Phylum Cnidaria
The phylum cnidaria is very diverse and includes organisms such as jellyfish, hydra, sea anemones and corals. Their bodies are organized by tissue level, whereby similar cells are associated into groups or combinations of tissues, and organs do not exist. Some of the cells are structured into two simple nerve nets, epidermal and gastrodermal, whose job is to help coordinate the muscular and sensory functions. Cnidarians are mostly epitheliomuscular, whereby the epithelia cells contain contractile fibers that act as muscle. All cnidarians have a hydrostatic skeleton, a fluid like cavity surrounded by muscles. The muscles of the body wall operate against the fluid to extend individual polyps and to effect the swimming of medusa. The body of a cnidarian may have two or three layers. Cnidarians have a gastrovascular cavity with a single exterior opening that serves as mouth and anus with tentacles surrounding the opening.
Cnidarians have two types of body forms, polyp and medusa. Adult jellyfish that are free-swimming or floating, are medusae. Their body is shaped like an umbrella and have a four part symmetry, with the mouth on the concave side and the tentacles on the umbrella rim. They swim in a form of jet propulsion whereby muscles mainly inside the rim of the umbrella squeeze water out of the cavity that powers the stroke. Some thin tissue layers can only help move within currents but not against currents. Polyps are immobile, fixed in place, and have a tubular body with one end attached to the substrate, and a mouth surrounded by tentacles on the other side.
The phylum cnidaria is very diverse and includes organisms such as jellyfish, hydra, sea anemones and corals. Their bodies are organized by tissue level, whereby similar cells are associated into groups or combinations of tissues, and organs do not exist. Some of the cells are structured into two simple nerve nets, epidermal and gastrodermal, whose job is to help coordinate the muscular and sensory functions. Cnidarians are mostly epitheliomuscular, whereby the epithelia cells contain contractile fibers that act as muscle. All cnidarians have a hydrostatic skeleton, a fluid like cavity surrounded by muscles. The muscles of the body wall operate against the fluid to extend individual polyps and to effect the swimming of medusa. The body of a cnidarian may have two or three layers. Cnidarians have a gastrovascular cavity with a single exterior opening that serves as mouth and anus with tentacles surrounding the opening.
Cnidarians have two types of body forms, polyp and medusa. Adult jellyfish that are free-swimming or floating, are medusae. Their body is shaped like an umbrella and have a four part symmetry, with the mouth on the concave side and the tentacles on the umbrella rim. They swim in a form of jet propulsion whereby muscles mainly inside the rim of the umbrella squeeze water out of the cavity that powers the stroke. Some thin tissue layers can only help move within currents but not against currents. Polyps are immobile, fixed in place, and have a tubular body with one end attached to the substrate, and a mouth surrounded by tentacles on the other side.