

Figures

Figure 1. Consensus tree from the Bayesian analysis of the combined COI, 16S and 28S dataset; numbers on nodes indicate Bayesian posterior probabilities; capital letters correspond with the clades discussed in the text.Species delimitation results inferred by morphology and DNA-based methods (COI, 16S, and 28S) are indicated right to the consensus tree followed by the final hypothesis based on all evidence combined. White bars indicate missing data.

Figure 9. Nothria digitata sp. nov. SEM micrographs of paratype AM W.49953. (A) anterior part, dorsal view; (B) same, ventral view; (C) parapodium of chaetiger 9, showing first branchia, dorsal view; (D) parapodium of chaetiger 12, showing fully developed branchia, dorsal view; br, branchia; dc, dorsal cirrus; ms, median section of ventral upper lip.

Figure 10. Nothria digitata sp. nov. Line drawings of holotype SAMA E8969. (A) robust bidentate simple hook from chaetiger 1; (B) very slender bidentate pseudocompound hook from same; (C) slender bidentate pseudocompound hook from chaetiger 2; (D) very slender bidentate pseudocompound hook from same; (E) slender bidentate compound hook from chaetiger 3; (F) mandibles, ventral view; (G) maxillae, dorsal view.

Figure 11. Nothria digitata sp. nov.(A) photograph ofparatypeAM W.49954, specimen in tube, dorsal view; (B) map of distribution; red dot represents type locality.