Hyastenus is a genus of crab that belongs to the family Epialtidae also known as spider crabs, due to their physical resemblance to spiders (Ng et al., 2008). This genus includes 38 species (Ng et al., 2008) which are mostly herbivores and generally decorate themselves with different materials that are available in their environment (Wicksten, 1993; Stachowicz and Hay, 1999; Stachowicz and hay, 2000).

Spider crabs of the family Epialtidae have a pyriform carapace, which is wider than it is long with several spines protruding from the dorsal surface. The carapace protrudes anteriorly, forming a distinct rostrum (Ng et al., 2008).

The carapace is commonly covered by pieces of algae or invertebrates, which gives them the popular name “Decorator crab”. This distinct behavior of masking themselves may be a strategy of defense against predators or may be related to food stock (Wicksten, 1993).