Question

discuss internal and external fertilization in Aurelia

what are the bases of classifying some animals as invertebrates

list 20 invertebrate animals with at least three animals from each of the phyla

Answer 1

* The external or internal fertilization in Aurelia:

After being released from the body through the outgoing water current the male reproductive cell, spermatozoa swim about till it reaches the female reproductive cell, ova. ova are fertilized inside female’s stomach or in brood pouches located on the oral arms. Because of this, fertilisation in Aurelia is said to be internal and external.

* Features of invertebrates to differentiate it from vertebrates (on the basis of which we can classify some animals as invertebrates):

1. Lack backbone

2. Compound eyes

3. Simple and unorganized nervous system

4. Lack well-developed skeleton system.

5. only one layer of skin is present.

* Nine main phyla of invertebrates:

1. Phylum Porifera - Sponges, sycon , leucosolenia

2. Phylum Cnidarians - Jellyfish, corals, hydra

3. Phylum Platyhelminthes - Flatworms, flukes, tapeworms
4. Phylum Echinodermata - Sea stars, sea urchins, sea cucumbers
5. Phylum Mollusca - Snails, clams, squids
6. Phylum Nematoda - vinegar eels, hookworms, pinworms
7. Phylum Arthropoda - scorpions, centipedes, barnacles
8. Phylum Annelida - Earthworms, leeches, lugworms
9. Phylum Chordata - Sea squirts, lancelets, tunicates