Early post-metamorphic ontogenesis of deep-sea spatangoids (Echinoidea, Spatangoida) of the NE Atlantic Ocean.

The early juvenile development of 3 species of irregular deep-sea echinoids of the NE Atlantic was examined using scanning electron microscopy. Although the post-metamorphic development of these 3 spatangoids is very similar, the morphology and development of fascioles (specialized bands of heavily ciliated minute spines) facilitates distinguishing the species. In Hemiaster expergitus and Spatangus raschi, the fascioles present in the early juvenile develop to form adult fascioles. In Brissopsis lyrifera, a juvenile fasciole of unknown function disappears during ontogenesis, and new adult subanal and periproct fascioles arise. Fascioles of S. raschi and B. lyrifera are present at a very early stage of development (similar to0.7 mm test length), whereas in H. expergitus the fasciole appears much later (similar to3 mm test length). Animals smaller than 0.8 mm test diameter have not yet developed a functional mouth and are still considered as endotrophic postlarval stages. Mouth development is similar for all spatangoids examined.