Testing Evolutionary Hypotheses Using Comparative AnatomyWritten and Performed by Ryan JahansoozWith Guest Appearances by Tyler Voss, Zac Foster, Hunter Drobenaire, Parm, and CarlosPremiering on 11-27-13 in BIO Lab 001 Section 16Abstract:This experiment put the group directly into the position of being real scientists. The process of dissecting and observing real creatures is one that is not a typical occurrence or one that could be simulated. The first step of the lab for my group was to dissect a snail. This task proved to be quite easy and entertaining. The process involved removing the shell, exposing theorgans, and then pinning down the most important ones to make them easy to see individually. The second part of the lab was a task involving categorization of a large number of preserved organisms by body type and phyla. By the end of both sections, we had confirmed that each type of organism has its specific differences that separate it from others that may be similar. We also learned about how a body is composed of so many small parts that work in unison to make a creature live. Introduction:Each living organism has a phylum. A phylum is that organism’s “body plan” that describes how the organs inside the organism are arranged. Many organisms that share common ancestors have similar phyla, but the possibilities are endless. Some examples of phyla are those of porifera, mollusca, arthropoda, chordate, and enchinodermata. Each of these body plans are the same for all organisms within it. Knowing an organism’s phyla is enormously usefulwhen dissecting it, as it allows the dissector to more easily identify the organs and parts of the specimen. The specimen in our group was a typical garden snail, or helix aspersa, which has the phylum Mollusca. It shares this group with other creatures such as squids, mussels, clams, slugs,and octopi. These are typically characterized by having a soft, slimy body. The defining property of the helix aspersa is its hard shell, which protects it from external harm as well as preventing itfrom losing to much moisture to the atmosphere. It has a single foot located underneath everything else which secretes mucus that allows the creature to slowly move. It also has two stalks with eyes at the tips. It is able to curl up inside of its shell through the use of a muscle located inside. The entire body is located within the shell, and only the foot and head are able to extend out. The helix aspersa belongs to the taxon Stylommatophora, which consists of over forty thousand species of terrestrial slugs and snails. This taxon is part of a larger taxon known as the Pulmonata which includes all other snails that have lungs, such as freshwater and marine species. This taxon is closely related to Opisthobranchia, or sea slugs (with some freshwater species). These groups are all part of Euthyneura (all snails, slugs, and marine/freshwater variations). All possible variations, however, fall under the category Gastropoda, which is one of the eight major taxa of the phylum Mollusca. This tree of relations is important to knowbecause knowledge of any one of these thousands of organisms will make any study of another organism from the same group much easier. It also makes the evolutionary tree clearer when you see the fine details that separate each species.The problem when deciding the correct evolutionary path for the helix aspersa is its lung. The lung is what separates this creature from its marine brethren. The species of marine snails and slugs usually have a set of gills which allows them to underwater indefinitely. Their close relative who live in freshwater have a pulmonary cavity in the lung which will hold air long enough to permit a life underwater, but still requires the creature to return to the water’s surface for air. The helix aspersa, while having the ability to live underwater, typically prefers a life on land. Because of this preference, how can we tell where the helix aspersa evolved from? Were its ancestors terrestrial or marine? We believe that the helix asperses ancient ancestors were marine, whiles its more recent ancestors were, in fact, terrestrial. We believe this because the shell is a characteristic more serving to a life on land. A shell underwater would weigh down the creature and make movement difficult by increasing weight and drag force. On land, the shell protects the snail from predators and abiotic forces.Materials and Methods:The experimental procedures for this lab were adapted from a previously supplied protocol.The defining error for the lab was the unfortunate incident in which my colleague Carlos was squirted in the eye by his specimen when he cut open a highly pressurized sac of liquid. This final act of vengeance by the snail temporarily stalled dissection of all other creatures in the room, and caused slight incision error due to a psycho- physiological reflex involving successive rhythmic expiration with open glottis and vibrating vocal chords accompanied by a barring of teeth and unique facial expressions.Another slight error was my group’s complete lack of the second part of the lab. This wasdue to a communication error between the groups printed document provider, who was inattentive when printing the required lab documents. Luckily, the data was easy to find outside of the lab by searching for pictures of the organisms online after writing down their names in- lab.Results:By dissecting the helix aspersa and observing/identifying the phyla of over twenty individual creatures, we learned a great deal about the anatomy of creatures in the same phyla as well as the differences between those in different phyla. As you can see in Fig 1, the sheer variety is astounding, with certain creatures having huge differences in appearance even while belonging to the same phyla. And because our group was focused on the dissection of the helixaspersa, we were able to see the core details that separate our specimen’s phylum from the phyla of the other dissected animals. In Fig 2, you can see how each piece of the helix aspersa iskey to the creature’s survival. Some of the organs are just smaller versions of the ones found in our own bodies (digestive tract with mouth, stomach, digestive tract, and anus), while some are unique to this phyla (eye stalks, collar, simultaneous vagina and sperm sacs). We also saw while dissecting the lung that this species has no gills, which is its key difference from those in nearby