MYSES 2(1) Dorsomedian spines not present on first five ab- 



( Fi 6 ) dominal segments Sicyonia 



Dorsomedian spine present on at least fourth and 



Carapace and abdomen with many spines; dorsal fifth abdominal segments 3 



organ present on dorsal surface of carapace 3 ( % ) Dorsomedian ine not ent on third abdominal 



Solenocera gegment 4 



Carapace and abdomen without many spines; r4 „. „„ ,. ... , . , 



F " ' Dorsomedian spine present on third abdominal 



dorsal organ absent -~> segment... ...5 



4(3) Lateral spine present on fifth abdominal segment; 



rostrum shorter than eye Trachypeneus 



Lateral spine not present on fifth abdominal seg- 

 ment; rostrum as long as or shorter than eye 

 a Xiphopeneus 



5(3) Dorsomedian spine on third abdominal segment 



elongate Parapenae us 



Dorsomedian spine on third abdominal segment not 

 elongate Penaeus 



POSTLARVAE 



(Fig. 7) 



1 Total length 6.0 mm. or less 3 3 



Total length greater than 6.0 mm 2 



2(1) Total length 6.0 mm. to 12.0 mm 5 



Total length 12.0 mm. to 25.0 mm 10 



3(1) No terminal spines on telson Sicyonia 



Terminal spines present on telson 4 



c 4(3) Medioterminal spines of telson longer than those 



adjacent to it Trachypeneus 



Dor5al0rg3n Medioterminal spine of telson equal in length 



^ „ to those adjacent to it Penaeus 



j/** '^^^-^fU^-l^- (s^ §{1) First abdominal segment with dorsal antero- 



U ^f"~f-^C~iz/r median spine Sicyonia 



**=. ~ First abdominal segment without dorsal antero- 



d ^K^^Z median spine 6 



6(5) Pterygostomian spine present; pleopods of fifth 

 abdominal segment with exopods and endopods 



of equal length 7 



Pterygostomian spine absent; pleopods of fifth 

 abdominal segment with endopods inferior to 



exopods 8 



7(6) Antennules round ; no cervical sulcus on carapace ; 



rostrum curved Parapenaeus 



Antennules flattened ; well-defined cervical sulcus 



present on carapace; rostrum straight. Solenocera 



8(5) Antennal spine absent or minute; if present, 



subrostral teeth also present . Penaeus 



Antennal spine very prominent; no subrostral 



teeth 9 



9(8) Rostrum shorter than eye Trachypeneus 



Rostrum longer than eye Xiphopeneus 



10(2) Rostrum usually with ventral teeth and shallowly 



compressed Penaeus 



Rostrum without ventral teeth and broadly 



compressed 11 



11(10) Pterygostomian spine present 12 



Figure 6.— Penaeid myses: a, Parapenaeus, Mysis I; Pterygostomian spine absent 13 



6, Penaeus, Mysis I; c, Sicyonia, Mysis I; d, Solenocera, 



Mysis I; e, Trachypeneus, Mysis I; /, Xiphopeneus, 3 Early Xiphopeneus postlarvae probably fall in the <6.0-mm. category, 



Mysis I . but none in this size range was noted during the study. 



PENEIDAE OF THE NORTHWESTERN GULF OF MEXICO 



