208 THE BIOLOGY OF MARINE ANIMALS 



and thence to the buccal funnel. MacGinitie has also described an altern- 

 ative mode of feeding by formation of a mucus-bag. This is produced by 

 the aliform notopodia and extends posteriorly to a dorsal cup organ where 

 it is rolled up. All the water which flows through the burrow must traverse 

 this net, which filters out suspended food matter. At intervals the front 

 margin is detached and the net is transported anteriorly to the mouth by 



Fig. 5.3. Mucus-bag Feeding in a Tubicolous Polychaete 

 Chaetopterus variopedatus. (From MacGinitie, 1939.) 



/~vX—>J^ . JV ■■ ■J\/~ % fyu«^J|ft~»4r»^^ 



Fig. 5.4. Extract from an Irrigation Record of 

 Chaetopterus variopedatus (duration 4 hours) 

 The worm was carrying out mucus-bag feeding and pumping steadily, except for 

 brief pauses at the peaks when the lever returns to null position. The frequency is about 

 1 fan stroke per sec, too fast for individual strokes to be distinguished on this record. 

 At the pauses, which occur every 18 min, a mucus-bag is passed forwards to the 

 mouth and swallowed. (From Wells and Dales (103).) 



reversal of ciliary beat in the dorsal groove. The mucus-bag forms a very 

 efficient straining apparatus, and by feeding proteins of different particle 

 sizes it has been calculated that the mesh openings are about 40 A in 

 diameter (63, 65, 103). 



In cryptocephalous polychaetes exemplified by Sabella, feeding is 

 carried out by a branchial crown consisting of a circlet of tentacles (Figs. 

 4.2, 15.9). These bear lateral pinnules which are ciliated and form a filtering 

 apparatus. Water is drawn into the branchial funnel by abfrontal cilia on 



