386 



ARTHROPODA 



In the terrestrial species the gills are adapted for breathing damp air. In 

 Porcellio and Annadillidiim the first or first and second opercula are permeated 

 with a system of air tubes, which physiologically, though not morphologically, 

 are comparable to the tracheae of insects. 



In the Isopoda the tendency to parasitism is greater than in the Amphipoda. 

 Many swimming forms attach themselves to fishes and feed by boring with 

 their modified mouth parts into the skin. The Bopyridae live in the branchial 

 chamber of shrimps. Cr \ptoniscus is a shapeless sac which attaches itself to the 

 stalk oiSacculina (p. 374), and, after causing the death of this parasite, uses its 

 network of 'roots' for its own nourishment. The Entoniscidae (fig. 413) 

 attack Dccapoda and, pressing the skin before them, penetrate the inte- 

 rior. Their strange shape is largely due to the lobe-like brood lamellae. 

 They are usually hermaphroditic, but have besides complemental dwarf males 

 (fig. 413* A )- 



A 



FIG. 414. .1, Idotea irrorata*; B, Limnoria lignorum*; C, &ga psora* ('salve bug'); 



D, Lcptochela algicola * (after Harger). 



Sub Order I. ANISOPODA. Six free thoracic segments; heart thoracic; 

 first thoracic foot (on head) chelate; abdomen with swimming feet; intermediate 

 between Amphipoda and other Isopoda. Tanais* Leptochela* (fig. 414). Sub 

 Order II. EUISOPODA. Seven free thoracic segments. OxisciDyE; terres- 

 trial, 'sow bugs'; Porcellio* Oniscus* Armadittidum,* 'pill bug.' ASELLID^E 

 (fig. 412), fresh water. SPH^ROMID^E, head broad, body rounded and convex; 

 Sphceroma* Limnoria lignorum* (fig. 414), gribble, destructive to submerged 

 wood. IDOTEID^;, free-living, marine, with usually elongate bodies; Idotea* 

 Ccecidotea* BOPYRID/E, parasitic on Caridea; body of female disc-like, asym- 

 metrical, without eyes; Bopyrus* CYMOTHOID^E, parasitic on fishes or in their 

 mouths. Cymoilioa* Mga* Cirolana* Sub Order III. ENTONISCIDA, 

 general features are described above. Entmiscus. 



