374 



ARTllROPODA 



Order II. Balanids. 



Sessile cirripeds with calcareous shell formed of carina, roslrum, and Urer- 

 alia; scnia and ieri;a formin.i,' the \-alves vfii;. 300). Bjldiiiis,'^ Coroiiiilj. allached 

 to whales. 



Order III. Rhizocephala. 



These differ sjreatly from other cirripeds. They are parasitic on the abdo- 

 mens of decapod cral'S and consist of a stalk which penetrates the body of the 

 host and a liodv which remains outside i,U^'. J04l- The stalk branches in a 

 root-like manner, penetrates the cephalothorax and absorbs its juices. Since 

 the stalk furnishes the food, an alimentary canal is absent. The body lacks 

 all appendages, is enclosed bv a soft-skinned mantle, and is almost entirely 



Fig. tQ4. — Sdcc'ulina cjrciui attaelicd to Civc'nnis niann^, whose abdomen {^T) is ex- 

 tended. HI, se.\ opening of Sjcciilina; r, network of roots ramifying the crab; .'.'. stalk. 



filled with the gonads. Since the adult ]iarasites lack all arthropodan features, 

 their position is onlv settled by their development (tig. ^o^b which is like that 

 of other cirripeds. These forms are rare on the .Vmericaii coast. Suicnliiio, 

 Piilo;^iislcr.* 



Two more orders, .-\RDO>[IX.\LT.V and .VPOD.V, parasitic in the mantle 

 and shells of molluscs and other cirripeds, scarcely need mention. 



Sub Class I'. Mahn'oslrdi'a. 



The ]\Ialacostraca arc sharply marked otT from the other Crustacea by 

 having a l.)otly wliich consists of twcittv segments, of wlijch seven, are 

 abdominal (Xclhilia has twenty-one, eight abdomiital). The e.xcretory 

 orgaits are represented by the antennal glands, and shell glaitds are lacking 

 except in the larvtv and some Isopoda. The male genital ducts open on 

 the tliirteenth, the female on the eleventh, segmeitt. 



