Environment Influences the Body Plan Essay

Pages: 2 (646 words)  ·  Bibliography Sources: 2  ·  File: .docx  ·  Topic: Anatomy

The bilateral sea urchins of the Early Jurassic period had an anus positioned near the end of the body and when engaged in locomotive activity, kept the anus oriented rearward. The slimming of the bilateral sea urchin body shape is believed to have facilitated digging into the sand for food because less sand had to be moved, and the rearward pointing anus more sanitary.

A recent study carefully examined the behavior of the bilateral sea urchin Anthocidaris crassispina and found evidence suggesting that the bilaterality facilitates defense (Yoshimura and Motokawa, 2010). Sea urchins use several strategies to avoid predation, including moving only during the night to avoid attracting attention. Sea urchins also elaborate spines. A. crassispina, in accordance with their bilateral symmetry, have body regions with shorter and longer spines. After observing the behavior of A. crassispina in the laboratory and in the field, it was noticed that the shorter spins were kept away from open waters and towards structures that provided barriers against predation. In addition, A. crassispina preferred to rest in the corners at the top of the water tank, rather than the bottom corners. Since A. crassispina prefer shallow tidal pools in the field, the authors interpreted this as indicating the primary predator threat is from the water column, rather than from above the water surface.


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The environmental forces that have driven the evolutionary emergence of bilateral symmetry are believed to be related to the use of locomotion to find food. Essential to this process is the development of a nervous system capable of sensing food and driving motor activity. Recent research also suggests that bilaterality could be facilitating defensive strategies.


Martindale, Mark Q. And Henry, Jonathan Q. (1998). The development of radial and biradial symmetry: The evolution of bilaterality. American Zoologist, 38, 672-684.

Essay on Environment Influences the Body Plan Assignment

Yoshimura, Kazuya and Motokawa, Tatsuo. (2010). Bilaterality in the regular sea urchin Anthocidaris crassispina is related to efficient defense not to… [END OF PREVIEW] . . . READ MORE

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