Limulus

In Limulus, the horseshoe crab, muscles from the anterior margin of the coxa (the leg segment nearest the body) are inserted on the endosternite, as are other muscles from the posterior margin.

…and mites), the horseshoe crab, Limulus, has a series of book gills (gills arranged in membranous folds) on either side of the body into which blood from the ventral sinus passes for oxygenation prior to return to the heart. The largely terrestrial arachnids may have book lungs that occupy a…

…ommatidia of the horseshoe crab Limulus.

…lens cylinder elements in the Limulus eye (see above Apposition eyes); the difference is that the telescope lenses would be twice as long. The lens cylinder arrangement produces the equivalent of a pair of lenses, with the first lens producing a small image halfway down the structure and the second…

…independently in the chelicerata (genus Limulus), the trilobites, and the myriapods (genus Scutigera). Compound eyes appear to have evolved once or several times in the crustaceans and insects, in the bivalve mollusks (genus Arca), and in the annelid worms (genus Branchiomma). There are comparatively few cases in which one type…

, genus Limulus, eurypterids) by a process of reduction. Something similar has occurred in the amphipod crustacean genus Ampelisca, where single-chambered eyes have replaced the compound eyes typical of the group.