Nereis Linnaeus, 1758

Georgieva, Magdalena N., Wiklund, Helena, Ramos, Dino A., Neal, Lenka, Glasby, Christopher J. & Gunton, Laetitia M., 2023, The Annelid Community of a Natural Deep-sea Whale Fall off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 167-213 : 189-191

Nereis Linnaeus, 1758

Nereis sp.

Fig. 17

Material examined. NHMUKANEA 2022.436 , AM W.52210, IN2017_ V03 _100; 9 June 2017; off Byron Bay , NSW, Australia, beam trawl, start: 28.05°S 154.08°E, 999 m, end: 28.10°S 154.08°E, 1013 m. DNA vouchers: NHMUK ANEA 2022.436 ( COI, 16 S, 18 S) , AMW.52210 (16 S).

Description. The best-preservedspecimen NHMUK.2022. 436 complete ( Fig. 17A ), 14.2 mm long and a maximum of 1.3 mm wide (excluding parapodia) for 55 chaetigers. Pharynx partially extended, body tapering towards the posterior. Specimen not observed alive, colour in ethanol pale yellow ( Fig. 17A ).

Specimen AMW.52210 posteriorly incomplete, 8.2 mm long anda maximum width of 0.9 mm (excluding parapodia) for 33 chaetigers; inmoderately poor condition probablydue to fixation in ethanol resulting in paragnath shedding and most cirri and some ligules/lobes in process of falling off.

Prostomium trapezoid ( Fig. 17B ), approximately as wide as long. One pairof cirriform, distally tapering antennae, approximately the same length as palps. One pair of robust palps, with cylindrical palpophores and smaller oval palpostyles. Eyes not observed. Tentacular belt (first adult annulus) approximately 1.5× length of the subsequent segments, with four pairs of tentacular cirri. Tentacular cirri with cylindrical tentaculophores, only two shorter pairs with styles attached, styles smooth not extending beyond prostomium ( Fig. 17B ).

Pharynx partially everted ( Fig. 17C ), with brown jaws with 9 teeth oncutting edge. Paragnaths allsmall (of similar size), conical, dark brownin colour and arranged as follows: Area I—2 paragnaths; II—clusterof 14–16 paragnaths; III—0–3 paragnaths (unclear, possibly damaged during dissection); IV—9 paragnaths; V—none; VI—6 paragnaths; VII–VIII—30–40 small paragnathsarranged intwoirregular rows.

First two chaetigers uniramous, the following biramous. Dorsal cirri on uniramous chaetigers slightly longer and inserted at the base of dorsal notopodial ligules. Dorsal and ventral ligules a similar conical shape and size, slightly longer than ligules adjacent to chaetae. Ventral cirri of a similar length to ventral ligules.

Biramous parapodia progressively change throughout the body in form and size, becoming smaller posteriorly ( Fig. 17D–17F ). Anterior notopodia ( Fig. 17D ) with long smooth dorsal cirrus, approximately twice the length of corresponding dorsal ligule ( Fig. 17D ); dorsal ligule large and broadly conical, prechaetal ligule reduced, postchaetal ligule large and conical, similar to dorsal ligule ( Fig. 17D ). Anterior neuropodia ( Fig. 17D ) with prechaetal ligule short, broadly conical ( Fig. 17D ), postchaetalligule elongated and conical ( Fig. 17D ); ventralligulebroadly conical, justshorter than postchaetal ligule; ventral cirrus slender, cirriform distally tapering, approaching the length of ventral ligule. Mid-body notopodia ( Fig. 17E ) with smooth dorsal cirrus shorter than in anterior parapodia, but greatly exceeding the length of the corresponding dorsal ligule to which it is medially attached; dorsal ligule short and very broad ( Fig. 17E ), prechaetal ligule short and broadly conical ( Fig. 17E ), postchaetal ligule very elongated, conical ( Fig. 17E ). Mid-body neuropodia ( Fig. 17E ) with reduced prechaetal ligule ( Fig. 17E ), postchaetal ligule very elongated, conical ( Fig. 17E ); ventral ligule elongated, relatively narrow and conical ( Fig. 17E ), approximately same length as corresponding postchaetal ligule; ventral cirrus slender, cirriform and distinctly shorter than corresponding ligule. Posterior notopodia ( Fig. 17F ) with smooth dorsal cirrus shorter than inpreceding notopodia but exceeding the length of corresponding dorsalligule towhich itismedially attached ( Fig. 17F ); dorsal ligule very short and broad somewhat constricted at the attachment of dorsal cirrus; prechaetal ligule short and broad, tapering into sharp tip ( Fig. 17F ), postchaetal ligule elongated, distally rounded ( Fig. 17F ). Posterior neuropodia ( Fig. 17F ) with prechaetal ligule reduced ( Fig. 17F ), postchaetal ligule elongated, conical with sharp tip ( Fig. 17F ); ventral ligule short and rounded; ventral cirrus slender, cirriform and distinctly longer than corresponding ligule ( Fig. 17F ).

Chaetae of two main types as spinigers and falcigers, both can be homogomph or heterogomph. All blades of spinigers finely serrated, all blades of falcigers unidentate, serrated. Presence/absence of chaetae and their number changes throughout the body. Each ramus with a straight, dark internal acicula ( Fig. 17D–F ). In anterior parapodia (represented by chaetigers 6, 7) the chaetae as follows ( Fig. 17G–J ): notochaetae all supra-acicular, 4–7 per fascicle all homogomph spinigers; supra-acicular neurochaetae consisting of 1–3 homogomph spinigers and 1–2 heterogomph falcigers; sub-acicular neurochaetae composed of 8–10 heterogomph falcigers. In mid-body parapodia (represented by chaetigers 20, 22) the chaetae as follows ( Fig. 17K–N ): notochaetae all supra-acicular, 4 per fascicle consisting of 1–3 homogomph spinigers and 1–2 homogomph falcigers; supra-acicular neurochaetae consisting of 4–5 homogomph spinigers with particularly long blades and 1–2 heterogomph falcigers; sub-acicular neurochaetae composed of 0–2 heterogomph spinigers and 3–7 heterogomph falcigers. In posterior parapodia (represented by chaetiger 36) the chaetae as follows ( Fig. 17O–Q ): all notochaetae homogomph falcigers, 3 per fascicle; supra-acicular neurochaetae composed of 2 homogomph spinigers and 2 heterogomph falcigers; sub-acicular neurochaetae composed of 3 heterogomph spinigers and 3 heterogomph falcigers.

Pygidium rounded; cirri not observed.

Distribution. IN2017_V03, Station 100. Pilot whale carcass, off Byron Bay, New South Wales, Australia in 999–1013 m.

Remarks. Two specimens collected as part of this study likely belong to genus Nereis , as they possess homogomph falcigers in the posterior notopodia. The description above builds upon that of Gunton et al. (2021; referred to as Nereis sp. 1 ) which was based on one of the two specimens examined here; despite the additional morphological information from thesecond specimen and the support from sequence data, we are reluctant to formally name the new species for the reasons below.

Nereis is currently the most species-rich genus within Nereididae , with many deep-water species, a problematic taxonomic history, morphological characters affected by the reproductive statusof thespecimen as well as exhibiting a high level of homoplasy (e.g., Bakken & Wilson, 2005; Santos et al., 2006). Further, molecular information obtained from the specimens included in this study suggests that specimens identifiedhere as Nereis sp. are geneticallysimilar to Neanthes shinkai ( Fig. 16 ; COI genetic p -distance between Nereis sp. and Neanthes shinkai was 12.6%; Table S16); N. shinkai is also described from a whale fall, but one located at 4200 m depth on the São Paulo Ridge in the Southwest Atlantic (Shimabukuro et al., 2017). Anumber of other Nereis species are also included in the well-supported clade containing Nereis sp. and Neanthes shinkai ( Fig. 16 ). We are also aware of colleagueswho are inthe process of describing a new eyeless species of Nereis fromthe southwest Atlantic, and there is a chance that it could be the same as our IN2017_V03 specimens. Solving taxonomic problems is beyond the remit of this study and as a result we assign the specimens to genus only.

Figures

Figure 16. Phylogeny of the Nereididae family based on Bayesian analysis of a combined dataset of the genes COI, 16S and 18S. Numbers adjacent to nodes indicate posterior probabilities, and taxa for which sequences have been contributed by the present study are indicated in bold.

Figure 17. See caption on facing page.