Intermittent submergence presents problems in connection with respiration because no respiratory organs function equally well in both air and water. The majority of shore-dwelling animals perform aquatic respiration, but within the littoral fringe the infrequency of immersion calls for the ability to breathe air. Some of the inhabitants of this fringe zone are essentially marine forms which have become adapted for aerial respiration. Talitrus saltator and Orchestia gammarella can live in moist air. In Melaraphe (Littorina) neritoides and L. saxatilis the gill (ctenidium) is reduced and the mantle cavity is modified to function as a lung. There are also a few animals which have colonized the shore from the land, and several of these show adaptations for storing air during the periods they are submerged. The collembolan insect, Anurida maritima, widespread among rocks above mid-tide level, carries a layer of air among its surface bristles. The intertidal beetle, Aepus marinus, has internal air sacs for air storage.
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