Three Cases Revealing Remarkable Genetic Similarity Between Vent-Endemic <em>Rimicaris</em> Shrimps Across Distant Geographic Regions: Toward a New Conservation Perspective

Deep-sea hydrothermal vent fauna is often regarded as highly endemic, although exceptions have been reported. We examined genetic connectivity across broad spatial scales within the alvinocaridid genus Rimicaris, which has undergone substantial adaptive radiation worldwide. We analyzed six Rimicaris species using three genetic markers (COI, 16S, and H3) and complete mitogenomes, using newly generated sequences combined with publicly available sequence data. Genetic tree and haplotype networks were constructed, and divergence analyses were performed. As a result, three clades of paired Rimicaris species were identified, each comprising taxa from different oceanic regions, but showing relatively low COI divergence (0.35–1.90%). In Clade I, Rimicaris chacei and Rimicaris hybisae are morphologically similar and exhibit bidirectional gene flow, suggesting a dispersal route between the Mid-Atlantic Ridge and Mid-Cayman Spreading Center. In Clade II, Rimicaris exoculata and Rimicaris kairei are morphologically, genetically, and ecologically distinct, reflecting restricted connectivity between the Mid-Atlantic Ridge and Carlsberg Ridge–Central Indian Ridge. In Clade III, Rimicaris variabilis and Rimicaris cf. variabilis differ in nutritional strategies, showing a unidirectional dispersal route from the northern Central Indian Ridge to the southwestern Pacific, but morphological data to distinguish them are currently lacking. Some Rimicaris lineages maintain connectivity across distinct oceanic regions while others still form unique regional populations. This finding highlights the need for conservation strategies that incorporate both global-scale connectivity and regional endemism, rather than treating vent ecosystems as a single homogeneous management unit.