In the region of La Spezia (Ligurian Sea, Italy), the bryozoan Schizoporella errata forms sizeable buildups, termed `giant colonies' or `compound colonies' by previous investigators. Buildups were encrusting (up to 40 cm wide) with flat or bumpy surfaces in an exposed site, and erect (more than 20 cm high) branching anastomosed structures in a semi-exposed and in a sheltered site. The buildup architecture was significantly different in the 3 sites, with higher vertical development and number of branches per dm(2) in the sheltered site. The internal structure of the buildups was also different: densely packed, extensive laminated sheets developed in the sheltered site; loosely packed, concentric sheets alternating with small cavities filled with sediment and shells of associated organisms were found in the semi-exposed and exposed sites. Functional groups could be recognised among the biota associated with S, errata buildups. The constructional pattern was interpreted as resulting from both interactions with other organisms and hydrodynamic conditions. While in the exposed site S, errata showed no vertical growth, in the sheltered site soft-bodied erect organisms formed the frame around which S. errata deposited a multilayered structure, which eventually caused the death and disappearance of the immured organisms. Breakage of branch tips by episodic disturbance and repeated binding through a complex array of budding patterns by S. errata resulted in tall buildups which preserved no trace of the soft-bodied organisms. Because of the role they played, these may therefore be defined as `ghost frame-builders'.