FISHERY BULLETIN: VOL. 71, NO. 1 



Maxilliped III biramous; exopodite two-seg- 

 mented, terminal segment being incomplete and 

 lacking setae. Endopodite with five segments; 

 segment 2 with 13 major marginal setae in 

 double row (7, 6); segment 3 with five or six 

 slender minor setae, outer margin, six major in- 

 ner marginals, and nine brush setae, inner mar- 

 gin; segment 4 with five major and three spike- 

 like brush setae, inner margin, 11 outer major 

 marginals, and 7 inner minor auxiliaries; seg- 

 ment 5 with five pairs of major feeding setae, 

 one or two pairs of minor terminal setae. 



Pereiopods well developed and functional. 

 Chelipeds large, swollen and bristly; two or 

 three prominent fixed spines on the anterior 

 margin of carpus. Three pairs of walking legs 

 similar in form and setation as figured. Perei- 

 opod 5 with 8 to 10 sickle-shaped setae and a 

 number of other bristles. 



Abdominal segments six in number, segments 

 2 through 5 with paired biramous pleopods bear- 

 ing setae as follows: 16 marginal setae on ex- 

 opodite; endopodite armed with four small hooks 

 and two setae. Chromatophores appear poster- 

 iorly in segments 1, 2, 3, 5, and 6. Segment 6 

 bears a pair of biramous uropods, the outer rami 

 each with about 19 plumose marginal setae and 

 the inner with 17 or 18 such setae. 



The telson has 15 or 16 major marginal setae. 

 Minor marginal setae are present between al- 

 most all major setae. The dorsal surface of the 

 telson is equipped with a number of very fine 

 short hairs arranged in approximate symmetry 

 as figured. Frontal margin of carapace as fig- 

 ured (Figure 13A). 



LARVAL DEVELOPMENT OF 

 PACHYCHELES RUDIS STIMPSON 



In the laboratory, only a single P. rudis larva 

 reared at 15°C and 33;^f salinity reached the 

 megalopa stage. Laboratory-reared material 

 was extensively supplemented with larvae from 

 the plankton for purposes of examination. 



Knight (1966) has dissected and accurately 

 described the two true zoeal stages of P. rudis. 

 She also adequately described the gross external 

 morphology of the megalopa stage. Owing to 

 high mortality in her cultures, she was forced to 



describe the larvae of this species on the basis 

 of very few specimens. In this study, numbers 

 of laboratory-hatched larvae surviving each 

 stage in cultures were comparable to numbers 

 obtained by Knight (1966), but the various 

 stages were extremely abundant in the plankton. 

 Knight's description of the species is expanded 

 here using this more plentiful material. 



PREZOEA 



Body form is the same as that described for 

 Petrolisthes cinctipes (Figure 2). Chromato- 

 phores occur as follows: one on either side of 

 the mouth; one posteriorly in abdominal seg- 

 ment 2 or between segments 2 and 3. This is the 

 least colorful of the species discussed here. 

 Knight (1966) does not mention a prezoeal 

 stage. 



ZOEA I AND II 



Table 2 indicates points in which the larvae 

 studied here diff"er from those described by 

 Knight (1966). Diff"erences are minor but are 

 included to establish a more accurate range of 

 variability for this species. 



MEGALOPA 



(Figures 13 and 14) 



Antennule biramous with three-segmented 

 peduncle. Dorsal ramus with six segments, seg- 

 ments 2 through 5 bearing 2, 2, 2, and 1 tier of 

 aesthetascs respectively. Aesthetascs are ar- 

 ranged 6, 6-7, 5-6, 3-4, 3-4, 2, 3 in tiers pro- 

 gressing distally. A single long plumose seta 

 is associated with the distal tier on segments 2, 

 3, and 4. Ventral ramus distinctly three-seg- 

 mented, the most distal segment being indis- 

 tinctly divided. Other setation and spination as 

 figured. 



Antenna long, slender, with three-segmented 

 peduncle; flagellum with 20 to 21 segments ; var- 

 iable numbers of fine hairs and bristles arranged 

 distally on most segments as figured. 



Mandible strongly sclerotized, partially cup- 

 shaped appendage with three-segmented palp; 

 distal segment of palp with about 13 terminal 

 spines as figured. 



214 



