Deep-sea caridean shrimps collected from the South China Sea with emphasizing their phylogenetic relationships.

Despite the high biological and ecological diversity of the South China Sea, limited research has been conducted on the deep-sea species diversity of caridean shrimps. Based on the collections from three scientific expeditions conducted in the South China Sea, 31 caridean species, belonging to nine families, were reported, including the identification of two species not previously documented in this region, namely Janicella spinicauda (A. Milne-Edwards, 1883) and Systellaspis curvispina Crosnier, 1988. In addition to morphological features, the COI and 16S gene sequences of these species were analyzed to assess their evolutionary relationships within each family. Phylogenetic analyses, with highest species coverage to date, indicated that similarity in morphological characteristics does not always lead to closer phylogenetic relationships and some defining characteristics for specific taxa are not always synapomorphies but may be the result of convergent evolution. Our results establish reliable evolutionary relationships within specific taxa and highlight the necessity for further taxonomic revisions within these taxa.