FISHERY BULLETIN: VOL, 69, NO. 1 



MYSIS II 



(Fig. 11) 

 Mean TL ^ 3-8 mm (3.3-4.2 mm) 

 Mean CL = 1.3 mm (1.2-1.4 mm) 



N = 11 



This substage can be distinguished from the 

 first mysis by the presence of unsegmented 

 pleopods and a spine on the antennal blade. 



The addition of a dorsal spine on the rostrum 

 is the only change in armature of the carapace 

 which now covers the entire thorax. 



The terminal branches of the first antenna are 

 almost equal in length. A developing statocyst 

 appears as a slight bulge near the base of the 

 appendage. 



Setation on the endopod of the second an- 

 tenna has been reduced to a single terminal seta. 

 The number of setae on the exopod has increased 

 to 18, and they occur along the medial border 

 and around the tip to the point of insertion of 

 a subterminal spine on the lateral margin. A 

 spine has been added to the terminus of the 

 protopod. 



The mandible has developed a small unseg- 

 mented palp. 



The exopod of the first maxilla is no longer 

 present; that of the second maxilla has increased 

 in size and now bears 13 setae. A seta now 

 arises from the protopod of the first maxilliped 

 at a point between the insertion of the endopod 

 and exopod. In addition to a seta on the distal 

 segment, the endopod of the second maxilliped 

 gains a fifth segment that does not possess setae. 

 The protopods of the third maxilliped and first 

 pereiopod have gained a seta. A single seta on 

 the basal segment is the only one present on the 

 three segments that have been added to the 

 endopod of the first pereiopod. Rudiments of 

 gills are present as small protuberances on the 

 bases of the protopods of the maxillipeds and 

 first pereiopods. 



The armature of the abdomen and uropods 

 is unchanged from the preceding substage. Ru- 

 dimentary, unjointed pleopods are present on 

 the ventral surface of the first five abdominal 

 segments. 



The telson has six pairs of terminal and two 

 pairs of lateral spines. 



MYSIS III 



(Fig. 12) 



Mean TL = 4.3 mm (3.9-4.7 mm) 



Mean CL = 1.4 mm (1.3-1.5 mm) 



N = 21 



In this substage, the pleopods and endopod 

 of the second antenna are composed of two seg- 

 ments. These characters serve to differentiate 

 third mysis from preceding substages. 



Spination of the carapace remains essentially 

 the same as in Mysis II, although a second 

 dorsal spine on the rostrum was found in approx- 

 imately one-half of the preserved specimens. 



The outer branch arising from the distal seg- 

 ment of the first antenna is longer than the in- 

 ner branch and is composed of two segments. 

 A lateral seta has been added to the endopod 

 of the second antenna which is now also com- 

 posed of two segments; the exopod likewise 

 possesses one more seta. 



The mandibular palp is slightly longer and 

 has a weak apical seta. 



The first maxilla and first maxilliped remain 

 unchanged. The exopod of the second maxilla 

 has become elongate and has 18 setae, while 

 those of the second and third maxillipeds and 

 first pereiopod have two segments. The fourth 

 segment of the endopod of the second maxil- 

 liped has gained one seta, as has the exopod. 

 One seta has been added to the second segment 

 of the endopod of the third maxilliped and two 

 to the third; the fourth has lost one. The en- 

 dopod of the first pereiopod is composed of five 

 segments, with the fourth forming the propodus 

 of the chela and the fifth the dactylus ; the sec- 

 ond segment has gained one seta, and the third, 

 two. The gills on the maxillipeds and first pe- 

 reiopod have enlarged. 



The only change of consequence in the pos- 

 terior portion of the body involves the pleopods, 

 which are now composed of two segments and 

 bear two or three terminal setae. 



234 



