Ascidians cover a wide range of benthic habitats. Most species require a hard substratum and firmly attach themselves to rocks, stones, shells, algae, and so on. Other species are adapted for living on soft, muddy or sandy bottoms; such species are not firmly attached but often have thin hairlike outgrows on the test, anchoring them in the mud. There is a group of several interesting interstitial species: these rarely recorded minute species live between gravel grains; some of them are not fixed and can move. Ascidians occur from the intertidal zone to abyssal depths and have been recorded in all deepwater trenches; the maximal recorded depth is 27,560 ft (8,400 m). Most species inhabit shallow waters, some of them, such as the thin calcified colonies of certain didemnids, can survive on the open shores under strong wave actions.

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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