Dichotomous Key and Questions, Research Paper Example

Which phyla lack organs? What type of symmetry do they have?

Only two phyla in the animal kingdom lack organs, and they are the phylum Porifera and the phylum Cnidaria.  The phyla Porifera contains species which have irregular symmetry.  The phyla Cnidaria has a symmetry that is radial.

List all of the phyla that show cephalization?

There are five phyla that show cephalization, and they are annelid, nematoda, mollusca, platyhelminthes and athropoda.

Do all organisms on the table have 3 germ layers (endoderm, ectoderm and mesoderm)? If not, which Phyla have fewer than three germ layers?

Not all the organisms listed in the above table have all 3 germ layers.  Phyla Cnidaria and Ctenophora only contain the endosperm and ectoderm and are termed diploblastic.  Porifera is the only phyla which lacks a germ layer.  Instead, they have an interior cavity called the spongocoel.

One phylum has more species than all the others. State the name of this phylum and provide several different examples of species found in this phylum.

Of all the phyla in the animal kingdom, Phyla Athropoda, overwhelmingly has the most diverse amount of unique species.  There are over 1 million identified species in Athropoda, and scientists predict it is possible another 10 million remain unidentified.  Examples include horseshoe crabs, butterflies, the praying mantis, scorpions, spiders, fireflies, ticks and mites.

According to chapter 24, fish do not all have the same skeletal structure. Describe the differences among fish from the most primitive to more advanced types.

More primitive fish have bony skeletons while the more advanced species have skeletons made of bone.  There are two types of fish with cartilage based skeletons, the Agnatha  and the Chondrichthyes.  The Osteichthyes are the bony fish and they are the more recent, advanced type of fish.  Agnatha fish are very primitive and lack a jaw.  These include hagfish and lampreys.  They are identified from the lack of a jaw and the presence of a notochord, a primitive backbone.   These fish have skeletons made of cartilage and in some places the cartilage is partly calcified and hardened.   The Chondrichthyes are a more primitive group of fish.  These creatures have a skeleton of cartilage.  Species include sharks, manta rays, chimeras and skates.  These fish have a notochord as well but it is spaced by vertebrae.  This gives them a true backbone.  They also have a skeleton of cartilage.

Describe the three types of mammals based on how their young develop.

Most of the mammals that we are familiar with reproduce by developing their young in the placenta, and these mammals area called placental mammals, and they are in the subclass Eutheria.  There are some mammals that lay eggs.  There are only 3 known species left that lay eggs, all the other species are extinct.  These types of mammals are called monotremes and they are in the subclass Prototheria.  Marsupials develop their young in a pouch.  Marsupials are in the subclass Metatheria.

References

Abedon, Stephen (2005) Important words and concepts  Chaper 32 Campbell and Reece, 2002 Web. Retrieved 28 May 2009 from http://www.mansfield.ohio-state.edu/~sabedon/campbl32.htm

Animal Bytes: Mammals, San Diego Zoo Online, 2010 Web Retrieved 28 May, 2010 from http://www.sandiegozoo.org/animalbytes/a-mammal.html

Meijerman, L., Ulenberg, S.A. Phylum Arthropoda Arthropods of Economic Importance. n.d. Web. Retrieved 28 May, 2010 from http://nlbif.eti.uva.nl/bis/tortricidae.php?menuentry=soorten&id=2

Ramel, Gordon  The Fishes Skeleton The Earthlife Web n.d. Retrieved 28 May, 2010 from http://www.earthlife.net/fish/skeleton.html