Theoretical morphology of modular organisms: Geometric constraints of branch and dissepiment width and spacing in fenestrate bryozoans

Modeling fenestrate bryozoan colony form as analogous to a woven screen comprised of warp-elements (the branches) and weft-elements (the dissepiments) we show that actual fenestrate fenestellid and polyporid bryozoans occupy only a small region of the theoretically possible spectrum of meshwork geometries Entirely possible screen geometries, possessing low to intermediate branch densities and high to intermediate dissepiment densities, are not found in the fenestellids and polyporids. The observed empty region of morphospace is due to phylogenetic constraint, rather than geometric constraint, in that the zooids of fenestellid and polyporid bryozoans are exclusively found on the branches (the warp-elements) of the colony meshwork.