NUTRITION AND FEEDING MECHANISMS 



209 



the pinnules and is directed between the latter by latero-frontal cilia 

 (Fig. 5.5). Suspended particles are thrown by the latero-frontal cilia into a 

 ciliated groove running along the inner face of each pinnule, whence 

 they are transported by frontal cilia to the base of the pinnule where there 

 are ciliary tracts running along the filament towards the base of the 

 crown. Here there is a ciliary mechanism in the basal folds by which 

 particles are sorted into three classes on the basis of size: the largest 

 particles are carried to the palps and rejected; medium-sized particles are 

 carried to ventral sacs below the mouth, and are stored there for use in 



Axis of fl lament 



Abfhonta.1 



CiUcL 



Fig. 5.5. Filtering and Sorting Mechanisms in the 

 Branchial Crown of Sabella pavonina 

 (a) Section through two gill filaments, showing direction of flow of water across the 

 filament, and direction of beat of the cilia which produce the current; (b) transverse 

 section through a pinnule to show ciliation (x 250); (c) lateral lip and base of gill 

 filament, showing ciliated tracts and sizes of particles passing along the basal folds; 

 id) section through basal folds, showing sorting of particles. (From E. A. T. Nicol (80).) 



tube formation (p. 656); the finest are carried to the mouth and ingested 

 (80). Sabellids and serpulids depend on finely divided suspended detritus 

 for food. Some data for filtering rates are listed in Table 4.5 (186). 



Echinodermata. Many asteroids such as Porania and Astropecten make 

 use of ciliary feeding currents to some extent. Ciliary mechanisms are 

 universal in crinoids, in which the ambulacral grooves possess mucous 

 glands and cilia and carry food particles (plankton and detritus) to the 

 mouth. 



Polyzoa and Phoronidea. Polyzoans capture plankton and fine detritus 

 by means of a lophophore or ring of ciliated tentacles surrounding the 

 mouth (Fig. 5.6). In ectoprocts such as Flustrella the extended tentacles 



