270 



THE SEA SHOEE 



interesting species are inhabitants of our seas we will briefly describe 

 the distinguishing characteristics of the group. 



"We have just mentioned the 

 fact that the head and thorax of 

 a decapod is usually covered by a 

 large shield the carapace. Now, 

 the general character of this cara- 

 pace may be seen at once in 

 either the shrimp or the lobster. 

 In these animals the segments 

 that form the head and the thorax 

 are all fused together, and are 

 completely covered by the pro- 

 tective buckler of hardened skin ; 

 but in the Stomapoda the carapace 

 is much smaller in proportion, 

 and a few of the segments of the 

 thorax, instead of being fused into 

 the general mass of the ceplialo- 

 thorax, are quite distinct from 

 it. The abdomen, also, is large 

 and strongly formed in these ani- 

 mals. Five pairs of the thoracic 

 limbs are directed forwards, and 

 FIG. 201. THE MANTIS SHRIMP are adapted both for catching food 

 (Squilla Mantis) and for climbing, while others 



are used in walking. The limbs 



of the abdomen generally number six pairs, of which the first five 

 bear feathery gills. 



Two species of Mantis Shrimps, one of which is represented in 

 fig. 201, have been found off the south and south-west coasts, but 

 these are not likely to be seen on the shore, since they inhabit 

 deep water. Allied to these, and sometimes included with the 

 Stomapods, are the Opossum shrimps, so called because the 

 females of some species carry their eggs in a kind of pouch, thus 

 reminding us of the marsupial quadrupeds of the same name. They 

 are of very slender build compared with the mantis shrimps, and 

 differ from them in that the carapace completely covers the thorax ; 

 but though this is the case, the fusion of the thoracic segments 

 is not complete, since the posterior ones have still a certain amount 

 of freedom of movement. Some species of opossum shrimps are 



