SEGMENTED SCHIZOCOELS 



241 



Most are scavengers upon all kinds of plant and 

 animal matter. Some are predaceous, feeding upon 

 microscopic organisms. 



ORDER STOMATOPODA (Manf is Shrimps) 



Diagnosis: carapace present, but not covering the 

 last four thoracic segments; second thoracic limbs 

 jacknife-like and large, but first five pair of thoracic 

 limbs are of similar structure; last three thoracic 

 limb pairs not so modified; abdomen typically wider 

 and longer than cephalothorax; strictly marine, bur- 

 rowers in sand or mud or inhabitors of crevices (Fig- 

 ure 14.13). 



The mantis shrimps are remarkable for their jack- 

 nife-like second thoracic limb, which is similar to the 

 jacknife claw of the praying mantis (Class Insecta). 

 Either "mantis" or "mantid" designates both groups. 

 In some mantis shrimps the jacknife blade is sharp; in 

 others the blade is comb-like. The blade is very ef- 

 fective in capturing or killing prey; some mantis 

 shrimps attack animals of like size and cut the prey in 

 two. 



As with most crustaceans, mantis shrimp sexes are 

 separate. The eggs are attached to the abdominal ap- 

 pendages of the female until the larvae hatch. 



ORDER DECAPODA (Decapods) 



Diagnosis: carapace covering the entire thorax; 

 first three pairs of thoracic limbs more or less modi- 

 fied as structures associated with the mouth; the last 

 five pairs are walking legs; abdomen of variable 

 length but generally not wider than cephalothorax; 

 mostly marine, some fresh-water, a few terrestrial 

 (Figure 14.14). 



The decapods contain a vast array of structural 

 types and all of the crustaceans normally used as food 

 by man. If we do not worry too much about taxo- 

 nomic relationships, we can identify decapods as 

 crabs, shrimps, crayfish, and lobsters. Crabs gen- 

 erally have a much reduced abdomen that is folded 

 under and upon the thorax; however, hermit crabs 

 have a large, soft, twisted abdomen that is usually 

 protected, because hermit crabs live in and carry 

 about empty snail shells. All crabs are marine. 



Shrimps, like crayfish and lobsters, have the ab- 

 domen longer than the cephalothorax, straight, and 

 not folded under and upon the thorax. Shrimps are 

 fresh water and marine, crayfish strictly fresh water, 



and lobsters strictly marine. Fresh-water shrimps are 

 distinguished from crayfish by having laterally com- 

 pressed rather than rounded bodies and by having the 

 last three pairs of thoracic legs without pincers rather 

 than only the last two pairs. Of the three pairs of 

 thoracic legs having pincers in crayfish, the first 

 pair often are quite large by comparison. Marine 

 shrimps, even the larger species called prawns, usu- 

 ally can be distinguished from lobsters by size alone. 

 Also, the much larger lobsters have a rounded body 

 rather than the shrimp-like compressed body. 



CLASS DIPLOPODA (Millipedes) 



Diagnosis: head with one pair of antennae and one 

 pair of maxillae; body long, usually cylindrical; 

 thorax of four segments, the first legless, the rest with 

 one pair of legs; abdominal segments variable in 

 number (each actually two segments), nine or more, 

 usually numerous, two pairs of legs per segment; 

 sexes separate, eggs laid; young with six body seg- 

 ments and three pairs of legs; up to ten molts to the 

 adult form (Figure 14.15). 



Millipedes, or thousand-legged worms, are entirely 

 terrestrial, being found in dark, moist places under 

 objects upon the ground. Contrary to the belief of 

 some, they are nonpoisonous and harmless to man. 

 Although not aggresive, if disturbed they frequently 

 will roll up in a spiral and exude an offensive, prob- 

 ably protective, odor from their stink glands. These 



Rgure 14.15 Closs Diplopoda, Spirobo/us, o millipede ( x 1). 



