Euphrosinella georgievae sp. nov.

Figs 13A-G, 14A-F, 15A, 16A-G

Material examined.

NHM_0587, NHMUK ANEA 2022.658, coll. 17/02/2015, EBS, 12.38624, -116.54867, 4202 m, UK-1, http://data.nhm.ac.uk/object/b7a0bf33-0dc4-4f61-90de-35865647a99f; NHM_0777, NHMUK ANEA 2022.659, coll. 20/02/2015, EBS, 12.38624, -116.54867, 4202 m, UK-1, http://data.nhm.ac.uk/object/a8f0e776-d7b6-4ec6-a549-78f40f17d89b; NHM_1737B, NHMUK ANEA 2022.660, coll. 11/03/2015, EBS, 12.17383, -117.19283, 4045 m, OMS, http://data.nhm.ac.uk/object/2784df45-eec0-4151-b12d-11d955985faa; NHM_0910, NHMUK ANEA 2022.661, coll. 23/02/2015, EBS, 12.57133, -116.6105, 4198 m, UK-1, http://data.nhm.ac.uk/object/05dfb32c-fc3a-4028-bf09-3eb840175661; NHM_1134 (paratype), NHMUK ANEA 2022.662, coll. 26/02/2015, EBS, 12.1155, -117.1645, 4100 m, OMS, http://data.nhm.ac.uk/object/00590d2b-f952-4c69-8bc2-ac2a408da17a; NHM_1514, NHMUK ANEA 2022.663, coll. 05/03/2015, EBS, 12.51316667, -116.491333, 4252 m, UK-1, http://data.nhm.ac.uk/object/96cb7b69-c0ea-4559-9b57-3abe6af4a4c7; NHM_2391 (holotype), NHMUK ANEA 2022.664, coll. 20/02/2015, EBS, 12.53717, -116.60417, 4425 m, UK-1, http://data.nhm.ac.uk/object/1ce8325f-74de-47de-a776-2dc50b8d69ae; NHM_4975, NHMUK ANEA 2022.665, coll. 28/10/2020, box core, 11.013923, -116.258737, 4234 m, NORI-D, http://data.nhm.ac.uk/object/677b7d67-d9cc-4ebd-8d79-cf5da5dc40da; NHM_6087, NHMUK ANEA 2022.666, coll. 14/11/2020, box core, 10.647709, -117.226887, 4183 m, NORI-D, http://data.nhm.ac.uk/object/eebfaecd-5ee2-49d6-be73-51eb91678487; NHM_5802, NHMUK ANEA 2022.667, coll. 11/10/2020, box core, 10.475094, -117.384872, 4306 m, NORI-D, http://data.nhm.ac.uk/object/c0e408e3-91e7-408f-aaef-3be86507105a; NHM_5057, NHMUK ANEA 2022.668, coll. 30/10/2020, box core, 10.929036, -116.26351, 4262 m, NORI-D, http://data.nhm.ac.uk/object/d92b1574-eccb-443c-a15d-b79357360b59; NHM_7235, NHMUK ANEA 2022.669, coll. 14/05/2021, box core, 10.3773, -117.1558, 4302 m, NORI-D, http://data.nhm.ac.uk/object/55637dc0-f9b9-4586-9bfb-7a821c785279; NHM_2908, NHMUK ANEA 2022.670, coll. 20/02/2015, EBS, 12.53717, -116.60417, 4425 m, UK-1, http://data.nhm.ac.uk/object/fba3fab7-ae4b-4415-a73c-a2ba6cd44601.

Diagnosis.

Holotype (NHMUK ANEA.2022.664) complete (except for tissue sampled for DNA), 4.2 mm long and 1.1 mm wide without chaetae for 15 chaetigers (Fig. 13A). Paratype (NHMUK ANEA.2022.662) complete (except for tissue sampled for DNA), with 13 chaetigers (Fig. 14A). Body short, oval, flattened, pale yellow in alcohol (Figs 13A, 14A). Prostomium longer than wide, with five prostomial appendages (Fig. 15A). Pair of short slender palps (Figs 13C, 14C, D); pair of slender lateral antenna (Figs 13C, 14C, D); median antenna of caruncle with long thick ceratophore and slender cirrus only slightly longer than caruncle (Fig. 13C). Caruncle as oval lobe reaching to anterior margin of chaetiger 4, mostly free of body wall, with median keel and two pairs of lateral ridges, with median keel slightly thicker than the lateral ones (Fig. 13C, D). Eyes not observed.

Parapodia biramous, two rami well separated. Parapodia of chaetiger 1 well developed, not reduced, with dorsal, lateral, and ventral cirri (Fig. 13C). Parapodial appendages of subsequent chaetigers in the following dorsoventral order: dorsal cirrus, branchia, lateral cirrus, ventral cirrus (Fig. 15C). All cirri as single filaments of various length and thickness with dorsal cirrus longest (extending over three chaetigers in midbody) (Figs 13E, 14E); lateral cirrus shorter and more stout inserted in the middle of notochaetal bundle (Fig. 13E, F); ventral cirrus slightly shorter than lateral cirrus, slender. Branchia one per chaetiger, simple (unbranched) cirrus, inserted laterally to dorsal cirrus, very short (ca. ½ the length of mid body chaetiger) (Figs 13E, F, 14E, 15C).

All chaetae well developed, but prone to breakage, all bifurcate (Fig. 16A). Notochaetae in approximately three tiers; differing mainly in their length and thickness with notochaetae of mid tear longest and thickest (Fig. 16B-E); prongs mostly smooth (Fig. 16B, C, E) or few with very faint serration (Fig. 16D); ratio of short to long prong in the short chaetae of anterior tier ranges from 1:3.5-4 (where possible to establish); in long chaetae of mid-tier ratio ranges from 1:4 to 1:5 (where possible to establish). Ringent notochaetae absent. Neurochaetae less numerous and thinner than notochaetae; all bifurcate, of varying lengths, prongs with noticeable serration (Fig. 16F, G), few prongs appearing smooth. Pygidium with paired anal cirri, resembling cylindrical tube feet (Figs 13G, 14B, F).

Molecular information.

One specimen, NHMUK ANEA.2022.658, was sequenced for 16S and 18S genes, while the 13 additional specimens were sequenced for 16S only (Table 1). There were no identical sequences for 16S on GenBank. In the phylogenetic tree this species falls as a sister taxon to Euphrosinella cf. cirratoformis from Antarctica (Fig. 5B).

Remarks.

Euphrosinella georgievae sp. nov. is consistent with the genus Euphrosinella in having five prostomial appendages, caruncle mostly free from body wall and absence of ringent chaetae. Only two valid species in Euphrosinella are currently known as mentioned earlier. A known Pacific species Euphrosinella paucibranchiata can be distinguished by having some branchiae branched, as well as much shallower depth distribution of 1737 m in Santa Cruz Basin. Euphrosinella georgievae sp. nov. is more similar to the Antarctic species E. cirratoformis in having simple unbranched branchiae. The species also share a similar form and length of caruncle and median antenna. However, the two species differ in the following characters: 1. The presence of two pairs of eyes in the Antarctic species, while CCZ specimens are eyeless; 2. Notochaetae arranged in 3 tiers in new species, rather than 2 tiers in the known species and 3. Branchiae are not developed on first chaetiger in E. georgievae sp. nov., whilst they are present in E. cirratoformis . As further evidence, the molecular data suggest that Antarctic specimens identified in a previous study as Euphrosinella cf. cirratoformis (see Brasier et al. 2016) are different to the specimens of E. georgievae sp. nov. (Fig. 5B).

Distribution.

Central Pacific Ocean, Eastern CCZ, the exploration areas UK-1, OMS, and NORI-D (Fig. 1).

Etymology.

This species is named for Dr. Magdalena Georgieva, who took part in ABYSSLINE expeditions to CCZ. She also collected Bathychloeia cf. sibogae specimens from CCZ used in this study as well as samples from the South Pacific during the RV Investigator cruise used here as a comparative material.