784 FRESH-WATER BIOLOGY 



much reduced. The antennae of the second pair are armed with 

 hooks at the ends, but they are much shorter than in the Ergasilidae. 



3. Dichelestidae. The body is elongated, the thoracic segments 

 distinct, the abdomen rudimentary except for the elongated genital 

 segment. At least the last two pairs of swimming feet are rudi- 

 mentary. The maxillipedes are armed with hooks. 



4. Lernaeidae. The body is worm-like and unsegmented, and 

 the abdomen rudimentary. Processes growing from the head serve 

 to attach the animal to the host. The four swimming feet are 



either very small or entirely lacking. A represen- 

 tative of this family is found on the sheepsheads of 

 the Mississippi Valley. 



5. Lernaeopodidae. The head is distinct, the rest 

 of the body sac-shaped, and generally unsegmented. 

 The second maxillipedes are very large, and, arch- 

 ing over the head, are joined together to form an 

 organ for attachment to the host. The swimming 

 feet are entirely lacking. 



6. Chondracanthidae. The body is indistinctly 

 ^fodalhni^m\lln, Segmented, and the abdomen rudimentary. The 



Sou? and Qili^nS first two palrs of swimming feet are rudimentary, 

 lo^^' *^ ^^^ '' the others lacking. The second antennae bear 



hooks. The male is small, distinctly segmented, and lives as a 



parasite on the female. 



KEY TO NORTH AMERICAN FRESH-WATER ERGASILIDAE 



I (8) Head completely fused with first thoracic segment, with no indi- 

 cation of union; carapace elongate, much longer than wide, 

 and more than half entire length 2 



2 (5) Anterior margin of carapace evenly rounded, first antennae hardly 

 reaching end of first segment of second pair _. 3 



3 (4) Second antennae one-third entire length. 



Ergasilus funduHKroyeT 1863. 



Basal segment of second antennae much swollen and widened distally; second segment with 

 I large process on its outer border. Foimd on the gills of Fundulus ocellaris. 



