WHITE SHRIMP FROM THE GULF OF MEXICO 



97 



The coxopodite remotor muscles act with some 

 power to turn the coxopodite rearward. 



COXOPODITE DEPRESSOR MUSCLE 

 OF FIFTH PEREIOPOD 



FlGCRF. 58 



The coxopodite depressor muscle arises from 

 phragmal material on the medial margin of the 

 ventral skeletal foramen entering the coxopodite 

 and runs to the medial margin of the coxopodite 

 (fig. 58). Apparently the muscle is able to lift 

 slightly the medial margin of the coxopodite, and 

 for this reason the structure has been named the 

 coxopodite depressor muscle. 



BASIPODITE LEVATOR MUSCLES 

 OF FIFTH PEREIOPOD 



Figures 55. 5G 



Four basipodite levator muscles are seen in the 

 fifth pereiopod of Penaeus. The two lateral leva- 

 tors constitute together a broad fan (fig. 55) 

 originating along the caudal margin of the coxo- 

 podite. They become narrow as they run to their 

 insertions on the lateral rim of the basipodite. 

 Two longer levators lying mesad of the lateral 

 levators originate in the dorsal apex of the coxo- 

 podite and run to heavy apodemal material com- 

 mon to the levator muscles. The basipodite leva- 

 tor muscles raise dorsally the basipodite and with 

 it the distal elements of the limb. 



BASIPODITE DEPRESSOR MUSCLES OF 

 FIFTH PEREIOPOD 



Figures 52, 53, 55 to 58 



The most important muscles of the fifth perei- 

 opod of Penaeus are the depressors of the basipo- 

 dite. Seven basipodite depressor muscles exist in 

 the limb. The first and second depressor muscles 

 are lateral (fig. 56). They take origins on areas 

 of the caudal margin of the coxopodite and insert 

 on the large common depressor apodeme of the 

 basipodite. The third depressor (figs. 55, 56) is 

 a large fan which originates broadly on the latero- 

 tergal plate of the body segment. The fourth 

 basipodite depressor (fig. 57), also fan-shaped but 

 narrower than the third, lies just mesad of the 

 third depressor muscle. It, too, has a broad ori- 

 gin on the pleural area. The fifth depressor is 

 a rather small muscle (fig. 58) which takes its 

 origin on medial phragmal material of the ven- 



tral skeleton. All of the foregoing five muscles 

 insert on the basipodite depressor apodeme. The 

 sixth and seventh depressor muscles (fig. 58) arise 

 on phragmal material on the medial side of the 

 ventral skeletal foramen and insert for some 

 length along the posteromedial rim of the basipo- 

 dite. The function of the basipodite depressor 

 muscles is to turn the fifth pereiopod ventrad, 

 providing support for the body. 



ISCHIOPODITE REDUCTOR MUSCLE OF 

 FIFTH PEREIOPOD 



Figure 53 



The ischiopodite reductor muscle has multiple 

 origins over a substantial area on the dorsal and 

 medial parts of the basipodite. It inserts on an 

 apodeme projecting from the ventral surface of 

 the ischiopodite. The muscle bends the ischiopo- 

 dite ventrad slightly and to some extent rotates 

 it, due to the oblique angle by which the basipo- 

 dite and ischiopodite are connected (fig. 52). The 

 muscle is not opposed by any other muscle. 



MEROPODITE REDUCTOR MUSCLE OF 

 FIFTH PEREIOPOD 



Figure 53 



Arising by multiple origins on the dorsal and 

 medial half of the ischiopodite, the meropodite 

 reductor muscle fibers insert on a small apodeme 

 on the ventral surface of the long meropodite, 

 proximally. The meropodite reductor bends the 

 meropodite ventrally a short distance. 



CARPOPODITE ABDUCTOR MUSCLE OF 

 FIFTH PEREIOPOD 



Figure 53 



The fibers of the carpopodite abductor muscle 

 originate over most of the dorsal half of the mero- 

 podite and insert on an extremely long apodeme 

 running nearly the whole length of the meropodite 

 along the midline. The length of pull of this 

 muscle and of its opponent, the carpopodite ad- 

 ductor, is very great. The long apodeme to which 

 it attaches arises from the proximal end of the 

 carpopodite, lateral to the condylic axis. The 

 muscle thus turns the carpopodite to a position 

 in which the axes of the meropodite and carpopo- 

 dite are in line. The carpopodite abductor mus- 

 cle easily could be described as an extensor. 



