

FUSIFORM PREHENSILE t 



=mm^> 



Figure I. — Various liarpacticoid copepods to illustrate the extreme diversity in body shape. All variations of har- 

 pacticoid body shape are not illustrated, only the most common. In the key that follows, a body form designation (e.g. 

 fusiform depressed) follows each keyed out genus. Defmitions of the body forms are as follows: Vermiform — narrow, 

 wormlike; Cy/indrica/— almost linear, squared off cephalothorax, nonarticulated rostrum; fusiform com- 

 pressed — broadened in prosome, narrow in urosome, thoracic somites compressed together from anterior to posterior; 

 fusiform prehensile— just slightly broader in cephalon than thorax, almost linear in shape with prehensile (grasping) 

 first leg; comprcsserf— compressed laterally like amphipods; depressed— dorsoventrally flattened, very little tapering 

 anterior to posterior; fusiform depressed— dorsoventrally flattened; fusiform {nonprehensile)— just slightly broader in 

 cephalon than thorax; almost linear in shape, first leg not prehensile; fusiform — torpedo-shaped, cephalon narrowing to 

 broad point anteriorly, anterior of metasome wider than cephalon and/or urosome (restricted to the family Ec- 

 tinosomidae). 



the Harpacticidae, the Thalestridae, the Diosaccidae, 

 the Ameiridae, the Canthocamptidae, and the Laophon- 

 tidae, and not all of the genera in these families conform 

 to this body form. The sketches in Figure 1 are given as 

 generalizations and imply no more than that. 



There are usually significant morphological differences 

 between males and females of the same species. Besides 

 the male always being smaller than the female, the most 

 significant and consistent difference is in the structure of 

 the first two urosomal somites. In females these two 

 somites are coalesced into a double genital somite. In 

 some species the female genital somite(s) has a dorsal 

 suture, but this suture is never present ventrally. In 

 males these two segments are always distinctly 

 separated. Most males also have a geniculate antennule 

 (A,) with a swollen segment about midlength. This 



modified (from the female condition) antennule is used 

 as a grasping appendage during copulation. In most cases 

 the fifth leg is also sexually dimorphic. When it is 

 dimorphic, it is always smaller in the male than the 

 female and it may differ structurally as well. Additional- 

 ly, males usually have a minute pair of sixth legs on the 

 second urosomal .somite, which project laterally and dis- 

 tally as small setiferous knoblike lobes. The females lack 

 the sixth legs. Other body parts may also be sexually 

 dimorphic, e.g., the rostrum, some of the mouthparts, 

 legs 1-4. and the caudal rami, but there is no general rule 

 as to where the morphological changes will be. One ex- 

 ample of swimming leg dimorphism is shown in Figure 

 8. 



Many times males of a species are rare and most of the 

 taxonomically important features are based on female 



2 



