FISHERY BULLETIN: VOL. 86, NO. 2 



"about 9 small spines" on the ischium of the third 

 maxilliped; we found no spines on M. adina or M. 

 mercenaria (Figs. 3B, 4B), but it is possible that 

 Kurata was referring to the acute borders of the 

 scalloped medial margin (our Figure 2A), in 

 which case the 2 species are similar. Spination of 

 the ischium of pereiopods 1-3 differs also; Kurata 

 described 5 or 6, 2 or 3, and 1 small spine on the 

 ischia of pereiopods 1, 2, and 3, respectively, 

 whereas we did not notice this condition in M. 

 adina or M. mercenaria (see Figures 3B, 4B). Fi- 

 nally, Kurata (fn. 4: pi. 74, fig. E) illustrated no 

 spines on the ventral surface of the fifth pereiopod 

 dactylus of M. mercenaria; these spines are obvi- 

 ous on both species (Figs. II, 4E). We found few 

 differences between megalopae of M. adina and 

 M. mercenaria. General morphology of the cara- 

 pace and chelipeds, spination of the dactylus of 

 the pereiopods, and setation of the pleopods 

 agreed almost exactly (compare Figures 3 and 4). 

 Ventral dactylar spines on the posterior walking 

 legs of M. mercenaria were not so serrate as in M. 

 adina and were sometimes armed with only 2 or 

 3 large spinules rather than the numerous spin- 

 ules seen in M. adina (e.g., Fig. 3D) and in the 

 more anterior legs of M. mercenaria (see Figure 

 3C, D, 4C). Also, in all but 1 of the 9 megalopae of 

 M. mercenaria examined there were 4 (rather 

 than 3) long serrate setae on the dactylus of the 

 fifth pereiopod (Fig. 4E). As in M. adina, one of 

 these setae was more serrate and concave than 

 were the other long setae (Fig. 4E, F). However, 

 we have not examined mouthpart morphology of 

 M. mercenaria in the detail in which we described 

 M. adina, and so it is possible that additional 

 characters will be found to separate these 2 

 species at the megalopa stage. 



The megalopa of M. adina is very similar to 

 that of M. nodifrons as described by Scotto (1979). 

 Although the 2 species differ in setation of some 

 of the mouthparts, this setation may differ from 

 side to side in a given individual. The salient 

 character that serves to separate megalopae of 

 these 2 species is the presence in M. adina of 4 

 stout serrate spines on the dactylus of pereiopod 

 5. Scotto (1979) figured only setae (and no spines) 

 on the dactylus of the fifth pereiopod in M. nod- 

 ifrons and the dactylar spines on other pereiopods 

 apparently are not serrate (Scotto 1979, fig. 9c, 

 pereiopod 3). 



The megalopa of M. rumphii described by 

 Kakati (1977) differs from that of M. nodifrons, 

 M. mercenaria, and M. adina in having a more 

 ovoid carapace with the rostrum only slightly de- 



flexed. Kakati did not describe the dactyli of 

 pereiopods 2-5 for M. rumphii, but his figure of 

 pereiopod 2 (1977:639, fig. 2, p. 50) does not show 

 stout ventral spines on the dactylus. Possibly 

 Kakati overlooked these spines; if not, the ab- 

 sence of these spines on pereiopod 2 would further 

 serve to separate the megalopa of M. rumphii 

 from those of A/, nodifrons, M. mercenaria, and M. 

 adina. All 4 species have been described as hav- 

 ing a rose-orange coloration in life. 



Although Rathbun (1930) and Monod (1956) 

 synonymized M. rumphii with M. nodifrons, de- 

 scriptions of the zoeal stages of M. rumphii and M. 

 nodifrons by Kakati (1977) and Scotto (1979), re- 

 spectively, show that larvae of the 2 species differ 

 considerably. In the first zoeal stage, M. rumphii 

 exhibits elongated posterolateral processes on ab- 

 dominal segment 5 that extend posteriorly to 

 more than half the length of the telsonal furcae, 

 which lack spines. The first zoea of M. nodifrons 

 has similar posterolateral processes but these do 

 not extend posteriorly beyond the fork of the tel- 

 son; the telsonal furcae bear 1 dorsal and 2 lateral 

 spines each. These differences are not apparent in 

 later zoeal stages, but their presence in the first 

 zoeal stage and the differences noted in the mega- 

 lopa stage may be reason to question the syn- 

 onymy of these 2 species. 



Xanthid larvae are known to be variable, and it 

 is often difficult to reconcile larval and adult 

 groupings based on morphology. Larvae of some 

 morphologically disparate (as adult) species are 

 very similar, whereas zoeal stages for species in 

 some genera differ markedly in their morphology 

 (see Martin 1984; Martin et al. 1984, 1985; Mar- 

 tin and Abele 1986). Because of the known mor- 

 phological variability of xanthid larvae, charac- 

 ters presented for taxonomic purposes here and 

 elsewhere (e.g., Martin 1984) must be used with 

 caution. 



It is not our intent to promote descriptions of 

 single stages in the life cycles of brachyuran 

 crabs. However, in those cases where a descrip- 

 tion of a single stage adds appreciably to our 

 knowledge of phylogeny (e.g.. Rice 1981b) or fills 

 a gap in the larval biology of a commercially im- 

 portant species complex (present study), we feel 

 such a description is justified. A detailed compari- 

 son of zoeal stages of the two species is planned for 

 the near future. 



ACKNOWLEDGMENTS 



We are grateful to D. H. Wilber and A. B. This- 



296 



