ASPECTS OF MALACOSTRACAN EVOLUTION

The outstanding success of the Crustacea Malacostraca is largely due to the tagmatization of the malacostracan body and its appendages, which has permitted the evolution of a wide spectrum of adaptations, particularly within caridoid taxa with series of specialized appendages. Non-caridoid ancestral malacostracans have not materialized, and recent proposals by Schram (Schram, F. R. 1986. Crustacea), according to which the Phyllocarida should be removed from the Malacostraca and transferred to a re-defined class Phyllopoda, was found to be built upon false premises. Manton (Manton, S. M. 1953.-Symposia of the Society for Experimental Biology 7: 339-376), discussing a hypothetical malacostracan ancestor, was of the opinion that in such an ancestor walking preceded swimming, an opinion which has received considerable support. This also implies that the Malacostraca were originally epibenthic, retaining a number of primitive features. The hypothetical `generalized malacostracan' envisaged by Calman (Calman, W.T. 1909. A treatise on zoology, Part 7, pp. 1-346) was also presumed to be epibenthic, representing what Calman called a caridoid facies, thereby emphasizing an important aspect of the eumalacostracan structural and functional plan.