Evolution and systematics

The phylum Gastrotricha is divided into two orders, Macrodasyida and Chaetonotida. The order Macrodasyida contains six families, 31 genera, and approximately 210 marine species. One species occurs in freshwater. The six families are Dactylopodolidae, Lepidodasyidae, Macrodasyidae, Planodasyidae, Turbanellidae, Thaumastodermatidae. The order Chaetonotida contains two suborders, seven families, 29 genera, and approximately 400 marine and freshwater species. The seven families are Neodasyidae, Chaetonotidae, Dasydytidae, Dichaeteuridae, Neogosseidae, Proichthydidae, Xenotrichulidae.

Evolutionary relationships within the phylum are not well known. There is no fossil record. Within the Macrodasyida, the Dactylopodolidae is the most primitive family. Relationships among the five remaining families are unknown; Lepidodasyidae is probably a polyphyletic taxon. The Chaetonotida is divided into two suborders, the Multitubulatina and Pauci-tubulatina. The Multitubulatina contains a single family, Neo-dasyidae, and is basal within the Chaetonotida. Species of Neodasyidae are superficially similar to macrodasyidans but possess a chaetonotidan-type pharynx. The remaining six families of Chaetonotida make up the suborder Paucitubulatina. Most members of Paucitubulatina have tenpin-shaped bodies, sculptured cuticles, and a combination of hermaphroditic and parthenogenetic reproduction. The largest family, Chaetonoti-dae, may be an unnatural taxon.

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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