JACKSON ET AL.: KEY TO GENERA OF PENAEID LARVAE 



killed Artemia nauplii were added daily, to a 

 final concentration of 2-5 nauplii per mL. 



Larval samples were removed from the cul- 

 tures twice daily and preserved in 2% formal- 

 dehyde. At this sampling frequency, at least two 

 samples were taken from any substage. For mi- 

 croscopic examination the preserved larvae were 

 cleared in a polyvinyl alcohol solution to which 

 Chlorazol Black had been added (Perkins 1956), 

 and permanent slides both of whole animals and 

 of dissections were made in this medium. For 

 each larval substage described, at least five indi- 

 viduals were examined except where fewer 

 larvae in good condition were available (Tables 

 1, 2). Where possible, the larvae examined came 

 from different spawnings; otherwise, they came 

 from the same spawning but were taken at dif- 

 ferent times. 



Figures were drawn with the aid of a camera 

 lucida used on a Wild M20 compound microscope. 

 Measurements were made with a calibrated 

 ocular micrometer. Body length was measured 

 from the anterior border of the carapace (exclud- 

 ing the rostrum) to the posterior border of the 

 telson, excluding any spines, and carapace 

 length was measured to the posterior border of 

 the carapace, along the midline. 



RESULTS 



General development 



Atypopenaeus for))iosus and Metapenaeopsis 

 palniensis followed the normal development pat- 

 tern for penaeid larvae (Dall et al. in press): a 

 number of nauplius substages, three protozoea 

 substages, three mysis substages, and a series of 

 postlarva substages gradually leading toward 

 the juvenile form. While it may be possible to 

 identify unknown penaeid nauphi into gi'oups of 

 one or more genera, prehminary studies con- 

 firmed the findings of Cook (1966a) that reliable 

 generic identification of nauplii is not possible. 

 To increase the numbers of cultured larvae avail- 

 able for samphng in later substages, the nauplius 

 substages were not sampled and therefore are 

 not described. 



The protozoea I of both species was character- 

 ized by separate cephalothorax and abdomen, 

 undeveloped eyes (which may be visible beneath 

 the carapace), and a lack of uropods. Protozoea 

 II had stalked eyes and a rostrum, while proto- 

 zoea III had spines on a variable number of the 

 abdominal segments and separate uropods. 

 Mysis I lacked abdominal pleopods, mysis II had 



pleopods of a single segment, while the abdom- 

 inal pleopods in mysis III had two segments. 

 During the postlarval substages the pleopods 

 became setose and the pereopod exopods became 

 reduced. We have not attempted to describe 

 specific instars or molt numbers of the post- 

 larvae. Instead we have presented a single de- 

 scription which is representative of the first few 

 instars; it is based on larvae sampled within two 

 to three days of the first appearance of post- 

 larvae. Earlier or later instars will, of course, 

 differ in some respects. The most obvious 

 changes with age are that the length of the 2nd 

 antennal flagellum increases, the dorsal rostral 

 spines increase in number, the telson becomes 

 more pointed, the number of telson spines 

 decreases, and the number of telson setae may 

 increase. 



Atypopenaeus formosus 



The details of setation and segmentation for 

 the various appendages are given in Figures 1 to 

 7 and in Table 1. Only general features, and 

 those with some taxonomic significance, are de- 

 scribed in the text below. For each major stage, 

 the important features that do not vary between 

 substages are presented first, followed by a brief 

 description of the characteristics of each sub- 

 stage. 



PROTOZOEA. Second antenna 0.7-1.0 times 

 length of 1st in each substage. Setal formula of 

 2nd antennal protopod and endopod 1 + 2-1-2 

 [hereafter refen-ed to as the 2nd antennal for- 

 mula: the numbers of setae at the distal end of 

 the protopod (Fig. Idi), partway along the 1st 

 endopod segment (Fig. Id2), and at the distal 

 end of the 1st endopod segment]. Second anten- 

 nal exopod (Fig. Ids) with 9 or 10 setae along 

 inner margin, including those on distal segment. 

 Telson with 7+7 setae in each protozoeal sub- 

 stage. 



Protozoea I (Table 1, Fig. la) with pear- 

 shaped carapace, less than half of total length, 

 bearing a pair of frontal organs without over- 

 lying spines. Long labral spine present (Fig. 

 lb). Mandible asymmetry not yet pronounced, 

 each mandible having a single, freestanding 

 tooth between incisor and molar processes (Fig. 

 le). First maxilla (Fig. If) protopod with 2 

 lobes, epipod (Fig. Ifj) with 4 long setae; 2nd 

 maxilla protopod with 5 lobes (Fig. Ig). Seg- 

 mentation of 1st and 2nd maxillipeds indistinct 

 and variable (most common arrangement 



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