FISHERY BULLETIN: VOL. 83, NO. 3 



telson, excluding telsonic setae or spines. 



unabbreviated development -five or more zoeal 

 stages. 



undeveloped pereopod-unsegmented pereopod 

 directed anteriorly under cephalothorax. 



zoea- larva vi^ith natatory setae on maxillipeds, wfith- 

 out setose natatory pleopods on some or all abdom- 

 inal somites 1-5. 



Examination Procedure 



It is usually necessary to dissect the animal and 

 mount certain appendages on a slide before the iden- 

 tification characters can be used. Visibility of 

 segmentation is often improved by clearing speci- 

 mens for several days in 10% KOH or full-strength 

 lactic acid. Larvae can be dissected with pins 

 designed for mounting small insects. (The pins are 

 available from most biological supply companies.) 

 After dissecting the larva, place the appendage in a 

 drop of mounting medium (I use Turtox^ CMC red 

 mounting medium) and cover with a cover glass. 

 Gently press the cover glass to splay hairs and setae 

 and make them easier to examine and count. After 

 mounting the appendages, examine them using a dis- 

 secting microscope. 



GENERAL MORPHOLOGY OF LARVAE 



Pandalid, hippolytid, and crangonid larvae have 

 three major body regions (Fig. 1): head, thorax, and 

 abdomen. The head and thorax are coalesced and are 

 dorsally covered by a common, unjointed cephalo- 

 thoracic shield, the carapace. The body is divided into 

 19 true somites which, with their appendages (Fig. 

 1), are grouped as follows: 



1) The head, five indistinguishable fused somites, is 

 covered by the anterior portion of the carapace 

 (C) and has the first five pairs of appendages: 

 antennules (or first antennae) (AJ, antennae (A2), 

 mandibles (Md), maxillules (Mxj), and maxillae 

 (Mx,). 



2) The thorax is composed of eight somites that are 

 dorsally fused with, and covered by, the carapace. 

 Each somite has a pair of appendages: Somites 

 1-3 each have a pair of maxillipeds (Fig. lA, 

 Mxpi.;j); somites 4-8 each have a pair of pereopods 

 (Fig. lA, P,.5). 



3) The abdomen is composed of six somites (Fig. 1 A, 

 Si.^) and a terminal segment, the telson (T). The 



'Reference to trade name does not imply endorsement by the Na- 

 tional Marine Fisheries Service, NOAA. 



first five somites each have a pair of pleopods 

 (Fig. lA, Pl?.^). The sixth somite has uropods (U). 

 The uropods, when present with the telson, com- 

 prise the tail fan. 



CHARACTERS USEFUL FOR 

 IDENTIFICATION OF LARVAE 



Understanding the development of morphological 

 characters is necessary for identifying genus, 

 species, and stage of larval development. The follow- 

 ing discussion emphasizes the characters most useful 

 for identification. It should be noted, however, that 

 these characters are based on relatively few species 

 of a limited number of genera. For instance, in the 

 family Hippolytidae, the subterminal seta is ap- 

 parently absent in larvae of Hippolyte clarki from 

 British Columbia (Needier 1934) but present in lar- 

 vae of H. inermis and H. varians from European 

 waters (Williamson 1957a). The seta may also be 

 present in undescribed Hippolyte larvae from the 

 northern North Pacific Ocean. Characterization of 

 the family Pandalidae is based on only two genera, 

 Pandalapsis and Pandalus. In the northern North 

 Pacific Ocean, described larvae of these two genera 

 develop exopodites only on pereopods 1-2 or 1-3, 

 never on pereopods 1-4. Other genera of the family 

 (e.g., Plesionika) may develop exopodites on pereo- 

 pods 1-4 (Williamson 1957b). Additional descriptions 

 of decapod larvae from the northern North Pacific 

 Ocean will undoubtedly modify the morphological 

 characterizations given here. 



Rostrum 



In pandalid larvae, the rostrum (Fig. lA, r) is 

 always long (at least one-third the carapace length). 

 For most species of Pandalidae, the rostrum is styli- 

 form in Stage I and does not have teeth (Fig. lA, rt) 

 until about Stage III. The exceptions are Pandalop- 

 sis coccinata, P. dispar, and Pandalus platyceros. In 

 these species, the rostrum is curved in Stage I and 

 has teeth in all larval stages (Berkeley 1930; Kurata 

 1964a; Price and Chew 1972). In Stage I Pandalus 

 preTisor, the rostrum curves ventrally between the 

 eyes (Mikulich and Ivanov 1983). 



The rostrum of hippolytid larvae may be absent, 

 or, if present, from minute to long. The rostrum is 

 usually without dorsal or ventral teeth in all stages. 

 European specimens oiEualus gaimardii, an excep- 

 tion, have two dorsal rostral teeth in the last zoeal 

 stage (Stage V) (Pike and Williamson 1961). If the 

 rostrum is short to long in Stage I, it is also styli- 

 form, except in Stage I Lebbeus groenlandicus (Fig. 



258 



