Musculature

The musculature of ascidians extends throughout the majority of the mantle and consists of distinct outer circular and inner longitudinal bands of smooth muscle (Ruppert et al., 2004). Each muscle band is made up of a number of strands, typically 100-150um in diameter, which in turn comprise of bundles of muscle fibres, each bundle is completely enclosed by an external lamina (Harrison and Ruppert, 1991). A network of connective tissue filaments separate the bundles and are attached to external laminae. This network connects the bundles within a strand allowing forces to be passed between them during contraction (Harrison and Ruppert, 1991).

The longitudinal fibres extend from the body to the siphons controlling their extension. The circular muscles predominate on the siphons as sphincters that regulate the size of their openings. Contraction of the body wall occurs periodically, compressing the body, forcing jets of water from the siphons, and eventually closing the siphons (Ruppert et al., 20014).