Hippocampus denise Lourie and Randall, 2003, one of the world’s smallest seahorses, was described from Indonesia and appears to be relatively widespread in the West Pacifi c (Lourie and Randall 2003). The widespread occurrence of this species has been recorded in books, dive magazines and on the internet (e.g. Kuiter 2000), and recently the occurrence of this species was reported from Holmes Reef (Coral Sea) based on samples collected, together with gorgonians Villogorgia sp. from a depth of ～100 m (Foster et al. 2012). Biological and ecological data on this species are, however, very limited as well as in situ observations of this species at such great depths.