EMERGENCE OF LIMB LIKE APPENDAGES FROM FINS IN CHAETOGNATHS

The origin of limbs represents a major problem in evolution. A number of benthic coastal chatognaths exhibit progressive stages of the acqui sition of one pair of appendages on the posterior half of tail by modi fying a part of their balancing fin. This situation is unique in anima ls and can throw light on this process in vertebrates. We suggest the following scenario. One species exhibits only appendages with numerous adhesive finger-like processes. In another species, the number of the latter decreases while an appendicular muscle appears at level of the ir insertion an the body wall. A last species exhibiting more complex appendages enabling it to raise the body in a vertical position has, i n addition, a further evolutionary novelty: 4 longitudinal bundles of raising muscle in the tail.