Animal Organ Systems & Symmetry

• Organs in Echinoderms and Chordates associate to form functional systems, each for a specific physiological function.
• The pattern of organs forming functional systems is called the organ system level of organization.
• Different animal groups show varying complexities in their organ systems.
• Platyhelminthes have an incomplete digestive system with only one opening serving as both mouth and anus.
• A complete digestive system has two openings: a mouth and an anus.
• The circulatory system can be either open or closed.
• The open circulatory system pumps blood out of the heart, directly bathing cells and tissues.
• In the closed circulatory system, blood circulates through vessels of varying diameters like arteries, veins, and capillaries.

Symmetry

• Animals are categorized based on symmetry.
• Sponges are mostly asymmetrical; no plane through the center divides them into equal halves.
• Radial symmetry is when any plane passing through the central axis divides the organism into two identical halves.
• Coelenterates, ctenophores, and echinoderms exhibit radial symmetry.
• Bilateral symmetry is when the body can be divided into identical left and right halves in only one plane.
• Annelids and arthropods exhibit bilateral symmetry.

Diploblastic and Triploblastic Organization

• Diploblastic animals have cells arranged in two embryonic layers: an external ectoderm and an internal endoderm.
• Coelenterates are examples of diploblastic animals.
• In diploblastic animals, an undifferentiated layer, mesoglea, is present between the ectoderm and endoderm.