DeBrosse et al : Megalopal stages of Cancer oregonensis and C productus 



47 



with 62-72 marginal setae and 3-5 scattered surface 

 setae (not shown in illustration). 



First maxilliped (Fig. 3F) Epipod with 12-20 mar- 

 ginal and/or submarginal setae. Exopod 2-segmented, 

 pro.ximal segment with 3 or 4 marginal plumose setae 

 distally, distal segment with 4-6 terminal plumose 

 setae. Endopod with 1-3 marginal setae basally and 

 4-7 distally, 1 terminal seta; coxal endite with 15-19 

 plumose setae; basal endite with 28-38 plumose setae. 



Second maxilliped (Fig. 3G) Epipod with 6-10 mar- 

 ginal setae; protopod with 1-7 scattered setae. Exopod 

 2-segmented, proximal segment with 1 or 2 marginal, 

 short spine-like setae, distal segment with 4 or 5 ter- 

 minal plumose setae. Endopod 4-segmented, merus 

 with 2-6 setae, carpus with 2 or 3 setae, propodus with 

 5-9 setae, dactyl with 3-5 submarginal setae and 4-6 

 terminal serrate setae. 



Third maxilliped (Fig. 3H) Epipod with 20-29 mar- 

 ginal setae. Protopod with 21-32 scattered plumose 

 setae. Exopod 2-segmented, proximal segment with 5 

 or 6 marginal setae, distal segment with 5-9 terminal 

 plumose setae. Endopod 5-segmented, ischium with 

 25-30 setae, merus with 11-14 setae, carpus with 

 12-17 setae, propodus with 12-16 setae, dactyl with 

 9-12 setae and 0-2 distinctly toothed bristles. 



Pereopods (Figs. 4B, C, E-G) Segments of all pereo- 

 pods with scattered short setae. Cheliped with ischium 

 armed with acute spine on ventrodistal margin, cutting 

 edge of fixed finger and dactyl each with 2-4 teeth. 

 Second pereopod with coxa and ischium each armed 

 with acute spine on distoventral margin (4D), ischial 

 spine smaller than coxal spine, dactyl with 5-7 spines 

 on ventral margin. Third pereopod with ischium fre- 

 quently armed with minute process on ventrodistal 

 margin, dactyl with 6 or 7 spines on ventral margin. 

 Fourth and 5th pereopods with coxae and ischia un- 

 armed, dactyls with 5-7 and 2-4 spines on ventral 

 margin respectively; dactyl of fifth also with 3 terminal 

 setae. 



Abdomen and pleopods (Figs. 3 A, 4H,I) Abdomen 

 six-segmented. Second pleopod with 3-5 and 3rd 

 through 5th each with 3 or 4 hooks on appendix inter- 

 nae. Exopods with 20-22, 21 or 22, 20-23, 18-22 

 plumose setae respectively. Uropods 2-segmented, 

 peduncle naked or with 1 basal marginal plumose seta. 

 Exopod with 12-13 plumose setae, endopod absent. 



Telson (Fig. 4J) Dorsal surface with 3 or 4 pairs of 

 short setae in midline distally, terminal margin usual- 

 ly slightly rounded, without marginal setae. 



Discussion 



Of concern to field biologists is the fact that larval 

 studies primarily report characters found in specimens 

 reared under laboratory conditions. Even though en- 

 vironmental conditions have been varied to ascertain 

 their influence on larval development, there often re- 

 mains a question as to the similarities of characters 

 reported for these laboratory-reared organisms and 

 those that would be found in naturally occurring popu- 

 lations of the same species. Although the megalopal 

 characters of Cancer oregonensis and C. productus 

 reported in this study were based upon specimens col- 

 lected from naturally occurring populations, counts for 

 some characters of C. oregonensis have been compared 

 with counts derived from laboratory-reared animals. 

 No appreciable differences were found between the two 

 populations; however, in carapace length, the labor- 

 atory-reared individuals fell in the lower half of the 

 length-frequency curve determined for the natural 

 population. 



As previously indicated, a number of differences be- 

 tween the megalopae of C. productus examined in this 

 study and those described by Trask (1970) have been 

 observed. Most obvious are the differences in setal for- 

 mulae for the coxal endite of the first maxilliped and 

 the epipod of the third maxilliped. Differences in anten- 

 nal setation were also observed; however, Trask did 

 not give a range for the number of setae occurring on 

 each article, thus overlap between C. oregonensis and 

 C. productus remains a possibility. Trask described the 

 endopod of the 3rd maxilliped as four-segmented; 

 however, five segments are clearly illustrated (1970, 

 Fig. 7i). Quintana and Saelzer (1986) suggested that 

 if the apparently contradictory descriptions of the 

 megalopal stage of Co nceranthonyi Rathbun presented 

 by Trask (1974) and Anderson (1978) were based on 

 correct identifications and observations, geographical 

 differences probably accounted for the great differ- 

 ences in the setation reported. A similar situation may 

 account for the differences in C. productus megalopae. 



Although Quintana and Saelzer (1986) recommend 

 the use of the antennal setation, as well as the seta- 

 tion of the epipods of the maxillipeds, for distinguishing 

 between Cancer megalopae, these characters cannot 

 be used to separate Puget Sound populations with any 

 degree of reliability. The antennal setation found in 

 C. oregonensis overlaps that reported for C. gracilis; 

 only the setae of the antepenultimate article differ 

 between C. oregonensis and C. productus. The setation 

 reported for C. magister that we have determined from 

 the figure presented by Poole (1966, Fig. 6C) differs 

 from counts made for northern specimens. With the 

 exceptions of larger numbers of setae on the epipods 



