Comparative Anatomy: Body Plans

Lesson Title: Comparative Anatomy (1 of 8): Animal Body Plans
Academic Standards: HS-LS1-2
Content Creator: Mrs. Wendy Martin
Level: High School
Duration: 30-40 min
  /  Comparative Anatomy (1 of 8): Animal Body Plans


  • Students will understand how to read a phylogenetic tree.
  • Students will understand the three types of symmetry in the animal kingdom.
  • Students will understand how symmetry relates to lifestyle.
  • Students will examine the basic body plan of the cat, pig, squid, dogfish, and starfish.


Differences in animal body plans mark branching points in evolutionary trees. In this comparative anatomy lesson students will look at the basic body plans in 5 animal specimens: the squid, the starfish, the dogfish, the pig, and the cat. Students will start with observing the types of symmetries displayed. Students will then look at similarities and differences in body plans. Also discussed will be how the body plan assists in the lifestyle of that organism. Students will handle and manipulate the discussed specimens. They will also be able to explore larger than life specimens.


1. Explain how body plans can be used to categorize animals on an evolutionary tree. 2. Introduce a phylogenetic tree and how it is organized. 3. Introduce the three types of symmetry and examples of animals with each one. 4. Spawn an animal for each type of symmetry. Blow it up and describe the symmetry. 5. Show class each specimen: squid, starfish, dogfish, pig, cat. 6. Include a short video clip of the animals moving and feeding. 7. For each specimen, discuss its basic body plan and how it relates to its lifestyle. Explain body shape, symmetry, skeleton, appendages, and any unique features. 8. Discuss some of the similarities that are seen amongst the organisms. 9. Discuss the differences also. 10. Relate this to the theme of evolution.

Demonstratives & Media

Suggested Ancillary Support

Define asymmetry - irregular shape, lack of body symmetry. No identifiable head/tail, left/right or top/bottom. Ex: sponge Define radial symmetry - Can be divided along any plane, through a central axis, into roughly equal halves. Can identify a top/bottom. Ex: cnidarians, adult echinoderms. Define Bilateral symmetry - Animal can be divided into mirror image halves only along one plane. Usually demonstrates cephalization. Has a top/bottom; left/right; front/back. Squid: Reduced internal shell reduces bulkiness Torpedo shaped body Holds arms behind them for locomotion Does not use tentacles for locomotion Siphon used for jet propulsion Fins used for steering- triangular and aerodynamic   Starfish: Endoskeleton of calcium carbonate plates Moveable plates allow them to move rays Often covered with spines and covered by thin layer of skin Radial symmetry beneficial for slow moving lifestyle Eyespots detect light and movement from all directions Pedicellariae are small pinchers on skin for cleaning or capturing small food items The tube feet on the undersides of starfish are used as a form of locomotion as these creatures don't have any fins or flippers   Shark: 1.cartilage endoskeleton lightweight and flexible 2. Streamlined shape, pointed head 3. Strong swimming muscles 4. Large, oily liver for buoyancy 5. Scales project posteriorly to reduce friction 6. Paired fins: dorsal (straight line), caudal (propel), pelvic (stabilize), pectoral (stabilize and lift), anal (stabilize)   Pig: Reduced hair Tetrapod- several joints homologous to ours Even toed ungulate Hooves with two digits Separate digits allow dexterity on different terrains Omnivore- 4 types of teeth Sensitive taste and tongue papillae Very sensitive snout for rooting Lack sweat glands- lay in shade or roll around in mud Large, floppy pinna collect sound   Cat: Predatory tetrapod Walk on toes- heels lifted from ground Flexible wrist allows foot to bend Flexible neck Friction pad on foot cushions step and provides traction Sharp retractable claws Quick reflexes Good smell, excellent vision Four types of teeth- carnivorous Long stiff whiskers around mouth allow them to feel their way around the dark, nocturnal hunters