Echinoderm biology

right|thumb|Bipinnaria larva A bipinnaria is the first stage in the larval development of most starfish, and is usually followed by a brachiolaria stage. Movement and feeding is accomplished by the bands of cilia. Starfish that brood their young generally lack a bipinnaria stage, with the eggs developing directly into miniature adults.

thumb|right|250px|Older brachiolaria larva of Asterias sp. from below, anterior end at topFrom [[Ernst Haeckel's Kunstformen der Natur (1904)]] A brachiolaria is the second stage of larval development in many starfishes. It follows the bipinnaria. Brachiolaria have bilateral symmetry, unlike the adult starfish, which have a pentaradial symmetry. Starfish of the order Paxillosida (Astropecten and Asterina) have no brachiolaria stage, with the bipinnaria developing directly into an adult.

400px|thumb|right|Diagrammatic reconstruction of Dipleurula from Encyclopædia Britannica, 1911, adapted from Bather, 1900. Bather drew the creature as crawling on the sea-floor, but echinoderm larvae are usually pelagic (free-floating). The ciliated bands are not drawn. Dipleurula is a hypothetical larva of the ancestral echinoderm. It represents the type of basis of all larval forms of, at least, the eleutherozoans (all echinoderms except crinoids), where the starfish, sea urchins, sea cucumbers and brittle stars belong. The dipleurula is a bilaterally symmetrical, ciliated echinoderm larva (