66 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



be verified by histological work before a decision 

 on this interesting point can be made. 



3. MAXILLAE 



3a. First Maxillae 



SKELETAL ELEMENTS 



The first maxillae articulate with the ventral 

 gnathal skeleton at relatively large foramina 

 slightly caudad and laterad of the paragnathal 

 foramina (fig. 28, A). The medial lobes of these 

 accessory feeding organs fit closely to the pos- 

 terior surfaces of the paragnatha (fig. 30), and 

 thus project anteroventrally over the mouth from 

 the gnathal framework. 



Although the first maxillae is true appendages, 

 they are much modified for functional ends. The 

 body of the first maxilla is produced into several 

 lobes and a flagellum (figs. 29, 40). The flat 

 medial lobes are the proximal coxopodite and the 

 distal basipodite. The medial edges of these lobes 

 are covered with stiff hairs or spines, those on the 

 basipodite margin being especially strong. The 

 spines function to hold food particles. Laterally, 

 the coxopodite is produced into a rounded lobe 

 from which a tuft of large, plumose, sensory setae 

 project. Endites of the basipodite, including an 

 anterior three-jointed flagellum, extend antero- 

 laterally from the basipodite. Schmidt (1915) 

 considers the endites the endopodite. Various 

 lobes of the basipodite endites bear sensorial 

 hairs. A single large seta projects anteriorly 

 from the base of the flagellum. 



MUSCLE ELEMENTS 



The musculature of the first maxilla in Penaeus 

 appears substantially similar to that of other 

 Decapoda. Groups of muscles function to bring 

 the spinous gnathal margins of the appendage to 

 the midline in feeding. Other muscles open the 

 opposing gnathal parts and make various posi- 

 tion adjustments. Peneaus appears to have at 

 least 10 muscles and muscle groups in the first 

 maxilla, against 9 each for Pandalus, Astacus, and 

 Callinectes. 



COXOPODITE PROMOTOR MUSCLE OF FIRST 

 MAXILLA 



Figure 40 



The first maxilla coxopodite promotor muscle 

 (fig. 40) originates on a large sternal apodeme 



arising from the brachia between the first and 

 second maxillary foramina. This apodeme pene- 

 trates the substance of the endosternite. The 

 promotor muscle runs ventrolaterally to insert in 

 the lateral lobe of the coxopodite. Upon contrac- 

 tion, the muscle turns the first maxilla forward 

 and upward. The first maxilla coxopodite pro- 

 motor muscle in Penaeus is homologous with the 

 musculus promotor I maxillae of Pandalus, As- 

 tacus, and Callinectes. Berkeley, Schmidt, and 

 Cochran state that the promotor muscle origi- 

 nates on the head apodeme, or endosternite, in 

 the above three crustaceans, whereas in Penaeus 

 the area of origin of the promotor and other lat- 

 eral muscles is not directly on the endosternite. 



COXOPODITE REMOTOR MUSCLE OF FIRST 

 MAXILLA 



Figure 40 



Taking origin on the sternal apodeme some dis- 

 tance ventrad of the origin of the coxopodite pro- 

 motor muscle, the first maxilla coxopodite remotor 

 muscle (fig. 40) passes laterad to the lateral lobe 

 of the coxopodite. Contractions of the muscle 

 draw the first maxilla posteroventrad. The cox- 

 opodite remotor in Penaeus is the homolog of the 

 musculus remotor a or b I maxillae of Pandalus, 

 Astatcus, and Callinectes. In the latter three 

 forms, two remotor muscles are described. 



LATERAL COXOPODITE ADDUCTOR MUSCLE OF 

 FIRST MAXILLA 



Figure 40 



The first maxilla lateral coxopodite adductor 

 muscle (fig. 40) is a long, slender muscle originat- 

 ing on the laterotergal wall and running antero- 

 ventrally to a point of insertion on the medial re- 

 gion of the coxopodite. Contractions of the muscle 

 raise the first maxilla and turn the gnathal lobes 

 towards the midline. Berkeley and Schmidt 

 maintain that the lateral coxopodite adductors in 

 Pandalus and Astacus originate on the lateral 

 carapace. Despite this difference, the lateral cox- 

 opodite adductors in the latter forms are homol- 

 ogous with those of Penaeus. Cochran (1935) 

 finds in Callinectes a muscle termed by her the 

 posterior adductor muscle. This muscle is a pos- 

 sible homolog of the lateral coxopodite adductors 

 in Penaeus. 



