A taxonomic revision of Pennella Oken, 1815 based on morphology and genetics (Copepoda: Siphonostomatoida: Pennellidae)

Abstract

Abstract The taxonomy of the genus PennellaOken, 1815, a large parasitic copepod, is in a deplorable state. We performed morphological and genetic analyses on 52 Pennella individuals collected from 12 species of definitive hosts. Based on the morphological characteristics and their hosts, 29 individuals were determined or suggested to be large-size species (P. balaenoptera, P. filosa, P. instructa, and P. benzi), whereas 20 were considered intermediate- or small-size species. The remaining three small individuals, presumed to be newly attached, exhibited insufficient morphological characteristics for species identification or grouping. Mitochondrial DNA cytochrome c oxidase subunit 1 (COI) sequence analysis detected 154 haplotypes from 52 individuals classified into Groups I–IV. Sequences of Group IV were determined to be pseudogenes. Levels of divergence between all groups were significant (FST = 0.488–0.830, P < 0.001). All haplotypes of Group I were detected in intermediate- and small-size groups possessing large and well-branched antennary processes on the cephalothorax. Although Groups I and II exhibited the smallest difference in nucleotide sequence divergence (FST = 0.488 and K2P = 1.485 ± 0.355%), the morphological characteristics of Group I appeared to be distinct from those of the other groups. The substantial sequence divergence (FST = 0.830 and K2P = 4.123 ± 0.719%) between Groups II and III also supported their species status, but no characteristic morphological difference was observed between individuals in these groups. Results suggest that Pennella may contain only two or three species. and that some morphological characteristics and definitive host species previously used for species identification are not valid.