Abstract
Scinaia is the second most diverse genus of the order Nemaliales, containing 45 species. While three species of Scinaia are currently recognized in Hawaii, occurring commonly to depths of 10 m, a thorough DNA-based analysis of Hawaiian Scinaia diversity is lacking. Mesophotic ecosystems in the Hawaiian archipelago, occurring from 30 to >150 m depths, are known to harbour high levels of endemism, and numerous new algal species and genera have been discovered in these habitats. Here, we characterize Scinaia specimens collected from the Papahānaumokuākea National Marine Sanctuary in the northwestern Hawaiian Islands and the Main Hawaiian Islands using both morphological and molecular approaches. Through phylogenetic analyses, six distinct lineages of Scinaia were identified, and three of these are described as new species: Scinaia ohulumoaula sp. nov. with long unconstricted segments, S. hekeuliuli sp. nov. with short unconstricted segments and S. uohulualii sp. nov. with large cartilaginous thalli and constricted branches. Of these six Hawaiian species, two are restricted to mesophotic depths (>30 m), two are found in both deep and shallow water reefs and two are observed only in shallow waters. Mitochondrial (a first for the Nemaliales) and plastid genomes were used to further characterize the new species. Plastid genomes were structurally similar to others available for the genus. These data provide additional evidence of highly diverse, distinct and endemic assemblages from mesophotic ecosystems in the Hawaiian archipelago.