A series of field experiments was conducted in a shallow sandflat in Tampa Bay, Florida, to examine the relationship between the abundance and diversity of meiofauna and the architectural complexity of tube-caps constructed by the polychaete, Diopatra cuprea. Two groups of azoic tube-caps were utilized: 1) tube-caps collected from the field and defaunated in the laboratory or 2) tube-caps created in laboratory aquaria with azoic sediment under controlled conditions. Tube-caps were designated "high" or "low" complexity based upon the amount of shell hash incorporated into tube-cap structure, replanted into sediments at 2 sites during February–April 1982 and collected 1, 3, or 4 days later. Meiofaunal-size organisms quickly recolonized experimental tube-caps. Harpacticoid copepods (adults, copepodites, nauplii) and juvenile amphipods displayed repeatedly higher abundance on tube-caps of high architectural complexity compared to those with low structural characteristics regardless of origin of tube-caps. This effect varied over space and time for some taxa. Examination of copepod species patterns revealed higher numbers of 72% of species on high complexity tube-caps over the experimental period; this relationship was modified occasionally by depth and day of retrieval. Correlation analysis of taxa abundance vs. quantitative measurements of architectural complexity reiterated the experimental trends, i.e. both copepod species richness and abundance of meiofaunal crustaceans were significantly positively correlated with the architectural complexity (amount of shell hash) of tube-caps. Two additional experiments were conducted in November 1983 and March 1984 to further investigate one possible explanation for the abundance/complexity relationships of meiofauoa taxa and tube-caps. To test whether large amounts of shell in tube-caps provide refuges from predators, recolonization experiments were conducted in both predator exculsion and open sites. Higher densities of harpacticoid copepods were recorded on tube-caps with greater amounts of shell hash regardless of predator activity. It is concluded that tube-cap complexity strongly influences abundance/species richness of meiofaunal crustaceans but a decrease of predator effectiveness on tube-caps with high complexity cannot explain the observed abundance/complexity relationship. The results from this study coupled with previous investigations on meioepibenthic assemblages provide a unique scenario of factors which, by controlling tube-cap turnover and architectural complexity, influence meiofaunal community structure.