Warm-up:
1. An animal without a backbone is called a(n) _________________________________.
2. Name the type of symmetry shown by the animals below:
_________________
____________________
_______________________
3. Why are pores important to sponges? (3 reasons)
4. What gives Cnidarians their name?
5. How does a Medusa differ from a Polyp?
Flatworms:
Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the
simplest animals to have three emrbyonic germ layers, bilateral symmetry, and cephalization. All
flatworms rely on diffusion for some essential body functions, such as respiration, excretion and
circulation. In free-living flatworms, several ganglia, or groups of nerve cells, control the nervous system.
Many have eye-spots that detect changes in light. Near the mouth is a muscular tube called a pharynx
that pumps food into the gastrovascular cavity. Excess waste is driven through a series of canals by hairlike cilia and out pores in the body. Asexual reproduction in flatworms takes place by binary fission, in
which an organism splits into two. Examples of flatworms include flukes and tapeworms.
1. Flatworms have __________________________ symmetry and have a defined _____________.
2. They show ___________________________ - sense organs, nerve tissue and the mouth are
concentrated in the head.
3. They have ____________ ______________ that detect changes in light and ______________groups of nerve cells in the head that form a simple brain.
4. The flattened body allows cells to take in oxygen via _____________________________.
5. A muscular tube known as a __________________ pumps food into the gastrovascular cavity
and hair-like ________________ push waste through canals out pores in the body.
Roundworms
Roundworms are slender, unsegmented worms. They have a one-way digestive tract with two
openings – a mounth, and an anus. A flexible, thick layer of epidermis and a cuticle form a protective
cover, and give the roundworm’s body its shape. Beneath this cover, a layer of muscle extends along the
length of the worm. These long muscles pull against the cuticle and the pseudocoelom (false body
cavity), whipping the worm’s body from side to side. Like flatworms, roundworms have a ganglionic
brain and depend on diffusion for respiration, excretion and circulation. Many act as important
decomposers. While some roundworms grow to be a foot or more in length, most are microscopic or
only a few millimeters long.
1. Roundworms have a tubular gut the runs from __________________ to ____________ for one
way digestion.
2. What are the two functions of the cuticle in roundworms?
3. What function do they serve in the environment?
Annelids
Annelids are easily recognized by their external segments, which are visible as a series of ring-like
structures along the length of their body. Internal body walls, called septa, separate the segments of
most annelids. Each segment contains digestive, excretory, circulatory, and locomotor (movement)
organs. Separate muscles control each body compartment aiding in movement. They have a true
coelom, or fluid filled body cavity, that acts as a hydrostatic skeleton. Some of the segments are
modified for specific functions, such as reproduction, feeding, sight or sensation. The cerebral ganglion,
or primitive brain, is located in one anterior segment. Nutrients, gases, and other materials pass
between the segments through a well-developed circulatory system, while sensory information is
delivered by a nerve cord that connects nerve centers in the segments to the brain. Many annelids get
their food using a pharynx. In earthworms, food moves through the esophagus to the crop, where it can
be stored, then through the gizzard, where it is ground into smaller pieces by muscular contractions and
sharp grains of sand.
1. Annelids are distinct from the other worms because they have __________________ or “little
rings.”
2. What organ types are found in each segment of an annelid’s body?
3. How is the circulatory system of an annelid similar to ours?
4. What is the purpose of the crop?
5. What is the purpose of the gizzard?