CRUSTACEA 



149 



Fig. 132. — Swimming-crab (Araneus bidens). 



new integument is in a thin and delicate condition. At other times the 

 shell is hard. These swimming-crabs crawl about like the others, but they 

 are also capable of swimming freely by means of the broad, flattened 

 paddle on the last pair 

 of feet, shown in the 

 figure, which represents 

 a species from Panama. 

 Some of these swimming- 

 crabs live a pelagic life, 

 being found on the sur- 

 face of the ocean far 

 from land. One small 

 species is very abundant 

 in the fronds of the sar- 

 gasso which forms large banks in the tropical seas. 



In our oysters we frequently find a small, thin-shelled crab which proves 

 a very acceptable morsel. It has the scientific name Pinnotheres, and 

 'thereby hangs a tale.' The ancients frequently found within the valves 

 of one of the Mediterranean molluscs, Pinna by name, a small crab to all 

 intents and purposes like our oyster-crab. Its presence there needed 

 explanation, and so arose the story that it was the Pinnotheres, the guar- 

 dian of the Pinna. It lived within the shell, and kept a sharp lookout for 

 danger, and when any enemy was seen approaching, it warned the mollusc, 

 which straightway closed its shell and rendered all safe and tight. The 

 story contains more poetry than truth. The crab is really an intruder 

 which seeks protection inside the valves of the mollusc, and it is a peculiar 

 fact that it is only the female which selects this retreat. She does not cat 

 the mollusc, but lives on whatever of food and fortune the passing currents 

 may bring. 



The fiddler-crabs are near relatives of this little form, but they lead a 

 free and active life. They are amphibious, and one walking along a sandy 

 shore where they abound, startles up large numbers of them, myriads hur- 

 rying and scuffling in the most amusing manner in their hurry to seek 

 safety in the sea. As they go along, their large claw is brandished about 

 in the most threatening manner, while the other smaller one works across 

 it like the bow of a violin. Fiddler-crabs make attractive pets in confine- 

 ment. All that is necessary is to provide them with plenty of moist sand 

 and food suited to their demands. They will quickly construct their 

 burrows in their new home, carrying up pellets of sand with some of their 

 smaller legs, and dumping it as far from the burrow as the limits of their 

 prison will admit. Their natural food is largely vegetable, and they scrape 



