Pinnotherids have been known since Aristotle and can be found at coasts all around the world. Nevertheless, they are often overlooked, probably due to their small size and their cryptic nature. This paper remarks on the phylogenetic diversity and complexity of this group of symbiotic crabs. Morphological, genetic and ecological analyses of pinnotherids can lead to a better understanding of evolutionary processes and diversity of marine organisms, as well as the associations among and between them.

Ants of the genus Acropyga are among the most abundant in tropical habitats, but they might not be easily encountered owing to their cryptic lifestyle. We studied their occurrence, phylogenetic and population genetic history in unexplored region of Papua New Guinea and revealed that many Acropyga species exhibit a patchy distribution not influenced by geological history. Our study emphasises the importance of geography, habitat associations and past climatic changes on the population level processes.

Hydroides brachyacantha, an important fouling species described from Mexico and reported invading numerous localities worldwide, was recently revealed to include a number of morphologically similar species. The aim of this study was to resolve the status of Australian and Mexican members of the Hydroides brachyacantas-complex. DNA sequence data supported morphology-based separation of Mexican H. brachyacantha from Australian H. amri and revealed a new cryptic species H. nikae, thus calling for a worldwide revision of the H. brachyacantha-complex.

The present study used multilocus data to examine species boundaries in a mountain living South African freshwater species complex and revealed the presence of five novel lineages. These results suggest higher levels of endemism in the countries freshwater crab fauna.

Fully troglobitic pseudoscorpions are rare in the Afrotropical Region, and we explored the identity and phylogenetic relationships of a highly modified troglobite from the dark zone of the Wynberg Cave system, Table Mountain, South Africa. This large pseudoscorpion – described as Gymnobisium inukshuk Harvey & Giribet, sp. nov. – lacks eyes and has extremely long appendages, and has been found together with 5 other troglobitic fauna endemic only to this cave system.

The Indo-Pacific is the largest biogeographic region in the world, although the Indian Ocean component has been largely ignored. We examine reasons for this neglect and review what is known about the Indian Ocean’s connections with the Pacific Ocean. We challenge the assumption that the peak of shallow-water marine biodiversity is solely centred in the Coral Triangle, and raise awareness of a hypothesis promoting a secondary peak of biodiversity in the western Indian Ocean.