Question

1. what evolutionary advances do Cnidaria have over the sponges?

2. How easily can you distinguish between polyps and medusae? in solitary animals? in colonial animals?

3. what type of symmetry is evident? Do all members of the phylum show the same type of symmetry?

4. Are all the examples of the phylum easily recognized as belonging to the Cnidaria?

Answer 1

1. Below evolutionary advances do Cnidaria have over the sponges –

• Radial Symmetry and Tissues, Radial symmetry is when an animal looks like it can be split like a pizza from above.
• Reproduction of Cnidaria is both asexual and sexual. Cnidarians also reproduce by budding. They reproduce sexually as well. Either one organism creates both cells or they create one each.
• Cnidarians are also hollow. Some polyps and some are medusas.

1. There are two body types for cnidarians: the polyp and the Medusa.

The polyp is shaped like a tube and is generally sessile. (Translation: it anchors somewhere so it can't wander off.) Cnidarians with a polyp body include sea anemones, coral, and hydra. The Medusa is a free-swimming, reverse version of the polyp. The polyp is anchored with its mouth and tentacles facing up. The Medusa is a flattened, more sack-like version, floating with its mouth down and tentacles hanging below. A jellyfish (or sea jelly, since it isn't really fish) is a medusa. Anthozoans (anemones and corals) form the largest class of cnidarians with multiple species. Anthozoan polyps are solitary or colonial, and there is NO medusa. Polyps can either be solitary or in groups.

1. The following points highlight the five main types of symmetry seen in animals. The types are:
   1. Asymmetrical Symmetry
   2. Spherical Symmetry
   3. Radial Symmetry
   4. Radial Symmetry
   5. Bilateral Symmetry

• Only sponges (phylum Porifera) have asymmetrical body plans.

Animals in the phylum Echinodermata (such as sea stars, sand dollars, and sea urchins) display radial symmetry as adults, but their larval stages exhibit bilateral symmetry. This is termed secondary radial symmetry. They are believed to have evolved from bilaterally symmetrical animals; thus, they are classified as bilaterally symmetrical.

Only members of the phylum Porifera (sponges) have nobody plan symmetry. There are some fish species, such as flounder, that lack symmetry as adults. However, the larval fish are bilaterally symmetrical.

1. Members of the phylum Cnidaria are defined by possessing nematocysts, a specialized type of stinging cell that, when stimulated by the organism, extends a thread or tube that can release a toxin or stick to or entangle an organism, incapacitating it and allowing it to be drawn into the central cavity of the predator. All Cnidarians are radially symmetrical (see Evolution section for more information on the evolutionary significance of radial symmetry). Members of the phylum have one of two body forms: the polyp form and the medusa form. Coral, sea anemones, and jellyfish are easily recognizable examples of Cnidarians.