Inclusion of fossils can be crucial to address evolutionary questions, because their unique morphology, often drastically modified in recent species, can improve phylogenetic resolution. We performed a cladistic analysis of 45 cassidulids with 98 characters, which resulted in 24 most parsimonious trees. The strict consensus recovers three major cassiduloid clades, and the monophyly of the family Cassidulidae is not supported. Ancillary analyses to determine the sensitivity of the phylogeny to missing data do not result in significantly different topologies. The taxonomic implications of these results, including the description of a new cassiduloid family and the evolution of some morphological features, are discussed. Cassiduloids (as defined here) most probably originated in the Early Cretaceous, and their evolutionary history has been dominated by high levels of homoplasy and a dearth of unique, novel traits. Despite their high diversity during the Palaeogene, there are only seven extant cassiduloid species, and three of these are relicts of lineages dating back to the Eocene. Future studies of the biology of these poorly known species, some of which brood their young, will yield further insights into the evolutionary history of this group.

The degree of isolation of oceanic islands makes these environments an excellent model for evolutionary studies. Proper knowledge of the species composition of oceanic islands, however, is required to better understand evolutionary processes (e.g. speciation events). A 3-year survey in the shallow waters (up to 30 m) of the Trindade and Martin Vaz oceanic insular complex, and a literature review on the data published for these islands and for Fernando de Noronha and São Pedro and São Paulo oceanic archipelagos have been conducted to document the biodiversity of echinoids and holothuroids from these isolated Brazilian oceanic islands. Sixteen species were collected and characterized morphologically, including two first records for the South Atlantic and one for Brazil. Comparison with conspecific specimens from the Brazilian coast and congeners was also done. Species richness increased from six to 18; the richness in Trindade Island being the highest among the South Atlantic oceanic islands. However, these islands remain undersampled beyond 30-m depth. Endemism was very low, suggesting the potential role of oceanic currents and seamounts as stepping-stones in transoceanic dispersal of species to remote islands. The Brazilian oceanic islands are impoverished oceanic outposts of the Brazilian Province; nevertheless, endemic species and intraspecific morphological variations compared with the mainland suggest they may also be regions of speciation. Documenting their biodiversity is critical for effective management and conservation of their marine ecosystems.