Nothria otsuchiensis Imajima, 1986

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 : 240-241

Nothria otsuchiensis Imajima, 1986 complex

Figs 1 , 24 , Tables 2 , 3 , S 1

Nothria otsuchiensis Imajima, 1986: 108 , fig. 8.— Imajima 1999: 46, fig 26.— Budaeva & Paxton 2013: 1492, figs 11–17.

Material examined (21). AM W.49014, IN 2015_C01_110 (1). AM W.49037, IN 2015_C01_110 (1). AM W.49038, IN 2015_C01_114 (1). AM W.49015, IN 2015_C01_117 (1). AM W.49025, IN 2015_C02_196 (1). AM W.49026, IN 2015_C02_330 (1). AM W.49939, IN 2017_ V 03_128 (1). AM W.51635, IN 2018_ V 06_184 (1). AM W.51636, IN 2018_ V 06_184 (1). AM W.51637, IN 2018_ V 06_184 (1). AM W.51638, IN 2018_ V 06_184 (1). AM W.53847, IN 2018_ V 06_184 (10).

Diagnosis. Prostomium anteriorly rounded to subtriangular. Small anterior and large posterior eyes present or absent. Palpo- and antennophores with 2–3 rings, median antennae extending to chaetiger 4–5, lateral to 3–4. Branchiae with short to long filaments, from chaetiger 8–9, most often 9. First 2 chaetigers enlarged, parapodia directed anteriorly, often surpassing peristomium. Last postchaetal lobe on chaetiger 15. Robust bidentate simple and slender pseudocompound hooks on chaetiger 1; slender bidentate simple and pseudocompound hooks on chaetiger 2; bidentate pseudocompound to compound hooks on chaetiger 3; pectinate chaetae with about 20 teeth and limbate chaetae from chaetiger 3; subacicular hooks from chaetiger 10–15.

Remarks. All of our specimens are anterior fragments measuring 1.9 to 3 mm in width. Nothria otsuchiensis was described from Otsuchi Bay, in 48–79 m depth based on the holotype and 27 paratypes. The complete holotype measured 18 mm in length for 49 chaetigers and 3 mm in width including parapodia, the morphological characteristics are here presented in Table 3 . In a monograph of the Onuphidae from Japan, Imajima (1999) reported numerous additional records of the species from Otsuchi Bay to Kagoshima Bay, in 26–1070 m depths. In spite of the huge increase of material examined and range of distribution and depth, the diagnostic features were almost identical. The only widening of parameters were the start of branchiae from chaetiger 9–10 rather than 10, and subacicular hooks from chaetiger 10–12 rather than 10 in the original description. In a study of ontogenetic variation of diagnostic characters Budaeva & Paxton (2013) examined a large number of N. otsuchiensis from off eastern Australia in 24–2900 m and a single specimen from New Caledonia in 440–450 m depth. Again, the morphological characteristics were basically the same, showed only a slightly wider range in the length of the antennae, last postchaetal lobes and start of subacicular hooks from the original description ( Table 3 ). As far as diagnostic characters could be evaluated, in spite of the large geographical and depth ranges all specimens examined appeared to match the description of N. otsuchiensis .

In the present study we examined material from three research cruises to the Great Australian Bight and eastern Australia in 400–1761 m depth with similar results ( Table 3 ). Several specimens were sequenced as discussed in the “Molecular Results” section. We obtained several clades, indicating that we are dealing with a species complex that can only be resolved with a deeper molecular investigation of a larger number of specimens .

Distribution. Eastern Australia and Great Australian Bight, in 400–1761 m depth ( Fig. 24 ).

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 24. Nothria otsuchiensis Imajima, 1986 complex. Map of distribution of RV Investigator collections; green dots represent sites of collection.

Tables

Table 3. Distinguishing features of the Nothria otsuchiensis complex. C, compound; PC, pseudocompound.

character	Imajima, 1986	Imajima, 1999	Budaeva & Paxton, 2013	present study
max. width (mm)	3.0 with parapodia	3.0 with parapodia	2.1 without parapodia	3.0 without parapodia
shape of anterior prostomium	rounded	rounded	subtriangular	rounded to subtriangular
antennae, to chaetiger median 10; lateral 5		median 10; lateral 5	median 6–12; lateral 4–9	median 4–5; lateral 3–4
eyes	small anterior &	small anterior &	small anterior absent;	small anterior pres./absent
	large posterior	large posterior	large posterior present	large posterior pres./absent
branchiae from chaetiger	10	9–10	9	8–9
branchiae, shape and length	flat; long	flat; long	flat; long	flat; short to long
last postchaetal lobe on chaetiger 14		14	14–17	15
anterior chaetigers with hooks 3		3	3	3
hooks of chaetiger 1	simple & PC	simple & PC	simple & PC	simple & PC
tips of hooks chaetiger 1	bidentate	bidentate	bidentate	bidentate
hooks of chaetiger 2	simple & PC	simple & PC	simple & PC	simple & PC
tips of hooks chaetiger 2	bidentate	bidentate	bidentate	bidentate
hooks of chaetiger 3	PC	PC	PC	PC to C
tips of hooks chaetiger 3	bidentate	bidentate	bidentate	bidentate
pectinates from chaetiger	3	3	3	3
number of teeth on pectinates	20	not stated	18–22	20
subacicular hooks from chaetiger 10		10–12	10–13	10–15
depth (m)	48–79	26–1070	24–2900	400–1761
distribution	Otsuchi Bay, Japan	Otsuchi Bay to Kagoshima Eastern Australia;		Eastern Australia;
		Bay, Japan	New Caledonia	Great Australian Bight