MARINE AETHEOPODS 



267 



We shall now consider the Sessile-eyed group, dealing first 

 with the order Isopoda or equal legged, and then the Amphipoda, 

 which have appendages adapted both for walking and swimming. 



The general nature of an Isopod may be readily understood 

 by the examination of the common woodlouse that abounds in 

 gardens and damp places almost everywhere, and the reader will 

 probably remember having seen similar creatures crawling over 

 the rocks on the sea shore. 



The body is generally depressed or flattened, but convex above, 

 and is composed of seven segments, each segment bearing a 

 pair of legs which terminate in a pointed claw, while the posterior 

 appendages are modified into flat, leaf -like organs of respiration. 



FIG. 199. MARINE ISOPOD 



1. Sphceroma serratum. 2. Limnoria lignorum. 3. Ligia oeeanica. 4. Netaa 

 bidentata. 5. Oniscoda macxlosa 



"When engaged in ' shrimping ' one frequently meets with 

 shrimps or prawns that are disfigured by a tumourous swelling 

 on the side of the body, and if the swelling be opened a little 

 parasite will be dislodged. This parasite is an Isopod (Bopyrus), 

 the appendages of which are imperfectly developed. The female 

 is very much larger than the male, and, as is usual with parasitic 

 creatures, the greater part of the body-cavity is occupied by the 

 well-developed organs of reproduction. 



There are several other parasitic isopods, some of which live 

 on the bodies of fishes, and are popularly known as fish-lice, but 

 these are not so likely to come in the way of the sea-side naturalist 

 as the more typical forms that crawl about on the rocks and among 



