ARTHROPODA 175 



The sea crayfishes, Palinurus vulgaris, sometimes called the spiny 

 or " rock lobsters," have no chelae and a much reduced rostrum. 

 They are valued by Europeans for food and are said to be similar to 

 the true lobster in flavor. The common prawn, Palaemonetes 

 vulgaris, reaches a length of about 1 inches. It is transparent. 

 The body is compressed and the exoskeleton lacks lime. The ros- 

 trum, eye stalks and antennae are very conspicuous. The common 

 shrimp, Crangon (Crago) vulgaris, is exceedingly abundant on the 

 Pacific coast, along the shore of the Gulf of Mexico, The edible 

 shrimp, Penaeus setijerus is found in shallow bays and estuaries 

 from Virginia to Texas. It reaches a length of 6 inches. Its value 

 as food is estimated to be over ^200,000 annually. While speaking 

 of shrimps, we might mention the order Stomatopoda which includes 

 Malacostraca with five pairs of anterior thoracic maxillipeds, three 

 pairs of thoracic legs and an extremely short carapace. The 

 mantis shrimp, Squilla {Chloridella) empusa, belonging to this order, 

 reaches a length of 10 inches. Several species of Squilla are eaten 

 in the Mediterranean and tropical Pacific. They are esteemed as 

 a delicacy in Tahiti and Samoa. Perhaps the American form may 

 yet come into use. 



The hermit crabs, Eupagurus, related to the shrimps and prawns, 

 live in the shells of gastropods which they seek out very early in their 

 life history and in which they are protected. Sea-anemones and 

 hydroids are commonly found attached to the shells occupied by 

 hermit crabs. (See Commensalism, p. 482.) Robber crabs {Birgus 

 latro) are related land forms found on coral islands in the Indian 

 Ocean, They ascend cocoanut trees, and feed on the pulp of the 

 cocoanut. The blue crab {Callinectes hastatus) is the commercial 

 soft-shell crab. Rock crabs and painted crabs are also used for food 

 when soft. Oyster crabs bring a high price in the market. The 

 ghost crab, a scavenger, destroys the eggs of sea birds. (Figure 80.) 

 A little marina crab, Melia, inhabiting coral reefs, uses small sea- 

 anemones for defense and for feeding. It captures an anemone 

 in each claw and when attacked it thrusts the anemone towards 

 the enemy for defense. When the anemones capture food, the crab 

 seizes the tidbit. 



Class 2. Onychophora. — The Onychophora (Gr. onux, a claw; 

 phoreo, bear) include approximately fifty species of the genus 

 Peripatus, found in Australia, New Zealand, Africa, South America, 

 and the West Indies. All the species of Peripatus are terrestrial, 



