Dipleurula

The dipleurula is a hypothetical existing larval form of the echinoderms ( Echinodermata ). It represents the base type of all larval forms of Eleutherozoa to which the starfish, sea urchins, sea cucumbers and brittle stars belong. The dipleurula is planktotroph and has a bilaterally symmetrical body with a ventral mouth bay, which is surrounded by an eyelash band. The anal opening is ventral.

From the hypothetical dipleurula are any known forms of larvae of echinoderms can be derived. This includes the bipinnaria and Brachiolaria of sea stars, sea cucumbers and the Auricularia of the plutei the sea urchin and brittle stars. The Doliolaria the primary fixed Pelmatozoa ( sea lilies and feather stars ) can be on the same basic pattern traced, even if they have no mouth opening.