KNIGHT: DEVELOPMENT OF EUPHAUSIA GIBBOIDES 



Calyptopis: Total length between midpoints of 

 anterior margin of carapace and posterior 

 margin of telson; carapace length from center 

 of anterior margin to distal point on posterior 

 margin excluding dorsal spine; carapace 

 width at widest point on anterolateral 

 margins; measurements exclude spinose 

 fringe of carapace and telson spines. 



Furcilia: Total length between midpoints of 

 anterior margin of carapace and posterior 

 margin of telson, the carapace measurement 

 excludes spines until median spine appears 

 and then is made from tip of spine, the telson 

 measurement excludes spines until develop- 

 ment of 1 terminal spine in last stage and 

 then is taken from tip of spine; carapace 

 length from posterior margin of orbit to distal 

 point on posterior margin excluding spine 

 in furcilia I; rostrum width at widest point 

 proximal to eyestalks, excluding spines; eye 

 height on cornea between upper and lower 

 lobes measured in lateral view. 



Juvenile: Total length as in last furcilia stage. 



The range, mean (x), and standard deviation 

 (SD) of each measurement with number of speci- 

 mens measured in) is given in Tables 5-8. 



Larvae were placed in glycerine for dissection. 

 The description of setation and form of appen- 

 dages is based on dissection of at least 10 speci- 

 mens of each developmental stage. The common 

 form of each appendage is figured; when the 

 setation varies within a stage, the number of 

 appendages v^dth each setation observed is given 

 in parentheses behind the number of setae. Only 

 changes in setation or structure from the preced- 

 ing stage are noted. Drawings were prepared with 

 a Wild M-20 microscope^ equipped with drawing 

 attachment. 



RESULTS 

 Developmental Stages 



The following larval forms of E. gibhoides 

 were found: nauplius phase, stages I, II; meta- 

 nauplius phase, one stage; calyptopis phase, 

 stages I-III; furcilia phase, stages I-VI. There 

 was no variation in the number of stages in 



nauplius, metanauplius, and calyptopis phases 

 or in the first half of the furcilia phase in which 

 stages are defined by the pattern of pleopod 

 development. In the later furcilia stages, usually 

 characterized by the sequential reduction in 

 number of terminal telson spines, dominant 

 and variant forms were found. The features used 

 to differentiate furcilia in the initial sorting 

 were: number and position of setose and non- 

 setose pleopods, form of antenna, number of 

 terminal telson spines, total length, and relative 

 abundance. The furcilia identified are listed in 

 Table 2. 



When representatives of each stage were dis- 

 sected and studied in more detail, two forms 

 of the furcilia with 3 terminal telson spines were 

 found; one was the dominant furcilia V and the 

 other an advanced form which was comparable 

 in size and development to the furcilia with 1 

 terminal telson spine. There also were two forms 

 of furcilia with 2 terminal telson spines; the 

 smallest was equivalent to furcilia V and the 

 largest to furcilia VI. The relatively large furcilia 

 with 2 and 3 telson spines considered to be var- 

 iants of furcilia VI lacked the 2nd (middle) pair 

 of posterolateral spines on the telson of the next 

 instar developing beneath the cuticle and pre- 

 sumably would be classified as juvenile after the 



Table 2. — The furcilia identified during initial survey. 



^Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



147 



