Reproductive biology

Ctenophores do not possess an alternation in morphologies (as seen in most scyphozoans and many hydrozoans) nor has the formation of a colonial structure ever been documented. Reproduction is primarily external, with the majority of ctenophores being simultaneous hermaphrodites. Pelagic ctenophores seem to be able to self-fertilize with close to 100% normal development achieved in the laboratory, although the sequential release of sperm and eggs and the mass spawning behavior that is often noted may reduce the percentage of self- fertilization in the field. Protandry has been documented for some platyctenids. Platyctene ctenophores are also unusual in that internal fertilization, brooding of embryos, and asexual reproduction by laceration is common.

Hermaphroditism is postulated as the ancestral state for the phylum and one genus is known to be dioecious, Ocyropsis. Breeding season for most ctenophores is year-round, with spawning peaks in the spring and the summer. Ctenophores may be utilizing photoreceptor cells for spawning cues, with different species spawning in response to different light/dark regimes. Other factors affecting gametogenesis are nutrients and possibly endocrine secretions. Diisogamy or paedogene-sis has been noted for Pleurobrachia, Bolinopsis, Dryodora, and Mnemiopsis.

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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