Nothria simplex, 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 : 241-243

Nothria simplex sp. nov.

urn:lsid:zoobank.org:act:7CC4D069-4172-4C24-8324-442FDCC320D2

Figs 1 , 26–27 , Tables 2 , S 1

Holotype. Australian Museum ( AM) W.49938, IN2017 _ V03 _86; 11 Jun 2017; Australia, Queensland, off Fraser Island ; 25.33– 25.35°S 154.07– 154.08°E; 2350– 2342 m depth . Paratypes (2). AM W.51645, IN2017 _ V03 _86(1). AM W.51646, IN2017 _ V03 _115 (1).

Diagnosis. Eyes absent; antennae extending to chaetiger 4–5; branchiae from chaetiger 10, becoming long and flat by chaetiger 15–20; 2 first chaetigers with anterior hooks: robust and slender bidentate simple hooks on chaetiger 1; slender bidentate simple and bidentate pseudocompound hooks on chaetiger 2; pectinate and limbate chaetae from chaetiger 3; subacicular hooks from chaetiger 13–14.

Description.All specimens lacking posterior ends. Length of holotype 10 mm for 18 chaetigers, width 2.5 mm; paratypes 9 mm (14 chaetigers) and 15 mm (24 chaetigers), 2.8 and 2.7 mm in width respectively. Alcohol-stored specimens overall cream-coloured. Paratype W.49938 with pale brown median spot on prostomium, some splotches on ventral lower lip and on sides of parapodia ( Fig. 26A ). Prostomium anteriorly rounded, wider than long, with 2 circular frontal lips, slightly separated from each other. Palpo- and antennophores with 2–3 proximal rings and longer distal ring. Antennostyles of holotype lost, greatly damaged or lost in paratypes; remaining ones short, tapering gradually, palpostyles to chaetiger 1, lateral antennostyles extending to about chaetiger 4, median to chaetiger 5. Nuchal grooves straight, with small middorsal separation. Eyes absent. Ventral upper lips globular, lower lips subtriangular, neither with median section. Peristomium short, peristomial cirri inserted subdistally on peristomium, about as long as peristomium ( Fig. 26A ).

First chaetiger greatly enlarged, about four times as long as peristomium, chaetiger 2 about three fourths as long as chaetiger 1, third only slightly longer than following ones ( Fig. 26A ). Anterior 2 pairs of parapodia modified; first pair greatly enlarged, directed forward, extending slightly beyond anterior margin of peristomium in paratype W.51646 ( Fig. 26A ). First pair of parapodia with large auricular prechaetal lobes, digitate postchaetal lobes and dorsal cirri, subulate ventral cirri ( Fig. 26B ). Second pair of parapodia almost as long but much slenderer with tongue-like prechaetal lobes, digitate postchaetal lobes, dorsal cirri and subulate ventral cirri ( Fig. 26C ). Third pair of parapodia directed laterally, with small prechaetal lobes, subulate postchaetal lobes and dorsal cirri; ventral cirri almost transitioned to oval glandular pads ( Fig. 26D ). From chaetiger 4 onwards parapodial structures becoming more uniform; prechaetal lobes continued to end of fragments, postchaetal lobes absent from chaetiger 11 (11–13), dorsal cirri decreasing in size, ventral cirri as glandular pads. Branchiae beginning on chaetiger 10 as small stump, increasing in size to about chaetiger 20 becoming long and flat ( Fig. 26E ) when becoming shorter again.

First pair of parapodia with 2 robust ( Fig. 26F ) and 1 slender bidentate simple hooded hooks ( Fig. 26G ). Parapodia 2 with 2 slender simple ( Fig. 26H ) and 1 very slender bidentate weakly pseudocompound hooded hooks ( Fig. 26I ). Anterior hooks absent from chaetiger 3; upper limbate chaetae, scoop-shaped pectinate chaetae with 20–25 teeth and lower limbate chaetae present. Subacicular hooks present singly from chaetiger 13(14–15), as pairs from chaetiger 14.

Mandibles ( Fig. 26J ) highly calcified, white, except for sclerotized protomandibles; shafts long and slender, cutting plates distally incomplete. Maxillae ( Fig. 26K ) calcified, almost white, except teeth, ligaments and attachment lamellae more sclerotized, appearing dark brown. Maxillary formula: MI = 1+1; MII = 9 + 8 (left most distal tooth fang-like); MIII = 8 + 0; MIV = 7 + 9; MV = 1+1. Ratio of mandibles/maxillae = 1.2. Pygidium unknown. Tube with parchment-like inner layer, covered on outside with foraminiferans and shell fragments ( Fig. 27A ).

Remarks. Only three damaged anterior fragments were available for study. Although some appendages and chaetae were absent or damaged, we were able to describe the morphology of this unusual species, albeit without any SEM images.

Six species of Nothria have only two pairs of parapodia with anterior hooks. Of these, N. abyssia and N. paxtonae are very slender, abranchiate species, whilst the new species is larger and has branchiae. Nothria edwardsi from the North Atlantic differs from N. simplex sp. nov. in having uni- to bidentate hooks on chaetiger 1 and only pseudocompound to compound hooks on chaetiger 2 rather than clearly bidentate hooks on chaetiger 1 and simple and weakly pseudocompound hooks on chaetiger 2. Nothria atlantica ( Hartman, 1965) from the Mid-Atlantic Ridge differs in a number of features, most notably in having cirriform prechaetal lobes on chaetiger 1 and almost unidentate anterior hooks whilst the new species has auricular prechaetal lobes on chaetiger 1 and distinctly bidentate anterior hooks.

That leaves N. mannarensis Rangarajan and Mahadevan, 1961 from the Gulf of Mannar and N. hawaiiensis Pettibone, 1970 from off Hawaii collected at depths of 4 m and 463–730 m respectively. The former species was described on the basis of two tiny complete specimens measuring 8 and 13 mm in length for 25 and 38 chaetigers respectively while the holotype of the latter is a complete specimen of 60 mm length for 64 segments and a width of 7 mm. Nothria mannarensis differs from the new species in having large posterior eyes, an earlier start of branchiae and subacicular hooks, simple and pseudocompound hooks on chaetiger 1 and most likely represents juveniles. Nothria hawaiiensis , although twice as large as N. simplex , resembles the new species in some quantitative characteristics, e. g., beginning of branchiae and subacicular hooks and absence of postchaetal lobes. However, the anterior hooks have delicate distal fang and second tooth, and the maxillae are calcified and white in N. simplex sp. nov. while those of N. hawaiiensis are thick and blunt, and the maxillae are strongly sclerotized and dark.

Orensanz (l990) discussed a sample of “ Nothria , unnamed species” from South of New Zealand, from a depth of 1026 m having only two anterior pairs of parapodia with hooks. It is similar to the new species but differs in having well developed eyespots, branchiae from chaetiger nine, 16 postchaetal lobes, composite hooks on chaetiger 2, and subacicular hooks from chaetiger 10–12.

Etymology. The name of the new species is suggested by having almost only simple hooded hooks on the anterior modified parapodia.

Distribution. Nothria simplex sp. nov. was collected from off Central Eastern Marine Park in 2429–2518 m and off Fraser Island in 2342–2350 m depth ( Fig. 27B ).

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 26. Nothria simplex sp. nov. Line drawings of paratype AM W.51646 (A), holotype AM W.49938 (B, E, F–I), and paratype AM W.51645 (D, J, K). (A) anterior part, dorsal view; (B) parapodium of chaetiger 1, anterior view (missing postchaetal lobe dotted); (C) parapodium of chaetiger 2, anterior view (missing postchaetal lobe dotted); (D) parapodium 3, anterior view; (E) parapodium 15, anterior view; (F) robust bidentate simple hook from chaetiger 1; (G) slender bidentate simple hook from same; (H) slender bidentate simple hook from chaetiger 2; (I) slender bidentate weakly pseudocompound hook from same; (J) mandibles, ventral view; (K) maxillae, dorsal view.

Figure 27. Nothria simplex sp. nov. (A) Photograph of tube of paraype AM W.51646; (B) map of distribution; red dot represents type locality, green dot other site of collection.