Ligia occidentalis, the western sea slater, is a species of sea slater of the family Ligiidae, in the genus Ligia. L. occidentalis is a habitat generalist of rocky shores. It is found on the Pacific coast of North America from Mexico to British Columbia. The western sea slater is separated from L. pallasii by its much longer uropods and its larger eyes which are set closer together, along with its sleeker body. This species has a tendency to bolt when disturbed. These sea slaters hide in rocky crevices above the high tide line during the day. It may emerge at night or in cooler weather to scavenge for algae and detritus along beaches or rocky cliffs. Western sea slaters must keep their gills moist in order to breathe but they cannot survive long underwater and will drown.

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