JACKSON ET AL.: KEY TO GENERA OF PENAEID LARVAE 



Figure 19. — Abdomen of Macropetasma (a) mysis II, (b) 

 postlarva (redrawn from Cockeroft 1985) and Parapenaeus 

 (c) mysis 11, (d) postlarva (redrawn from Heldt 1938). Scale 

 = 0.1 mm. 



5(3) Telson with 8+8 spines 6 



Telson with 7+7 spines 7 



6(5) Thoracic sternal spine formula 0+0+ 



0+1 + 1 (Fig. 15a) Penaeus 



Thoracic sternal spine formula 0+0+ 

 0+1+0 (Fig. 15c) Trachypenaeus 



7(5) Thoracic sternal spine formula 0+0+ 



0+1+0 (Fig. 15b) Metapenaeus 



Thoracic sternal spine formula 0+0+ 

 0+1 + 1 (Fig. 15e) Atypoperiaeus 



DISCUSSION 



Previous Descriptions of Penaeid Larvae 



The only way to describe the morphology and 

 to be certain of the identity of penaeid larvae is 

 to rear them in the laboratory, beginning with 

 eggs from adults of known identity. Techniques 

 for inducing penaeids to spawn and for culturing 

 the larvae have been known for many years 

 (Hudinaga 1942). For the genera Penaeus and 

 Metapenaeus there are over 30 descriptions of 

 larvae whose identity is certain (Dall et al. in 

 press). Laboratory-reared larvae of other penae- 

 id genera, also commercially important, are less 

 well described. There are only a few useful de- 

 scriptions of any species of Parapenaeopsis 

 (Hassan 1984; Rao 1973), Parapenaeus (Heldt 

 1938; Pearson 1939) or Trachypenaeus (Pearson 

 1939; Kirkegaard 1969, protozoea I only), and 

 this study is the first description of any species 

 of Metapenaeopsis or Atypopenaeus based on 

 laboratory -reared material. 



Many workers have attempted to describe 

 particular species or genera of penaeid larvae, 

 based solely on planktonic material (see Dall et 

 al. in press, for review). However the morphol- 

 ogy of penaeid larvae undergoes major changes 

 between each stage: egg to naupUus, nauplius to 

 protozoea, and protozoea to mysis. Even be- 

 tween the protozoeal substages, changes are so 

 great as to defy any attempt to link one substage 

 with the next. A full larval life history cannot, 

 we believe, be accurately reconstructed from 

 larvae caught from the plankton unless at least 

 some substages are subsequently reared (as in 

 Pearson 1939). 



The presence of commercial fisheries for a cer- 

 tain species is also a poor guide to the identity of 

 larvae found in the same area. There may be 

 significant populations of penaeid genera present 

 that are not, for various reasons (small size, 

 untrawlable habitat), represented in commercial 

 catches. Larvae also have considerable potential 

 for advection up to 150 km (Rothhsberg 1982; 

 Rothlisberg et al. 1983b). 



In several older studies, workers based their 

 identification of larvae from the plankton on the 

 temporal or spatial distribution of the adult 



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