Most eicosanoids are derivatives of

Most eicosanoids are derivates of arachidonic acid.

Explanation:

Eicosanoids are a group of lipid molecules originating from the oxidation of the essential fatty acids of omega-3 and omega-6 carbons. They fulfill extensive functions as mediators for the central nervous system, the events of inflammation and the immune response in both vertebrates and invertebrates.

Eicosanoids are carboxylic acids, by virtue of which they obtain their metabolic properties. Those derived from omega-3 usually have anti-inflammatory peculiarities, not so much those derived from omega-6. Of the eicosanoids, prostaglandins and thromboxanes include saturated and heterocyclic rings, while leukotrienes and hydroxy acids are linear (open from the beginning to the end of their chain). All of them are derived from arachidonic acid, and are essential fatty acids. In addition to arachidonic acid, other essential fatty acids can also serve as precursors in the formation of these molecules, for example, linoleic acid.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

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