Physical characteristics

The Automedusa class is represented only by medusae; there are no polyp stages. Development is usually direct, sexes are separated; each fertilized egg leads to a planula that develops into a single medusa, except in some Narcomedusae, in which parasitic stages issued from the egg may give rise to several medusae by asexual budding. Medusae are not formed through a medusary nodule: the subumbrellar cavity and velum are formed by folding and deepening of the oral embryonic ectoderm, being only analogous to the subumbrellar cavity and velum of the Hydroidomedusa. The primary marginal tentacles are always formed before the subumbrellar cavity and the gastro vascular system. The marginal tentacles are deprived of tentacular bulbs. Sensory organs are in the form of ecto-endodermal statocysts, with an endodermal axis, growing out from the circular canal, with sensory cells characterized by numerous kinocilium-lacking rootlets, surrounded by stereocilia, innervated by the upper nerve ring; statoliths are of endodermal origin. Asexual reproduction is present only in "actinula"-like larvae and adults of Narcomedusae. The Act-inulidae are all members of the interstitial fauna; they look like actinula-larvae, and the statocysts are the most distinctive medusan feature of these highly specialized medusae. The Narcomedusae have a flattened exumbrella, with lobed margin, incised by deep grooves. Usually with no radial canals, gametes are carried on the wide manubrium. Their intermediate tentaculated post-embryonic stages are juvenile medusae reproductive polyp

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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