4. What are characters that are specific to cnidarians? (see#8 ) 15. How do they

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4. What are characters that are specific to cnidarians? (see#8 ) 15. How do they digest food? How do they reproduce? 16. What is a nerve net? How do they move? 17. Know the 3 different classes of cnidarians and what characters they possess that put them in those classes. Protostomes in general 18. What morphological characters would place an animal phylum in the group Lophotrochozoa? Does an animal need to have both of those traits to be in this group? 19. What trait would place an animal in the Ecdysozoa? 20. Know the definitions for the following terms: lophophore, trochophore larva, ecdysis, segmentation. Know which of these terms apply to each of the phyla we talk about in lecture. Practice placing these characters on the phylogenetic tree of animals. 21. How are pseudocoeloms different from coeloms? Are they different in structure? In function? What are the 3 main functions of a coclom? What advantages would a triploblast with a coelom have over a diploblast like a cnidarian? Previous Next Courses Calendar To Do Notifications Messages

Explanation / Answer

14) All cnidarians are characterized by radially symmetric and bilaterally symmetric body plans that are found in most other animal phyla. They possess tentacles and many nematocysts, which are specialized stinging cells and both are involved in feeding. They have three tissue layers, an outer protective epidermis, a middle layer known as the mesoglea, and an inner layer known as the gastrodermis.

They only one digestive opening, that as both the mouth and the anus. This opening is surrounded by tentacles and leads to an internal digestive cavity known as the gastrovascular cavity .

15) Cnidarians are carnivores. They catch their food using their nematocysts or through filter feeding. They feed using tentacles, which are present with stinging nematocysts. The nematocysts are springing barbs are activated by contact with prey. At the same time, the nematocysts inject the prey with an immobilizing toxin with the help of a long hollow thread within the barb. The prey has been captured and tentacles are used to bring the prey into the gastrovascular cavity. The food is broken into small particles by digestive enzymes in the gastrovascular cavity and digestion is completed in digestive vacuoles within these cells. The indigestible remains of the prey are expelled from the mouth of the gastrovascular cavity.

Cnidarians reproduce asexually by budding, however, some produce gametes such as eggs and sperm in sexual reproduction. Medusae usually reproduce sexually using eggs and sperm.

16) Nerve net is primitive nerve arrangement, which forms the entire nervous system of cnidarians. It is a part of more advanced nervous systems. Cytoplasmic processes join the nerve cells of nerve nets. In cnidarians the neurons are joined to epithelial receptors and to contractile cells.

Cnidarians move by flexing weak, gelatinous muscles in the body walls of their bells against a pressurized hydrostatic skeleton. The hydrostatic skeleton is a basic water-based chamber with branches which their muscles compress to form movement.

17) Three different classes of cnidaria:

Anthozoa (flower like animals) - They are exclusively marine, solitary or colonial. Medusa stage is absent

in this class of organisms. Mesogloea contains fibrous connective tissue and amoeboid cells.

Example: Sea anemone.

Hydrozoa(water animal) - They are mostly marine, few are fresh water. Some are solitary and some are colonial organisms in this class. Asexual Polyps is dominant form in this class of organisms and medusa possess true velum. Mesogloea is simple and acellular in this class.

Examples: Hydra and Obelia.

Scyphozoa - They are exclusively marine, solitary and freely swimming. Medusa is dominant and it is Large bell or umbrella shaped and polyps is short lived or absent in this class of organisms. Mesogloea is usually cellular. Example: Jelly fish.

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