In this exploration, you will look carefully at pictures of animals and consider some physical characteristics that scientists use to classify each organism. For each characteristic, it may be difficult to reach an accurate conclusion using only a picture. Actual classification relies on far more characteristics than are considered in this exploration, but by comparing your results, you can begin to get an idea of how each kind of organism is similar to and different from the others. Examine the pictures of the organisms in the lesson. Then fill in the Observations Table using the pictures as references. In each case, use your best judgment based on what you can see in the picture.

Observations Table

Representative organism
Type of symmetry (Radial, Bilateral, or None)
Type of skeleton (ENdoskeleton, EXoskeleton, or None)
Type of appendages (Jointed, Not Jointed, or Absent)
Segmentation (Present or Absent)
Sponges

Cnidarians

Roundworms

Annelids

Mollusks

Arthropods

Echinoderms

Vertebrates

Questions

Which grouping in the animal kingdom is the only one that contains organisms with vertebrae?

Which grouping has the least complex body plan? If you were on a research expedition in the kingdom of Tonga, a coral atoll in the South Pacific, would you find these organisms?