HAGEMAN, S.J.: Growth patterns and complexity in colonial (modular) organisms

Complexity in colonial organisms can be described in terms of the degree of integration of polymorphs (a collection of identical, independent individuals sharing a colony structure, vs. a highly integrated collection of specialized individuals whose interdependence results in a “super-organism”). A second level of complexity, independent of polymorphism, relates to the overall growth habit of the colony. Although properties of colonial growth can be reduced to mathematical functions or combined into holistic archetypal concepts, an intermediate approach to growth habit analysis has been developed for Bryozoa. Surprisingly complex and varied growth habits can be generated in colonial organisms from the arrangement of otherwise identical modules in a hierarchical motif (e.g. the joy of old fashioned Lego� blocks). The growth habits of bryozoans can be summarized in eleven fundamental characteristics, which describe the orientation of the colony and its occupation of, and placement in space: 1) Orientation relative to substrate; 2) Attachment to substrate; 3) Construction; 4) Arrangement of zooecial series; 5) Arrangement of frontal surfaces; and 6) Secondary skeletal thickening. and those character classes that describe the overall shape of the colony based on arrangement of modules: 7) Structural units; 8) Dimensions of structural units; 9) Frequency of bifurcation; 10) Dimensions of bifurcation; and 11) Connection of structural units. This classification provides a common ground for comparison of character states among varied bryozoan growth habits and allows for correlation among these states and specific environmental conditions in which they develop. In addition, these fundamental growth habit characters can be used to recognize, characterize and evaluate growth form groups in other modular organisms, i.e. some of the Ediacara biota.