Most urchins are nocturnal foragers, although some locomotor^ activity can coincide with tidal changing if they occur during the day. Generally, these are small movements to compensate for change in seawater level associated with an out going or incoming tide. On wave-exposed shores, urchins can aggregate together to interlock spines, thus reducing the risk of being dislodged by a strong wave surge. Other aggregation patterns occur in defensive moves directed at predators, whereas other patterns usually signify feeding aggregations.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.