Taxonomic status and phylogenetic analyses based on complete mitochondrial genome and microscopic ossicles: Redescription of a controversial tropical sea cucumber species (Holothuroidea, Holothuria Linnaeus, 1767)

To explore the taxonomic status of a tropical sea cucumber species with controversy, we conducted an investigation into its morphological characteristics (external form and ossicles) and mitochondrial genome and rearranged the historical materials of the species and its confusing species. The species was first described in the middle of the 18 th century but later synonymized with Bohadschia ocellata Jaeger, 1833, Holothuria hamata Pearson, 1913, or Holothuria kurti Ludwig, 1891, by different scholars. The observed ossicles encompassed multiple types, including buttons, C-shaped ossicles, rods, and tables, with a distinct subtype identified as tack-like tables. Ventral and dorsal body walls exhibited similar table and button ossicle shapes. The mitogenome contained 13 protein-coding genes (PCGs), 2 ribosomal RNAs (rRNAs), and 22 transfer RNA (tRNA) genes, with a sequence length of 15,797 bp. Subsequent construction of a phylogenetic tree using Bayesian inference (BI) and maximum likelihood (ML) methods indicated that the species was grouped into a separate branch firstly with Holothuria (Theelothuria) spinifera Théel, 1886, so suggesting its taxonomic classification under subgenus Theelothuria Deichmann, 1958. Based on the data of this study and previous literature, we suggested that the Latin name for this species should tentatively be “ Holothuria ocellata Jaeger, 1833 sensu Théel 1886.” The morphologic and genomic information in the current study could be valuable in further biological studies of this sea cucumber species.