How do cnidarians eat and digest food?
Cnidarians are carnivores, and some can also consume plant matter. They catch their food using their nematocysts or through filter feeding. Cnidarians digest their food using a primitive digestive system that contains no organs--they have a mouth (which also serves as the anus) and a gastrovascular cavity.
Like Porifera, Cnidaria lacks a complete digestive system, but does have a Gastrovascular Cavity (GVC). Extracellular digestion takes place within the central cavity. Like the Cnidarians, Platyhelminthes have a GVC, an incomplete digestive system. Free living worms, such as Planaria, use extracellular digestion.
- Rotifers are multicellular animals with body cavities that are partially lined by mesoderm. These organisms have specialized organ systems and a complete digestive tract that includes both a mouth and anus. Most species of rotifers are about 200 to 500 micrometers long.
- Starfish Digestion and Circulation. Starfish have a complete digestive system with a mouth at the center of their underside (the "oral" side) and an anus on their upper surface (the "aboral" side). The figure below (from Brusca and Brusca) is a cut-away view of the digestive system and associated structures.
- Unlike the flatworms, the roundworms have a body cavity with internal organs. A roundworm has a complete digestive system, which includes both a mouth and an anus. This is a significant difference from the incomplete digestive system of flatworms.
Cnidaria have no organs like hearts or lungs. They have an internal cavity used for respiration and a gastrovascular cavity (a "stomach") with a mouth but they do not have an anus. They possess a body wall made from two layers (the ectoderm and the endoderm) separated by a jelly-like layer called the mesoglea.
- The gastrovascular cavity in Cnidaria is surrounded by an inner tissue layer called the gastrodermis. The outside of the organism has a tissue layer called the epidermis. Between these two tissue layers is a gel-like region called the mesoglea.
- Digestion, respiration, and excretion. Food is taken in and wastes are discharged through the mouth. Respiration and excretion in cnidarians are carried on by individual cells that obtain their oxygen directly from water—either that in the coelenteron or that of the environment—and return metabolic wastes to it.
- The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Cnidaria (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into a system of canals.
Cnidaria do not have a circulatory system simply because it is not needed; all cells are in contact with the water, which contains oxygen and nutrients. This is different from the Porifera phylum because Cnidarian species do not have pores.
- Cnidaria have no organs like hearts or lungs. They have an internal cavity used for respiration and a gastrovascular cavity (a "stomach") with a mouth but they do not have an anus. They possess a body wall made from two layers (the ectoderm and the endoderm) separated by a jelly-like layer called the mesoglea.
- Taxonomic level: phylum Cnidaria; grade of construction: two tissue layers; symmetry: radial; type of gut: blind gut; type of body cavity other than gut: none; segmentation: none; circulatory system: none; nervous system: network of nerve cells; excretion: diffusion from cell surface.
- Sponges and Cnidarians. Let's look at two very simple types of invertebrates; Sponges and Cnidarians. Sponges (Phylum Porifera), found in oceans all over the world, are made up of colonies of specialized cells—some help push water through the sponge, some help it feed, some are responsible for reproduction, etc.
Updated: 26th November 2019