Abstract

Two methods are used to examine feeding strategies in graptoloids; the first profiles different sets of zooids on the colony, the second treats the colony as a whole. Both of these techniques have advantages. The choice between them brings into question our concepts of the degree of coloniality shown by graptoloids. Using a whole colony model, graptoloids can be shown to have sampled the water with variable efficiency, as defined in this paper. Planar forms were relatively inefficient, generally sampling less than 10 of the available water. Inclined forms frequently approached 75 efficiency. Biserial forms and straight monograptids routinely exceeded 100, sampling each unit of water more than once. Rotation of the rhabdosome during movement increased the efficiency of horizontal and inclined forms. It reduced the efficiency of scandent biserials and straight monograptids. These were both advantageous effects. Astogenetic changes in colony size and form would have had a profound effect on feeding efficiency. -Author