Rediscovery of Malaysia’s marine tardigrades after over half a century: a new species (<i>Batillipes malaysianus</i> sp. nov.) and a new record of <i>B. rotundiculus</i>

Abstract This study marks the first update on Malaysia’s marine tardigrades after more than 50 years, presenting both the discovery of a new species, Batillipes malaysianus sp. nov. , and a new record, Batillipes rotundiculus . The specimens were collected from the intertidal zone at Pantai Pancur Hitam, Labuan, Malaysia, during two separate sampling efforts. Despite extensive sampling, the density of marine tardigrades in the area was found to be exceptionally low, with only a single specimen of B. malaysianus sp. nov. and a limited number of other Batillipes individuals collected. The new species, B. malaysianus sp. nov. , is distinguished by unique morphological features, including setae scattered across the ventral cuticle – a trait not observed in any other species of the genus – and constricted primary clavae, a characteristic absent in other species of the B1 toe arrangement group. Additionally, B. rotundiculus represents the first confirmed record of this species in Malaysia, expanding its known distribution. This study also updates the global species count of Batillipes to 42, incorporating recent taxonomic changes and this new addition. An updated dichotomous key for the genus is provided, incorporating all species described to date. These findings underscore the importance of exploring understudied marine habitats and highlight the potential for discovering more tardigrade species in Malaysia.