Against Which Hard Structure Do the Circular and Longitudinal Muscles

Question

Against which hard structure do the circular and longitudinal muscles of annelids work?
A) bristles
B) cuticle
C) shell
D) endoskeleton
E) hydrostatic skeleton

Accepted Answer

Annelids have a hydrostatic skeleton where circular and longitudinal muscles work against the pressure of fluid-filled body cavities to produce movement. Bristles are used for anchorage and defense, a cuticle is a protective outer layer but does not provide support, and endoskeletons and shells are hard structures found in other phyla.