The taxonomy of tardigrades is challenging as these animals demonstrate a limited number of useful morphological characters, therefore several species descriptions are supported by only minor differences. For example, Echiniscus oihonnae and Echiniscus multispinosus are separated exclusively by the absence or presence of dorsal spines at position Bd. Doubts were raised on the validity of these two species, which were often sampled together. Using an integrative approach, based on genetic and morphological investigations, we studied two new Portuguese populations, and compared these with archived collections. We have determined that the two species must be considered synonymous with Echiniscus oihonnae the senior synonym. Our study showed generally low genetic distances of cox1 gene (with a maximum of 4.1%), with specimens displaying both morphologies sharing the same haplotype, and revealed character Bd to be variable. Addition-ally, a more detailed morphological and phylogenetic study based on the 18S gene uncovered a new evolutionary line within the Echiniscidae, which justified the erection of Diploechiniscus gen. nov. The new genus is in a sister group relationship with Echiniscus and is, for the moment, composed of a single species.

This is an identification guide to the 47 currently described genera of marine heterotardigrades. We provide clear definitions and illustrations of relevant anatomy and an easy to use dichotomous key. The aim of the present contribution is to enable more people to identify collected specimens of marine heterotardigrades, and hopefully, encourage more people to study this intriguing group of animals. The paper is divided into three parts. The first part gives a brief introduction to heterotardigrade morphology with special emphasis on taxonomically important characters. The second part is the actual key, which is accompanied by illustrations of both habitus and detailed foot morphology of the marine heterotardigrade genera. The third part provides up to date diagnoses of the orders, families, subfamilies and genera of marine heterotardigrades according to the most recent emendments. With the generic diagnoses, we provide a bibliography with selected literature that relates to each specific genus.

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Tardigrade taxonomy is particularly nebulous in the so-called Pseudechiniscus suillus complex, a group of species very difficult to distinguish from one another. This species complex needs complete revision. In this study, traditional morphometric and geometric morphometric relationships among five populations of the P. suillus group, from four different Atlantic islands (three in the Azores and S. Tome´) and one from the Portuguese mainland, were investigated to explore their potential for discriminating cryptic species. Seven traditional morphometric variables were used to describe variation by means of principal component analysis. In addition, two traits, claws and dorsal segmental plates, were analysed using a geometric morphometric approach that has the ability to determine very subtle differences in shape. The results of both analyses suggest the occurrence of four morphs exhibiting different sizes and shapes of cirrus A, claws and dorsal plates. The high taxonomic value of those characters joined with some other qualitative aspects, such as the cuticle sculpture, seems to indicate that different species can be distinguished among these morphs. This leads to the conclusion that the geometric morphometric approach is a useful complementary tool to the traditional morphometric approach for discriminating cryptic species of heterotardigrades.

A new tardigrade, Diphascon (Diphascon) faialense sp. nov., is described from a moss sample collected on Faial Island, the Azores. This species belongs to the Diphascon pingue group. It differs from all other species of the group mainly by quantitative characteristics of the bucco-pharyngeal apparatus and of the claws.