Phylogeny and classification of the shrimp genera A cetes, P eisos, and S icyonella ( Sergestidae: Crustacea: Decapoda).

Despite their role in marine systems, Sergestidae remain one of the most poorly understood families amongst planktonic shrimps with regard to phylogeny. Recent morphological and phylogenetic revisions of a number of sergestid genera have disentangled classificatory problems and emphasized the importance of reproductive structures for the taxonomy and phylogeny of the Sergestidae. Only three genera, A cetes, P eisos, and S icyonella, remain unrevised phylogenetically. We undertook a phylogenetic analysis of these groups based on 124 morphological characters (120 binary, four multistate). Eighteen new characters were based on scanning electron microscopy studies of the clasping organ and petasma. The phylogenetic analysis revealed statistically supported monophyly of the clades S icyonella and A cetes + P eisos. We combine P eisos and A cetes into a monophyletic genus A cetes, give emended diagnoses and keys to all species of S icyonella and A cetes, and discuss morphological trends within these genera. We present maps of geographical distribution for all valid species of A cetes. © 2015 The Linnean Society of London [ABSTRACT FROM AUTHOR]