Direct Peristaltic Progression and the Functional Significance of the Dermal Connective Tissues During Burrowing in the Polychaete Polyphysia Crassa (Oersted)

Abstract

1. Polyphysia excavates its burrow in soft, sublittoral mud by sinusoidal waves of the septate anterior region of the body and the lateral scraping action of the prostomial horns. 2. Associated with discrete, direct peristaltic constrictions, in which the longitudinal muscles shorten to 40%, and the circulars to 80%, of their distended lengths, hydraulic deployment of coelomic fluid converts the periodic advance of the trunk segments into continuous head progression. 3. Direct peristaltic progression advances the body by one-fifth or less of a wavelength per cycle, which is comparable to the figure for earthworm locomotion. 4. A three-dimensional dermal collagen fibre lattice accommodates extensive folding of the cuticle and epidermis while permitting a three- to fourfold increase in the radial dimension of the body wall during peristaltic constriction. Elastic fibre columns oppose the radial distension and control the cuticular folding. 5. These features are seen as adaptations to burrowing in the soft mud habitat. The high degree of body-wall flexibility permits the transition from contracted to distended configuration within the length of one segment. Some three-quarters of the body surface may be in contact with the burrow wall at any one time. Unlike other soft-bodied burrowing animals the force exerted on the burrow wall is unidirectional and the applied pressure is probably small, relatively constant and spread over a wide area.