HAYNES: LARVAL MORPHOLOGY OF PANDALUS TRIDENS 



Stage I zoeae agrees in all essential aspects with 

 Ivanov's description. 



Larvae of P. tridens are similar to larvae of P. 

 borealis, P.goniiirus, P. jordani, and P. stenolepis: 

 all have poorly developed pereopods and exopo- 

 dites on pereopods 1-3 in Stage I. Larvae of P. 

 borealis (described by Haynes [1979]), and P. 

 goniurus (described by Haynes [1978]), andP.jor- 

 dani (described by Modin and Cox [1967]) are 

 readily distinguishable from larvae of P. tridens 

 by the lack of spines on the posterior margins of 

 the abdominal somites and by the rostrum, which 

 in early stages is spiniform and projects downward 

 rather than being sinuate and projecting upwards 

 as in P. tridens. In addition, the antennal scales of 

 larvae of P. borealis, P. goniurus, and P. jordani 

 are markedly shorter and wider than in larvae of 

 P. tridens. 



Zoeae of P. tridens described in this report are 

 most similar to zoeae ofP. stenolepis described by 

 Needier (1938), especially in Stage L In Stage I 

 zoeae of both species the carapace bears denticles, 

 the abdominal somites are fringed with spines, 

 and the antennal scale is relatively long and nar- 

 row. The Stage I zoeae of these species differ: the 

 carapace and abdominal somites of Stage I zoeae of 

 P. stenolepis are flared laterally, and the antennal 

 scale bears 9-12 plumose setae; the carapace and 

 abdominal somites of Stage I zoeae of P. tridens 

 are not flared, and the antennal scale bears 17 

 plumose setae. Also, the telson of Stage I zoeae of 

 P. stenolepis is considerably wider and the posteri- 

 or margin more emarginate than the telson of 

 Stage I zoeae of P. tridens. Other morphological 

 differences between zoeae of the two species are 

 the antennal flagellum and rostrum. The antennal 

 flagellum in all zoeal stages of P. stenolepis is 

 longer than the antennal scale; the antennal 

 flagellum of zoeae of P. tridens remains shorter 

 than the antennal scale through at le^st Stage V. 

 The rostrum of P. stenolepis zoeae is as long as, or 

 longer than, the carapace and bears teeth as early 

 as Stage II; the rostrum of P tridens zoeae remains 

 shorter than the carapace as late as Stage VII and 

 does not bear teeth until Stage IV. 



The morphology of Stages I-VII zoeae of P. tri- 

 dens from lower Cook Inlet confirms the opinion 

 llvanov 1971; Squires^) thatP. montagui tridens, 

 the Pacific subspecies of P. montagui Leach, 



'Squries. H, J. 1965. Decapod crustaceans of Newfound- 

 land, Labrador and the Canadian Eastern Arctic. Fish. Res. 

 Board Can., MS Rep. Ser. Biol. 810:1-212. Biological Station. 

 Nanaimo, B.C. V9R-.5K6. 



should be given the full specific rank of P. tridens 

 Rathbun 1902. Rathbun's (1902, 1904) separation 

 of the Pacific subspecies, P. montagui tridens, from 

 the Atlantic species, P. montagui, was based on 

 slight differences in adult morphology. For in- 

 stance, the rostrum of the Pacific subspecies was 

 lVi-1% times the length of the carapace compared 

 with P/s-l'/o times the length of the carapace for 

 the Atlantic species. Also, termination of the dor- 

 sal rostral spines of the Pacific subspecies was 

 behind the middle of the carapace rather than in 

 the middle or in front of the middle of the carapace 

 as in the Atlantic form. Squires' (see footnote 3) 

 conclusion that the Pacific subspecies should be 

 given specific status was based on coloration of 

 adults. Ivanov's (1971) conclusion was based on 

 morphological differences between Stage I larvae 

 of P. tridens from the Gulf of Alaska and Pike and 

 Williamson's (1964) description of Stage I larvae 

 of P. montagui from the North Atlantic. In Stage I 

 P. montagui the margins of the carapace and ab- 

 dominal somites are smooth; in Stage I P. tridens 

 the carapace bears pterygostomian spines, the an- 

 tero- and posterolateral margins of the carapace 

 bear denticles, and the posterior margins of the 

 abdominal somites bear minute spines. In P. tri- 

 dens, the rostrum is longer and the number of 

 setae and spines on the antennal scale is greater 

 than in P. montagui. Also, P. tridens larvae are 

 larger than larvae of P. montagui. My comparison 

 of the seven zoeal stages of P. tridens from Cook 

 Inlet with the zoeae of P. montagui raised in the 

 laboratory and collected from North Atlantic 

 plankton by Pike and Williamson ( 1964) confirms 

 the morphological differences found by Ivanov 

 (1971) for Stage I and shows that these differences 

 persist through later stages. 



SUMMARY OF PRINCIPAL 

 MORPHOLOGICAL CHARACTERISTICS 



Certain characteristics of larvae of pandalid 

 shrimp from the North Pacific Ocean change form 

 as the larvae develop. I discuss changes of these 

 characteristics and categorize the larvae by 

 number of stages. I also discuss the probable mor- 

 phology of larvae of Pandalopsis ampla Bate, P. 

 aleutica Rathbun, andP. longirostis Rathbun and 

 larvae tentatively identified as Dichelopandalus 

 leptocerus (Smith). 



Although the number of pereopods bearing 

 exopodites does not change during larval de- 

 velopment, the exopodites themselves degenerate 



637 



