A Critical Look at the Idea of Terminal Molt in Male Snow Crab (Chionoecetes opilio)

Whether or not male snow crab (Chionoecetes opilio) undergo a terminal molt when they develop large chelae is reviewed. Evidence supporting terminal molt includes laboratory studies in which large-clawed animals failed to molt and field studies which failed to find large-clawed males with mouth parts indicating imminent molting. Both studies were poorly documented. The field studies were largely conducted during inappropriate seasons and molt status based on a questionable mouth part stage. There is also an unsubstantiated claim that large-clawed animals fail to form limb buds for limb regeneration during the next molt and an inconclusive study of the degeneration of the Y-organ. We present new data against terminal molt including capture of large-clawed males with internal carapaces indicating impending molts, capture of two large-clawed animals with mouth parts indicating active premolting, recovery of two tagged large-clawed animals which molted while at liberty, and that the largest small-clawed animals usually are not large enough to account (through growth in a single molt) for the largest of the large-clawed animals. Also, one large-clawed male reportedly molted in captivity. We conclude that the existence of a terminal molt in male snow crab is not proven.