CONOR and CONOR: BEHAVIOR IN LARVAL PORCELLANID CRABS 



Figure 5. — Megalopa respiratory and feeding structures 

 Pachycheles pubescens. Setules omitted from all plumose 

 setae. Ex - Exopodite; en - endopodite; arrow - detail 

 of a plumose seta. A - Maxilliped III ; B - Maxilliped II ; 

 C - Maxilla II; D - mandible, anterior view, palp folded 

 in place. 



and the under side of the carapace in the branch- 

 ial chamber. The foremost one-fourth of the 

 carapace cannot be reached by these legs, and in 

 dense algal suspensions, fine hairs on this por- 

 tion of the megalopa may become entangled with 

 algae and other detritus. 



The chelipeds are freed of foreign matter by 

 rubbing the dorsal surface of one on the ventral 

 surface of the other in a simple lateral scraping 

 motion. The antennules are cleaned singly or 

 simultaneously in the following manner. An 

 antennule is lowered to the level of a raised third 

 maxilliped and inserted into a notch on the max- 

 illiped formed by a long and a short group of 

 dense setae. The setae and aesthetes of the 

 antennule are then effectively combed free of 

 particles as the maxilliped is drawn forward and 

 down and the antennule passes between the setal 

 brushes. 



The grooming of the feeding mechanism is the 

 most complex cleaning behavior. This behavior 

 can be seen in actively feeding animals as well 

 as in nonfeeding megalopae which have been 

 placed in a dense suspension of algal cells. The 

 long feeding setae of the third maxilliped (Fig- 

 ure 5A) are combed clean by the short dense 

 setal brushes located on the two terminal seg- 

 ments of the second maxilliped (Figure 5B). 

 The short setal brush is inserted at the bases 

 of the feeding setae and rolled downward and 

 inward toward the mouth following the long 

 curve of the setae being combed. When the en- 

 tire length of the filtering setae has been combed 

 free of particles, the brushes of the second max- 

 illiped are then combed out by the first max- 

 illiped and inner mouth parts. Undesirable 

 particles are rejected into the exhalent current 

 and swept out by the flicking of the exopodite 

 on maxilliped II. 



The diet and feeding behavior of the megalopa 

 are drastically different from those of the zoeal 

 stages. Predatory habits are replaced imme- 

 diately by filter-feeding habits when the molt 

 is completed and the megalopal skeleton has be- 

 come hard enough to permit motion. The mega- 

 lopae of all four species rejected newly hatched 

 Artemia nauplii as food and would feed only on 

 suspended phjrtoplankton. Several monoalgal 

 and diatom cultures (Tetraselmis sp., Isochrysis 

 sp., and several unidentified diatoms) and nu- 

 trient culture medium inoculated with raw sea- 

 water were tried singly and in various combi- 

 nations as food. In each case the megalopae fed 

 on the suspended organisms in the cultures in 

 the same manner. 



The behavioral change from prey capture to 

 suspension feeding is reflected in changes in 

 mandibular and maxilliped form. The natatory 

 second maxilliped and the functionless third 

 maxilliped of the zoea become highly specialized 

 parts of a complex feeding mechanism in the 

 megalopa. The feeding pattern most commonly 

 observed in the laboratory is composed of the fol- 

 lowing sequence of events. 



The endopodite of the highly setose third max- 

 illiped is extended and a "setal net" spread open. 

 After a moment, the maxilliped is lowered and 

 swung in toward the body, where the setae are 



229 



