lafera/ 



f/age//um^ 



WHITE SHRIMP FROM THE GULF OF MEXICO 



rostrum^ 



31 



s 2nd anfennu/ar 



segment 



media/ , 



flagellurri'' 



3rd anfennu/ar / 



'antenna/ 



sca/e 



Segment ' 



Figure 17. — Enlarged view of left antennular flagella showing sexual modification to medial flagellum in adult male. 



the point of articulation with the antennal scale, 

 the second antennal segment is deeply notched an- 

 teriorly providing an articular foramen for the 

 large antennal scale. Strong dorsal and ventral 

 points of articulation, or condyles (figs. 18, 22, 23) 

 on the rim of the scale foramen permit the scale 

 considerable horizontal movement. As brought 

 out earlier, the great weight and strength of the 

 second antennal segment exists as support for 

 the antennal scale, rather than for the long, slender 

 antennal flagellum. The second antennal segment 

 articulates with the third antennal segment, or 

 ischiopodite, by a small foramen located ventro- 

 mesially (Hgs. IS, 23). The extent of movement 

 between the second and third antennal segments is 

 very limited. 



The third antennal segment (figs. 18, 23) is a 

 small, heart-shaped structure whose apex is di- 

 rected posteriorly. Its small vertical movement, 



at right angles to its long axis, against the second 

 antennal segment permits some rotation of the 

 distal antennal segments. Movements of the little 

 shield-shaped fourth antennal segment (figs. 18, 

 23) against the third antennal segment are, on 

 the other hand, extensive. The fourth antennal 

 segment attaches laterally to the third segment 

 at about a 45° angle. By means of a dicondylie 

 articulation, the fourth segment rotates through 

 an arc of nearly 90°, and with it the distal an- 

 tennal parts. 



According to Schmidt (1915), the third anten- 

 nal segment represents the fusion of the ischiopo- 

 dite and meropodite and he evidently has morpho- 

 logical support for this view in Astacus. Curi- 

 ously, no trace of a division is apparent in the third 

 antennal segment of Cambarus. nor does Berkeley 

 ( 1928) find one in the caridean Pandalus. No evi- 

 dence for the fusion of the ischiopodite and mero- 

 podite can be seen in /'< h<i< us setiferus. 



