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The order isopoda is the largest order of crustaceans aside from the decapoda. Most of the 4000 described species are marine, but a considerable number live in fresh water. The pill bug or wood lice are also isopod crustaceans.
Sometimes Ligia pallasii is common in caves and crevices on rocky cliffs, especially those with a fresh water seep, often with green alga Enteromorpha, high intertidal zone and above, western Aleutian Islands and Alaskan mainland to Santa Craze Co.
Body to 35mm long, eyes separate by a distance equal to twice the greatest diameter of an eye; uropods short, with basal segment as long as broad ; adult male with greatly expanded side plates.
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| Sample 1 |
Sample 2 |
Sample 3 |
| Three populations used by Mersiha in her extended essay |
These samples are included here to give an indication of the variation in specimen size within each population |
The 1 cm. divisions can be seen on the caliper for size estimation. |
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| Dorsal view |
Ventral view |
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Sexual dimorphism in body proportions is marked in L.pallasii. Males, with their large, laterally expanded epimeral plates, have a length/width ratio of about 1.6; females and immature males are narrower, with a corresponding ratio of about 2.1. Half- molted males are occasionally found in which the rear half of the body has molted and is abruptly significantly wider than as yet unmolted front half, an odd sight, usually several days after the posterior molt.On the walls of cliffs and sea caves, the larger and broader males often cover and shield the females and juveniles.
L.Pallassi prefers sea cliffs. At Race Rocks, the loose upper intertidal rocks and crevasses on the Western side of the main island provide ideal habitat. There are differences in the osmoregulatory responses shown by these species associated with their behavior and ecology.The slower -moving pallasii lives permanently in cool, moist habitats characterized by fluctuating hyposaline condition. L. Pallasii are air breathers with gill-like pleopods not equipped with tracheal trees.The respiratory pleopods must be kept moist to function properly.This is done by immersion or by dipping the tail in water in such away that the uropods serve as capillary siphons.
Ligia species are fed upon by birds, especially gulls, and by the intertidal crab. Life span of L.pallasii is 1.5 to 2 years , with breeding occurring in spring and early summer, and the average brood size is 48 plus or minus 11 young.The overall sex ratio is 1:1.
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