# New and known free-living nematode species (Nematoda: Chromadorea) from offshore tsunami monitoring buoys in the Southwest Pacific Ocean

## TL;DR

This paper describes two new nematode species found on tsunami monitoring buoys in the Southwest Pacific Ocean and discusses their long-distance dispersal capabilities.

## Contribution

The study introduces two new free-living nematode species and provides updated taxonomic keys for related genera.

## Key findings

- Two new nematode species, Atrochromadora tereroa and Euchromadora rebeccae, were identified from offshore buoys.
- Halomonhystera refringens was found to include the previously described species Halomohystera zhangi as a synonym.
- Nematodes on buoys suggest long-distance dispersal via drifting macroalgal fragments.

## Abstract

Deep-ocean Assessment and Reporting of Tsunami (DART) buoys are deployed across the Southwest Pacific and provide substrates for biofouling communities. Two new free-living nematode species, Atrochromadora tereroa sp. nov. and Euchromadora rebeccae sp. nov. (family Chromadoridae), and one known species, Halomonhystera refringens (Bresslau & Schuurmans Stekhoven, 1933) comb. nov. (family Monhysteridae), are described from buoys deployed off Raoul Island in the Kermadec/Rangitāhua region and off New Zealand’s East Cape. Thalassomonhystera refringens (Bresslau & Schuurmans Stekhoven, 1933) Jacobs, 1987 and T. anoxybiotica (Jensen, 1986) Jacobs, 1987 are transferred to Halomonhystera based on the presence of precloacal and caudal papillae in males. In addition, Halomohystera zhangi Li, Huang & Huang, 2024 is synonymised with Halomonhystera refringens. Updated keys to Atrochromadora, Euchromadora and Halomonhystera species are provided. The presence of nematodes on buoys located more than 100 km from the nearest landmass and in deep waters (>3,500 m water depth) shows that some nematode species are capable long-distance dispersal to colonise new substrates. Such dispersal by Atrochromadora, Euchromadora and Halomonhystera species likely occurs via drifting macroalgal fragments.