74 



CRUSTACEA COPEPODA 



The females carry two long egg-sacs ; the general structure may 

 be made out from the ventral view of Caligus nanus (Fig. 43). 



Some of the Caligidae are distinguished by the terga of the 

 thoracic segments being expanded to form large chitinous elytra, 

 e.g. Cecrops, found parasitic on the gills of the Tunny and on the 

 Sun-fish (Orthagoriscus mola) . Caligus rapax is parasitic on the 

 skin and in the gills of Sea-Trout, Pollan, etc. ; and C. lacustris is 

 common in fresh-water lakes and streams on Pike and Carp. 



eph ------ 



-\--Th.l 



---Th.5. 



Abd.1 



FIG. 43. Caligus nanus, x 10. Abd.l, 

 1st abdominal segment ; Ant.l, Ant. 2, 

 1st and 2nd antennae ; Mx.l, MX. 2, 

 1st and 2nd maxillae ; Mxp, maxilli- 

 pede ; s, siphon ; Th.l, Th.5 1st and 

 5th thoracic appendages. (After Ger- 

 staecker. ) 



FIG. 44. Lernaea branchialis from 

 the Haddock, ? , x 1. Ceph, 

 cephalothorax ; e.s, egg - sacs. 



(After Scott. ) 



Fam. 11. Lernaeidae. These parasites burrow with their 

 heads deep into the skin, or even into the blood-vessels or body- 

 cavity, of various marine fish. The body of the adult female 

 Lernaea is extraordinarily deformed, consisting of a mere shape- 

 less sac with irregular branched processes on the head, and two 

 egg-sacs attached behind (Fig. 44). Pennella sagitta * bores so 

 deeply into the flesh of its host, Chironectes marmoratus, that 

 only the egg-sacs and some remarkable branchial processes 

 attached to its abdomen protrude outside the host to the 



1 The genus Pennella also includes parasites on the whales Hyperoodon and 

 Balaenoptera. 



