Summary
Physical Description
Ecology
Symbiosis
Life History & Behavior
Feeding Behavior
Movement
Reproduction and Development
Respiration
Response to Light Changes
Anatomy & Physiology
Circulatory and Excretory Systems
Defense Mechanisms: Cnidocytes and Cnidae
Digestive System
Nervous and Sensory Systems
Skeleton and Musculature
Evolution and Systematics
Biogeographic Distribution
Conservation and Threats
References and Links | Digestive System
Ingestion of prey is effected by ciliary currents that reverse their normal outward beating on the actinopharynx, in response mainly to chemical stimuli1. Prey is mixed with mucus after entering the mouth and swallowed slowly by the pharynx, through a combination of ciliary action and peristaltic movements of the pharyngeal wall. The food mass then comes in contact with cnidoglandular bands of the septa upon release into the coelenteron and extracellular digestion is initiated. Extracellular digestive enzymes are secreted by enzymatic gland cells in the gastrodermis, and are mainly proteases and lipases. They break down large prey items into a mixture of juice and smaller particles and molecules, which are circulated in the coelenteron for phagocytic uptake by gastrodermal cells, including the gametes. Circulation of the coelenteric fluid is carried out by flagellar bands and flagella elsewhere on the gastrodermis3 (see Anatomy & Physiology). Additionally, there are also intracellular digestive enzymes that break down smaller particles taken up by phagocytes2. Sea anemones also harbor symbiotic intracellular yellow-brown zooxanthellae, and provide nutrients and carbon dioxide in return for photosynthate which is used to supplement their nutrition2.
Additionally, apart from animal prey, many sea anemones also take particulate organic detritus and dissolved organic matter (DOM) in their diets2, the latter of which is directly absorbed through ectodermal cells with abundant microvilli to increase surface area4. It has been suggested that taking in DOM may be particularly important to the ectoderm, which is always in contact with seawater and partially isolated from the nutritive endoderm by the mesoglea, which acts as a barrier to the free diffusion of glucose and amino acids5,6.
1Holley & Shelton 1984
2Shick 1991
3Ruppert, Fox & Barnes 2004
4Schlichter 1980
5Schlichter 1973
6Brafield & Chapman 1983
|
|