Molluscs and Natural Selection

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  • Topic: Mollusca, Mutation, Bivalvia
  • Pages : 3 (846 words )
  • Download(s) : 80
  • Published : April 19, 2013
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Molluscs and Natural Selection

The process of natural selection is one of the most cited reasons for the evolution of a species, and it was made famous by Charles Darwin’s famous observations of finches in the Galapagos Islands. It is believed to work by way of random mutations; random mutations occur, as it indicates, randomly and spontaneously in a population for a multitude of genetic reasons. Mutations help to create variation of different traits within a species, and they can be expressed with different phenotypes. In times where a mutation has no negative effect on the individual organism, this trait could be advantageous in a new habitat or predatory situation, etc. With an advantage in survival, and thus reproduction, these organisms are often selected for over other members of the species, creating a change in variation of a species over generations.

Molluscs, although a very large and diverse group of animals, often share certain features: a mantle, radula, shell, and foot. The mantle is a thin and fleshy layer which secretes the hard shell of a mollusc. The radula is a grate-like structure in the mouth used to scrape surfaces and drill holes. The foot is a muscle which assists in locomotion and movement of the molluscs. It is hypothesized that all current-day molluscs share a common ancestor, called the hypothetical ancestral mollusc or HAM, because of the similar characteristics and body plans that have been modified in diverse ways over time to adapt to different environments. Two members of the mollusc family include the clam, of the class bivalvia, and the squid, of the class cephalopoda, and these are an example of variation from the HAM that helped them adapt for their particular environment, feeding behavior, and movement (Sigwart, 2007). The squid species has undergone many adaptations. The squid’s radula resembles a beak-like structure that it uses to devour its food, very different from the chiton-like HAM which probably had a...
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