User:Charlotte E. Vogler/Notebook/Lab 5: Invertebrates, Transect 2 on July 15, 2014

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Lab 5: Invertebrates, Transect 2 on July 10, 2014

Introduction, Purpose, and Objectives

Today’s lab explored the evolutionary history of invertebrates, starting with the early and simple sponges (phylum Porifera), which lack true tissues. Next, we learned about Cnidaria and Ctenophora, which are the most primitive of animals with radial symmetry. Following Cnidaria, bilateral symmetry came to be, which consists of a head and tail, as well as right versus left sides. Bilateral symmetry also allows for organ and tissue organization. The most significant evolutionary innovation came to be with the development of the mesoderm. This allows invertebrates to be far more complex than their more primitive counterparts, allowing for muscle, the circulatory system, organs, and bones. Today, we studied the invertebrates that inhabit transect 2 to get a clearer picture of the organisms living within our ecosystem. Our objectives were to understand the importance of invertebrates and to learn how simple systems such as specialized cells and body plan evolved into more complex systems.

Materials and Methods

Procedure I: Using a dissecting scope, we observed Planaria. However, the Planaria provided had arrived to the lab already dead, so we were unable to study its movement. Next, we observed nematodes and Annelida in order to compare body plans and observe their increasingly complex structures.

Procedure 2: After leaving our Berlese funnel to sit for a week, we disassembled the funnel and carefully poured the tube of ethanol into two petri dishes labeled “top” and “bottom” in order to determine where certain invertebrates were found in the mix of ethanol and water. We then studied the invertebrates under a dissecting scope in order to make observations that will be recorded in the Data section of this lab (see Table 1), such as size and number in sample.

Procedure 3: Each lab member returned to Transect 2 in order to record observations about vertebrates possibly living in or around the transect site in order to later create a food web.

Data and Observations

Procedure 1: Three species of worm were viewed under a dissecting microscope. Planaria, an acoelomate, was observed to have no enclosed body cavity. This is the simplest body plan we viewed. Planaria’s movement was not recorded during lab, as our samples were dead upon arrival. However, upon viewing, it can be determined that planaria move in a very slow slithering fashion similar to snakes. Next, we viewed Nematodes, which are pseudocoelomates, meaning that they have an enclosed body cavity partially lined with a mesoderm. These organisms are more complex than Planaria, but still relatively simple. They move with a thrashing motion, such as Finally, we viewed Annelida, a coelomate that had an enclosed body cavity entirely lined with a mesoderm. These organisms move in an undulated fashion, such as


Procedure 2: Several species of invertebrates were found in the sample from Transect 2. The majority of these invertebrates hailed from the class insecta. 5 organisms were chosen and identified using a dichotomous key. See table 1 below for results.


The largest organism was the millipede and the smallest was the biting lice. There were several different types of organisms in the leaf litter, but spiders and beetles were most common in our sample.


Procedure 3: Table 2: Screen Shot 2014-07-18 at 3.16.10 PM.png

The vertebrates in table 2 complete the ecosystem that is transect 2. Though transect 2 often appears to be void of animal life, it is quite the opposite. The sun provides light energy to the trees and ground plants, which are then food and shelter for invertebrates and most vertebrates. The vertebrates are also able to eat the invertebrates. Carnivorous vertebrates are also likely in the area, therefore the vertebrates living in and around transect 2 are likely a food source for them as well. Overall, the transect is full of resources for many invertebrates and vertebrates. Figure 3 below shows a small piece of the food web of transect 2 based on our findings.


According to the Freeman text, "A biological community consists of populations of different species that interact with each other within a particular area." Transect 2 represents a community because it is an area where several populations interact. These populations interact by living amongst each other and competing for resources. Carrying capacity is defined as "the maximum number of individuals in a population that can be supported in a particular habitat over a sustained period of time." Carrying capacity depends on many factors, such as availability of resources, space, water, etc. The carrying capacity of Transect 2 is relatively low because it is a small area. However, if you take into account the area surrounding, the carrying capacity is actually quite high. Currently, within the bounds of the 20x20ft. site, transect 2 hold a small, but dense amount of resources. Finally, it is defined that organisms that get energy from the same type of source were said to occupy the same trophic level, or feeding level. In transect 2, this means that the ground coverage and trees are on the same trophic level, because they both receieve their nutrients from the sun.

Conclusions and Future Directions

This lab concluded our study of transect 2. We are still waiting on the data from the 16s DNA samples, however. In the weeks to come, we will present our findings on transect 2.


1. Freeman, S. et al. (2008). Biological Science (5th ed.). Boston, MA: Pearson. 2. Bentley., Walters-Conte., & Zeller. (2014). Biology 210 Lab Manual. Washington: American University.