HAVNKS:1'ANDAL11)AK. llll'I'OI.VTlDAK. ANDCRANGtWIDAE LARVAE 



and Williamson (1964), the seta is probably the 

 vestige of an exopodite; however, Williamson (1982) 

 regards it as a vestigial epipodite or pseudoepipodite. 



Maxillae 



Development of the scaphognathite (exopodite) of 

 the maxilla (Fig. IG) is related to development of the 

 larvae. Most species that lack precocious develop- 

 ment have a scaphognathite that is not lobed proxi- 

 mally and has only a few (usually < 12) plumose 

 setae only on its outer margin. The scaphognathite 

 gradually becomes lobed proximally in subsequent 

 stages, and the outer margin becomes fringed with 

 many plumose setae. In species with precocious 

 development, the scaphognathite is lobed proximally 

 and fringed with many plumose setae in Stage I. 



The number of plumose setae is sometimes used 

 for distinguishing Stages I or II of similar species. 

 For instance. Stage I zoeae oiPandalus horealis and 

 P. goniums are similar morphologically, and in these 

 species the scaphognathite has 12 and 5 plumose 

 setae, respectively. In later stages, however, the 

 number of plumose setae fringing the scaphogna- 

 thite becomes too great to be practical for distin- 

 guishing zoeae of similar species. 



Maxillipeds 



The number of natatory setae on the exopodite of 

 each maxilliped (Fig. IH-J) is helpful for distinguish- 

 ing Stage I hippolytid and crangonid zoeae from 

 Stage I pandalid zoeae. All Stage I hippolytid and 

 most Stage I crangonid zoeae have 4, 5, 5 natatory 

 setae on the exopodites of maxillipeds 1-3. In the 

 Pandalidae, all Stage I pandalid zoeae, except Pan- 

 dahis stenolepis, have ^ 8 natatory setae on the ex- 

 opodites of at least two pairs of maxillipeds. Stage I 

 P. stenolepis, however, cannot be differentiated from 

 Stage I hippolytid and crangonid zoeae based only on 

 natatory setae because Stage I P. stenolepis also has 

 4,5,5 natatory setae on the exopodite of each max- 

 illiped. 



The absence or reduction in numbers or size of 

 natatory setae on the exopodites of maxillipeds is 

 associated with markedly precocious development. 

 This is especially true for Pandalopsis coccinata, 

 Sclerocrangon boreas, and S. zenkevitchi. Each of 

 these species has only one zoeal stage before molting 

 to the megalopa. In P. coccinata, the natatory setae 

 are absent from the third maxilliped. In 5. boreas, 

 the number of natatory setae on maxillipeds 1-3 is 2, 

 3, 4, respectively; and the setae are reduced in size. 

 Sclerocrangon zenkevitchi zoeae do not have nata- 

 tory setae on the maxillipeds. 



Apparently, the absence or reduction in size of 

 natatory setae prevents zoeae from being planktonic. 

 Zoeae of S. boreas and S. zenkevitchi (collected at 

 sea) cling to the pleopods of the adult (Birshteyn and 

 Vinogradov 1953; Makarov 1968). Zoeae of P. cocci- 

 nnta are rarely, if ever, taken in plankton tows 

 (Kurata 1964a). 



Pereopods 



The presence of exopodites (Fig. IJ, ex) on certain 

 pereopodal pairs is an important morphological 

 character for identifying shrimp larvae. Exopodites 

 are present on pereopods 1, 1 and 2, 1-3, or 1-4, 

 depending on genus or species (Fig. IK-M). 



Species with unabbreviated development usually 

 develop an exopodite on each pereopod. In most 

 species with > 5 zoeal stages, the exopodites are 

 characteristically small, naked, and nonfunctional at 

 Stage I but functional (have natatory setae) at Stage 

 II or III. Development of exopodites on pereopods 

 tends to be suppressed in species with < 5 zoeal 

 stages. 



In the Pandalidae, species that have segmented 

 pereopods directed vertically under cephalothorax 

 (i.e., developed pereopods) in Stage 1- Pandalopsis 

 coccinata, Pandalopsis dispar, Pandnlus kessleri, 

 Pandalus danae, Pandalics hypsinotus, and Pari'- 

 d/ilus prensor- also have exopodites or vestigial exo- 

 podites on pereopods 1 and 2. Species that have 

 unsegmented pereopods directed anteriorly under 

 cephalothorax (i.e., undeveloped pereopods) in Stage 

 I -Pandalus tridens, P. stenolepis, P. borealis, P. 

 goniurus, and P. jordani -a\so have exopodites on 

 pereopods 1-3 (the exopodites are undeveloped in 

 Stage I and develop in later stages). An exception is 

 P. platyceros, which in Stage I has developed pereo- 

 pods and exopodites on pereopods 1-3 (Haynes 

 1980b). 



Of the Hippolytidae, only larvae of the genus 

 Lebbeus have developed pereopods in Stage I. 

 Lebbeus polaris has vestigial exopodites on 

 pereopods 1 and 2 in Stage I and on pereopod 1 in 

 Stage II. Lebbeus groenlandicus has vestigial exo- 

 podites on pereopods 1 and 2 in Stage I and no exo- 

 podites on pereopods in Stages II or III (Haynes 

 1978b, 1981). 



In the Crangonidae, most species with developed 

 pereopods in Stage I {Argis crassa, A. lar, A. deno- 

 tata, Sclerocrangon boreas, and S. salebrosa) are 

 either without exopodites or have rudimentary exo- 

 podites. An exception is S. zenkevitchi, which has an 

 exopodite on pereopod 1 in Stage I (Birshteyn and 

 Vinogradov 1953). 



261 



