Even though the species are very numerous, they are largely unknown, as detailed observations have been made of only a few groups.

Large and diverse assemblages of amphipods were found at the three study sites. Amphipods occur as free-living algal grazers, scavengers, and also as symbionts of ascidians, sponges, and hydroids. About one-third of all Indo-Pacific amphipods belong to families that form tubes.

Alpheus sp., an Alpheid shrimp, lives in a variety of habitats. Many are free-living animals which live in burrows, and feed on both plant and animal matter. Others are commensal on crinoids or in sponges. Several species of Alpheus have a remarkable association with gobies, excavating and sharing the burrow with fish.

The Anthuridae are a suborder of isopods. Isopods, also called fish lice, slaters or pillbugs, are a morphologically diverse group. There are over 4,000 species and more than 700 genera. They are second in size only to the Amphipods. As most of them are free-living, they are found everywhere, even in the nasal passages of fish, although a few are planktonic. Large numbers of isopods are carnivorous and include some voracious predators.

They are even known to bite bathers or attack divers. A significant number of species are parasitic, living on fishes and other crustaceans.

Upogebia sp., which was particularly abundant at Bayu-Undan, belongs to the group Thalassinidea, which are commonly known as ghost shrimps, mud shrimps, yabbies or sponge shrimps. The Upogebia sp. constructs extensive burrows and are filter-feeders.