Freshwater Harpacticoida from Borneo (Malaysia): New Records and Faunistic Insights into an Overlooked Group

Borneo, one of the world’s largest tropical islands, has so far been poorly explored for freshwater harpacticoid copepods. Until recently, only twelve species were known, all from the Malaysian state of Sabah. Based on 31 samples collected across Sabah and Sarawak in 2024, we report new faunistic data that expand our current knowledge. Harpacticoids were detected in 17 sites, from high-altitude mountain brooks to shaded streams in primary rainforest, and ten taxa were identified. Our study documents two genera and two species newly reported from Borneo: the genera Parastenocaris Kessler, 1913 and Nitocra Boeck, 1865, each represented by morphologically distinct and likely undescribed species, and the species Elaphoidella javaensis (Chappuis, 1928) and E. cf. thienemanni Chappuis, 1931, newly recorded from the island. The occurrence of specimens identified as Attheyella (Canthosella) cf. silvicola Löffler, 1973, more than five decades after the original description, documents the continued occurrence of a morphologically similar form near Mount Kinabalu and its presence in Sarawak, but with some differences from the original description, while widespread taxa such as Elaphoidella bidens decorata (Daday, 1901), Epactophanes richardi Mrázek, 1893, and Phyllognathopus viguieri (Maupas, 1892) form the core of the island’s fauna. Our findings increase the number of known freshwater harpacticoids from Borneo to at least 15 taxa and reveal a diverse assemblage reflecting both Sundaland–Indochina faunal continuity and the presence of several, still undescribed forms, highlighting Borneo as an important hotspot of overlooked copepod diversity.