WHITE SHRIMP FROM THE GULF OF MEXICO 



103 



CARPOPODITE ADDUCTOR MUSCLE OF 

 FIFTH PEREIOPOD 



Figure 53 



In like fashion to the carpopodite abductor, the 

 carpopodite adductor muscle fibers originate on 

 a large area of the meropodite, but on the ventral 

 half of the article. The muscle inserts on a long 

 apodeme arising from the proximal portion of 

 the carpopodite, medial to the axis of the dicon- 

 dyles. Carpopodite adductor muscle contractions 

 serve to turn the carpopodite toward the bocty, and 

 in fact deeply on the meropodite. The muscle 

 might better be considered a flexor of the carpo- 

 podite. 



PROPODITE EXTEXSOR MUSCLE OF 

 FIFTH PEREIOPOD 



Figure 53 



The arrangement of the propodite muscles in 

 the carpopodite is very similar to that of the 

 carpopodite muscles within the meropodite. The 

 propodite extensor muscle originates over much 

 of the dorsal part of the carpopodite and inserts 

 on a long apodeme projecting proximally from 

 the base of the propodite. The apodeme is so con- 

 nected to the propodite that a pull on it extends 

 the propodite witli respect to the carpopodite. 



PROPODITE FLEXOR MUSCLE OF 

 FIFTH PEREIOPOD 



Figure 53 



The propodite flexor muscle opposes the action 

 of the propodite extensor muscle. The fibers of 

 the flexor muscle arise from the ventral surface 

 of the carpopodite and, like those of the extensor, 

 attach to a long apodeme of the propodite. This 

 apodeme arises from a position opposite to that 

 of the extensor apodeme. Contractions of the 

 propodite flexor muscle flex the propodite upon 

 the carpopodite. 



DACTYLOPODITE EXTEXSOR MUSCLE OF FIFTH 

 PEREIOPOD 



Figure 53 



The dactylopodite extensor muscle originates 

 along the lateral side of the propodite and inserts 

 on a long apodeme arising from the proximal end 

 of the dactylopodite. The muscle straightens the 

 dactylopodite on the propodite. 



DACTYLOPODITE FLEXOR MUSCLE OF FIFTH 

 PEREIOPOD 



Figure 53 



The dactylopodite flexor muscle bends the dac- 

 tylopodite upon the propodite. Like the extensor 

 muscle, the flexor lias multiple origins upon the 

 medial surface of the propodite. The muscle in- 

 serts on the long flexor apodeme of the dactylo- 

 podite. 



C. Abdomen 



Unlike the head and gnathothorax, the abdo- 

 men is almost entirely devoted to the propulsion 

 of the white shrimp. Except for slender com- 

 ponents of the gut, the gonads, and the nervous 

 and circulatory systems, the space within the ab- 

 dominal skeleton is filled with muscles, most of 

 them concerned with the powerful flexion of 

 which the animal is capable. The abdomen con- 

 sists of six segments, all of which bear append- 

 ages, and a posterior telson which does not. The 

 abdominal segments are attached to one another 

 by deep folds of thin articular cuticle which allow 

 each segment great freedom of movement with 

 respect to its neighbors and with the thorax. 

 Intersegmental connections in the abdomen are of 

 several types. The simplest and perhaps most 

 movable is that between the thorax and first ab- 

 dominal segment ( fia'. 59). Here, cuticular folds 

 of great depth reinforced by heavy muscles in- 

 ternally make ventral flexion possible between 

 these body tagmata. The junction is without 

 special, restrictive condyles, allowing extensive 

 lateral movements of the abdomen on the thorax 

 at this point. 



The junctions of the first and second, and of the 

 second with the third abdominal segments (fig. 

 59) are identical. Motion at these joints is limited 

 to flexion and extension by lateral condyles of simi- 

 lar design. In contrast, the joint between the 

 third and fourth adbominal segment differs from 

 those between the first three segments. This con- 

 nection is much simpler. The condyles are rather 

 loosely connected, affording flexion and extension 

 and a certain amount of lateral motion. The 

 fourth, fifth, and sixth abdominal segments arti- 

 culate with one another by means of two pairs of 

 identical condyles similar in their rigidity to those 

 between the first, second, and third segments, but 

 different in structure (see enlargements of con- 

 dylic structure, detail of articulation, fig. 59). 



