Ligia occidentalis

Dana, 1853

Western Sea Slater

Ligia occidentalis is a supralittoral isopod inhabiting rocky shorelines along the eastern Pacific coast. The occupies the high intertidal zone, hiding in crevices above the high tide line during daytime to avoid desiccation and emerging nocturnally to feed. It is distinguished from the sympatric Ligia pallasii by longer uropods, larger set closer together, and a sleeker body form. The species harbors mycoplasma-like bacteria as hepatopancreas and shows remarkable morphological stasis across highly genetically divergent lineages.

Ligia occidentalis by (c) Don Loarie, some rights reserved (CC BY), uploaded by Don Loarie. Used under a CC-BY license.

Ligia occidentalis by Justin Johnsen. Used under a CC BY-SA 4.0 license.

Pronunciation

How to pronounce Ligia occidentalis: /ˈlɪd͡ʒiə ˌɒksɪˈdɛntəlɪs/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from Ligia pallasii by three consistent morphological differences: (1) uropods substantially longer relative to body length, (2) larger in size and positioned closer together medially, and (3) overall sleeker, more streamlined body profile. These characters are visible in specimens without magnification. The cannot be reliably identified by body shape alone due to strong stabilizing selection maintaining morphological similarity across genetically divergent .

Images

Habitat

High rocky intertidal zone, specifically the supralittoral fringe above the high tide line. Occupies crevices and spaces under rocks in cliff and boulder fields. Requires moist microhabitats for respiratory function but cannot survive prolonged submersion.

Distribution

Pacific coast of North America from southern Oregon to Baja California, Mexico, including the Gulf of California. Sympatric with Ligia pallasii between southern Oregon and central California; the two partition vertically with L. occidentalis occupying higher intertidal positions.

Diet

constitute the preferred food source, including both microalgae and macroalgae; also consumes detritus. foraging occurs along beaches and rocky cliffs when conditions are cooler and humidity is higher.

Behavior

: hides in rocky crevices above the high tide line during daylight hours to prevent desiccation. to forage when temperature and humidity conditions permit. Exhibits rapid escape response ('bolting') when disturbed. Must maintain moist gills for respiration; will drown if submerged for extended periods.

Ecological Role

Herbivore and in high intertidal rocky shore . Contributes to nutrient cycling through algal consumption and processing of organic detritus. Serves as for mycoplasma-like bacterial in the hepatopancreas.

Similar Taxa

Ligia pallasiiOverlapping distribution from southern Oregon to central California; distinguished by shorter uropods, smaller and more widely separated , and stockier body form; occupies lower intertidal positions than L. occidentalis where sympatric.