26 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Hon, their mesial margins overlap beneath the an- 

 tennules. Movements of the antennules ventrad 

 are thereby prevented. In Panddhis and Astacus 

 the first antennular segments may be raised and 

 lowered about a transverse axis through the artic- 

 ular foramina of the antennules, in the sagittal 

 plane. That Schmidt (1915) in his study of 

 Astacus named the muscle a "promotor" is open to 

 question. The muscle might better be described 

 as a levator of the first antennular segment. 

 Berkeley (1928) and Cochran (1935) adopted the 

 terminology of Schmidt for this muscle in 

 Panda! us and Callinectes, although, in Cal- 

 linectes the musculus promotor I antennae ap- 

 parently moves the antennule toward the midline 

 of the animal. 



ANTENNULAR ADDUCTOR MUSCLE 

 Figure 14 



The antennular adductor muscle of the first an- 

 tennular segment originates on a vertically- 

 oriented apodeme arising from the ventromesial 

 region of the articular foramen between the anten- 

 nule and the protocephalon. The muscle courses 

 anteriorly along the mesial margin of the first an- 

 tennular segment, inserting in the cuticle at many 

 points along the mesial edge of the first segment 

 (fig. 14). The antennular adductor muscle func- 

 tions to turn the first antennular segment toward 

 the mid-sagittal line of the shrimp. 



The musculus remotor I antennae described by 

 Berkeley (1928) in Pandalus, by Schmidt (1915) 

 in Astacus, and by Cochran (1935) in Callinectes 

 are in all probability the homolog of the first 

 segment adductor muscle in Penaeus. In the case 

 of the former three animals, two musculi remotor I 

 antennae have been found in the antennule of each, 

 a remarkable uniformity in animals as distantly 

 related as these. Penaeus, too, has these muscles, 

 but the dorsal-most, discussed in the following 

 section, appears to have a function different from 

 that of remotion or adduction. 



DORSAL EYE BRUSH MUSCLE 



Figure 14 



The dorsal eye brush muscle, or prosartema 

 muscle, lies upon the adductor muscle of the first 

 antennular segment, and is almost certainly the 

 homolog of the musculus remotor b I antennae 

 found in the antennules of Pandalus, Astacus, and 



possibly of Callinectes. However, instead of tak- 

 ing part in the adduction of the first antennular 

 segment, the eye brush muscle in Penaeus serves to 

 stiffen the dorsal eye brush (figs. 12, 13). Fibers 

 of the muscle enter the eye brush at its point of at- 

 tachment to the first antennular segment, and their 

 contractions presumably enhance the function of 

 the brush as an eye cleaner. 



ABDUCTOR MUSCLE OF SECOND BASAL SEGMENT 

 Figure 14 



The second antennular segment is turned away 

 from the midline on its points of articulation with 

 the first antennular segment by contractions of the 

 abductor muscle of the second basal segment (tig. 

 14). This muscle originates on the anteroventral 

 part of the first antennular segment at about the 

 midpoint between the anterior margins of the seg- 

 ment. The muscle runs a short distance antero- 

 lateral^ to insert on a posterolateral apodeme of 

 the first antennular segment. 



The second basal segment abductor muscle of 

 Penaeus has a homologue in the musculus produc- 

 tor 2 I antennae of Pandalus, Astacus, and Cal- 

 linectes. although the use of the term "productor" 

 for the action of the muscle in Callinectes is ques- 

 tionable. In the blue crab musculus produc- 

 for 2 I antennae is said by Cochran (1935) to pull 

 the second antennular segment downward, indicat- 

 ing that the muscle functions as a depressor. 



ADDUCTOR MUSCLE OF SECOND BASAL SEGMENT 



Figures 14, 15 



The adductor muscle of the second basal seg- 

 ment originates ventrally in the anteromesial cor- 

 ner of the first antennular segment and inserts on 

 a small apodeme at the posteromesial corner of the 

 second antennular segment (figs. 14, 15). Contrac- 

 tion of the adductor muscle turns the second anten- 

 nular segment, together with the distal elements 

 of the antennule, toward the mid-sagittal plane 

 of the animal. The second basal segment adductor 

 muscle of Penaeus has a counterpart in the mus- 

 culus reductor 2 I antennae of Pandalus, Astacus, 

 and Callinectes. The muscle functions in Pan- 

 dalus and Astacus to depress the distal antennular 

 segments and flagella, while in Callinectes the dis- 

 tal elements are raised toward the midline by the 

 action of the musculus reductor 2 . The muscle 

 might better have been called a second segment 

 levator in the blue crab. 



