Body Plans and Adaptations

Symmetry: Shape and balance in proportions of the organism –Asymmetry: without symmetry, no pattern to the body plan. Body is randomly shaped. Examples: sponges –Radial Symmetry: Can be divided along any plane through a central point. Like slicing a pie. Example: hydra, starfish –Bilateral Symmetry: Can be divided down the middle into two almost equal mirror images. Example: Butterfly, humans

Anatomical terms Anterior: head end Posterior: tail end Dorsal: back surface Ventral: belly surface

Coeloms Acoelomate: has ectoderm, mesoderm, and endoderm but no coelom or body cavity Example: flatworms Pseudocoelomate: has the three layers and a fluid filled body cavity partially lined with mesoderm. Example: roundworm Coelomate: Has a fluid filled space completely surrounded by mesoderm. This is where we see the greatest diversity in body plans. Examples: Humans, fish, earthworms, insects

Image taken from Image taken from

Body Support Exoskeleton: A hard waxy covering on the outside of the body. Protect soft body tissues and prevent water loss. Growth is limited because they must shed the exoskeleton. This leaves them vulnerable for part of their life. Mainly found in invertebrates: animals without a backbone. Endoskeleton: Internal framework of cartilage and bone that provides structure. Does not have to be shed to grow. Mainly found in Vertebrates: Animals with backbones. Echinoderms (starfish are the exception. They are invertebrates with an endoskeleton.