ISOPODS OF NORTH AMERICA. 497 



V. BOPYROIDEA OR EPICARIDEA. 



Parasitic forms, ectoparasites, their hosts being other Crustacea. 

 Sexual dimorphism in all the forms is strongly marked. 



Female is often very asymmetrical; segmentation is sometimes 

 entirely lost. 



Head usualty carries two pairs of rudimentary antennas. Mouth 

 parts are reduced, the mandibles and maxillipeds only being developed. 



Rudiments of the second maxillae sometimes present. 



Legs, when present, are prehensile. 



Pleopods, in adult, all branchial in character. 



Uropoda simple, usually very small, and terminal. 



Male, when compared with female, is of diminutive size, and dif- 

 ferent in appearance from female. Development is in the form of a 

 regressive metamorphosis; there are two and in some forms three 

 larval stages. 



ANALYTICAL KEY TO THE FAMILIES OF BOPYROIDEA. 



a. Body of female not a simple sac filled with eggs, and having true limbs and some 

 or all of the appendages. Male passing beyond the last larval stage of female 

 into a stage different from it. 



b. Body of female distinctly segmented, more or less asymmetrical, twisted either 

 to right or left. Maxillipeds lamellar, biarticulate, and more frequently exhib- 

 iting a small terminal joint. Legs in seven pairs, sometimes obsolete on one 

 side with the exception of the first. Five pairs of incubatory plates present, 

 more or less arching over the ventral surface of the thorax. Pleopoda 

 simple, biramous or triramous, all of the same structure, rarely obsolete. 

 Male with all the segments of the thorax sharply defined. Last larval stage 

 with the flagelluui of the second antennae composed of four articles; legs of uni- 

 form structure; u'ropoda with inner branch shorter than outer. Parasitic on 



decapodous Crustacea Family XX. BOPYEID^E 



b'. Body of female perfectly symmetrical, the segmentation, when present, only 

 visible in the middle of the dorsal face. Maxillipeds lamellar, without any 

 terminal joint. Only five pairs of legs present. Incubatory plates compara- 

 tively small, sometimes greatly reduced in number, and scarcely at all par- 

 taking in the formation of the marsupium, which constitutes two separate 

 cavities bounded by the lateral walls of the body. Pleopoda generally rudi- 

 mentary or wholly absent. Male with head and first segment of thorax 

 coalesced. Last larval stage with the flagelluui of the second antennae com- 

 posed of five articles; legs of the first pair shorter and thicker than the 

 others; uropoda with the branches subequal. Parasitic on Schizopoda. 



Family XXI. DAJLD.E 



a'. Body of female forming a simple sac, with no true limbs, and all or most of the 

 appendages lost. Male not different from last larval stage of female, and not 

 passing beyond this stage Family XXII. CRYPTONISCID.S: 



See G. O. Bars for characters of tribe or superfamily, Crust, of Norway, II, 1899, 

 pp. 19&-194. 



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