Ligia is a genus of isopods, commonly known as rock lice or sea slaters. Most Ligia species live in tidal zone cliffs and rocky beaches, but there are several fully terrestrial species occur in high-humidity environments.
Coastal Ligia species exhibit a mixture of terrestrial and marine characteristics, drying out easily, needing moist air and proximity to water to retain water. While they have gills and can exchange gas under water, they only do so when escaping terrestrial predators or being dislodged by wave action. They do not move swiftly in the water and are open to marine predation. They are well adapted to rocky surfaces and avoid sand, which opens them to terrestrial predation and desiccation.[1]
Species separation is at times difficult because of sexual dimorphism. For example, males usually have longer and wider antennae than females. The males also tend to be larger but narrower, with the difference sometimes attributed to the female’s brood pouch.[2] Complicating matters is the possible existence of cryptic species in the genus.[3]