SCOTTO: LARVAL DEVELOPMENT OF CUBAN STONE CRAB 



Table 5. — Taxonomically important characters of the sixth 

 zoeal stage in two species of Menippe. Data on M. mercenaria 

 taken from Porter 1 1960). 



indicates that his supposition may not hold for all 

 members of the genus, notably for M. nodifrons. 



Regardless of whether a sixth zoeal stage is a 

 laboratory artifact, the appearance of which seems 

 to be temperature-dependent, it is apparent that 

 larvae of at least two species of Menippe undergo 

 at least five zoeal stages. The ramifications of this 

 fact will be discussed below. 



Few other brachyuran species e.xhibit an incon- 

 sistent number of instars in their larval develop- 

 ment. Boyd and Johnson ( 1963) reported that out 

 of 20 species of brachyuran crabs observed by 

 Costlow, only two species, both Portunidae, exhib- 

 ited variation in the number of zoeal stages. The 

 phylogenetically primitive Portunidae have at 

 least seven and sometimes eight zoeal stages 

 iBookhout and Costlow 1974, 1977). The extra 

 stages resulted in reduced viability, with only a 

 few zoeae developing to megalopae. Boyd and 

 Johnson ( 196.3) also suggested that the sixth stage 



in some normally five-staged Brachyura is a result 

 of laboratory conditions because the extra stage 

 has never been found in the plankton. This sup- 

 ports Gurney's ( 1942) and Porter's 1 1960) conten- 

 tions that laboratory conditions produce aberrant 

 larval forms. However, Boyd and Johnson (1963) 

 also stated that extra stages might possibly occur 

 in nature under certain conditions. Now that lar- 

 vae of A/, iiodifrona are known it should be rela- 

 tively easy to identify a sixth stage zoea of this 

 species in the plankton based on criteria produced 

 earlier in my study. 



Plesiomorphy and Larval Development 



Lebour (1928) set forth the genus Portun us as 

 the most primitive of the Brachyrhyncha, based on 

 the following characters: many zoeal stages (up to 

 eight, Bookhout and Costlow 1977); telson with 6 

 long internal setae plus 3 lateral spines on each 

 furca, making 7 spines on each side, with 2 extra 

 pair of internal setae in later stages; knobs on the 

 second and third abdominal somites, those on the 

 third disappearing in later stages; and antenna 

 with a well-developed exopodite, about one-half as 

 long as the spinous protopodital process. 



Larvae of the western North Atlantic species of 

 Menippe also exhibit these characters, differing 

 only in the number of larval stages (up to six) and 

 in the retention of the knob on the third abdominal 

 somite. Larvae of the Cancridae, considered to be 

 more primitive than the Xanthidae (Rathbun 

 1930; Gurney 1939) and by some authors (Bor- 

 radaile 1907; Lebour 1928; Glaessner 1969) than 

 the Portunidae, also exhibit the primitive charac- 

 ters enumerated by Lebour for the Portunidae, 

 differing mainly in number of zoeal stages (five), 

 armature of the telson (2 lateral spines on each 

 furca), and possession of a knob only on the second 

 abdominal somite. 



Based on the assumption that a gi-eater number 

 of zoeal stages is a primitive character, I agree 

 with the phylogenetic arrangement of Rathbun 

 ( 1930 ) and Gurney ( 1939), both of whom placed the 

 Cancridae primitive to the Xanthidae but more 

 advanced than the Portunidae. However, in com- 

 paring the number of larval stages, the genus 

 Menippe shows a closer relationship to the Can- 

 cridae than to the Xanthidae. This relationship is 

 discussed below in light of additional larval 

 characters. 



Excluding Menippe. the laboratory cultured 

 genera of xanthids have four zoeal stages (e.g.. 



381 



