Rotifers are found in all aquatic and semiaquatic habitats, but they reach the greatest diversity and largest population sizes in freshwater. They may inhabit the sediment, live in association with submerged plants (live as well as dead and partly decayed), or be restricted to plankton. They also may be adapted for more special habitats, such as the ice of the Arctic Ocean, terrestrial mosses and lichens, or meltwater ponds on glaciers. Furthermore, some species are specialized para sites and live in the intestines or gills of various invertebrates. The optimal environment for many species is warm, nutrient-rich, slightly alkaline freshwater, but several species also are capable of surviving in more demanding habitats, such as temporarily dry or frozen ponds. Many bdelloid rotifers have cryptobiotic capabilities, which means that they are able to stop their metabolism, dehydrate their cells, and enter a state of dormancy. When entering cryptobiosis, the animal is capable of surviving under conditions that normally would be hazardous, such as complete dehydration, freezing, or oxygen deficiency. Many monogonont rotifers may survive under similar conditions by producing thick-shelled resting eggs. When the circumstances become more optimal, the populations may grow rapidly, because of their ability to reproduce asexually. The population and species richness is generally lower in marine habitats. The greatest diversity is found in the periphyton, but many species also may inhabit the interstices of sand grains on beaches. Marine rotifers are found mostly in the plankton or in the littoral zone and are extremely rare in deeper waters.

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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