Nothria deltasigma, 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 : 225-227

Nothria deltasigma sp. nov.

urn:lsid:zoobank.org:act:700F6979-DC3B-481B-A897-62E9E97937DB

Figs 1 , 6–8 , Tables 1 , 2 , S 1

Holotype. Australian Museum ( AM) W.51639, IN2018 _ V06 _169; 14 Dec 2015; Australia, Tasmania, flat area south of Brians , 44.24– 44.23°S 147.29– 147.30°E; 1422–1443 m depth . Paratypes (2): AM W.51640, IN2018 _ V06 _169 (1). AM W. 53497, mounted for SEM, IN2018 _ V06 _169 (1).

Other material examined (7). AM W.53846, IN 2018_ V 06_169 (7).

Diagnosis. Eyes absent; antennae extending to chaetiger 11–13; short branchiae from chaetiger 10–12; first 3 chaetigers with anterior hooks: robust uni- to weakly tridentate and slender bidentate simple hooks on chaetiger 1; robust uni- to bidentate simple hooks and slender bidentate weakly pseudocompound hooks on chaetiger 2 and very slender bidentate pseudocompound to compound hooks on chaetiger 3; pectinate and limbate chaetae from chaetiger 2; subacicular hooks from chaetiger 11–14.

Description. All examined specimens lacking posterior ends. Length of holotype 11 mm for 23 chaetigers, width 2.4 mm; paratypes 10 and 16 mm (15 and 32 chaetigers) long, 1.8 and 2.2 mm wide respectively. Non-type material ranging from 1.7–2.3 mm in width. Alcohol-stored specimens overall cream-coloured. Holotype lacking any pigmentation but some specimens with brown spot dorsally on anterior part of prostomium. Prostomium anteriorly rounded to subtriangular, wider than long, with 2 ovoid frontal lips, separated from each other by small space ( Fig. 6A,B ). Palpo- and antennophores with 2–3 proximal rings and a longer distal ring. Palpostyles tapering, extending to chaetiger 1, lateral antennostyles extending to chaetiger 11, median antennostyle to chaetiger 13 (in holotype); antennostyles tapering gradually, becoming very thin towards distal end ( Fig. 6A ). Nuchal grooves straight, with small middorsal separation. Eyes absent. Ventral upper lips rounded, lower lips subtriangular, neither with median section ( Fig. 6B ). Peristomium short, peristomial cirri inserted subdistally on peristomium, slightly longer than peristomium.

First chaetiger greatly enlarged, about three times as long as peristomium, chaetiger 2 about twice length of peristomium, subsequent chaetigers about 1.5 times as long as peristomium ( Fig. 6A,B ). Anterior 3 pairs of parapodia modified; first pair greatly enlarged, directed forward, extending slightly beyond anterior margin of prostomium ( Fig. 6A,B ), with large auricular prechaetal lobes, subulate postchaetal lobes, dorsal and ventral cirri. Second pair of parapodia similar but smaller, with smaller prechaetal lobes ( Fig. 6C ). Third pair only slightly larger than subsequent parapodia, directed laterally, with further reduced, tongue-like prechaetal lobes; ventral cirri transitioning to glandular pads ( Fig. 6B ). From chaetiger 4 onwards parapodial structure becoming more uniform; dorsal cirri gradually becoming thinner and shorter, prechaetal lobes becoming short and rounded, postchaetal lobes gradually decreasing, last on chaetigers 16 (13–16), ventral cirri replaced by round glandular pads from chaetiger 4. Simple branchiae present as short filament from chaetiger 11 (10–12), increasing only slightly in length ( Figs 6D , 7G ) remaining as relatively short structure until end of incomplete worms; total extent unknown.

First pair of parapodia with 2–3 robust uni- to weakly bi- ( Fig. 7A ) to tridentate ( Fig. 7B ) simple hooded hooks and a lower slender bidentate simple hook ( Fig. 7C ). Second pair of parapodia with 2–3 robust bidentate simple hooks ( Fig. 7D ), a slender bidentate weakly pseudocompound hook ( Fig. 7E ), as well as 2 limbate and numerous pectinate chaetae with 18–20 teeth. Third pair with 3–5 slender, bidentate pseudocompound to compound hooks with serrated upper shaft and appendage ( Fig. 7F ), limbate chaetae and numerous scoop-shaped pectinate chaetae ( Fig. 6E ). Hooks absent from chaetiger 4, limbate and pectinate chaetae present in reduced numbers presumably up to end of body. Subacicular hooks present singly from chaetiger 12 (11–14), as pairs from 14 (12–16). Pygidium unknown.

Mandibles ( Fig. 7H ) highly calcified, almost white, except for darkly sclerotized, unusually long protomandibles. High cutting plates with weakly defined median and large distal tooth. Maxillae ( Fig. 7I ) lightly sclerotized except for teeth and attachment lamellae; carriers with unusually dark outer edges and curved basal extensions, perhaps indicating imminent moult of jaws. Maxillary formula: MI = 1+1; MII = 8+8; MIII = 9+0; MIV = 8+11; MV = 1+1. Ratio of mandibles/maxillae = 1.3. Flattened tube ( Fig. 8A ), covered mainly with larger pieces of shells dorsally and ventrally, sides filled in with foraminiferans; lining transparent.

Remarks. Orensanz (1974) described the subspecies N. conchylega anoculata lacking the eyes that are present in the stem species from off Buenos Aires, Argentina from a depth of 700–900 m; Fauchald (1982) subsequently raised the subspecies to full specific level. Nothria delta sp. nov. and N. deltasigma sp. nov. are morphologically similar to each other and to N. anoculata . Some of the noticeable differences are in the presence of simple vs. pseudocompound anterior hooks on chaetiger 1 and 2 ( Table 1 ). This could be interpreted as a function of size and thus a pseudocompound hook could be a juvenile characteristic as discussed by Orensanz (1990) and Budaeva & Paxton (2013). However, extrapolating from his drawings, the original Argentinian specimens consisted of a width of 1.2 mm ( Orensanz, 1974: pl 7, fig 1) while our material measured 1.7–2.7 mm in width, having three chaetigers with anterior hooks, and thus representing the adult stage.

The differences between the three species are detailed in Table 1 and to the remaining species in Table 2 . They can be summarized as follows: hooks of chaetiger 1 are only simple in N. anoculata and N. deltasigma sp. nov, simple and pseudocompound in N. delta sp. nov.; hooks of chaetiger 2 are only pseudocompound in N. anoculata and N. delta sp. nov, and simple and pseudocompound in N. deltasigma sp. nov.; hooks of chaetiger 3 are pseudocompound to compound in all three species. The antennae are shorter in N. anoculata (median to chaetiger 10) and longer (median to chaetiger 13–14) in N. delta sp. nov. and N. deltasigma sp. nov. Branchiae are about twice as long in N. anoculata as in the other two species.

In Table 1 we have listed the values stated in the original description of N. anoculata from Argentina separately from those given later for the subantarctic records by Orensanz (1990) as they do not always agree and seem to represent an expansion of the original N. anoculata definition to fit the wider distribution. Thus, it supports our suspicion that rather than a widely distributed species in the southern seas, N. anoculata as characterized by Orensanz (1990) represents a species complex.

Etymology. The specific epithet refers to the manuscript name “Ds” of the new species, referring to its great similarity and thus second version of “D” in the Greek language.

Distribution. The new species was only collected on the flat area south of Brians, south of Tasmania in 1422–1443 m depth ( Fig. 9B ).

Diagnosis. Eyes present, ventral upper lip with median section; antennae extending to chaetiger 7–9; branchiae long, digitate, from chaetiger 9–10; 3 first chaetigers with anterior hooks: robust bidentate simple and very slender bidentate pseudocompound hooks on chaetiger 1; slender and very slender bidentate pseudocompound hooks on chaetiger 2 and very slender bidentate pseudocompound to compound hooks on chaetiger 3; pectinate and limbate chaetae from chaetiger 3; subacicular hooks from chaetiger 10–11.

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 6. Nothria deltasigma sp. nov.SEM micrographs of paratypeAM W.53497. (A) anterior part, dorsal view; (B) same, ventral view; (C) parapodium of chaetiger 2, posterior view; (D) chaetiger 14 to show branchia; (E) pectinate chaetae of chaetiger 3.

Figure 7. Nothria deltasigma sp. nov. Line drawings of holotype AM W.51639 (A, C, F) and paratype AM W. 51640 (D, E, G, I). (A) robust weakly bidentate simple hook from chaetiger 1; (B) robust weakly tridentate simple hook from chaetiger 1; (C) slender bidentate simple hook from chaetiger 1; (D) robust bidentate simple hook from chaetiger 2; (E) slender bidentate pseudocompound hook from chaetiger 2; (F) slender bidentate compound hook from chaetiger 3; (G) parapodium of chaetiger 17 to show branchia; (H) mandibles, ventral view; (I) maxillae, dorsal view.

Figure 8. Nothria deltasigmasp.nov.(A) photograph of tube ofAM W.53846. (B) map of distribution; red dot represents type locality.

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.