Hemocoel: Open Circulatory System in Arthropods & Mollusks

Structure

The hemocoel (haemocoel) is the primary body cavity (blastocoel homolog) filled with hemolymph – a fluid combining blood and interstitial functions.

Circulation

• Dorsal tubular heart pumps hemolymph into sinuses.
• No capillaries; direct bathing of organs.
• Low pressure, slow flow.

Exchange

Diffusion across large surface area; efficient for small/medium invertebrates.

Examples

Insects, crustaceans, arachnids, most mollusks (except cephalopods).