These organisms can be induced to release their gametes by injecting 0.5 molar potassium chloride in the region surrounding their mouths, and they are commonly used in developmental biology to study external fertilization ?.
Tim Hunt's studies on the oscillatory levels of cyclins were first performed on A. punctulata, which is one of these organisms.  Th-nectin and Pl-nectin are analogues of fibronectin found in two specific species to this type of organisms, and the earliest zygotic protein expressed in these organisms is simply called the hatching enzyme.  Bindin proteins, found in sperm cells of these organisms, are involved in species specific interaction of sperm and egg cells, and unlike mammals, their acrosomal reaction doesn't require the binding of the sperm to the zona pellucida. The larval stage of their development is called pluteus. These organisms can be induced to release their gametes by injecting 0.5 molar potassium chloride in the region surrounding their mouths, and they are commonly used in developmental biology to study external fertilization ?. For 10 points, identify these echinoderms, examples of which include Aristotle's lantern, and which derive their name from Old English for "hedgehog" according to Wikipedia.  
Tim Hunt's studies on the oscillatory levels of cyclins were first performed on A. punctulata, which is one of these organisms.  
{Sea urchin} [prompt on {echinoidea} or {echinodermata} until "{echinoderm}"]