Uncommon ossicle shape in Holothuria leucospilota from Pangkor Archipelago, Malaysia
There was a lack of studies on Holothuria (Mertensiothuria) leucospilota from Pangkor Archipelago, Perak, Malaysia due to the popularity of a commercial sea cucumber species i.e. Stichopus horrens, the main ingredient of gamat-based traditional medicine on the resort island. Therefore, this study aimed to isolate ossicles from a specimen of morphospecies H. leucospilota collected from Teluk Nipah Beach, Pangkor Archipelago; to determine the shapes of the ossicles for species verification, and to further confirm its species status using non-protein-coding 12S and 16S mitochondrial ribosomal RNA (rRNA) gene sequences. At least six ossicle shapes were documented. Beside the common ossicle shapes i.e. the buttons and the tables; I-shaped rod, long I-shaped rod, branched rod, and spider-shaped rod were also observed. Nevertheless, the spider-shaped rod is an unusual ossicle shape in H. leucospilota as there was no previous record on it, therefore it could be considered as a new finding. Two partial sequences of the mitochondrial rRNA genes were registered with the GenBank (Accession No.: KX768273 - KX768274). The blastn results indicated that the specimen was H. leucospilota with Identities scores of 99% for both genes. Interestingly, only one corresponding 12S mitochondrial rRNA gene sequence was displayed in the blastn results showing a lack of 12S mitochondrial rRNA gene sequences of H. leucospilota in the GenBank until 15th June 2016. This study also suggested that the species identification based on the mitochondrial rRNA gene sequences gave better inference than the ossicle shape identification. In summary, the results verified the species status of the specimen as H. leucospilota, consequently proposed its uniqueness as a result of the presence of the spider-shaped rod. More studies with more samples, more different types of mitochondrial DNA genes, and more morphological and molecular techniques need to be incorporated in future in order to get a better insight.