Reproductive biology

Most nemerteans are dioecious, although there are a few hermaphroditic hoplonemerteans (class Enopla). Palaeonemerteans are traditionally regarded as direct developers, whereas het-eronemerteans all produce pilidium larvae (free-swimming, planktotropic larvae), or larvae that seem to be derived from a pilidium. These heteronemerteans are broadcast spawners, but there are also heteronemerteans (Lineus rubber and L. viridis) known to reproduce by a kind of pseudocopulation in which the

Kjell Sandved
Unsegmented ribbon worm (Lineus sp.) seen near Panama. (Photo by Kjell B. Sandved/Photo Researchers, Inc. Reproduced by permission.

fertilized eggs are deposited in a gelatinous cocoon producing pilidium-like larvae known as Schmidt's and Desor's larvae, respectively. Only a few species are known to reproduce vegeta-tively by fission (a few species in genus Myoisophagus).

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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