Data on worm-eating gastropod microhabitat use and abundance within microhabitats were collected along transects located on the Heron Island Reef crest between November 1975 and June 1978. All transects were placed parallel with the reef edge within the study area, which was 10-40 m wide by about 1,500 m long, bounded by a rim of coral and coralline algae to seaward and inshore by a rubble bank. The study area was approximately 50 cm above MLW, but remained covered at low tide due to runoff from the reef lagoon.A series of transects were sampled over a period of 4-8 weeks on three occasions: November 1975 (25 transects); June 1978 (20 transects); and June 1978 (20 transects). Each 10 x 1 m transect was divided into forty 0.25 m² quadrats, with 20 quadrats on each side of a 10 m chain. The first two samples were made during daylight low tides and the June 1978 sample was taken on night low tides. Within each transect an estimate of the substratum composition was made by recording the microhabitat type under every 10th link in the chain (17 cm between points). Gastropod use of these microhabitat types was recorded by noting the microhabitat type occupied by each snail, in addition to its species and shell length to the nearest 0.1 mm. All predatory gastropods found in and near the transects were collected in order to determine the gastropods' diets by faecal sample analysis. These gastropods were subsequently returned to within 30 m of their collection sites.Microhabitat resource use was quantified by calculating niche breadth and overlap estimates for all species with numbers of individuals not less than five. These estimates were calculated separately for the November 1975, June 1977 and June 1978 samples.