CONOR and CONOR: LARVAE OF FOUR PORCELLANIDAE 



legs, the fifth pereiopods, the telson and sixth 

 segment, and the frontal margin of the carapace 

 are as figured. 



DISCUSSION 



The four species whose larvae are described 

 here are the only porcellanids known (Haig, 

 1960) on the Pacific coast of North America 

 north of Bodega Head, Calif., and we have found 

 their larvae simultaneously in the plankton off 

 the central Oregon coast. Both preserved and 

 live zoea larvae of these four species can be read- 

 ily assigned to genus on the basis of the number 

 of long telson setae bearing conspicuous distal 

 spines and the nature of these spines (Table 3) . 

 Once live or freshly killed zoeae are separated by 

 genus using telson characters, individuals of the 

 congeneric species can be separated to species 

 on the basis of the distribution of the primary 

 red chromatophores. Zoea larvae from pre- 

 served plankton samples cannot be identified to 

 species easily once the chromatophores have 

 faded. The only other nonvariable character 

 found which distinguishes the species was max- 

 illipedal setal counts, and it is possible that 

 further study will indicate that these counts are 

 also variable. 



The two Pachycheles species diflFer in both 

 zoeal stages by a single seta on the inner margin 

 of segment two of the endopodite on maxilliped I 

 (Table 4). In addition, second zoea larvae of 

 these two species differ by a single seta on the 

 outer margin of endopodite segment 1 on max- 

 illipeds I and II (Table 4). Similar characters 

 separate the larvae of the two Petrolisthes spe- 

 cies. First zoeae differ by one seta on the inner 

 margin of segment two of the endopodite of both 

 maxillipeds I and II (Table 5). Second zoeae 

 of these Petrolisthes differ by a single seta on 

 the outer margin of the first segment of the 

 endopodite on maxilliped II (Table 5). Mega- 

 lopae of all four species can be readily differen- 

 tiated on the basis of cheliped form and other 

 finer characters (Figures 12-14). 



Available knowledge of the larvae of Pach- 

 ycheles species does not support Haig (1960) 

 who, studying adult animals, suggested that P. 

 rudis is most closely related to P. stevensii. A 



comprehensive comparison (Table 4) of the four 

 most similar larvae of the Pachycheles species 

 studied thus far does not definitely indicate such 

 a relationship. On the basis of larval form and 

 setal numbers, all four of the species are equally 

 similar. 



At this time too few porcellanid larvae have 

 been described to use larval characters to draw 

 firm conclusions about generic and specific rela- 

 tionships. There is however a need for means 

 to identify as closely as possible porcellanid zoea 

 larvae taken from the plankton in regions where 

 larvae of all of the porcellanid species have not 

 been reared. For all known porcellanid larvae 

 of established specific identity, we have listed in 

 Table 3 three morphological characteristics 

 which appear to assign porcellanid zoeae to ge- 

 nera or generic groups. The following discus- 

 sion evaluates the usefulness of these charac- 

 teristics in grouping presently known larvae 

 systematically. Planktonic larvae of uncertain 

 adult origin are included and grouped with 

 known larvae they most closely resemble, but 

 are not discussed further. Two New Zealand 

 porcellanids for which larvae have been de- 

 scribed, Petrolisthes novaezelandiae and P. elon- 

 gatus, have some unusual characteristics in both 

 the larval and adult forms which distinguish 

 them from all other porcellanids known. For 

 this evaluation, they are conditionally placed 

 with groups with which they share the larval 

 characters listed in Table 3. 



All presently known porcellanid zoeae can be 

 placed in one of three groups on the basis of 

 telson form. Lebour (1943) originally estab- 

 lished two of these groups (A and B, Table 3) 

 by distinguishing larvae of the genus Porcellana 

 from larvae of the genus Petrolisthes as the gen- 

 era were known at that time. Lebour's orig- 

 inal Petrolisthes type telson group (B, Table 3) 

 now includes all described species of the genera 

 Pachycheles and Megalobrachium and all but 

 one of the described Petrolisthes larvae, P. nov- 

 aezelandiae. Wear (1964a) has suggested that 

 the exceptional P. novaezelandiae be placed in 

 the genus Pisidia on the basis of both larval and 

 adult characters. Lebour's original Porcellana 

 type telson group (A, Table 3) now includes all 

 described larvae of the genera Euceramus, Poly- 



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