Ascidians are sessile, usually firmly fixed to the substratum. In response to an external stimulus, they can only slowly contract the body and close the siphons. Some of the very few interstitial species can actively move between gravel particles. Very slow movement of the colony also has been recorded in one or two tropical colonial species. Abyssal Situla and Mega-lodicopia species can quickly close their enormously large, bilobed branchial siphons in attempt to catch small swimming invertebrates, such as copepods.

Essentials of Human Physiology

Essentials of Human Physiology

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.

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