New marine heterotardigrade lineages (Echiniscoididae) from the tropics

Echiniscoididae are the only family of the clade Echiniscoidea residing in marine habitats. Their characteristic feature is the multiplication of claws on legs, commonly regarded as an adaptation to unstable tidal environment. Although DNA barcoding data indicated the presence of numerous unnamed candidate species within Echiniscoides about a decade ago, only recently have new species been formally described. In this paper, we present new genetic, morphological and morphometric data and establish five Echiniscoides species found in samples acquired from various tropical regions: Echiniscoides basalticus sp. nov. (Mauritius, Indian Ocean), Echiniscoides bufocephalus sp. nov. (Qatar, Indian Ocean), Echiniscoides lichenophilus sp. nov. (Dominican Republic, Atlantic Ocean), Echiniscoides musa sp. nov. (Brazil, Atlantic Ocean), and Echiniscoides trichosus sp. nov. (Rapa Nui, Pacific Ocean). We discuss the taxonomic importance of cuticular sculpturing in Echiniscoididae. Finally, we elevate all subspecies of Echiniscoides sigismundi to species level. The key to all echiniscoidids is provided.