Functional morphology of musculature in the acoelomate worm, Convoluta pulchra (Plathelminthes) |
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Authors: | S Tyler R M Rieger |
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Institution: | Department of Biological Sciences, University of Maine 5751 Murray Hall, Orono, ME 04469–5751, USA, US
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Abstract: | Convoluta pulchra is a small worm living in the surface sediment of mud flats where it feeds on diatoms. It is roughly teardrop in shape with
a ventral groove in which the mouth sits, and it can move in a variety of ways, readily distorting its body in bending, twisting,
and turning motions. Fluorescently labeled probes for filamentous actin revealed the musculature in whole mounts of the worm.
In the body wall, the musculature consisted of a grid of circular, longitudinal crossover (that is, with a longitudinal orientation
in the anterior half of the body but arcing medially to cross over to the contralateral side of the body behind the level
of the mouth), and a few diagonal fibers. Inside the body was a strong, irregular brush of muscles originating at the rostral
tip of the body and anchoring laterally and posteriorly along the body wall, and strong dorsoventral muscles flanked the ventral
groove. Two fans of muscles in the ventral and dorsal body wall reached posteriorly and laterally; that on the dorsal side
originated at junctures of the dorsoventral muscles with the body wall and that on the ventral body wall originated from the
mouth. By their positions, certain groups of muscles could be correlated with given movements: the crossover muscles with
some turning motions and feeding, and the inner muscles with probing and retraction motions of the rostrum and with a tuck-and-turn
motion the worm used to turn itself around. Electron microscopy showed numerous maculae adherentes junctions linking all muscle
types and special junctions linking the musculature with the epidermis. The latter myoepidermal junctions were of dimensions
larger than those of maculae adherentes and contained an interlaminar material which we believe represents islands of basal
matrix comparable to basement membrane.
Accepted: 12 July 1999 |
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