studies. Spaulding (1904) found the crab able to 

 profit by experience in vision and taste experi- 

 ments, and able to learn faster than P. poUicaris. 

 Fink (1941) was able to demonstrate decondition- 

 ing of fear-reflex activity over a period of 18 days, 

 the older crabs responding more slowly than 

 young ones. Allee and Douglis (1945) found that 

 a shell-less P. longicarpus would not feed, but if 

 it were given a shell to occupy it would feed nor- 

 mally. Crabs in shells fight for food, the larger 

 often fending smaller ones from a food supply. 

 Movement from small to larger shells is accom- 

 plished only after several trials and thorough 

 investigations of new shells, but shell-less crabs 

 will accept almost any shape of shell in any condi- 

 tion. Shell-less crabs placed in a finger bowl tend 

 to fight continuously until one or both are dead, 

 usually within 24 hours. If an empty shell is 

 dropped into a container with two shell-less crabs, 

 one will immediately enter the shell. If the larger 

 individual does not enter first, it will extract the 

 smaller forcibly and enter in its place. Shell-less 

 crabs will attack housed individuals regardless of 

 size, but attackers were never seen to be successful 

 when the two combatants were of equal size or 

 when the housed individual was the larger. 



Kropp and Perkins (1933) showed that in P. 

 longicarpus and other remotely related decapods 

 the chromatophore activity substance in the eye- 

 stalk will induce contraction of chromatophores 

 in other species, and postulated that the substance 

 is genetically similar throughout the group. 



Finally, Keinhard (1944, 1945) and Reinhard 

 and Buckeridge (1950) discussed parasitism in P. 

 longicarpus. An examination of 8,000 crabs 

 showed a 1-percent infestation with a larval 

 acanthocephalid belonging to the genus Poly- 

 morphus. The worm was found in the abdominal 

 cavity(?) usually attached to the hind gut or 

 sometimes among tubules of the hepato-pancreas. 

 The usual number of cysts per host was one, 

 though as many as three occurred. Reinhard also 

 described an entoniscid isopod, Paguritherium 

 (datum, from this species. Entering the crab's 

 body through the dorsal side of the eyestalk, and 

 remaining in contact with this point of entry, the 

 parasite elongates with but little damage to tho- 

 racic organs, but becomes greatly distended in the 

 abdominal region. There it restricts the hepato- 

 pancreas and nearly obliterates the gonads as it 



grows. Infestation does not externally modify the 

 male host. In females, the parasite reduces size of 

 the first three pleopods, especially length of the 

 endopod, and causes partial or complete loss of 

 ovigerous hairs on the external surface of the 

 endopod and protopod. Thus, secondary sexual 

 characters of the female crab are altered. One 

 percent of the crabs investigated were infested 

 with this parasite. 



Pagurus defensus (Benedict) 



Figure 102 

 Eupagurus defensus Benedict, 1892, p. 7. 



Figure 102. — Pagurus defensus (Benedict). A, anterior 

 part of female in dorsal view ; B, right chela, outer 

 surface ; 3 mm. indicated. 



Recognition characters. — Anterior portion of 

 carapace broader than long, subcordate. Rostral 

 projection broadly rounded, lateral processes tri- 

 angular, armed at apex with a short spine. Eye- 

 stalks stout, much dilated and flattened distally; 

 eye scales broad, rounded, anterior margin forming 

 a semicircle, armed with a subterminal spine. 

 Antennular peduncles extending beyond eyestalks 

 by two-thirds or more length of terminal article. 

 Antennal peduncle extending beyond eyestalks by 

 one-half length of terminal article; acicle curving 

 outward and extending somewhat beyond eye- 

 stalk. 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



127 



