PENAEIDAE. 



269 



Later Protozoaea forms (Fig. 123 A) which Claus (No. 8) 

 observed are chiefly characterised by the development of five 

 abdominal segments (a x -a b ) still hidden under the larval cuticle, 

 they also show a greater development of the paired eyes and the 

 division of the protopodite of the first antenna (1) into five joints 

 (a feature which recurs in the Protozoaea of Sergestes). The sixth 



Fig. 123.— Later larval stages of Penaeus (after Claus, from Lang's Text-hook). A, older 

 Protozoaea, dorsal aspect. B, thoracoabdominal region of a somewhat older larva with 

 rudiments of limbs, ventral aspect. C, Zoaea, ventral aspect. D, Mysis stage, lateral 

 aspect. 1, 2, first and second antennae; 3, mandible; U, 5, first and second maxillae; 

 J, II, III, first three maxillipedes ; IV-VIII, first five ambulatory limbs; (IV-VIII), five 

 posterior thoracic segments; (a^a,.), the six abdominal segments ; a t -a 6 , the six pleopoda ; 

 ab, abdomen ; en, endopodite ; ex, exopodite ; fr, frontal sensory organ ; /,, liver ; t, telson. 



abdominal segment is still fused with the telson. Besides the 

 rudiments of limbs already mentioned, the truncated rudiment of 

 the third maxillipede (III) can now be seen. 



The Zoaea which proceeds from the above (Fig. 123 B and C) 

 is marked by the development of the movable stalked eyes, and 



