588 EVOLUTION OF ANIMALS Part V 



sacs, one on each side of the tail. Copepods are prodigies in reproduction. 

 Tisbe furcata, common in salt-water aquaria, goes through its life cycle from 

 egg to reproducing adult in 9 to 10 days (Fig. 29.5). 



Ostracods 



Ostracods are minute crustaceans, about one millimeter long. An ostracod 

 might be mistaken for a microscopic clam were it not for the appendages that 

 kick out between the valves, neither in structure nor character like a clam, 

 Ostracods live in fresh water and salt, usually creeping over plants, occasion- 

 ally swimming out into surface waters. They range into new places during the 

 free swimming naupHus stage. 



Crustaceans as Human Food 



Of all the crustaceans, shrimps probably take first place as human food 

 with crabs and lobsters close followers and crayfishes far behind. 



Texas and other Gulf states furnish most of the shrimps for the American 

 market. They are fished from South Carolina southward and to some extent 

 on the northern Pacific coast. There are several "edible" species, one or 

 another being more highly regarded in different regions. Those of the same 

 species are called prawns or shrimps depending on their size, the shrimps 

 being smaller. Shrimps have long been thought of as little shrunken lobsters 

 and their name is derived from the Old English, scrimman, meaning shrink. 

 Thus, somebody may be a "little shrimp." The main edible crab of the east 

 coast of North America is the blue swimming crab (Callinectes sapidiis, Cape 

 Cod to Florida). On the west coast, the edible crabs include several species; 

 in some of them the thorax of the adults is commonly nearly a foot wide. 



The American lobster, Homarus americana, ranges from Labrador to South 

 Carolina, along rocky coasts, in the shallows in summer, in deeper water in 

 winter. The female lays her eggs in July and August, about 10,000 by a 

 10-inch lobster. The mating and egg laying are similar to those of crayfishes 

 except that the lobster carries the eggs 10 to 11 months before they hatch 

 and spawns only every other year. Lobster culturists claim that a modest crop 

 of two adults from each 10,000 eggs is sufficient to maintain the species. The 

 smaller spiny lobster {Panulirus interruptus) is the edible lobster of the Pa- 

 cific Coast. Whether it has a quality of flavor equal to the New England lobster 

 is difficult to discover, in New England. 



