Description of Stages 



Three stages are described below: mature 

 ovigerous female, immature adult female, and 

 female copepodid. 



Mature ovigerous female: — Body (fig. 1) 

 noncyclopoid, 1.51 to 2.92 mm. long, composed 

 of head, neck, trunk, and "tail." Head (fig. 2) 

 small, 0.46 by 0.71 mm., representing a fusion 

 of cephalosome and first pedigerous segment; 

 inflated dorsally, flattened ventrally (fig. 25), 

 and with two wide lobed wings laterally, which 

 in a fully grown adult female protrude beyond 

 anterior margin of cephalosome. Ventral sur- 

 face of head deeply invaginated at center, form- 

 ing a hollow disk (fig. 2) which is reinforced 

 anteriorly by rostrum and bases on first anten- 

 nae and posteriorly by flattened leg 1. Second 

 antennae, mouth parts, and maxillipeds found on 

 bottom of this disk. Rostrum (fig. 2) well de- 

 veloped, bearing some refractile points, two 

 sclerotic protrusions, and one fairly strong 

 hook pointing posteroventrally. 



Head jointed to trunk by a short neck (fig. 2) 

 which is formed by second pedigerous segment ; 

 this segment completely fused with head anteri- 

 orly. This portion of body highly variable in 

 length in diflferent individuals, fully extended in 

 some specimens and completely contracted in 

 others, leaving practically no space between head 

 and trunk. Trunk (fig. 1) made up of third and 

 fourth pedigerous segments, 1.54 by 1.31 mm., 

 nearly square, with rounded corners. Posterior 

 corners slightly produced on each side into one 

 dorsal and one ventral lobe (fig. 25), and a 

 third lobe produced from po.steromedial end of 

 trunk between two dorsal lobes. Four depres- 

 sions (fig. 1) on dorsal surface of trunk. "Tail" 

 (fig. 3) flattened, 0.17 by 0.26 mm., attached to 

 trunk posteroventrally (fig. 25), totally or par- 

 tially concealed by dorsal posteromedial lobe. 

 No appreciable segmentation seen in "tail," 

 which apparently represents a fusion of the 

 narrow fifth pedigerous segment, the circular 

 genital segment, and one small postgenital seg- 

 ment. Egg sac attachment area (fig. 4) well 

 developed, occupying about two-thirds of lat- 

 eral surface of "tail." Caudal ramus (fig. 5) 

 small, 23 by 20 ,i, armed with five short setules 

 and one long seta 114 ,* long. Egg sac elongate, 

 cylindrical; fully grown sac longer than body, 



containing numerous small eggs with a dia- 

 meter of 90 /!(. Many micropits on surfaces of 

 head and trunk, as shown in detail in figs. 2 

 and 4, penetrating deeply into sclerotic cover- 

 ing of body. 



First antenna (fig. 6) distinctly 5-segmented, 

 but second segment suggesting a division into 

 two segments. Armature on these five seg- 

 ments, from proximal to distal: 15 + 1 hook 

 (on ventral surface), 8, 3, 3, + 1 aesthete, and 

 7 + 1 aesthete. 



Second antenna (fig. 7) 3-segmented ; basal 

 segment longest, naked; second segment bear- 

 ing one seta. Terminal segment having sub- 

 terminally a rod-shaped process and one pec- 

 tinate, lamelliform process (fig. 8), and carry- 

 ing terminally three setae and five weak claws ; 

 several rows of teeth on posterior surface. 



Labrum (fig. 9) well developed, with fine 

 teeth on posterior free margin; labium weak. 

 Mandible (fig. 10) compo.sed of a large plate 

 produced into long process, armed with one 

 terminal masticatory process and one sub- 

 terminal, bilaterally denticulated spine. Parag- 

 nath (fig. 11) bearing setules, located postero- 

 medially to mandible. First maxilla (fig. 12) 

 a small rounded protrusion, located laterally to 

 paragnath, bearing four setae, one of which is 

 fairly long. Second maxilla (fig. 13) 2-seg- 

 mented, terminal segment armed with three 

 bilaterally denticulated spines. 



Maxilliped (fig. 14) powerfully developed, 

 indistinctly 3-segmented; terminal segment 

 strongly bent inward and almost perpendicular 

 to first two segments. Last segment sharply 

 pointed, with well-developed sclerites cutting 

 into ventral and posterior surfaces, thus mak- 

 ing these surfaces corrugated. In many speci- 

 mens, the terminal, pointed process, broken 

 when the parasite was removed from the host, 

 appeared as a blunt process. 



Formula of spines and setae on first four 

 pairs of legs as follows (Arabic numerals rep- 

 resent setae and Roman numerals spines) : 



LCK 1 



Leg 2 

 Leg 3 

 Leg 4 



Protopod 

 00 10 

 00 l-I 

 00 10 

 00 10 



Exopod 

 10 1-1 7 

 10 IIM-5 

 10 1111-5 

 10 III-5 



Endopod 

 0-1 0-1 5 

 0-1 7 



1 



1 



Leg 1 (fig. 15) strongly flattened, its setae 



290 



U.S. FISH AND WILDLIFE SERVICE 



