Abstract
Metazoans are well represented in temperate environments but few occur at the thermal edges of life. Only three animal phyla-Annelida, Arthropoda and Rotifera-are known to have representatives in both psychrophilic and thermophilic habitats. Here we report species of Nematoda, Platyhelminthes and Rotifera that have independently colonized both ends of the thermal spectrum, from maritime glacier ice to geothermal hot springs in New Zealand. By phylogenetic analyses with nuclear and mitochondrial loci, we present evidence that glacial populations have deep haplotype diversity and have likely persisted throughout the Pleistocene, while residents of geothermal environments appear more contemporary. Bdelloid rotifers in particular display robust dispersal capabilities both within New Zealand (thermophiles) and worldwide (psychrophiles), linking genetically with populations in Antarctica and the northern hemisphere.