Confirming the systematic position of two enigmatic shrimps, Amphionides and Procarididae (Crustacea: Decapoda)

Abstract

Since their discovery, the systematic placement of two shrimp taxa, Amphionides and Procarididae, has been controversial. Both exhibit primitive features yet also possessing caridean traits. Amphionides was initially classified as a monotypic genus in the order Amphionidacea, while Procarididae was the only family in the superfamily Procaridoidea. Recent molecular studies have presented evidence that Amphionides is a larval form of pandalid shrimp, while Procaridoidea is elevated to an infraorder of Decapoda. To confirm the systematic status of the two shrimps, we report here the complete mitogenome sequences of Amphionides reynaudii and Procaris hawaiana. The phylogenetic tree of mitochondrial protein-coding genes from all decapod infraorders provides strong support for the systematic position of procaridid shrimp as the sister of Caridea, and the evolutionary divergence of the sequences substantiates the infraordinal status of Procarididae. The tree also verifies Amphionides as a caridean genus in Pandalidae, and further analysis using eight gene markers from the family indicates the sister relationship between Amphionides and Dorodotes. We also review the morphological characters of these two taxa and identify morphological features in support of their respective systematic status.