Planktonic larva of the starfish, Asterina pectinifera becomes competent to metamorphose once the attachment organs composing of the papillae and adhesive disk have formed in the brachioarms. This larva, which is defined as brachiolaria, begins to metamorphosis in response to aquarium filter pebble stones which mimic the environmental cue(s). The adult rudiment at this stage possesses five hydrocoelar lobes and spicules. During metamorphosis, each lobe branches to form juvenile podia. Larval spicules develop into the fenestrated plates and spines. Without metamorphic induction, the sibling larvae are increasing in size. Growth of the adult rudiment of those larvae is characterized by enlargement of five hydrocoelar lobes without branching and extension of spicules with a few bifurcations in their tips. These observations suggest that the phase of competent larva shifts from larval growth to juvenile formation in response to environmental cue(s).