120 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



COXOPODITE REMOTOR MUSCLE 

 Figures 65 to 69 



The coxopodite remotor muscle, a broad up- 

 right fan, originates in fibrous connective tissue 

 attached to the tergum, the arched dorsal plate of 

 the abdominal skeleton, and inserts about an arc 

 which represents approximately the posterior 

 third of the coxopodite. The area of insertion of 

 this muscle is located on the proximal margin of 

 the coxopodite. Upon contraction the muscle 

 draws the posterior edge of the coxopodite dorsad 

 on the points of coxopodite articulation. The pull 

 is an efficient one. since the coxopodite remotor 

 contracts in an almost straight line. The con- 

 traction of the muscle thereby draws the distal 

 pleopod elements through an anterior-to-posterior 

 arc. 



Berkeley illustrates the muscle in her work on 

 Pandalus. Schmidt in Astacus and Hart (1952) 

 in Cambarm describe a coxopodite remotor muscle 

 (musculus remotor III pedis spurii) for each of 

 these species of crawfishes. On the basis of in- 

 formation presently available, the coxopodite re- 

 motor muscle of Penaeus is homologous with the 

 musculus remotor III pedis spurii of Astacus, 

 Cambarus. and Pandalus, although proof must 

 wait upon a comparative study of the nerves. 

 Cochran does not find a coxopodite remotor in 

 CaUinectes. 



COXOPODITE PROMOTOR MUSCLE 

 Figures 65 to 69 



The coxopodite promotor muscle originates on 

 the abdominal tergum anteroventrally to the coxo- 

 podite remotor muscle and inserts on the proxi- 

 mal margin of the coxopodite anterior to a line 

 through the lateral and mesial articulation points 

 at which the coxopodite articulates with the ven- 

 tral abdominal skeleton. Mechanically, the ac- 

 tion of the coxopodite promotor is much weaker 

 than are the contractions of the coxopodite re- 

 motor, since the coxopodite promotor is smaller 

 than the remotor and its area of insertion is much 

 closer to the proximal fulcra! line of the coxopo- 

 dite than is that of the remotor muscle. 



The coxopodite promotor pulls the preaxial 

 margin of the coxopodite dorsad. The distal 

 pleopod elements thus are drawn through an arc 

 anteriorly, in opposition to the action of the coxo- 

 podite remotor. The coxopodite promotor muscle 



has no exact functional counterpart in Astacus 

 and Cambarus. The only muscle in the. latter 

 animals which could be homologous with the 

 coxopodite promotor in Penaeus is the musculus 

 rotator dorsalis basipoditis II pedis spurii de- 

 scribed by Schmidt in Astacus and by Hart (1952) 

 in Cambarm. The fact that the dorsal rotator 

 muscle inserts on the basipodite in Astacus and 

 Cambarus argues against this conclusion. 



Berkeley describes a musculus rotator dorsalis 

 basipoditis III pedis spurii in Pandalus that is 

 very likely the homolog of the coxopodite pro- 

 motor muscle in Penaeus. despite the difference in 

 origin. However, her adoption of Schmidt's 

 name for this muscle is unfortunate, since the 

 musculus rotator dorsalis basipoditis in Pandalus 

 actually promotes the basipodite, rather than ro- 

 tates the pleopod. An appendage rotates about its 

 long axis, not about an axis transverse to the 

 appendage. 



Cochran describes a coxopodite promotor muscle 

 (musculus promotor coxopoditis I pedis spurii) 

 in the pleopod of the second abdominal segment 

 of CaUinectes, and possibly the muscle is homolo- 

 gous with the coxopodite promotor in Penaeus. 

 To remove from the realm of speculation a discus- 

 sion of muscles having similar functions in two 

 forms as distantly related as Penaeus and Cal- 

 linectes will require careful study of the nerves. 



COXOPODITE ADDUCTOR MUSCLES 



Figures 65 to 67, 69 



Two coxopodite adductor muscles are found in 

 the pleopod of the white shrimp. The lateral 

 coxopodite adductor muscle (figs. 65 to 67) is a 

 small, short muscle originating on the lateral 

 tergal surface and inserting on the dorsomedial 

 rim of the coxopodite. The muscle pulls the 

 mesial side of the coxopodite dorsally, and in so 

 doing brings the distal pleopod elements mesad. 

 The action of the lateral adductor muscle is rein- 

 forced by a second coxopodite adductor muscle 

 (fig. 69) located on the mesial side of the ventral 

 skeletal support. The mesial adductor originates 

 on a phragmal fold of the postcoxal sternum and 

 inserts on the dorsomedial margin of the coxopo- 

 dite. 



The lateral coxopodite adductor muscle has 

 been lost in the Astacura to which reference has 

 been made, but appears in CaUinectes as the 

 largest muscle in the blue crab pleopod. The 



