female (0.32 by 0.51 mm.) is not much differ- 

 ent from that of the cephalothorax in the cope- 

 podid (0.31 by 0.42 mm.) ; the shape, however, 

 is markedly different. The expansion is seen 

 mostly in anterior corners, posterior subcorn- 

 ers, and the dorsal surface of the head. The 

 head of an ovigerous female (0.33 by 0.59 mm.) 

 differs from that of the immature adult female 

 chiefly in the more globular appearance of the 

 middorsal surface; it is not lengthened but 

 definitely widened. The metamorphosis in the 

 head involves changes in form from semicir- 

 cular to rectangular (in dorsal view) and from 

 slightly convex to globular (in lateral view of 

 the dorsal surface) . The amount of increase in 

 proportions of the head is about 10 percent in 

 the length and 45 percent in the width ; this 

 widening rather then lengthening during meta- 

 morphosis is due to the formation of the lateral 

 wings. 



The second and third pedigerous segments 

 are completely fused into a unit at the onset of 

 metamorphosis (fig. 21). This fused trunk is 

 then enlarged in three dimensions, the shape 

 (in dorsal view) changes from oval (as in fig. 

 21) to guitar-shaped (as in fig. 22) or nearly 

 circular (as in fig. 23) and then to squarish (as 

 in fig. 1 ) . The posterior lobes, three on the 

 dorsal and two on the ventral surface, are not 

 formed in the immature adult female. The four 

 chitinized platelets on the dorsal surface of the 

 thorax of the copepodid are retained through- 

 out metamorphosis. As these platelets are the 

 points of attachment of trunk muscles on the 

 tergum of the second and third pedigerous seg- 

 ment, they have not been elevated by the en- 

 larging action in the course of metamorphosis. 

 Thus, the four platelets form the bottom of the 

 "four pits" on the dorsal surface of the oviger- 

 ous female. The amount of increase in pro- 

 portions of the trunk is about 270 percent in 

 the length and 120 percent in the width. The 

 metamorphosis of the trunk, contrary to that 

 of the head, involves more lengthening than 

 widening. 



Specimens 4, 5, 6, 7, and 8 of table 2 have 

 trunks distinctly longer than wide; they look 

 like that in fig. 22. The remaining four speci- 

 mens (1, 2, 3, and 9) of the immature adult 

 females in the same collection have trunks 



nearly as long as wide and resemble fig. 23. In 

 the present state of knowledge, we can say only 

 that immature adult females have two forms. 

 Which form comes first in the process of meta- 

 morphosis is unknown. 



A comparison between table 2 and table 4 

 shows that the maturity of the females can be 

 judged by the size of the trunk, in addition to 

 the presence or absence of egg sacs. The trunk 

 is definitely longer and wider in ovigerous fe- 

 males than in immature adults, although the 

 size of the head overlaps broadly in the two 

 stages. 



The first ovigerous female in table 4 has 

 smaller body length, but a definitely larger 

 trunk, than the largest immature adult female 

 in table 2. As noted in the previous section, the 

 neck of this ovigerous female is unusually 

 shrunken ; therefore, body length alone is not a 

 good measure for determining the maturity of a 

 female. 



GEOGRAPHICAL VARIATION 



According to our present knowledge of para- 

 sitic copepods of fishes, Tucca impressus is para- 

 sitic exclusively on two families of fishes, Tetra- 

 odontidae and Diodontidae — especially the fishes 

 of the latter family (porcupine fish or boxfish) . 

 Our past records show that it is most abundant 

 on the fishes of the genus Chilomycterus (Dio- 

 dontidae) and always found either on the fins 

 or on the body surface. 



A certain degree of variation is observed in 

 the head and the trunk of the ovigerous females 

 collected from three different areas, namely the 

 west coast of North Atlantic Ocean, the Gulf of 



Table 4. — Measurements of smallest, largest, and eight 

 randomly selected ovigerous females taken from Chilo- 

 mycterus schoepfi off Cape San Bias, Fla., in the Gulf of 

 Mexico 



Specimen 

 number 



1... 



2 



3 



4 



5 



6 



7 



8 



9 



10 



Average, 



Head 



Mm. 

 0.29 by 0.50 

 .30 by 0.61 

 .33 by 0.55 

 .31 by 0.56 

 .31 by 0.64 

 .30 by 0.60 

 .35 by 0.56 

 .36 by 0.65 

 .38 by 0.59 

 .33 by 0.65 



Neck 



Mm. 



0.06 



.11 



.09 



.09 



Trunk 



•Tall" 



Mm. 

 1.30 by 0.95 

 1.10 by 1.22 

 1.12 by 0.93! 

 1.19 by 1.02i 

 .09;1.14by 0.87j 

 .08|1.33by 1.12 

 .10 1.30 by 1.40 

 .09|l.31 by 1.31 

 .11 1.28 by 1.48 

 .10 1.59 by 1.14 



0.33 by 0.59 0.09 1.24 by 1.17 0.17 by 0.26 



Mm. 



17by 0. 

 16by0. 

 17by 0. 

 18by0. 

 19by0. 

 18by 0, 

 18by 0. 

 18by 0. 

 16by 0. 

 18by 0. 



Egg 

 sac 



Mm. 



0.84 



1.29 



.75 



1.10 



broken 



broken 



1.34 



1.84 



broken 



1.41 



Total 

 length 



Mm. 

 1.38 

 1.51 

 1.54 

 1.59 

 1.68 

 1.71 

 1.75 

 1.77 

 1.78 

 2.02 



1.67 



CYCLOPOID COPEPODS OF GENUS TUCCA 



295 



