FEEDING AND DIGESTION 2
SLIDE 2: Feeding
Feeding is the process of obtaining nutrients
Feeding behavior is modulated to meet nutrient needs of the animal
o They took beetles and they fed them one of two diets for a week (either a lipid-rich diet
or protein-rich diet).
o After a week, they took the beetles and let them choose whichever food they wanted to
o When they were given the choice, the beetles that were eating protein-rich foods
before were now eating lipid-rich foods and vice versa.
SLIDE 3: Feeding Methods- Passive absorption through body wall
Endoparasites, surrounded by gut fluids of their hosts
Tapeworms are endoparasites (they live in the gut of the host). They hold on to one spot in the
intestine with their mouth and absorb nutrients right across their body walls.
The head end is called scolex which has sucking discs which can bite on to intestinal wall and
hold on while the rest of the body floats in the nutrient rich fluid.
These tapeworms have repeating segments, each is called a proglottid. There is no gut in these
segments. The stuff inside the proglottid is filled with gonads so they have a huge capacity to
These tapeworms are primarily gutless, meaning none of their ancestors ever had a gut. These
tapeworms evolve from ancestors that never had a gut.
SLIDE 4: Feeding Methods- Passive absorption through body wall
Another animal that absorbs nutrients passively through the body wall is the parasitic barnacle.
There’s an egg sac underneath the crab, and inside is the eggs from the parasitic barnacle.
The parasitic barnacle invade the crab, castrate the crab, prevent it from molting, and force the
crab to generate an egg sac and make them look after their babies.
The way which people figured out that parasitic barnacles are related to other barnacles is that
they have similar looking larval stage.
The parasitic barnacles have an inner mass of undifferentiated cells. The barnacle larva
approaches a host, and injects the mass of undifferentiated cells into the crab. The mass of
undifferentiated cells is basically the parasitic barnacle. The mass of undifferentiated cells don’t
really take on a form of an animal, they spread throughout the body of the crab and absorbs
nutrients from all the cells.
Eventually the crab is castrated and develops an egg sac.
There’s no gut in the parasitic barnacle. The other barnacles have a gut but the related parasitic
barnacle doesn’t. This means the parasitic barnacle is secondarily gutless, meaning they evolved from an ancestor with a gut. Over evolutionary time, once they adopted a parasitic lifestyle, the
gut was no longer needed and the trait was lost.
SLIDE 5: Feeding Methods: Filter/Suspension Feeding
Sponges are filter feeders. They pass water through their body tissues, and filter out any food in
the water that they can eat.
SLIDE 6: Feeding Methods: Filter/Suspension Feeding
The large opening is called the osculum. Water is flowing out of the osculum. If water is flowing
out, there’s water flowing into the animal at some point.
This is done through porocytes, cells that create a pore in the animal’s body to allow water to
flow in the animal.
The water flows into the central cavity called the spongocoel and flows through other cells
called choanocyte where any food in the water is removed. Then the water flows out of the
The picture on the right shows a choanocyte in greater detail. Choanocyte translates into
meaning a collared cell.
The cell appears to have a collar, and has a single flagellum which extends through the center of
The flagellum is constantly beating and this is what draws water that’s come into the
spongocoel to flow through the mesh-like collar, into the inside of the collar, and then out.
The collar is covered in mucus. The water is drawn by the beating of the flagellum, and any food
that passes is trapped into the mucus but water passes through freely.
The food particles are engulfed in the cell by phagocytosis and passed along to the neighboring
amoebocyte which carries out digestion of the food particles.
SLIDE 7: Feeding Methods: Filter/Suspension Feeding
An example of filter feeders is tunicates. These animals are chordates but they’re invertebrates.
They have one large opening and another subopening next to it. The water flows into the big
opening, and out the small one. The food particles are stripped out of the water as it flows
through the animal.
SLIDE 8: Feeding Methods: Filter/Suspension Feeding
The larger opening is called the buccal siphon. The side opening is called the atrial siphon.
Water comes into the buccal siphon and out the atrial siphon.
How do you separate food from water?
o Unlike sponges, tunicates have a gut.
o The large blue structure is the pharynx. It has many slits. The water and the food is
separated at the pharynx. o Much like the sponges, the pharynx is covered with mucous. The mucous originates
from the endostyle (orange structure) which produces the mucous.
o The pharynx is ciliated, and the cilia’s role is to push the mucous across from the
endostyle, across the pharynx, over to the structure at the other end called the gutter.
o The mucous coats all the slits as it moves through the pharynx.
o The water comes into the animal through oral siphon, flows into the pharynx, flows out
of the slits into open space, and continues out of the animal through the atrial siphon.
o The food gets caught in the mucous. The mucous gets pushed from the endostyle to the
gutter. At the gutter, the mucous is taken and wrapped up into a mucous thread. That
mucous thread containing the food is pushed down into the gut, where it’s digested and
the waste products exit from the atrial siphon.
SLIDE 9: Feeding Methods: Filter/Suspension Feeding
Another filter feeder example is Baleen whales.
The order Cetacea gets broken into Mysticeti (Baleen whales or non-tooth whales) and
These whales are able to expand their oral cavity through pleats by a tremendous amount which
increases the amount of water they take in at once and maximizes the amount of food they can
take in in a single gulp.
These pleats allow the oral cavity to expand. Also, rather than having teeth, they have baleen
plates. This is what they use to separate water from the food.
The plates are made of keratin. This is the protein that makes up our hair, nails, skin.
The whales open their mouth as wide as possible, suck in as much water as they can, close their
mouth, and then use their tongue to compress the oral cavity. The water has to get out of the
oral cavity, the water passes through the baleen plates, and out to the surrounding water.
Anything big enough to be caught by the plates gets trapped in the baleen. The whale then
scrapes the stuff off the baleen with its tongue and ingests it through the esophagus.
One of the other characteristics of these whales is that its jaws are flexible which facilitates how
wide they can open their mouth.
There are two points:
o The lower jaw articulates with the skull very loosely.
o At the same time, where the two lower jaw bones come together, the jaw is elastic
because they can separate the jaw bones. These two points facilitate the opening of the
The odontoceti includes dolphins, or spermwhales which have teeth and don’t use filter
mechanisms at all. The Mysticeti whales are filter feeders.
SLIDE 10: Fluid Feeding
Another kind of feeding is fluid feeding used by free-living flatworms.
The pharynx of a flatworm has a major role for feeding. It’s a muscular organ which is used to penetrate the body wall of the animal they’re trying to
feed on and suck its body fluids.
To facilitate this process, they pump proteolytic enzymes to break the tissues up and liquefy
them to make it easy to take up.
SLIDE 11: Feeding Methods: Fluid Feeding
Another animal that uses fluid feeding are lamprey fish.
Lamprey are jawless fish (Agnatha means jawless).
They feed by latching on to things using oral discs (oral suckers) which is like a suction cup with
teeth on it. The suction cup is used to attach to the side of the animal. The lamprey has a long
tongue. They use this tongue to tear into the side of the animal and suck out of the blood or any
fluid that comes.
To prevent the blood from clotting, they pump in anticoagulant into the animal. This is done to
extract as much blood and fluid as they can.
SLIDE 12: Feeding Methods: Fluid Feeding
Example of a fish that’s been recently fed on by a lamprey.
Lamprey has been a problem in lots of areas.
There are lampreys in the Great Lakes.
A lot of money is spent to use lamprocides and other stuff that kills lamprey and don’t harm the
fish to get the population under control.
SLIDE 13: Feeding Methods: Seizing Prey- Verebrates
Another method of feeding is called seizing prey method. Vertebrates seize prey through teeth.
True teeth are teeth that are formed from two compounds: enamel, and dentin.
Other structures are found in other animals which are like teeth but for example a pointy type
of a bone will not b