Polyphyly and cryptic diversity in the hydrozoan families Lafoeidae and Hebellidae (Cnidaria: Hydrozoa)

Abstract

The taxonomy of the putative superfamily Lafoeoidea (Hydrozoa), which includes the families Hebellidae and Lafoeidae, has been widely disputed at all systematic levels, mainly because these are morphologically simple and plastic animals. We used the molecular marker 16S mRNA to address phylogenetic relations of 'Lafoeoidea' hydroids mainly from shallow and deep waters of the north-east Atlantic and west Mediterranean. This study proves that the morphological simplicity of the 'Lafoeoidea' has led to several erroneous taxonomic assignments. We demonstrate that the superfamily 'Lafoeoidea' is not monophyletic and thus not valid; the families Hebellidae and Lafoeidae are polyphyletic. The 'Lafoeidae' subfamilies 'Lafoeinae' and 'Zygophylacinae' were recovered as monophyletic but quite distantly related and should be erected to the level of distinct families. The 16S haplotype data analysed in conjunction with morphological characters and distribution data were useful in differentiating morphologically undistinguishable, nominal and cryptic or pseudo-cryptic species, including undescribed taxa. Particularly within the 'Lafoeinae' group, unexpectedly high genetic biodiversity (including cryptic species) was encountered in the possibly not monophyletic genera Lafoea, Acryptolaria and Filellum. Cryptic diversity is also likely associated with the 'Zygophylacinae' nominal species Cryptolaria pectinata. The indications of genetic segregation by geographical distance of the 'Lafoeoidea' hydroids, particularly verified in deep waters, is probably a consequence of their reduced potential for large-scale dispersal, which likely interacts with the influence of the seabed topography, oceanographic circulation and adaptability to tolerate different abiotic conditions.