134 NORSE 



Callinectes have sparse granules of low relief (C sapidus) or large 

 areas devoid of granulation (C. bocourti and C. maracaiboensis). 

 Callinectes, Arenaeus, Portunus, gind Cronius spp. from higher 

 salinities have carapaces adorned by more even, higher, or denser 

 granules; strong ridges; dense pile; or depressions. 



Portunids possess another antipredation mechanism, spininess, 

 for which variation in the degree of development may reflect similar 

 variation in predation pressure. Spines may stimulate the release of 

 improperly seized crabs or, failing that, may prevent the predator 

 from swallowing the crab. Indeed, Burnett and Snyder (1954) found 

 starved eider ducks with blue crabs lodged in their throats. With a 

 few exceptions, American portunids in equable climates are spinier, 

 having longer, sharper, and/or more spines, reaching maximum 

 development in deepwater species such as P. spinicarpus (Stimpson). 



Yet despite extrinsic and intrinsic evidence that predation 

 pressure (at least for islands) increases as physicochemical stress 

 decreases, regions with greatly differing human fishing pressures have 

 similar portunid replacement sequences along salinity gradients. This 

 may imply that Callinectes have evolved proximate antipredation 

 behaviors that still operate despite relaxed predation pressure (e.g., 

 avoidance of higher salinities or waters with lower concentrations of 

 terrigenous organics). Such behaviors may not be selected out 

 because portunids seem to have long larval lives (Costlow and 

 Bookhout, 1959; Bookhout and Costlow, 1974; 1977), and adults in 

 one place may have hatched hundreds of kilometers distant, where 

 predation pressures were not relaxed. Thus, in some areas, down- 

 stress distributions may be intrinsically limited in response to 

 predation pressures that no longer exist. 



Parasitism 



Parasites can be divided into two functional groups: endopara- 

 sites, which receive the benefits of host osmoregulation (if present) 

 and may be unaffected by salinity fluctuations of the host's 

 environment, and ectoparasites (in the broad sense, epibionts that 

 diminish the host's health), which must be as eurytopic as their hosts 

 to survive. Some Callinectes in Pacific Colombian river-mouth sites 

 had carapaces fouled with Balanus, but heavier incrustations of 

 Balanus, Chelonibia (another balanomorph barnacle), bryozoans, and 

 sabellid polychaetes occurred on Callinectes in shelf waters. Marine 

 portunid species were much freer of external fouling organisms. 

 Parasites living on the gills are also ectoparasites. I have found stalked 

 (lepadomorph) barnacles of the genus Octolasmis on the gills of all 

 common Jamaican and eastern Pacific Callinectes, particularly adult 



