io8 



A BIOLOGY OF CRUSTACEA 



pectoralis because the mature females are usually found under the 

 pectoral fins of the host. The eggs, which are compressed into a 

 cylindrical shape in the egg sacs, give rise to nauplii which swim 

 freely in the plankton. The nauplii moult several times and then 

 change into copcpodids which seek out a fish and attach themselves 

 to it. Attachment is effected by means of a thread made by a gland 

 on the front of the head. Several moults are passed through in the 

 attached copepodid, or chalimus, stage before the adult form is 

 assumed. This type of life cycle is not vc:y different from that of a 

 free-living copepod, and though L. pectoralis prefers flatfish it is 



HNTENNUU 



JJA^&fe 



CENITftL 

 SEGMENT 



ABDOMEN 



Fig. 46. Parasitic Copepoda. A, Ascomyzon asterocheres, 

 from the common starfish, Asterias rubens. Dorsal view 

 of female; actual length about 1.3 mm. (After G. O. Sars). 

 B, Trebius caudatus, a common caligoid parasite of 

 skates (Rata spp.) Ventral view, actual length about 

 8 mm. 



not very particular about which sort of flatfish it attaches to. A 

 closely related species, L. pollachii, is much more specific in its 

 choice of habitat and is only found under the tongue of the 

 pollack (Gadus pollachius). 



Deviations from the typical copepod shape can occur in various 

 ways. Eudactylina (fig. 47A), a parasite of sharks and rays, has 

 become maggot-like, but it still has limbs which are quite typically 

 copepodan. Mytilicola intestinalis, which lives in the gut of the 

 common mussel (Mytihis), is even more maggot-like and the limbs 

 are but poorly developed. The copepodan form becomes more 



