1) While the shell is a good defensive strategy, it also carries certain costs/p

Question

1) While the shell is a good defensive strategy, it also carries certain costs/problems. Identify at least one of these problems and briefly discuss how this phylum (Mollusca) has overcome this issue?

2) Define convergent evolution, and discuss how the cephalopods’ eye and the vertebrates’ eye demonstrate this phenomenon.

3) If you were an engineer hired to design an articial eye, would you base your model on the eye of the mammal or on that of the squid? Explain your decision      

4) How does the circulatory system viewed in the squid differ from that viewed in other molluscs? What advantage does this confer? What route does blood follow as it moves through the squid? Start at the systemic heart.

5) Describe the route that water follows as it passes through a clam starting from the incurrent siphon and finishing with the excurrent siphon

6) What is adaptive radiation? Identify two examples of adaptive radiation that you observed in lab today. Be specific and speculation on the advantages conferred in each example.

7) Members of such a large and diverse phylum as Mollusca impact humans in many ways. Discuss this statement. 500 words max.

Explanation / Answer

1) Most of the members of the phylum mollusca are provided with shells which provides them with good defensive strategy. But, the presence of shell also carries certain problems. One major problem that is offered by the preence of shell is the incresae in weight. It takes much energy for the organism to move around.

This problem is faced by molluscans by evolutionarily adapting to reduced shell or even no shell at all. Two major groups of mollusca , Gastropods and cephalopods have reduced shell or no shell at all. Examples include Squids and Octopuses. This loss of shell enables them to incease their speed of movement and also helps them to enter in small cracks, crevices or holes becuase of their less size.

2) Convergent evolution is the process by which organisms of differernt phyla ( ie., organisms that does not have a common ancestor) develop similar traits or characters. This may be bacuase of similarities in their environment.

Convergent evolution leads to analogous organs. Cephalopode eye and vertebrate eyes are considered as an example for analogous organs. Cephalopods eyes are commonly called as a camera type eye and pocess Iris, Circular lens,Vitreous chamber, Pigment cells and Photoreceptor cells. The vertebrates have also evolved a camera type eye which posess the same parts as that of cephalopods eye and functional similarity.

3) As an Engineer, if I were hired to make an artificial eye, I would use the squids eye as a model than that of a mammalian eye. The main reason behind this is the presence of a blind spot in mammalian eye, whereas this blind spot is absent in Squids. Since they lack this blind spot, they are able to see whatever things that come their way. This helps them deal better with predators and their enemies. This also helps in capturing the prey that comes in their way. In addition to this, cephalopods usually posses more number of photoreceptors than a mammalian eye which makes their vision better.

But, one most disadvantageous thing that is present with squid eyes is that, as they doesnot pocess cone cells, colour vision is not posible for them.ie., they cannot detect between light and dark conditions. Even then also, I think, squid eye will be better as an artificial eye.

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