Sweeper polyps of the coral Goniopora tenuidens (Scleractinia : Poritidae)

The massive coral Goniopora tenuidens can develop elongated "sweeper" polyp s. These are thought to be involved in aggressive interactions with neighbo uring benthic organ isms, like the sweeper tentacles of other corals. The c nidoms of sweeper polyps and ordinary polyps of G. tenuidens from the Great Barrier Reef were compared. Sweeper polyps had significantly greater densi ties of elongate holotrichous isorhizas (34577 +/- 3839/mg; mean +/- SD, n = 6) than ordinary polyps (936 +/- 371/mg; p < 0.05), while ordinary polyps had significantly greater densities of spirocysts (75994 +/- 15992/mg) tha n sweeper polyps (19469 +/- 7808/mg; p < 0.05). This suggests that sweeper polyps of G. tenuidens, like the sweeper tentacles of other corals, are mod ified for aggression, and that they probably act through nematocyst dischar ge. However, the scattered distribution of sweeper polyps observed on colon ies of G. tenuidens in the field suggests that sweeper polyps may have othe r functions.