A jelly is shown (a) photographed and (b) in a diagram illustrating its morphology. In between the two layers, a non-cellular mesoglea is present. General Characteristics of Phylum Cnidaria: Some of the important General Characters of Phylum Cnidaria are listed below: 1. In this case, digestion is unique with extracellular digestion followed by intracellular digestion.They have a short and slender body with tentacles which encircle the mouth in one or two whorls.

They have calcareous skeletons which form the framework of the reefs and atolls in most tropical seas. The larva settles on a suitable substratum and develops into a sessile polyp.Class Scyphozoa includes all the jellies and is exclusively a marine class of animals with about 200 known species. 2)Hackle in 1891 proposed the name Scyphozoa. Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers.Nearly all (about 99 percent) cnidarians are marine species. When hairlike projections on the cell surface are touched, (b) the thread, barb, and a toxin are fired from the organelle.View this video animation showing two anemones engaged in a battle.Figure 2. is the phylum of animals that contains corals, jellyfish (sea jellies), sea anemones, sea pens, and hydrozoans. Cnidarians contain specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts (stingers). Their variety, diverse colorful symmetry body forms, and complex life histories attract the scientists. Both gametes are produced by the polyp, which can fuse to give rise to a free-swimming planula larva.
All cnidarians share several attributes, supporting the theory that they had a single origin. In this case, the polyp stage is the dominant and medusa possesses true velum. Like the septa in anthozoans, the branched gastrovascular cells serve two functions: to increase the surface area for nutrient absorption and diffusion; thus, more cells are in direct contact with the nutrients in the gastrovascular cavity.In scyphozoans, nerve cells are scattered all over the body.

Therefore, Cnidaria is the most suitable name for his phylum. (credit a: modification of work by “Jimg944″/Flickr; credit b: modification of work by Mariana Ruiz Villareal)In the jellyfish, a mouth opening is present on the underside of the animal, surrounded by tentacles bearing nematocysts.

A prominent difference between the two classes is the arrangement of tentacles. The nerve cells show mixed characteristics of motor as well as sensory neurons. The cnidocyte is a specialized cell for delivering toxins to prey as well as warning off predators.

The mouth leads to the gastrovascular cavity, which may be sectioned into four interconnected sacs, called diverticuli. An example is the colonial hydroid called an Figure 3. This short quiz does Use this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.Identify the life cycle stages of jellies using this

These animals are further classified into orders based on the presence of single or multiple tentacles per pedalium. The notable cnidarians include hydras, the corals, Portuguese men-of-war, jellyfish, sea anemones, sea whips, sea pens, and sea fans. Sea anemones are usually brightly colored and can attain a size of 1.8 to 10 cm in diameter. Many hydrozoans form colonies that are composed of a branched colony of specialized polyps that share a gastrovascular cavity, such as in the colonial hydroid Answer the question(s) below to see how well you understand the topics covered in the previous section. These polyps show limited mobility along the substratum and, like scyphozoans, may bud to form more polyps to colonize a habitat.
The defining characteristic of this class is that the medusa is the prominent stage in the life cycle, although there is a polyp stage present. Scyphozoans live most of their life cycle as free-swimming, solitary carnivores. These animals also show two distinct morphological forms—medusoid and polypoid—at various stages in their lifecycle.Figure 1. In this case, polyps are sessile (asexual stage) while medusa is free-swimming (sexual stage).In their body, circulatory, respiratory and excretory systems are absent. These animals are usually cylindrical in shape and are attached to a substrate. These forms may produce additional polyps by budding or may transform into the medusoid form.

Cubozoans display overall morphological and anatomical characteristics that are similar to those of the scyphozoans. In this case, planula larva is a common but ephyra larva is found in some animals.They are diploblastic animals. Animals in this class are polymorphs, and most exhibit both polypoid and medusoid forms in their lifecycle, although this is variable.The polyp form in these animals often shows a cylindrical morphology with a central gastrovascular cavity lined by the gastrodermis. About 99 % cnidarians are marine species and few inhabit in freshwater. Cnidarians represent a more complex level of organization than Porifera. This nerve net may show the presence of groups of cells in the form of nerve plexi (singular plexus) or nerve cords. In tropical seas, they form reefs by secreting calcium carbonate (CaCOThey are diploblastic animals with a radially symmetrical body.They are mostly marine organisms but some inhabit freshwater.Some species inhabit solitary and some form colony. Cnidarians have separate sexes and have a lifecycle that involves morphologically distinct forms. Knide=nettle and L. aria=like or connected with.

General Characteristics Of Phylum Cnidaria. Tentacles also play a vital role in the movement.The nervous system is poorly developed which makes the network of nerve fibers in the body walls and the tentacles. The Cnidaria (Cnidaria spp.) The body bears single or complicated sensory organs with eyespots called statocysts.They reproduce either asexual by external budding or sexual by the formation of ova and sperm.They show alternation of generation (metagenesis) in their life cycle, in which asexual colonial polypoid generation alternate with sexual free-swimming medusoid generation.Fertilization is internal or external and development is indirect with a larval stage.


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