Practice question

Respiratory gas exchange in annelids occurs primarily via moist general body surface through cutaneous diffusion facilitated by thin highly vascularized epidermis covered by permeable cuticle and extensive subepidermal capillary network. Terrestrial lumbricid earthworms lack gills entirely relying exclusively on skin maintained moist by mucus requiring humid habitats nocturnal activity. Aquatic polychaetes often supplement cutaneous respiration with specialized appendages: parapodial branchiae dorsal cirri tentacular filaments increasing surface area. No lungs tracheae present. Efficient skin respiration supported by mucus and vascularization maintains oxygen uptake complemented by high-affinity pigments binding oxygen under hypoxic conditions enabling colonization of diverse habitats from soil to sea.