Further morphological and molecular studies of driftwood hoppers (Crustacea: Amphipoda: Talitridae) from Mediterranean/north-east Atlantic coastlines.

An unknown talitrid was discovered in 2011 in the Swale, UK, living in driftwood. Sequencing of multiple mitochondrial and nuclear genes (cytochrome oxidase I, 18S rDNA and 28S rDNA) confirms that the unknown taxon was close toOrchestia mediterraneaA. Costa 1857. The driftwood in which it was found was of Douglas fir (Pseudotsuga menziesii), probably imported from North America. Relative growth methods allow us to reject the null hypothesis that the unknown taxon was a juvenileOrchestia mediterranea. This is because the unknown taxon initiates sexual maturation at an earlier moult number (neoteny) and is predicted to reach terminal moult stages at a much smaller size (dwarfism) than its closest relativeO. mediterranea. Both molecular and morphological data confirm that the unknown taxon from the Swale, UK, is a new driftwood specialist taxon, distantly related to the driftwood specialist genusMacarorchestia. Additional data for body length and sex ratios are presented forMacarorchestia. In addition, relative growth methods have shown that the driftwood speciesOrchestia microphtalmaAmanieu and Salvat 1964 is closer to the genusMacarorchestiarather than to the wrack generalist one,Orchestia.This evidence is in line with the molecular results that do not cluster morphologically defined species ofOrchestiamonophyletically. [ABSTRACT FROM PUBLISHER]