CONOR and CONOR: BEHAVIOR IN LARVAL PORCELLANID CRABS 



cleaning behavior described below^ for the zoeal 

 stages has not been observed in this stage. It 

 probably is not present since the stage is short- 

 lived and the major natatory and telson setae 

 are confined beneath the larval cuticle. 



Prezoeal locomotion consists of violent spas- 

 modic flexions of the abdomen, and there is no 

 feeding during this stage. The larva appears 

 to be only slightly photopositive. The strong 

 abdominal flexions finally split the cuticle long- 

 itudinally along the dorsal midline of the cara- 

 pace just behind the point where the rostrum 

 joins the carapace, and a first zoea emerges from 

 the thin prezoeal cuticle. 



ZOEAL STAGES 



The behavior patterns of the first true zoea 

 are considerably more complex than those of the 

 prezoeal stage. Respiratory currents are still 

 produced by the beating of the maxillae and are 

 aided by swimming, as was also noted by Foxon 

 (1934). Detrital particles often become en- 

 tangled in the plumose setae of the maxillipeds 

 and telson. Cleaning behavior is simple but well 

 defined in this stage. The telson and the plumose 

 setae along its posterior margin are cleaned by 

 curving the abdomen under the thorax and drag- 

 ging the telson posteriorly across the functional 

 mouth parts, thus loosening and scraping oflf 

 clinging debris. This scraping also serves to 

 remove large pieces of detritus from the periph- 

 eral setae on the mouth parts and from the setae 

 of the endopodites on both sets of maxillipeds. 

 The endopodites are used in feeding and require 

 frequent cleaning. Direct cleaning of the exop- 

 odites and natatory setae and of the carapace 

 spines was never observed, however. The clean- 

 ing observed was indirect and probably acci- 

 dental, since it consisted simply of freeing the 

 body surface of entangled debris by larval mo- 

 tion and reversal of swimming direction. 



The first zoea swims primarily by beating the 

 maxillipedal exopodites (Figure 2) which have 

 long natatory setae, but this may be augmented 

 by motions of the telson. The maxilliped endop- 

 odites are held extended ventrally and do not 

 function in swimming. The zoea are strong 

 swimmers and due to the configuration of the 



Figure 2. — Maxillipeds of Zoea II, Pachycheles pubes- 

 cens, with setules omitted from most plumose setae. 

 Ex - exopodite; en - endopodite; A - Maxilliped I; B - 

 Maxilliped II; C - Maxilliped III. 



0.5 mm 



Figure 3. — Zoea II of Pachycheles pubescens, in forward 

 swimming posture. Maxillipeds I and II rotated slightly 

 for clarity. 



carapace spines (Figure 3), swim predominant- 

 ly backward and forward. 



Forward motion is accomplished by synchro- 

 nously beating both sets of exopodites downward 

 and posteriorly, with the telson extended poster- 

 iorly. Reversal of direction can be achieved very 

 quickly by a forward snap of the telson and a 



227 



