FISHERY BULLETIN: VOL. 71, NO. 1 



combed out by the process described earlier. 

 The terminal brushes of the second maxilliped 

 are subsequently cleaned by the first maxilliped 

 and so on, until the particles initially trapped in 

 the extended net finally reach the mandibles. 

 Somewhere in this chain of events particles are 

 sorted, and undesirable portions of the catch are 

 ejected in the exhalent respiratory stream. Par- 

 ticles which are acceptable as food are ground 

 up between the curved bladelike edges of the 

 mandibles (Figure 5D) and passed into the 

 mouth with the aid of the mandibular palp. 



Most often the maxillipeds work rapidly and 

 alternately, with one extended while the other 

 is being combed. However, when a strong cur- 

 rent of water runs steadily from a single direc- 

 tion, megalopae often extend only one maxilliped 

 and leave it out for a time. When the setae have 

 gathered a sufficient quantity of particles, the 

 maxilliped is withdrawn and cleaned. At this 

 point, the free maxilliped may be extended, or 

 the same maxilliped may be extended again after 

 it has been cleaned. The appearance of variable 

 feeding behavior under varying conditions led to 

 the question of the importance of water move- 

 ment to megalopal feeding. 



A 36-hr experiment was conducted in an eff'ort 

 to determine the effect of turbulence on feeding. 

 Eighteen healthy megalopae, nine each of Pachy- 

 cheles rudis and P. pubescens, were used. Each 

 of the megalopae and a stone for it to cling to 

 were placed in a flask of filtered seawater and 

 starved for the first 13 hr of the experiment. 

 A mixed algal suspension of Isocrysis sp. and 

 Tetraselmis sp., previously found to be accept- 

 able to megalopae as food, was supplied to the 

 same 18 larvae for the remaining 24 hr of the 

 experiment. At intervals of 2 hr, throughout 

 the 36-hr period, the number of animals showing 

 feeding motions was recorded before and after 

 stirring the water. The flasks with the mega- 

 lopae were held at 12°C in a water bath. The ex- 

 periment was started at 0100 on one day and 

 continued to 1300 the next before food was in- 

 troduced, so that observations were made for 

 both starved and fed conditions at night and 

 during daylight hours. 



Figure 6 summarizes the observations on the 

 number of animals feeding under each condi- 

 tion, before and after stirring the water. When 

 no food was present and the water was still, 

 virtually no feeding activity was observed. 





STARVED 



FED 



I 



13 



\3 



15 



23 



7 8 



10 n 12 13 



TIME 



Figure 6. — Histogram showing effect of water movement on feeding behavior in megalopae 

 of Pachycheles pubescens and P. rudis under starved and fed conditions. Left bars, P. 

 pubescejis ; lower, open part of bar, number of larvae feeding in still water; cross-hatched 

 part of bar, number feeding after agitation of water. Right bars, P. rudis ; open part of 

 bar, number of larvae feeding in still water; solid part of bar, number feeding after agi- 

 tation of water. 



230 



