Morphological redescription and complete mitochondrial genome of Deima oloughlini (Holothuroidea, Synallactida, Deimatidae), with a new record from the northern Indian Ocean.

The family Deimatidae is widely distributed throughout the deep sea but remains poorly represented by both morphological and molecular data. During a 2022 scientific expedition to the Ninety East Ridge, Indian Ocean, two deep-sea holothurian specimens were collected at depths of 2447-2557 m. Following morphological re-examination together with phylogenetic analyses based on the mitochondrial COI and 16S genes, the specimens were identified as Deima oloughlini Mackenzie & Davey in Mackenzie et al. 2024, representing the first record of this species from the northern Indian Ocean. Detailed observations of ossicles from five body regions are provided to facilitate future taxonomic comparisons within the genus Deima. The complete mitochondrial genome of D. oloughlini was also characterized as a circular molecule of 16,263 bp containing 13 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes, with an overall A+T content of 72.2%. This mitogenome is among the few genomic resources currently available for Deimatidae and provides additional molecular data for future studies of the phylogeny, taxonomy, and biogeography of this deep-sea family.