Mechanisms of breathing vary among different groups of animals, primarily depending on their habitats and levels of organization.

Respiratory Mechanisms in Different Animals

1.Lower Invertebrates

Examples: Sponges, coelenterates, flatworms.

Mechanism: Exchange O ₂ and CO ₂ through simple diffusion over their entire body surface.

2.Earthworms: Use their moist cuticle for gas exchange.

3.Insects: Have a network of tubes (tracheal tubes) that transport atmospheric air within the body.

4.Aquatic Arthropods and Molluscs: Use specialized vascularized structures called gills (branchial respiration).