Three new species of Argathona (Isopoda: Corallanidae) from Indonesian and Malaysian Borneo, with the first records from elasmobranch hosts

Although Borneo lies within the highly biodiverse Coral Triangle, its reported isopod diversity remains poorly documented and underexplored. This study documents four species of the corallanid isopod genus <i>Argathona</i> collected from elasmobranch hosts in Indonesian and Malaysian Borneo, namely <i>A. lineata</i>, <i>A. magnocula</i> sp. nov., <i>A. lebara</i> sp. nov., and <i>A. terputa</i> sp. nov. Specimens were identified based on detailed morphological characters. <i>Argathona magnocula</i> sp. nov. is characterised by a posteriorly elongate frontal lamina that is three times longer than its posterior width; eyes separated by ∼34 % of head width; a pleotelson with a sub-truncate posterior margin and dorsal fields of hyaline setae; and uropodal rami barely extending beyond the pleotelson. <i>Argathona lebara</i> sp. nov. is distinguished by its short, broad frontal lamina (shorter than wide), small eyes, deeply concave maxillula mesial lobe, and exceptionally long antennae reaching pereonite 7. <i>Argathona terputa</i> sp. nov. features a broadly truncate pleotelson, short antennula (extending only to the eye's posterior), and uropodal rami that do not extend past the pleotelson apex. It can be separated from <i>A. lineata</i> by its broader pleotelson margin, shorter frontal lamina, reduced setation, and the presence of two simple setae on the maxillula mesial lobe. This study describes three new species, reveals novel host associations with four elasmobranch species, and transfers <i>Alcirona grandis</i> into the genus.