COPEPODS OF THE WOODS HOLE REGION 397 



urosome. It was recorded by Fish under the name TTiawrnaleus cla- 

 'paredii Giesbrecht, which is a synonym of the present species. It is 

 another tropical visitor from the south and gets into the present 

 area by way of the Gulf Stream. 



Suborder CALIGOIDA 



Fourth thoracic segment usually forming a movable articulation 

 with the third segment, but firmly attached to the fifth. In some of 

 the fixed parasites, however, the whole body becomes rigid in the 

 female and the movable articulation is lost. Urosome sometimes 

 shorter and narrower than the metasome, sometimes longer and 

 wider, both divisions depressed. 



First antennae reduced to one or two segments; second antennae 

 prehensile, armed with claws;, maxillary palp in the form of a pre- 

 hensile claw, removed from the maxilla toward the margin of the 

 carapace, behind the second antenna; maxillipeds the chief organs 

 of prehension, often considerably swollen and the terminal claw 

 replaced by a sort of forceps. Between the basal segments of the 

 maxillipeds is the furca, or sternal fork, a structure peculiar to the 

 Caligoida. Swimming legs usually more or less modified, such 

 modification consisting of loss of swimming setae, fusion and re- 

 duction of the segments, loss of the entire endopod, making the leg 

 uniramose, and often the disappearance of one or more pairs of legs. 



Two ovisacs, each with a single row of strongly flattened eggs 

 like a roll of coins, except a few genera among the Lernaeidae, in 

 which the ovisacs are baglike and the eggs multiseriate. Both sexes 

 parasitic on fishes, aquatic mammals, and rarely invertebrates; the 

 males and less frequently the females sometimes leave their host and 

 swim about freely in the plankton. 



Remarks. — This and the following group are made up entirely ot 

 parasites, and every genus exhibits some modification of normal 

 structure as a result of parasitism. Comparatively few of the 

 present group, however, become fixed to their host with sufficient 

 rigidity to prevent moving about at will, and most of them retain 

 their ability to swim about freely. They thus become a menace to 

 food fishes and fish development b}'^ being able to concentrate upon 

 a host that becomes in any way weakened. 



Family CALIGIDAE 



Genus CALIGUS Muller, 1785 



Head fused with first three thoracic segments, fourth segment free, 



without dorsal plates; genital segment also without dorsal plates; 



abdomen 1- to 4-segmented. Frontal plates with lunules; first and 



second antennae 2-segmented; maxillae simple spines; first and 



71937—32 27 



