326 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 3. — First nauplius. (A) Ventral view. 

 (B) Lateral view. 



Newly hatched first nauplii resemble two spheres 

 joined at the middle (fig. 4), but shortly there- 

 after they completely unfold and become typically 

 pyriform (fig. 5). 



Viewed laterally, the anterior part is elliptical, 

 due to development of the labrum (fig. 3B) . This 

 structure is present at the point where the anterior 

 and posterior halves join and where the posterior 

 half is flexed ventrally. The body appears to be 

 divided into anterior and posterior parts with a 

 constriction between ; nevertheless, it is not truly 

 segmented. 



An ocellus, or "nauplial eye," is present near 

 the anterior end of the body. Posteriorly, there 

 is a dorsally flexed pair of furcal spines which 

 are approximately two-fifths as long as the body. 

 A small dorsomedian triangle-shaped spine 

 (fig. 3B) is present near the posterior end of the 

 body. 



Three pairs of appendages, natatory in func- 

 tion, are present : first antennae, second antennae, 



and mandibles. The antennae are considerably 

 larger than the mandibles. 



The first antenna is imiramous and finger- 

 shaped and is slightly more than three-quarters 

 the length of the body. It bears 2 short lateral 

 setae, 2 long terminal setae, and a third long seta 

 which appears to be terminal, but which actually 

 arises from the dorsal surface of the appendage. 

 The bud of a third tenninal seta is present. 

 "Short" setae measure less than 0.1 mm. in length, 

 "moderate" setae between 0.1 and 0.2 mm., and 

 "long" setae more than 0.2 mm. 



The second antenna is biramous, the exopod 

 slightly longer than the endopod and equal in 

 length to the first antenna. The endopod bears 

 2 short lateral and 2 long terminal setae. The 

 bud of a third terminal seta is present. The exo- 

 pod bears 3 long lateral and 2 long tenninal 

 setae. 



The mandible is biramous arid approximately 

 half the length of the first appendage. Each 

 ramus bears 3 long setae. All setae on the exopod 

 are terminal. Two of the setae on the endopod 

 are terminal, the third seta arises from a con- 

 striction in the appendage approximately four- 



FiouRE 4. — Photomicrograph of first nauplius immediately 

 following hatching. 



