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- Title
The evolution of arthropodan locomotory mechanisms.
- Authors
Harding), S. M. MANTON (Mrs J. P.
- Abstract
The evidence was presented in Part 10 for the conclusions that the Onychophora, Myriapoda and Hexapoda comprise a separate arthropodan phylum, the Uniramia; that the myriapod classes have evolved in parallel from multilegged ancestors and not one from another; that the hexapod classes did not come from any myriapodan stock connected with the modern groups; and that the hexapod classes are independent, parallel evolutions from multilegged ancestors with little trunk sclerotization, descendant neither from each other nor from one sort of ancestral insect. Here in Part 11 are demonstrated the fundamental differences between the morphology and modes of action of a parapodium and a lobopodium. The latter could not have arisen from the former, but could have given rise to all types of uniramian limbs, together with their jointing, which differs in many ways from those of other arthropods. Consideration is given to the diversification of habits which must have occurred in the early terrestrial Uniramia and to those which set in later and led to the evolution of the extant classes. A diversification of feeding, locomotory and other habits must have taken place at a lobopodial stage in which considerable sclerotization first became established on the head. The trunk morphology and leg jointing in the various uniramian taxa could have arisen from animals with lobopodial limbs and little trunk sclerotization. A review is given of the data assembled in Parts 1 to 11 and of the conclusions reached concerning:- the mechanical uses of the haemocoel in evolving Uniramia and the essential features of the locomotory mechanisms, including:- the uses of trunk musculature; speeds of progression; the phase differences between the legs; the loading on the legs; segment numbers; etc. The relationships between the gaits used by the various Uniramia and their probable evolution are considered, together with an outline of the facilitating morphology. Finally the diversification of habits in the Uniramia is considered along with the morphological consequences. The detailed evidences of evolution of the Uniramia derived from the study of functional morphology far exceeds that derived from any other field. A comparison between the locomotory mechanisms and facilitating morphology of the Arachnida and Uniramia shows great differences. The usual fixation of the arachnid coxa on the body has led to a variety of subtle leg rocking mechanisms differing from those of the Uniramia and often secondary arrangements giving a promotor-remotor swing which are quite unlike those of the Uniramia. Arachnid gaits are different from those of Uniramia and show little variability. Stability is gained by arachnids in different manners from those in Uniramia and the parallel evolution of hexapody in the two groups results in marked differences.
- Publication
Zoological Journal of the Linnean Society, 1973, Vol 53, Issue 4, p257
- ISSN
0024-4082
- Publication type
Article
- DOI
10.1111/j.1096-3642.1973.tb00790.x