FISHERY BULLETIN: VOL. 84, NO. 2 



Leg 2 (Fig. 9c).— Endopod showing sexual dimor- 

 phism in having variable nodose outer margin on 

 second segment (Fig. 9d, e, f). Number of nodes from 

 4-6, and not always same in 1 individual, as in Fig. 

 9d, e 



Leg 5 (Fig. 9g, h).— Resembling that of female 

 Second segment in 2 individuals 101 x 47 /mi (Fig. 

 9g) with 4 major elements from proximal to distal 

 45, 42, 80, and 78 /mi, and 86 x 42 M m (Fig. 9h) with 

 elements 22, 26, 65, and 73 /mi. 



Leg 6 (Fig. 9i).— Represented by single smooth seta 

 49 /mi and adjacent group of small spines on corner 

 of genital area. 



Spermatophore (Fig. 9j).— Elongate, approximately 

 220 x 78 /mi without neck. 



Color— As in female 



DISCUSSION 



This study permits certain observations to made 

 concerning the postnaupliar development of Leptino- 

 gaster major. A summary of these is given in Table 3. 



1) All five copepodid stages are present in the 

 mantle cavity of My a arenaria. 



2) The presence of Copepodid I in Mya suggests 

 that either the last nauplius molts outside the clam 

 and then enters, or that this nauplius enters the clam 

 and then molts. 



3) Copepodid I is SaphirellaAike in body form; 

 Copepodid II and later copepodids have a body form 

 more like the adult. 



4) The number of body segments increases from 

 5 in Copepodid I to 9 in the adult female and 10 in 

 the adult mala 



5) The armature of the caudal ramus remains 

 unchanged from Copepodid I onward, but the caudal 

 ramus lengthens in successive copepodid stages and 

 in the adults. 



6) The first antenna is slow in reaching final 

 form, being 5-segmented in Copepodid I and not 

 reaching its fully 6-segmented condition until the 

 adult. 



7) The second antenna has an indistinct fourth 

 segment in Copepodid I, but is clearly 4-segmented 

 thereafter. 



8) The labrum of Copepodid I is broad and or- 

 namented with spines, but in Copepodid II and 

 subsequently it is pointed and smooth. 



9) The mandible of Copepodid I is a simple 



blade, but in Copepodid II and succeeding stages 

 there are 3 terminal elements as in the adult. 



10) The first maxilla of Copepodid I is similar to 

 that of Copepodid II and following stages. 



11) The second maxilla has terminal setae in 

 Copepodid I but a terminal claw thereafter. 



12) The maxilliped in Copepodid I is elongate and 

 4-segmented with long setae but in Copepodid II and 

 Copepodid III it is small with 4 weak unarmed seg- 

 ments. From this point on, the maxilliped in the 

 female shows further reduction, while in the male 

 it undergoes enlargement and specialization. In the 

 female of Copepodid IV it is minute 2-segmented, 

 and unarmed; in Copepodid V and in the adult it is 

 reduced to 2 small setae In the male of Copepodid 

 IV the maxilliped is 3-segmented, pointed, with 2 

 setae; in Copepodid V it is 4-segmented, pointed, 

 with 3 setae; in the adult male it is 4-segmented with 

 a long terminal claw. 



13) The full complement of 4 biramous 3-seg- 

 mented legs is not reached until Copepodid V 



14) The inner spine on the basis of the endopod 

 of leg 1 first appears in Copepodid II. 



15) Leg 5 is absent in Copepodid I and Copepodid 

 II, is represented by 2 setae in Copepodid III, and 

 abruptly becomes 2-segmented with full armature 

 in Copepodid IV 



16) Sexual dimorphism in legs 1-4 occurs only in 

 the endopod of leg 2 in the adult male 



17) Sexual differentiation during copepodid 

 development first occurs in Copepodid IV, where 

 the male and female maxillipeds are differently 

 formed. 



The maxilliped in the adult female is said to be 

 absent in Leptinogaster histrio (Bocquet and Stock 

 1958; Bacescu and Por 1959), in the genus Myocheres 

 (Wilson 1950), in Leptinogaster inflata (Allen 1956), 

 in Leptinogaster scobina (Humes and Cressey 1958), 

 and in Leptinogaster dentata (Humes and Cressey 

 1958). The maxilliped has now been traced through- 

 out copepodid development, and it is apparent that 

 a remnant of this appendage exists in the adult 

 female of L. major. 



This discovery prompted a reexamination of adult 

 females of two species of Leptinogaster, L. scobina 

 and L. dentata. In both the maxilliped is represented 

 by two very small setae, as in L. major. It is not sur- 

 prising that these setae were overlooked, since they 

 are very minute and readily seen only in well-cleared 

 specimens. 



Although the remaining species of Leptinogaster, 

 L. histrio (Pelseneer, 1929), L. pholadis (Pelseneer, 

 1929), L. inflata (Allen, 1956), and a new species con- 



242 



