Against which structure do the circular and longitudinal muscles of annelids work?

Answer: The circular and longitudinal muscles of annelids work against Hydrostatic skeleton.

Explanation:

Annelids also called segmented worms are invertebrate, bilateral symmetrical, ceolomate and tripoblastic animals. They lived in marine, fresh water and moist terrestrial habitats. Examples include rag worms, leeches, and earthworms.

They have hydrostatic sketelon which is a flexible skeleton and it is fluid filled or it contains water. This skeleton has ability to affect shape, movement and its has two mechanical units which are the muscles and body walls. The muscles are circular and longitudinal. The circular muscles contraction lengthens the annelids body while contraction of the longitudinal muscles shorten the annelids body. The fluid within the organism are concentrated evenly, the muscles spread out muscles in the whole body and shape changes continue.