Download Animal Advances: Digestive

Joseph Leprince
Brandon 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.
GVC
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.
Planaria: Note
the GVC
(black) which
acts as a fake
intestine.
Cestoda: note
the lack of
GVC;
reproductive
organs only.
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.
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.
Ascaris: Intestine
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
Cecum
Stomach
Crop
Gizzard
Intestine
Annelids have a complete
digestive system. The crop
stores food, and the gizzard
grinds the food. The intestine
absorbs nutrients via
extracellular digestion.
Arthropods have a
complete digestive
system, and in the
Crustaceans, the
stomach contains
chitinous teeth, which
form the gastric mill,
used to grind food.
Pyloric Stomach
Digestive Gland
Intestine
Summary:
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.