NHM_2107, NHMUK ANEA 2022.630, coll. 20/03/2015, EBS, 19.46457, -120.02542, 4026 m, APEI-6, http://data.nhm.ac.uk/object/c79b4600-e8e9-4484-b06a-e18330a1421d; NHM_2109, NHMUK ANEA 2022.631, coll. 20/03/2015, EBS, 19.46457, -120.02542, 4026 m, APEI-6, http://data.nhm.ac.uk/object/ac3dd714-64ac-44ea-9168-22437dc3cfba.

Amphinomidae spp.; AM. W.52607; 3 specimens; IN2017; sta. V03_110; 4005 m; South Pacific, Australia, off Fraser Island (-25.220, 154.160); col. 11/06/2017; EBS.

This very small species is represented by two specimens, up to 2.9 mm long and 0.75 mm wide for ten chaetigers. Body compact, spindle-shaped, of bloated appearance (Figs 2A–C, F, 3A, 4A). Preserved specimens pale yellow (Figs 2A, 3A), live specimens translucent to slightly tanned.

Prostomium rounded, longer than wide; anterior lobe broadly rounded, bearing a pair of cirriform lateral antennae (Figs 2C, 3C), a pair of slightly shorter ventrolateral palps and posteriorly prostomium with longer median antenna (Figs 2C, 3C). Prostomium with pair of very small reddish eyes (Fig. 2A, D); posteriorly extended into a conspicuous caruncle reaching the anterior margin of 3^rd chaetiger; caruncle large, ramified, and with deeply folded margins (Fig. 2B, C).

Parapodia biramous. Parapodial appendages often broken off, where attached dorsal, lateral and ventral cirri observed, including on chaetiger 1 (Fig. 3C, D). In anterior chaetigers cirri slightly more robust with thickened bases. Bipinnate branchiae observed only on chaetiger 6, with a large primary stalk and up to seven short lateral branches (Figs 2B, C, G, 3E). Branchiae on preceding segments likely absent (no scars or stalks observed), but those on subsequent segments likely present, but damaged (scars or stalks observed). Chaetae mostly broken off, only few long bifurcate noto- and neurochaetae arising directly from body wall observed, where observed prongs smooth. Pygidium as a conical lobe (Fig. 2G), with dorsal anus and with a pair of short terminal cirri (Fig. 3F).

Specimen, NHMUK ANEA.2022.630, was successfully sequenced for 16S, 18S and COI while for specimen, NHMUK ANEA.2022.631, only 16S was obtained (Table 1). There were no identical sequences for either 16S or COI found on the GenBank. In the phylogenetic tree this species falls out as sister taxon to Bathychloeiacf.sibogae and the Bathychloeia clade is in an unresolved trichotomy with clades consisting of species from the genera Chloeia and Notopygos, although this trichotomy has low support (Fig. 5A).

The CCZ-collected specimens correspond morphologically to another abyssal species Bathychloeiaballoniformis Böggemann, 2009 described from Cape and Guinea Basins in SE Atlantic, 5048–5144 m depth. The specimens agree in small, spindle-shaped body, having ca. 10 chaetigers, the form of greatly folded and crenulated caruncle and the form and distribution of branchiae (see comparative Fig. 4A, C). Additionally, specimens recently collected from the abyssal South Pacific (ca. 4000 m) as part of the RV ‘Investigator’ voyage ‘Sampling the Abyss’ were made available for examination (see also Gunton et al. 2021). Originally identified as Amphinomidae sp. (Fig. 4B), morphologically these specimens also agree well with the description of Bathychloeiaballoniformis from the NE Atlantic (Fig. 4C) and with CCZ-collected specimens (Figs 2, 3, 4A). However, molecular work on specimens from South Pacific was not successful and no molecular work was carried out on specimens from the abyssal Atlantic (Böggemann pers. comm.). Due to lack of molecular data from the other locations, we cautiously ascribe CCZ-collected specimens to Bathychloeiacf.balloniformis.

Central Pacific Ocean, Eastern CCZ, in the Area of Particular Environmental Interest, ‘APEI-6’ only (Fig. 1).