Brooding of pelagic‐type larvae in Ophiopeza spinosa: reproduction and development in a tropical ophiodermatid brittlestar

.Ophiopeza spinosa , a small ophiodermatid ophiuroid, is locally abundant in shallow water rubble habitat at Lizard Island, northern Great Barrier Reef, Australia. This species is a protantric hermaphrodite. The switch from reproduction as a male to a female is progressive, involving a simultaneous hermaphrodite as a transitional stage. Members of O. spinosa brood their young in the respiratory bursae. Cohorts of eggs (280 μm diameter) develop synchronously in the gonad and are spawned as a group into the bursa. Despite non‐pelagic development, the larvae of O. spinosa are a vitellaria type typical of broadcast‐spawning ophiodermatids, providing a link to an ancestral form with a dispersive larva. The vitellaria has prominent ciliary bands and swims in the same manner as pelagic vitellaria. In vitro , the larvae developed to the juvenile stage independent of the parent. There was no evidence of extraembryonic nutrition; a proportion of the maternal provisions were retained through metamorphosis. This is the first ophiuroid known to brood a pelagic‐type vitellaria larva. Juveniles appear to leave the parent at the two‐ to three‐arm segment stage, slightly larger than the newly settled juveniles of ophiodermatids with pelagic vitellariae. The presence of functional larvae in the bursa suggests a recent switch to the incubatory life history in O. spinosa and the possibility of a reversal back to a dispersive life history. O. spinosa have the potential to both brood and broadcast their young.