How do cnidaria feed

Cnidarian bodies have two or sometimes three layers. A gastrovascular cavity coelenteron has a single exterior opening that serves as both mouth and anus. Often tentacles surround the opening. Some cells are organized into two simple nerve nets, one epidermal and the other gastrodermal, that help coordinate muscular and sensory functions.

Cnidarians have two basic body forms, medusa and polyp. Medusae , such as adult jellyfish, are free-swimming or floating. They usually have umbrella-shaped bodies and tetramerous four-part symmetry. The mouth is usually on the concave side, and the tentacles originate on the rim of the umbrella. Polyps , in contrast, are usually sessile. They have tubular bodies; one end is attached to the substrate, and a mouth usually surrounded by tentacles is found at the other end.

Polyps may occur alone or in groups of individuals; in the latter case, different individuals sometimes specialize for different functions, such as reproduction, feeding or defense. Reproduction in polyps is by asexual budding polyps or sexual formation of gametes medusae, some polyps. Cnidarian individuals may be monoecious or dioecious.

The result of sexual reproduction is a planula larva, which is ciliated and free-swimming. Sarsia has a lifestyle similar to Obelia , but some species have both asexual and sexual reproduction in the medusa stage. During the asexual stage medusae bud off of the manubrium , the elongated structure surrounding the mouth.

The medusa stage is also morphologically distinct from other species in that it only has four tentacles and no statocysts. Muggiaea is a type of cnidarian called a Siphonophore. Siphonophores are floating or swimming colonies of gelatinous zooids organisms that function together. Each individual in the colony performs a different activity and is given a name that defines its role. For example, Muggiaea has one angular nectophore, or bell, which moves the colony by pulsating.

The stem of the colony is composed of gastrozooids, or polyps used in feeding, gonozooids are involved in reproduction, and dactylozooids are covered in nematocysts and used for protection. Many Cnidaria live in colonies made up of large numbers of individuals joined together in some way. These individuals called zooids can either be directly connected by tissues or share a common exoskeleton made from chiton or calcium carbonate.

In the Cnidaria sexual reproduction often involves a complex life cycle with both polyp and medusa stages. For example in Scyphozoa jellyfish and Cubozoa box jellies a larva swims until it finds a good site, and then becomes a polyp. This grows normally but then absorbs its tentacles and splits horizontally into a series of disks that become juvenile medusae, a process called strobilation. The juveniles swim off and slowly grow to maturity, while the polyp re-grows and may continue strobilating periodically.

The adults have gonads in the gastroderm, and these release ova and sperm into the water in the breeding season. Other Cnidaria have shorter forms of this cycle, for example cubozoan polyps have only one medusa stage. All Cnidaria can reproduce asexually by various means, in addition to regenerating if their bodies are divided into segments or are attacked by predators.

Some produce buds, others divide down the middle, others do both. Cnidarians range in size from Hydra, 5—20 millimetres to the Lion's mane jellyfish, which may exceed 2 metres in diameter and 75 metres in length. Thanks to I would sincerely like to thank the many members of the Flickr community who have given me permission to use their wonderful images for this unit. Their contributions really make this unit come alive!

Next: Anthozoa Cnidaria Cnidaria is a phylum containing over 9, species found only in aquatic and mostly marine environments. Diversity in Cnidara. Body form of Cnidaria.