COMPARATIVE MORPHOLOGY AND LOCOMOTORY COORDINATION OF THE TUBE FEET OF ICONASTER LONGIMANUS AND STELLASTER EQUESTRIS

Abstract

The suckered tube feet of Iconaster longimanus and Stellaster equestris were examined using light and electron microscopy. The structural organization of both starfishes follows that of a typical asteroid tube foot. The Stellaster tube foot, however, differs from that of Iconaster in terms of the thickness of the mucles and the connective tissue layer, and also in the distribution of the secretory granules in the tube foot epithelium. The unusual motion of the Stellaster and the coordination of its tube feet movement were also observed using video recording system. A large majority of the Stellaster tube feet were observed to beat in synchrony in the same direction, producing a sudden rapid motion measured at 0.87 cms-1, resulting in a discontinuous movement. This is not reported in any literature on asteroid mode of locomotion. The Stellaster tube feet were also observed not to be firmly attached to the horizontal substratum during the stepping process. It is postulated that the morphology of the Stellaster tube feet and its mode of locomotion could be an adaptation to its muddy environment.