82 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



CalUnectes has 16 muscles grouped into 15 muscle 

 types. 



COXOPODITE PROMOTER MUSCLE OF THIRD 

 MAXILLIPED 



Figures 46, 47, 48 



The coxopodite promoter muscle is a strong, 

 lozenge-shaped muscle (fig. 47, B) originating on 

 the pleural plate along the anterodorsal margin 

 of the muscle. The insertion is on the anterior 

 margin of the coxopodite ( fig. 46) . The promoter 

 turns the coxopodite forward and, since the distal 

 parts extend directly anterior, the latter are raised 

 against the other mouthparts. The promoter mus- 

 cles of Pandalus, Astaeus, and CalUnectes are the 

 counterparts of the coxopodite promoters in 

 Penaeus. 



COXOPODITE REMOTOR MUSCLES OF THIRD 

 MAXILLIPED 



Figures 4(5, 47 



The third maxilliped of Penaeus contains two 

 coxopodite remotor muscles. They are much more 

 powerful than the coxopodite promoter muscles 

 which they oppose. The remotors originate on the 

 the laterotergal plate dorsad (fig. 47) and insert 

 on the posterior margin of the coxopodite. They 

 turn the coxopodite caudad and thus the distal 

 elements ventrad as well as laterally. The larger, 

 lateral coxopodite remotor of Penaeus is fully 

 homologous with the remotors in the three crusta- 

 ceans to which we have referred. 



BASIPODITE LEVATOR MUSCLES OF THIRD 

 MAXILLIPED 



Figures 46, 47 



The two basipodite levator muscles that have 

 been found in Penaeus have different origins. The 

 short, stout lateral levator takes origin on the 

 anterolateral margin of the coxopodite and inserts 

 on the anterior margin of the basipodite. The 

 larger basipodite levator lies internal to the 

 smaller muscle. The origin of the former is on 

 the laterotergal plate and its insertion on the an- 

 terior rim of the coxopodite. The levators pull 

 the anterior side of the basipodite upward and 

 with it the distal maxillipedal elements. Three 

 levators of the third maxilliped are described in 

 Pandalus, Astaeus, and CalUnectes. Part of this 

 group is very likely homologous with the levator 

 pair in Penaeus. 



BASIPODITE DEPRESSOR MUSCLES OF THIRD 

 MAXILLIPED 



Figures 46, 47. 48 



Considerable variation from the pattern of the 

 depressor musculature of Penaeus is seen in the 

 third maxillipeds of Astaeus, Pandalus, and Cal- 

 Unectes. Schmidt and Berkeley describe two de- 

 pressors of the third maxillipeds of Astaeus and 

 Pandalus, whereas Cochran shows one depressor in 

 CalUnectes. By contrast, Penaeus has at least 

 four basipodite depressor muscles in the third 

 maxilliped, just as in the second maxilliped. 



The lateral basipodite depressor takes origin 

 on the posterolateral margin of the coxopodite 

 (fig. 47) and inserts, together with the other de- 

 pressors, on the large apodeme on the posterior 

 rim of the basipodite. Interior to the lateral basip- 

 odite depressor is a long, two-part depressor 

 muscle (fig. 47, B) originating on the laterotergal 

 plate mesad of the coxopodite remotor muscle. 

 This depressor joins the short lateral depressor 

 on the basipodite depressor apodeme. Immedi- 

 ately mesad of the long depressor lies a small, 

 flat basipodite depressor muscle (figs. 46; 47, A) 

 which originates on a medial apodeme of the 

 maxillipedal foramen and inserts on the basipo- 

 dite apodeme. The most internal basipodite 

 depressor muscle (figs. 46, 48) is a semicylin- 

 drical structure originating on medial phragmal 

 apodemes and inserting on the posteromedial edge 

 of the basipodite. 



The total action of the basipodite depressor 

 muscles is relatively powerful. By their contrac- 

 tions the basipodite and distal elements of the 

 third maxilliped are turned ventrad. The homol- 

 ogies of these muscles with those of Astaeus, 

 Pandalus, and CalUnectes are not entirely clear. 

 The depressor muscle a of Astaeus and Pandalus 

 is the same muscle as the innermost, medial basip- 

 odite depressor muscle in Penaeus. Undoubt- 

 edly, the depressor muscles Oj and b in Astaeus, and 

 «i, a 2 and b in Pandalus have counterparts in the 

 third maxilliped of Penaeus. but their exact rela- 

 tionships are difficult to determine. 



EXPODITE ABDUCTOR MUSCLES OF 

 THIRD MAXILLIPED 



Figures 46, 47 



Similar to the arrangement in the second maxil- 

 liped, the third maxilliped exopodite of Penaeus 

 is moved by 2 exopodite abductor muscles, 1 ex- 



