This lab is very important. You must know this lab inside and out. Look at the cover of the lab book for a minute. The little chart that ends with "Echinodermata" and "Chordata" is the most important single document in this course. Learn it.
Learn the classifications and use them like a road map. You'll see what I mean in a bit.
Kingdom Animalia breaks into Subkingdoms Parazoa and Eumetazoa. Parazoans dont have organs systems. Eumetazoans do. The only animals in Parazoa are sponges. Everything else is in Subkingdom Eumetazoa.
Eumetazoa breaks down into two branches: Radiata and Bilateria. This division is based on symmetry in the earliest stages of development. If the organism is radially symmetric in the larval/fetal stage it goes in Branch Radiata. If it is bilaterally symmetric (two halves) as a youngster, it goes in Branch Bilateria. Currently, there are only two phyla in Branch Radiata: Ctenophora and Cnidaria (the C's are silent in both). Sea anemonies and jellyfish are ctenophorans and cnidarians respectively. Everything else goes into Branch Bilateria.
Bilateria breaks into 3 groups: Grade Coelomata (pronounced "Seelomata"), Grade Pseudocoelomata, and Grade Acoelomata. Here the difference is based on the body cavity.
The anatomical structures of all the organisms is Branch Bilateria come from three layers of cells during development:
Not all organisms actually have a mesoderm. Coelomates have a body cavity that is lined with tissue from the mesoderm. Acoelomates dont have any body cavity and pseudocoelomates have a body cavity that is not lined with mesodermal tissue.
Currently, only Phylum Platyhelminthes (flatworms) is in Grade Acoelomata. Phyla Nematoda and Rotifera are the only phyla in Pseudocoelomata. Everything else goes into Grade Coelomata.
Grade Coelomata breaks into two subgrades: Schizocoela and Enterocoela. The difference is based on how the mesoderm surrounds the body cavity. It can either pouch off or split entirely. In schizocoela, it splits. In enterocoela, the mesoderm pouches off.
An easy way to differentiate between the two groups of coelomates is this:
Now we use our roadmap. We want to list the classification of chordates. We know chordates are animals, so they must be in Kingdom Animalia. We know they have organs so they are in Subkingdom Eumetazoa. We know that they have bilateral symmetry so they are in Branch Bilateria. We know that they have true body cavities so they are in Grade Coelomata. We know that their mesoderm pouches (it doesnt split) off to form the lining so they are in subgrade Enterocoela.
Now we want to classify Nematodes. Ok, they are animals so they are in Kingdom Animalia. They have organs, so they are in Subkingdom Eumetazoa. They have bilateral symmetry so they are in Branch Bilateria, they have body cavities not lined with mesodermal tissue so they are in Grade Pseudocoelamata.
The only way to do this (and you will have to do it for quizzes and the practical along with the odd exam question) is to do it constantly. When you're studying, pick a phylum and work it out. You will get it with practice. The hardest thing to remember is what you're choosing next: which comes first? body cavity or symmetry? You'll only get it with practice.