NUTRITION AND FEEDING MECHANISMS 237 



Corymorpha, a solitary hydroid living on soft bottoms, feeds on detrital 

 matter and has characteristic feeding movements which are repeated in 

 quiet water about twenty times a minute. When feeding, the stalk bends 

 over, mouth and distal tentacles touch the mud, after which the stalk 

 straightens out and food material adhering to the tentacles is conveyed to 

 the mouth. 



In hydromedusae, food is grasped by the marginal tentacles which 

 respond to chemical and tactile stimuli. In the subsequent feeding reaction 

 the stimulated margin bends towards the manubrium (Phialidium) or, 

 when the manubrium is long, the latter structure bends towards the 

 margin (Stomatoca). The food is seized by the lips of the manubrium and 

 swallowed. Some species display a fishing behaviour in which they swim 

 to the surface and then float downwards with tentacles fully extended (49). 



Siphonophores are colonial animals, entirely oceanic and pelagic in 

 habit. Special polyps known as dactylozooids, bearing long tentacles, 

 capture and digest the prey. As the animals drift through the water, their 

 long trailing tentacles act like nets, capturing animals which strike against 

 them. The tentacles are muscular and highly contractile, and when the 

 prey is paralysed by nemotocyst-action it is drawn up to the mouths of the 

 gastrozooids by contraction of the tentacles (9, 106). 



Feeding behaviour in Scyphomedusae differs in detail but usually 

 involves stinging and manipulating the prey with tentacles and manubrium, 

 after which the food is transferred to the mouth. The food consists of small 

 planktonic animals — small Crustacea, worms, small medusae and the 

 like. In Chrysaora the tentacles, laden with food, contract and the food 

 particles are swept off by the lips which form a temporary receptacle 

 beneath the stomach. Food material collected by the bell of Amelia is 

 licked off by the oral arms and conveyed by cilia to the mouth and gastric 

 pouches. Experiments have shown that the arms respond to mussel juice, 

 proteins, peptones and amino-acids but not to carbohydrates. Cassiopeia, 

 a sedentary form, lies on the bottom with oral surface upwards. Pulsations 

 of the bell produce a current of sea water from which planktonic organisms 

 are seized by the oral arms. The food, entangled in mucus, is swept by 

 ciliary action into the numerous mouths which lie along the arms (91). 



Actinians (sea anemones and corals) are exclusively carnivorous. In 

 less specialized corals the collection of food is reserved for the tentacles. 

 These paralyse their prey with nematocysts and convey it to the mouth 

 by muscular action. In some other corals, however, the general ectoderm 

 participates in the capture of food, and ciliary tracts transport particles 

 to the mouth (112, 113). 



In sea-anemones the presence of suitable food evokes an orderly series 

 of feeding reactions. When a piece of meat is placed on the tentacles there 

 is first a discharge of cnidae. The tentacles then clasp the food and bend 

 towards the mouth, which turns towards the food and opens. The food is 

 gradually thrust in and swallowed, and the tentacles subsequently return 

 to their normal feeding position. The feeding response is initiated by both 



