Freshly hatched larvae of Callinectes similis Williams, the lesser blue crab, were reared to the first crab stage. Eight zoeal stages and one megalopa stage are described with particular reference to types of setae on appendages. Updated information on the development of the
commercial blue crab, Callinectes sapidus Rathbun, is also given, as well as similarities and differences between C. similis and C. sapidus. The zoeae of C. similis and C. sapidus are so similar that they can only be separated by a number of minor differences.
The dorsal spine of C. similis is significantly longer than that of C. sapidus in all zoeal stages. Other structures, such as the rostrum and antennae, are either longer in early zoeal stages of C. sapidus than in C. similis, or the structures of the two species
are not significantly different. In later stages, however, structures measured were generally significantly longer in C. similis than in C. sapidus. Also in later zoeal stages, there are generally small differences in setation of appendages. There are diagnostic differences
in lengths of parts of the claw of the first leg and setation of pleopods of the megalopa of the two species. There are also minor differences in the setae of the scaphognathite, in seta of the epipodite of the 3rd maxilliped and in aesthetascs of antennules of the two species.
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