Dominant species Excirolana spp. The dominant, defining species of the mid-littoral zone is the cirolanid isopod, Excirolana. Excirolana is a carnivorous scavenger, subsisting in Monterey Bay mostly on dead Emerita and Emerita eggs, but vigorously attacking any animal material encountered. Excirolana burrows into the top 1 cm of sediment at low tide, and leaves the sand to swim rapidly about looking for food when inundated. This rhythmic activity pattern persists for several days even after animals are removed to laboratory aquaria.
Females brood their young in a brood pouch.
The upper limit of their distribution is probably determined by having sufficient inundation time for feeding, while the lower limit may be determined by the mechanical stress of wave action. They are preyed upon by various shorebirds. The species generally encountered on exposed sandy beaches is Excirolana linguifrons . Another cirolanid, Cirolana hardordi is found in large numbers in sand patches in rocky intertidal zones. C. Swash zone 1.