76 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The second maxilliped is an active participant in 

 the process of feeding. 



SKELETAL ELEMENTS 



The coxopodite (fig. 44) of the second maxil- 

 liped projects ventrad from a region of the ven- 

 tral skeleton thta is much more heavily sclerotized 

 than are the corresponding areas anteriorly. The 

 foramen of the second maxilliped is surrounded 

 by several large sternal and laterotergal apodemes 

 upon which muscles originate. The whole struc- 

 ture is distinctly heavier than is that of the an- 

 terior gnathal appendages, in keeping with the 

 greater movability and strength of the second 

 maxilliped compared to that of the anterior acces- 

 sory mouth-parts. Projecting laterally from the 

 coxopodite is a small gill, the podobranchia (fig. 

 44), and a mitten-shaped mastigobranchia, or 

 epipodite. (See fig. 32.) The articular membrane 

 dorsal to the coxopodite bears two arthrobran- 

 chiae. 



The short, curved carpopodite is connected by 

 dicondyles between the meropodite and the pro- 

 podite placing the propodite laterad of the distal 

 end of the meropodite. The propodite is a short, 

 square article containing muscles operating the 

 heart-shaped dactylopodite on its distal end. The 

 dactylopodite lies laterad of the proximal part of 

 the meropodite, its apex nearly touching the 

 ischiopodite. The condyles between the carpopo- 

 dite and propodite and between the propodite and 

 dactylopodite are rotated 90° from the axis of the 

 condyles between the meropodite and the carpo- 

 podite. Thus the movements of the distal seg- 

 ments are at right angies to those of the proximal 

 segments. 



The coxopodite articulates with the basipodite 

 (fig. 44) by dorsoventral condyles which permit 

 extensive lateral movements. The coxopodite and 

 basipodite are said to be fused in Pandalus and 

 Astacus. To the basipodite is articulated the exop- 

 odite, a long, annular, plumose flagellum (fig. 

 44) that extends anteriorly and then curves grace- 

 fully laterad. The ischiopodite (fig. 44) is im- 

 movably fused to the basipodite in Penaeus. as 

 in Callinectes, but a fine line of light cuticle clearly 

 distinguishes the two articles. The meropodite 

 (fig. 44), the longest article of the endopodite, is 

 attached to the ischiopodite so as to allow the distal 

 segments limited movements from side to side 

 as well as up and down. This article projects an- 

 teriorly from the ischiopodite to a position be- 



neath the mandibles. Stiff spines on the medial 

 side of the meropodite opposing those on the 

 lateral side of the dactylopodite produce a func- 

 tional chela or claw. 



MUSCLE ELEMENTS 



The musculature of the second maxilliped of 

 Penaeus is substantially similar to that of Panda- 

 Ins. Astacus, and Callinectes, although Penaeus 

 has a larger number of discrete muscles. The sec- 

 ond maxilliped of Penaeus contains 14 types of 

 muscles including 23 muscles. Astacus has 15 mus- 

 cle types with 17 muscles. The second maxilliped 

 of Pandalus has 14 types of muscles and 16 dis- 

 crete muscles, whereas Callinectes has 16 muscle 

 types and 17 muscles. The classical muscle nomen- 

 clature has been changed slightly here as elsewhere 

 to conform to the appendage article in which the 

 muscles insert. 



COXOPODITE PROMOTOR MUSCLE OF SECOND 

 MAXILLIPED 



Figures 44, 45 

 Taking origin on a paraphragmal apodeme on 

 the lateral pleural wall, the coxopodite promotor 

 muscle passes mesad to insert in connective tissue 

 on the medial wall of the coxopodite. The muscle 

 turns the coxopodite, and with it the distal seg- 

 ments, anterior and dorsad. The musculus pro- 

 motor II pedis maxillaris of Astacus, Pandalus. 

 and Callinectes is homologous with the coxopodite 

 promotor muscle of Penaeus. 



COXOPODITE REMOTOR MUSCLE OF SECOND 

 MAXILLIPED 



Figures 44, 45 



The coxopodite remotor muscle originates on a 

 paraphragmal apodeme above the posterolateral 

 margin of the foramen and runs to an insertion 

 in connective tissue on the posterior wall of the 

 coxopodite. Its contractions turn the coxopodite 

 caudad and the distal elements ventrad. The 

 coxopodite remotor muscle in Penaeus is fully 

 homologous to the second maxilliped remotor 

 muscle in the other crustaceans mentioned. 



BASIPODITE LEVATOR MUSCLES OF SECOND 

 MAXILLIPED 



Figures 44, 55 



The basipodite levator muscles originate at two 

 different points. The medial portion is attached 



