AN AUTORADIOGRAPHIC ANALYSIS OF MELANOGENESIS IN THE FIDDLER CRAB, UCA PUGNAX (S. I. SMITH)

¹ Division of Biological and Medical Sciences, Brown University, Providence, Rhode Island 02912 and Department of Invertebrate Zoology, Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. Autoradiographs prepared from whole mounts and sections of Uca pugnax epidermis labelled in vivo with ³H-tyrosine showed incorporation only into melanin granules within melanophores.

2. Incorporation occurred whether the pigment was in a concentrated (e.g., destalked crabs) or expanded (e.g, entire crabs—black background) condition.

3. Fiddler crab melanin granules appear spherical in light micrographs and have a mean diameter (±S.E.) of 0.98 µ±0.02.

4. The epidermis of the back of the fiddler crab shows two layers of melanophores, one lining the hemocoel basement membrane, the other lining the exoskeleton. This may be a result of the formation of the carapace as a fold from the maxillary segment. Melanophores and melanophore processes also are found in the spongy at intra-epidermal connective tissue.