Joseph LeprinceBrandon Studt

Sponges use intracellular digestion in individual cells; they are filter feeders and do not have a digestive system. They have water canals and a spongocoel for water to flow through, and the choanocytes absorb the food.

Cnidarians use both intracellular and extracellular digestion. Like Porifera, Cnidaria lacks a complete digestive system, but does have a Gastrovascular Cavity (GVC). Extracellular digestion takes place within the central cavity.

GVC

Like the Cnidarians, Platyhelminthes have a GVC, an incomplete digestive system. Free living worms, such as Planaria, use extracellular digestion. Parasitic Platyhelminthes, such as classsesTrematoda and Cestoda, use intracellular digestion, absorbing nutrients from their environment.

Planaria: Note the GVC (black) which acts as a fake intestine.

Cestoda: note the lack of GVC; reproductive organs only.

Ascaris: Intestine

Nematodes have a more advanced digestive system than earlier phyla, complete with a mouth, intestine and an anus. The intestine absorbs nutrients via extracellular digestion.

Mollusks have a complete digestive system. As shown, the cephalopods also have a cecum, which sorts out indigestible particles.

Mouth Esophagus Stomach Intestine/cecum Anus

StomachCecum

Annelids have a complete digestive system. The crop stores food, and the gizzard grinds the food. The intestine absorbs nutrients via extracellular digestion.

Crop

Gizzard

Intestine

Pyloric Stomach Digestive Gland Intestine

Arthropods have a complete digestive system, and in the Crustaceans, the stomach contains chitinous teeth, which form the gastric mill, used to grind food.

Porifera – Have a primitive digestive system, extracellular digestion only.

Cnidaria – Have an incomplete digestive system, but does have a GVC. Uses both intracellular and extracellular digestion.

Platyhelminthes – Have a GVC and an incomplete digestive system. Free living worms use extracellular digestion, while parasitic worms use intracellular digestion, absorbing nutrients from their environment.

Nematoda – Have a more advanced digestive system with a mouth, intestine and an anus. The intestine absorbs nutrients via extracellular digestion.

Mollusca – Have a complete digestive system, including a mouth, esophagus, stomach, intestine and anus.

Annelida – Have a complete digestive system, with a crop that stores food, and a gizzard grinds the food. The intestine absorbs nutrients via extracellular digestion.

Arthropoda – Have a complete digestive system, from mouth to anus.

Summary: