The helical colony model has five basic geometric parameters (see McKinney and Raup 1982, figure 3). Two parameters determine the geometry of the central helix of the colony:

1. ELEV: the rate of climb of the helix (a measure of the repeat distance, or pitch, of the helix), and
2. RAD: the radius of the helix.
   Three parameters determine the geometric arrangement of the filtration-sheet whorls that are attached to the helix axis and the pattern of branching within the whorls:
3. ANG: the radial angle between the initial branches that originate from the central helix of the colony (a measure of the density of the initial branches in the core of the colony),
4. BWANG: the angle between the branches in the filtration-sheet whorls and the axis of the central helix of the colony, and
5. XMIN: the minimum distance between the outer two of three adjacent branches within the filtration-sheet whorls, at the point at which the central branch bifurcates. This parameter controls the frequency of branching, and hence the density of the branches, within the filtration-sheet whorls.
   

The geometric parameters ELEV, BWANG, and XMIN have been used to construct a three- dimensional morphospace of hypothetical helical colony forms in bryozoans (McKinney and Raup 1982), a morphospace that has subsequently been used in the analysis of actual helical colony forms in both extinct and living bryozoans (McGhee and McKinney 2000, 2002; McKinney and McGhee 2003, 2004).