Diversity of muscle fibers in the abdominal dorsal superficial muscles of the hermit crab,Pagurus pollicarus

Abstract

The dorsal superficial abdominal muscles of the hermit crab,Pagurus pollicarus, are divided into three subregions of muscle fibers with different properties: a lateral group of tonic muscle fibers and two groups of medial muscle fibers, a superficial layer with intermediate properties and a central layer of twitch fibers. Fast muscles like those in the central medial region are not found in homologous muscles of crayfish and lobster. The number of muscle fibers (74) is the same on the two sides, but there is a tendency for there to be larger fibers on the left side. Length-tension measurements in these muscles resemble results obtained from other crustacean muscles despite their modification as part of a hydrostatic skeletal system. It is concluded that muscle fibers in homologous muscles of different species may vary in their contractile properties, the degree of their segregation into discrete sub-regions, laterality, and number.