Circulatory and Excretory system

Bryozoans lack a heart and blood vessels and posses no specialized respiratory organs.  Respiration is entirely though gas exchange across the epidermis, primarily of the tentacles.  The ascus in ascophorans is likely an important respiratory surface, as it is refilled with fresh, oxygenated seawaterevery time the lophophore is retracted and protruded (Ryland 1970).

Bryozoans lack nephridia and thus allow ammonia to diffuse across the thin surface of the protruded lophophore.  Within the animal, the transport of wastes and gasses is through the coelomic fluid while nutrient transport is primarily the job of the funicular system.  Coelomocytes likely absorb waste materials inside the zooids, though insoluble waste products tend to accumulate.  This means that individual zooids have a short life span—typically a few weeks at most—after which the polypide follows either one of two fates: it may regress and parts are phyagocytosed and the material recycled, or it forms what it known as a brown body.  The formation of a brown body is a waste storage method that involves creating a lump of necrotic cells which remains either temporarily or permanently in the coelom (Ruppertet al. 2004).  The brown body can be enveloped by the gut of the new zooid as it develops from the cystid, and then voided through the anus (Ryland et al. 1970).