1923] 



Murphy: The Life Cycle of Oithona Nana 



453 



Figs. 4—5, camera lueiila drawings. Abbreviations: ant., anterior antenna; 

 ap., appendage. Fig. 4, nanplius stage 1, ventral aspect, X 700. Fig. 5, nanplius 

 stage 5, lateral aspect, X 212. 



Key to General Diagnostic Characters, Immature Stages, 

 Oithona nana 



Ai. Urosome present (fig. 2) Copepodid 



6 X . Urosome of 1 segment; 3 thoracic segments (fig. 3a) Stage 1 



b„. Urosome of 2 segments (partially fused in ?, fig. 2) ; 4 thoracic segments 



(fig. 3b) Stage 2 



6 3 . Urosome of 3 segments; 5 thoracic segments (fig. 3e) Stage 3 



h t . Urosome of 4 segments Stage 4 



6 5 . Urosome of 5 segments. 



c\. Anterior antennae reaching to anterior margin of third thoracic 



segment .' Stage 5 



c 2 . Anterior antennae reaching to posterior margin of third thoracic 



segment (fig. 2) Adult 



A 2 . Urosome absent (figs. 4, 5) Nauplis 



61. Body segmented. 



<\. Body with 3 pair of appendages Stage 3 



Cj. Body with 4 pair of appendages. 



d,. Thorax of 1 segment Stage 4 



(7,. Thorax of 2 segments (fig. 5) Stage 5 



c 3 . Body with 6 pair of appendages, 3 thoracic segments Stage 6 



&.. Body not segmented. 



c,. Anterior antenna with 3 bristles on distal segment (fig. 4 ant.) 



Stage 1 



<*.. Anterior antenna with 4 bristles on distal segment Stage 2 



