Paramytha cf. ossicola Queirós, Ravara, Eilertsen, Kongsrud, & Hilário, 2017

Fig. 3

Ampharetidae gen. spp. Gunton et al., 2021: 19–20.

Material examined. AMW.51926, AMW.52208, 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: AMW.51926 (16S, 18S), AMW.52208 (16S), WF_AMH_3 (16S).

Description. Based on AM W.52208. Anterior section only (~ 1 mm length, ~ 0.5 mm width) for 14 chaetigers, posterior used for molecular analysis. Body cylindrical (Fig. 3A). Prostomium and peristomium fused, not divided into lobes (Fig. 3B). Prostomium without glandular ridges; nuchal organs and eyespots not observed. Buccal tentacles not observed. Paleae absent. Four pairs of branchiae, arrangement 2+2 (Fig. 3A), branchiae somewhat flattened, with longitudinal median furrow. Branchiophores distinct lobes attached to body wall.

Notopodia as rounded lobes, with capillary chaetae starting from segment 3 (Fig. 3D). Uncini from segment 5, thoracic uncini arranged in single row of approximately 13 in number (Fig. 3C). Thoracic uncini with teeth arranged in 3 horizontal rows above main rostral tooth and basal prow (Fig. 3E). The rest of body not observed.

Methyl green staining, prostomium speckled on ventral side andventral bands encompassing whole ventral surface. Notopodia and neuropodia not darkly stained.

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

Remarks. Morphologically this material very closely resembles Paramythaossicola Queirós, Ravara, Eilertsen, Kongsrud, & Hilário, 2017, described from cow carcasses submerged in the Setúbal Canyon (NE Atlantic), 1000 m depth (Queirós et al., 2017). It resembles P. ossicola in all observablemorphological characters exceptfor arrangement of branchiae where it differs, 2+ 2 in this species and 2+1+ 1 in P. ossicola . The close evolutionary relationship between ourspecies ( Paramytha cf. ossicola) and Paramythaossicola is also supported by our molecular analysis (Fig. 4). The three Paramytha species ( Paramythaschanderi Kongsrud, Eilertsen, Alvestad, Kongshavn, & Rapp, 2017 —described from the Arctic Loki Castle hydrothermal vent field at 2350 m, Paramythaossicola and Paramytha cf. ossicola) were recovered in a strongly supported clade (posterior probability, pp 1.0; Fig. 4), while Paramythaossicola and Paramytha cf. ossicola were recovered as sister groups (pp 1.0; Fig. 4). Uncorrected intraspecific divergence between 16S sequences of Paramytha cf. ossicola was 0% (Table S13), this islessthan the intraspecificdivergence recorded in Paramythaschanderi 0.4–1.1% and Paramytha sp. 0–0.4% (Kongsrud et al., 2017). The 16S interspecific genetic distance between Paramytha cf. ossicola and the closely related Paramytha ossicola averaged 3.9%; this is less than the distance recorded between Paramytha schanderi and Paramytha sp. which ranged from 17.6–19.4% (Kongsrud et al., 2017). It is difficult to definitively designate these specimens to Paramytha ossicola or to a separate species, as all specimens are in poor morphological condition. We therefore identify thesespecimens as Paramytha cf. ossicola .