Brittle and Basket Stars

The Ophiuroidea are commonly known as brittle stars and basket stars.  They have a similar body plan to that of the Asteroidea (sea stars) with a central disk and five appendages radiating out.  Dissimilar to sea stars this group maintains a more strict adherence to pentaradial symmetry and all digestive organs remain within the central disk and almost never expand out into appendages.  Here the ventral (1) and dorsal (2) views of a typical central disk with the five calcereous jaws which lead to a blind ended gastrvascular cavity (stomach) can be seen.  Sections through the central disk at adult (4) and juvenile stages (7) are shown along with the respiratory organs called bursae (5 & 6, blue).  Also shown are the “ball and socket” vertebrae that make up the arms (8 – 11).

Sea Cucumbers, Sea Stars and Brittle Stars

This chart shows the early developmental stages of three classes of Echinoderm.  Holothuroidea are the class of sea cucumbers, Asteroidea the sea stars and Ophiuroidea the brittle stars.  Note the change in classification of brittle stars from within the Echinoidea (sea urchins) to an independent class within the same Subphylum which differentiates feather stars from all other Echinoderms.  Progressive development of an auricularian larva (from a sea cucumber) is shown (fig. 1-9) with it’s bands of cilia in place and adult tentacles forming (fig. 9).  Different stages of the bipinnaria larva of a sea star can be seen developing structures from gastrodermal and meso dermal tissue (fig. 10, 17 & 19). An ophiopluteus larva of a brittle star is shown forming it’s arms (fig. 11).