Nereididae (Annelida) of the Coral Triangle, Indonesia, with some notes on nyale worms, new genus records, and a review of national species discovery

Taxonomic information on Indonesian polychaetes is limited. In the present work, 20 nereidid species (10 genera) from ten locations within the Indonesian part of the Coral Triangle were identified. The specimens were collected between 2009 and 2018 from intertidal reef (mostly) and mangrove habitats. The genera with the most species were Perinereis (6 species), followed by Neanthes (5 species), and the most common species were Perinereis helleri (Grube, 1878), Perinereis larentukana (Grube, 1881), Perinereis obfuscata (Grube, 1878) and Pseudonereis trimaculata (Horst, 1924). Two genera represent first records for Indonesian waters: Cheilonereis sp. and Hediste sp., and three species are potentially new to science: Cheilonereis sp., Hediste sp., and Neanthes cf. gisserana. Five nyale species (reproductive polychaete swarms in Nusa Tenggara) were identified: Composetia marmorata (Horst, 1924), Neanthes cf. gisserana, Neanthes unifasciata (Willey, 1905), P. helleri , and P. larentukana . These findings suggest that nyale are mostly the same species as wawo (reproductive polychaete swarms in Maluku) and hence refute the common belief in central and eastern Indonesia that both groups of worms are unique to Nusa Tenggara and Maluku, respectively. During the period of circa 1.5 centuries (1865–2025), 84 Indonesian nereidid species (24 genera in 29 publications) have been identified, 44 of which (15 genera in 16 publications) are new to science. Despite its status as a country with mega-marine biodiversity, Indonesia’s contribution to global nereidid species discovery has been disproportionately small. To expedite the discovery of additional Indonesian nereidid species potentially new to science, further studies involving integrative taxonomic studies should be concentrated on the three big islands with the least data, i.e., Sumatra, Kalimantan, and Papua. The provided key to all genera of Nereididae in Indonesian waters will facilitate preliminary identification.