No Chaetognatha species is listed by the IUCN Red List. Planktonic species have huge populations with very large distributions and as such, are not expected to die out. There is
no other animal on the planet with such a large distribution area, and species worldwide are not threatened. However, climate changes have been known to cause distribution areas to shift and local populations of species are able to appear and disappear. For example, we can expect populations of warm-water species in the North Atlantic to begin moving northwards if ocean temperatures continue to increase, and it is possible that the arctic-subarctic cold-water species Sagitta el-egans could disappear from the North Sea, which is its southernmost area of distribution.
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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.