Ophryotrocha dahlgreni sp. nov.

urn:lsid:zoobank.org:act: DCE44401-C339-4560-BD58-874DB82EECD3

Fig. 7

Holotype: AMW.53694 (length 1 mm for 18 chaetigerous segments), 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 . Paratypes: NMV F296816–296818, NHMUKANEA 2022.769 – 771, same locality as holotype. DNA vouchers: AM W.53692–53693, samelocalityas holotype .

Description. Small species, body length up to 1.2 mm for examined specimens. Body compressed dorsoventrally, similar width throughout the body until last few segments where it tapers slightly (Fig. 7A). Head of similar width as anterior body, roundedwithsimple antennaeand palps, equal in length (Fig. 7A, 7B). Mandibles rod-like without visible dentition in the examined specimens, apophyse triangular pointing outwards (Fig. 7C). Maxillae of P-type with a pair of forceps and seven pairs of free denticles (D1–7). Forceps with coarse teeth, D1–3 with slightly finer teeth. Denticles 4–7 with fine, evenly sized teeth (Fig. 7D). Parapodia uniramous with large dorsal cirri placed distally, no ventral cirri (Fig. 7E). Supra-acicular chaetae simple (Fig. 7F), sub-acicular chaetae compoundwith short blades (Fig. 7G), sub-acicular lobe with one simple chaeta. Pygidium with terminal anus, pygidial appendages not observed.

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

Etymology. This species is named in honour of Dr Thomas Dahlgren, NORCE, Norway, and University of Gothenburg, Sweden for his work with whale-fall fauna.

Remarks. This is a small species with few complete specimens. Although pygidial cirri were not observed in any of the most complete specimens, they might not be truly lacking and may have fallen off. In the phylogenetic tree based on 16S (Fig. 8) this species falls in a trichotomy with Ophryotrocha langstrumpae Wiklund et al., 2012 described from whale fall in eastern Pacific Ocean, and O. geoffreadi Ravara, Wiklund, and Cunha, 2021 described from experimentally deployed wood substrate in Gulf of Cadiz. The new species differs from O. langstrumpae in the shape of the parapodia and chaetae, where the new species lacks ventral cirri and has short blades on the compound sub-acicular chaetae. Ophryotrocha geoffreadi has large, triangular-shaped apophyses, but itsrod-like mandibles have straight, serrated cutting edges, while in the new species the tips are gently curving outwards and lack serration.