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 which is a fluid-filled cavity surrounded by circular and longitudinal muscles. The contraction and relaxation of these muscles help in movement and provide support to the body. Therefore, annelids work against their hydrostatic skeleton.