Echinoderms and Hemichordates

• Deuterostomes undergo radial, indeterminate cleavage
• Superphylum Ambulacraria contains two deuterostome phyla: Echinodermata and Hemichordata
• Members of Clade Ambulacraria share a three-part (tripartite) coelom, similar larval forms, and an axial complex (specialized metanephridium).
• Echinoderms include sea stars, brittle stars, sea urchins, crinoids, and sea cucumbers.
• Echinoderms are entirely marine.
• Echinoderms lack the ability to osmoregulate.
• Echinoderms are almost entirely benthic.
• Echinoderms are non-segmented
• The mouth of deuterostomes forms from a second opening
• The coelom of deuterostomes undergo enterocoelous development
• Five extant classes of echinoderms are currently recognized.
• Echinoderms have spiny endoskeleton of plates
• Echinoderms have a water vascular system
• Echinoderms have pedicellariae
• Echinoderms have dermal branchiae (skin gills)
• Echinoderms have pentaradial symmetry in adults
• Echinoderms are bilaterally symmetrical as larvae.
• This means the ancestors of echinoderms were bilaterally symmetrical.
• As adults, echinoderms show secondary radial symmetry - pentaradial (5 parts).
• Today’s echinoderms are mostly motile.
• Echinoderms have no well defined head or brain.
• Echinoderms have a true coelom with deuterostome development.
• Echinoderms undergo radial, indeterminate cleavage
• Echinoderms have a water vascular system derived from part of the coelom.
• The mouth of an echinoderm forms at the end of the embryo opposite the blastopore.
• Enterocoelous


  The mesoderm lined coelom develops from outpocketing of the primitive gut.
• The water vascular system is a system of canals and specialized tube feet that functions in locomotion, food gathering, respiration, and excretion.
• Canals of the water vascular system lead to the tube feet.
• The water vascular system opens to the outside through small pores in the madreporite.
• Echinoderms have an endoskeleton of calcareous ossicles often with spines.
• The endoskeleton of a echinoderm is covered by an epidermis.
• Sea urchins have a very substantial endoskeleton
• Some sea cucumbers have only a few scattered dermal ossicles on their endoskeleton.
• Eggs of echinoderms (which may be brooded or laid as benthic egg masses) hatch into bilateral, free-swimming larvae.
• Metamorphosis involves a reorganization into a radial juvenile.
• Class Asteroidea 


  Type of larva: Bipinnaria and Brachiolaria
• Class Ophiuroidea


  Type of larva: Ophiopluteus
• Class Echinoidea


  Type of larva: Echinopluteus
• Class Holothuroidea


  Type of larva: Auricularia
• Class Crinoidea


  Type of larva: Doliolara