Evolution and systematics

The Rotifera traditionally have been considered part of a group called Aschelminthes or Pseudocoelomata that comprised most of the microscopic animal groups without a true body cavity. Modern phylogenetic analyses have rejected this group, however, and today most studies support a close relationship between Rotifera, Acanthocephala (thorny-headed worms), Gnathostomulida (jaw worms), and the recently described Micrognathozoa (jaw animals) and unite them in a su-perphylum named Gnathifera (meaning, "those that possess jaws"). The acanthocephalans usually are considered a sister group to Rotifera, but this has been questioned by molecular data, which imply that acanthocephalans are highly advanced rotifers. This hypothesis still needs support from morphological data. The phylogenetic position of Gnathifera remains uncertain, but the most recent phylogenetic analyses suggest that they either are a basal group in Spiralia or form a mono-phyletic group with Gastrotricha and Platyhelminthes. In 2003 Rotifera included about 1,817 species, distributed among five orders and 34 families and divided into three classes: Seisonidea, Bdelloidea, and Monogononta. The latter class contains approximately 80% of the known species and displays the greatest morphological diversity.

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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