NUTRITION AND FEEDING MECHANISMS 



227 



currents responsible for locomotion and feeding are produced by rotary 

 movements of the thoracic limbs (Fig. 5.21). As these whirl around they 

 draw water towards them from all directions and pass it into an area of 

 low pressure near the base of the limb. The separate water streams join 

 to form a forwardly directed current beneath the mid-ventral body wall. 

 Anteriorly the food stream is sucked forwards by vibration of the maxillae. 

 Food particles are collected by setous combs on the maxillae and are pushed 

 on to the mandibles, where the food mass is ground up and sucked into the 

 oesophagus by peristalsis. Less palatable material is thrown out laterally 

 by the mouth parts. Food may be filtered directly from the sea water as 



Fig. 5.21. Feeding Currents Produced by Hemimysis 



Dorsal view of an animal swimming freely in the water (x 4.8). (From Cannon and 

 Manton, 1927.) 



the animals swim about, but when live plankton is sparse the animals 

 swim to the bottom where they stir up particles from bottom deposits. In 

 this way mysids are able to increase the amount of material in suspension 

 and can feed upon it (98). 



Leptostraca. This group includes sedentary, burrowing and pelagic 

 species. Nebalia is a littoral form which burrows into mud and lives just 

 beneath the surface. Food particles are filtered off a stream of water which 

 enters the carapace anteriorly and makes its exit at the posterior end. This 

 feeding current is produced by oscillatory movements of the thoracic 

 limbs, and food particles are filtered off by rows of setae on these same 

 appendages. The collected food is then brushed on to proximal (gnatho- 

 basic) setae and passed forwards to the mouth parts (11). 



