A species complex within the isopod genus Haploniscus (Crustacea: Malacostraca: Peracarida) from the Southern Ocean deep sea: a morphological and molecular approach

Seven new species of the genus Haploniscus from the deep Scotia and Weddell Seas are presented, combining morphological and molecular data (mitochondrial 16S rDNA and nuclear 18S rDNA). Haploniscus cassilatus sp. nov. , H. cucullus sp. nov. , H. weddellensis sp. nov. , H. procerus sp. nov. and H. kyrbasia sp. nov. are characterized by a prominent rostral process, the size and shape of which vary among species. The rostrum of H. microkorys sp. nov. is distinctly smaller than that of the former species, while H. nudifrons sp. nov. does not possess a rostrum. The status of the latter as separate species is obvious, owing to the stronger morphological differences. DNA was sequenced from three of the other five species. Genetic distances together with the more subtle morphological variation justify the erection of separate species. Overall morphological variations between these species are small yet noticeable and include, among others, the rostrum, the shape of the pleotelson and setation of pereopods. Our molecular data sets reveal detailed phylogenetic insights within the Haploniscus cucullus complex, supporting the monophyly of all species. We found p -distances of at least 0.0732 (16S rDNA) and 0.0140 (complete 18S rDNA) between pairs of species and show that both genes can be used as a marker for DNA taxonomy.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 655–706.