Exploring molecular and morphological diversity of Ostracoda: a combined approach based on COI sequences and morphological characters

Ostracods are diminutive aquatic invertebrates with a broad geographical distribution across a diverse range of aquatic habitats, including lentic and lotic freshwater environments as well as marine waters. Due to their sensitivity to environmental changes, ostracods are valuable tools in biodiversity monitoring, providing a link to past, present, and future ecological conditions. Despite the significance of classical taxonomic studies in species identification, molecular approaches remain underutilized in ostracod research, representing an area of potential growth for advancing our understanding of this diverse group. Thus, molecular studies in ostracods have the potential to greatly enhance our understanding of morphology, ecological variation and adaptation, and species diversity. While adaptation through morphological characters (e.g., carapace variation serving as a protective structure) and form (e.g., size, shape, and mineral composition) vary in response to environmental factors, molecular tools such as DNA sequence analyses can be useful for exploring how ostracods thrive in different aquatic habitats and how they speciated over time. In this study, we isolated total DNA and amplified 658 bp of the cytochrome c oxidase I (COI) gene from nonmarine ostracod species collected from Denizli Province, Türkiye. In addition, we included 5068 publicly available COI sequences retrieved from NCBI. Our analyses provide a broader molecular framework for examining evolutionary relationships, morphological congruence, and ecological differentiation across ostracod lineages. The results emphasize the need for more integrated studies that combine molecular, ecological, and morphological data to improve species delimitation and understand habitat-driven divergence in this underexplored group.