Male/Female Blue crab (Callinectes sapidus, USNM 1182904), left side (male) and right side (female). Above: male claw (left) and red female claw (right).
The practice of telling male and female blue crabs apart has been around for many decades, from school kids to experienced watermen. A male is a “Jimmy”, and has an “apron” (abdomen) pointed like the Washington Monument. A female is a “sook”, and has the “apron” rounded like the Capitol Dome, although there’s “Sally”, for those immature (adolescent) female blue crabs that don’t yet have a so rounded “apron”. But there’s no name (yet) for a blue crab that may show half of the Washington Monument and half of the Capitol Dome. However, this story has nothing to do with politics or teenagers, and instead everything to do with the importance of scientific collections.
When Mr. Mike Storm, General Manager of Shoreline Seafood Inc., Crofton, Maryland, and experienced seafood dealer, called IZ to offer a blue crab (Callinectes sapidus Rathbun, 1896) that he considered extremely rare because it was “half male and half female”, we knew it would be a valuable addition to our collections. Mike found the specimen in a batch of crabs from the Gulf of Mexico (possibly Louisiana), purchased by his company to be sold or consumed at their Shoreline Seafood market/restaurant. In over 20 years of handling blue crabs from various regions, Mike had only seen a crab like this only once before, and immediately thought it best belonged in a museum and research institution. This bisexual crab was still alive when Mike called, but by the time the IZ crew arrived 2 days later to accept and carry it back to IZ, it had died and the body placed in a freezer.
Underside of Blue Crab (Callinectes sapidus, USNM 1182904) showing both female (left side) and male (right side) shaped apron.
We are very grateful to Mike for preventing that his crab end on the table and stomach of one his clients, for indeed the specimen is a rare example of a bilateral gynandromorph Callinectes sapidus. It is now officially deposited under USNM catalog number 1182904, in the IZ alcohol-preserved crustacean collections at the Museum Support Center, and available for study. A bilateral gynandromorph is an animal that contains both male and female characteristics, one side female and other side male, both externally and internally, and each side is different even in having the male or female coloration. The cause of this condition can be traced to very early embryonic development (when the organism has only few cells), and when one of the dividing cells does not split its sex chromosomes normally. This produces one of the two cells with sex chromosomes that cause male development, and the other cell with chromosomes that cause female development.
While cases of bilateral gynandromorphs are not uncommon in insects, and have been recorded in birds, only rarely have specimens been reported in the scientific literature for brachyuran crabs. In fact, only one case of a bilateral gynandromorph has been published for Callinectes sapidus, when Sara V. Otto, a scientist from the Maryland Department of Natural Resources, recorded a specimen from a tributary of the Chesapeake Bay in 1979. A second specimen was found in 2005 by a watermen near Deltaville, Virginia, and given to the Virginia Institute of Marine Sciences, Gloucester (VIMS), although the case appeared only in news media or VIMS blog, and a formal report was apparently never published. Considering that blue crabs have been fished commercially for more than a century and that male and female crabs are easily distinguished, it must be concluded that bilateral gynandromorphism is extremely rare in this decapod species. This also makes Mike’s crab an extremely valuable specimen.
By Rafael Lemaitre and Karen Reed