conclusion of non chordates
Answers
Explanation:
The first and most simple phylum is Porifera, the sponges. Sponges are clearly the most basic animal as they do not have any true tissues or body cavities. As well, they are sessile filter feeders and do not display any symmetry, a nervous system or cephalization. In addition they are highly dependant on water and require it for all body functions (i.e reproduction, circulation, digestion, excretion and respiration). Although they are very basic, they are still considered animals because they are multicellular, heterotrophic, eukaryotic and do not have any plant cell structures.
The next phylum is Cnidaria, the jellies. They are more advanced than the sponges because they are diploblastic (meaning they have two germ layers: Endoderm and ectoderm) and they have radial symmetry. As well, they have developed a nerve net nervous system and a very effective defence/hunting mechanism: stinging cells. Also, unlike the sponges, they are motile in their medusa stage. However, they still do not have a complete digestive system (a gastrovascular cavity with one opening), do not show any segmentation or cephalization and don't have any body cavities.
Although their digestive system is still incomplete, they now have flame cells for excretion, meaning their mouth is no longer their anus. As well they have excellent regenerative powers and are hemaphroditic. However, they are acoelomates, meaning they still do not have any body cavities.