Morphological and Molecular Identification of Holothuria (Merthensiothuria) leucospilota and Stichopus horrens from Pangkor Island, Malaysia

This preliminary study aimed to identify a commercial gamat species, Stichopus horrens Selenka, 1867, and a timun laut species, Holothuria (Mertensiothuria) leucospilota (Brandt, 1835), from Pangkor Island, Perak, Malaysia, employing morphological techniques based on the shape of the ossicles and molecular techniques based on the cytochrome c oxidase I (COI) mitochondrial DNA (mtDNA) gene. In Malaysia, a gamat is defined as a sea cucumber species of the family Stichopodidae with medicinal value, and timun laut refers to non-gamat species. S. horrens is very popular on Pangkor Island as a main ingredient in the traditional production of air gamat and minyak gamat, while H. leucospilota is the most abundant species in Malaysia. In contrast to previous studies, internal body parts (the respiratory tree and gastrointestine) were examined in this study to obtain better inferences based on morphology. The results showed that there were no ossicles present in the gastrointestine of H. leucospilota, and this characteristic is suggested as a unique diagnostic marker for the timun laut species. In addition, the presence of Y-shaped rods in the respiratory tree of S. horrens subsequently supported the potential to use internal body parts to identify the gamat species. Phylogenetic analysis of the COI mtDNA gene of the sea cucumber specimens using the neighbour-joining method and maximum likelihood methods further confirmed the species status of H. leucospilota and S. horrens from Pangkor Island, Perak, Malaysia. The COI mtDNA gene sequences were registered with GenBank, National Center for Biotechnology Information (NCBI), US National Library of Medicine (GenBank accession no.: KC405565-KC405568). Although additional specimens from various localities will be required to produce more conclusive results, the current findings provide better insight into the importance of complementary approaches involving morphological and molecular techniques in the identification of the two Malaysian sea cucumber species.