FISHERY BULLETIN: VOL. 83. NO. 3 



Which pereopods have exopodites can differ for 

 different species of a genus. For example, the genus 

 Pandahis includes larvae that have exopodites on 

 pereopods 1 and 2 or 1-3 (Haynes 1980a). The genus 

 Eualus includes larvae that have exopodites on 

 pereopods 1-3 or 1-4 (Haynes 1981). Larvae of 

 Crangon typically have an exopodite only on 

 pereopod 1; however, larvae of C. franciscorum 

 angustimana have exopodites on pereopods 1 and 2 

 (Haynes 1980b). 



Abdomen 



The presence or absence of posterolateral spines 

 (Fig. lA, pi) on the abdomen is often an important 

 character for identif^'ing the families of caridean lar- 

 vae. Specimens of pandalid larvae from the northern 

 North Pacific Ocean do not have posterolateral 

 spines. Crangonid larvae, however, usually have 

 posterolateral spines on somite 5, except for larvae 

 of Sclerocrangon boreas and S. zenkeintchi (Birsh- 

 teyn and Vinogradov 1953; Makarov 1968). Larvae 

 of Hippolytidae also have posterolateral spines. 

 Posterolateral spines are present on somites 4 and 5 

 in Lebbeiis larvae and on somite 5 in Hippolyte lar- 

 vae, but are absent in Heptacarpus larvae. 



The number of abdominal somites with postero- 

 lateral spines is not always the same for all species of 

 a genus. For instance, Spirontocaris larvae and most 

 Eualus larvae have posterolateral spines on somites 

 4 and 5, or 5. In some species oiEualua, the postero- 

 lateral spines may be absent. 



Most pandalid and hippolytid larvae lack dorsal 

 spines or teeth on the abdomen. The only known 

 exception is Spirontocaris spinus, which has a 

 distinct dorsal tooth on the posterior margin of 

 abdominal somite 3 in the megalopa (Stage VI) (Pike 

 and Williamson 1961).^ 



Of the described crangonid larvae of the northern 

 North Pacific Ocean, only Crangon septemapinosa, C. 

 affinis, C. alaskensis, and C. franciscorum angusti- 

 mana have a dorsal spine (Fig. lA, ds) on somite 3 

 (Makarov 1967; Loveland 1968; Haynes 1980b). 

 Paracrangon echinata has dorsal spines on somites 

 1-5 (Kurata 1964b). 



Some zoeae have spinules on the posterior margins 

 of abdominal somites. These spinules are present in 

 zoeae of Pandaliis platyceros, P. tridens, P. steno- 

 iepis, Eualus suckleyi, E. fabricii, Argis crassa, A. 

 dentata, and Crangon communis. The number and 

 size of spinules decrease in later stages. 



*This spine is present in ail subsequent stages (juvenile and adult) 

 and should probably not be regarded as a larval character. 



Telson 



The shape of the telson is useful in determining the 

 stage of development of caridean larvae. For most 

 Stage I-III pandalid and hippolytid larvae, the 

 posterior margin of the telson is about twice the 

 width of the anterior margin. At about Stage IV, the 

 shape of the telson narrows posteriorly, and from 

 Stage IV on, the posterior margin of the telson is 

 noticeably less than twice the anterior width. Even- 

 tually, the telson narrows posteriorly, as in the adult. 

 Although the telson remains triangular in all stages 

 of crangonid larvae, it is somewhat narrower in the 

 megalopa or first juvenile stage than in earlier 

 stages. 



For caridean larvae with unabbreviated develop- 

 ment, the typical number of telsonic setae (Fig. 1 0, 

 ts) is 7 -I- 7 in Stage I and 8 -i- 8 in later stages. 

 These numbers of telsonic setae are seldom exceeded 

 in later stages and are often reduced by either loss or 

 transformation of certain pairs (usually pairs of 2 or 

 3) into small setae or hairs. 



A larger number of telsonic spines are more com- 

 monly associated with abbreviated development than 

 with unabbreviated development (Gurney 1942; Pike 

 and Williamson 1964), and this is generally true for 

 caridean larvae of the North Pacific Ocean. For ex- 

 ample, Pandalus kessleri, a species with four larval 

 stages, has 16 -h 16 telsonic setae in Stage I, and 

 Pandahpsis coccinata, a species with three (or two) 

 larval stages, has 28 + 28 telsonic setae in Stage I 

 (Haynes 1980a). Examples can also be found in the 

 other families of Caridea. In the Crangonidae, 

 Sabinea septemcarinata has 16 -(- 16 telsonic setae in 

 Stage I and three larval stages, whereas Sr/frorraw- 

 gon salehrosa has 22 + 22 telsonic setae in Stage I 

 and one larval stage (Williamson 1960; Makarov 

 1968). In the Hippolytidae, Lebbeus polaris has 9 + 9 

 telsonic setae in Stage I and four larval stages; L. 

 groenlandicus has a total of 21 telsonic setae in 

 Stage I and three larval stages (Haynes 1978b, 

 1981). 



All larvae of Hippolytidae except larvae of the 

 genus Hippolyte have an anal spine (Fig. 10, al). For 

 Hippolyte larvae, the anal spine is absent in all 

 described stages. When pandalid and crangonid lar- 

 vae have unabbreviated development, the anal spine 

 usually appears at about Stage II in pandalid larvae 

 and about Stage IV in crangonid larvae. 



However, the presence of an anal spine has little 

 value in the identification of pandalid and crangonid 

 larvae with abbreviated development. In pandalid 

 larvae with abbreviated development, the anal spine 

 first appears at different stages in different species. 



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