The Earthworm




Earthworms are annelids so they go in Kingdom Animalia. They have organs so they go in Subkingdom Eumetazoa. They have bilateral symmetry so they go in Branch Bilateria. They have a body cavity so they go in Grade Enterocoela. They have Spiral, Determinate cleavage and are Protostomes (SDPS) so they go in Subgrade Schizocoela

Take a look at the aortic arches. They are sometimes referred to as "pseudohearts". Questions like, "how many hearts does an earthworm have?" are inherently unfair because they can go either way. Your instructor could be making a point that they are NOT hearts or they could be asking for the number of aortic arches. Its a distinction many biologists can't agree on. For the time being, remember that they perform the function of a heart.

The seminal vesicles are next. They are storage containers for sperm. There is no such thing as a male worm. They're hermaphroditic. They've all got male and female reproductive structures.

Next come the crop and gizzard. They seem to be the same structure but they perform different functions. The crop is closer to the head than the gizzard is. The crop is where food passes into when it leaves the esophagus. The gizzard, which is the next stop for food after leaving the crop, is where food is ground. It serves the same purpose as your mouth. It is where food gets mechanically processed (ground/chewed) to increase the surface area for the chemical processing and then passes into the intestine, which digests and absorbs the nutrients.