sentences:  Sea urchins may appear to be incapable of moving but this is a false impression.Sometimes the most visible sign of life is the spines, which are attached to ball-and-socket joints and can point in any direction; in most urchins, touch elicits a prompt reaction from the spines, which converge toward the touched point.Sea urchins have no visible eyes, legs, or means of propulsion, but can move freely but slowly over hard surfaces using adhesive tube feet, working in conjunction with the spines.