What kind of symmetry tends to be associated with cephalization

Cephalization is associated with bilateral symmetry and forward head movement. Bilateria: Cephalization is a distinguishing feature of the Bilateria, a large group that includes the vast majority of animal phyla. These have the capacity to move using muscles and a body plan with a front end that encounters stimuli first as the animal begins to move and has evolved to contain many of the body's sense organs, able to detect light, chemicals, and sometimes sound.

A collection of nerve fibres capable of processing information from these sense organs is often present, forming a brain in some phyla and one or more ganglia in others. Acoela: The Acoela are a type of basal bilaterian that belongs to the Xenacoelomorpha. They are small and simple animals with slightly more nerve cells at the head end than anywhere else, resulting in the absence of a unique and compact brain.

This is a very early stage of cephalization. Flatworms: Platyhelminthes flatworms have a more complex nervous system than Acoela and are lightly cephalized, with an eyespot above the brain near the front end, for example.

Cephalization provides three benefits to an organism-. For starters, it promotes brain development. The brain serves as a command and control centre for organising and controlling sensory information. Animals can evolve complex neural systems and higher intelligence over time.

The second benefit of cephalization is that sense organs can be concentrated in the front of the body. This allows a forward-facing organism to scan its environment more efficiently, allowing it to find food and shelter while avoiding predators and other dangers. As the organism moves forward, the front end of the animal senses stimuli first.

Third, cephalization moves the mouth closer to the sense organs and brain. As a result, an animal can quickly analyse food sources. Predators frequently use special sense organs near the oral cavity to gather information about prey when vision and hearing are insufficient.

Cats, for example, have vibrissae whiskers that detect prey in the dark and when it is too close to see. Sharks have ampullae of Lorenzini electroreceptors that allow them to map prey location.

The cells are called blastomeres. Draw the 2-cell stage, labeling the fertilization membrane. Find an eight-cell embryo and draw that. Notice that even though the embryo contains more cells, blastomeres, that the overall size of the embryo is essentially the same as the zygote.

The next stage to look for is the morula , 16 to 32 cells in a tight ball. Draw an embryo at this stage. Find an embryo that appears as a hollow ball of cells.

The space in the center of the embryo is the blastocoel. An embryo at this stage is referred to as a blastula. Sketch the blastula. After the formation of the blastula, one surface of the hollow ball begins to move into the space. With this inward sweep of cells, two tissue layers are established: the outer surface layer called the ectoderm and the inner layer called the endoderm. The opening is called the blastopore and leads to the primitive gut tube, or the archenteron. Find an embryo at this stage, called the gastrula , and draw and label the structures: blastocoel, gut or archenteron also called the gastrocoel , endoderm, ectoderm, blastopore, and mesoderm.

In Chordates and Echinoderms, like you and this starfish, respectively, the blastopore becomes the anus of the primitive gut tube, and this tube touches the other surface of the embryo and forms the mouth. Organisms in this line of descent, with the two openings formed in this order, are called the deuterostomes. The other phyla are called protostomes ; in protostomes the blastopore becomes the mouth.

In both of these lines of descent, a space, called a coelom , may form within a third layer of tissue called the mesoderm which arises between the outer surface of the body, the ectoderm, and the gut, composed of endoderm. The three primary tissue layers, endoderm, ectoderm, and mesoderm, differentiate into the following structures in the mature organism:.

The next developmental stages occur relatively rapidly. You should be able to find a multicellular larval form, that is no longer spherical, that possesses the third tissue layer, the mesoderm , which cannot be specifically detected but makes up some of the internal structures of the organism. Draw the larva. This background on development, the diagram provided in this lab, your textbook remember to use its index! Examine preserved specimens of jellyfish and sea anemones, both members of the Phylum Cnidaria.

What kind of symmetry do they have? Is a complete gut present? Do they have a skeleton? Name several characteristic specimens and fill in the column under Cnidaria in the chart.

Obtain a live flatworm, or planaria of the Phylum Platyhelminthes , in a depression slide and watch it under a microscope. How does it move? Is it segmented? Draw a sketch of the specimen. Observe the other platyhelminthes on display—flukes and tapeworms. Fill in the proper column in the chart. Make a wet-mount slide from the culture of vinegar eels, a minute nematode worm from the Phylum Nematoda. How do the worms move? This worm has a pseudocoelom that helps it move in this fashion.

Observe the other "roundworms" on display. Fill in the proper column on the chart. Observe a live earthworm from the P hylum Annelida in the fingerbowl. Notice how the shapes of the segments change as the worm crawls across the towels. Does this worm show homonomous or heteronomous segmentation? Observe the segmented worms on display.

These worms have a true coelom. Look at the trays of insects, Phylum Arthropoda and other specimens provided; identify the three tagmata. Is this homonomous or heteronomous segmentation? What is the nature of the skeleton? How many tagmata does a crawfish or lobster have? Observe other arthropods on display. Fill in the chart. A display of shells on demonstration suggests something of the variety of types to be found in the Phylum Mollusca.

Make careful observations concerning the other mollusks available. Refer back to the information given earlier in this lab concerning skeletons v. Remember, a shell is not a skeleton. Give examples of a few of these shell types and other specimens of interest.

A small sea animal called a lancelet, Amphioxus or Brachiostoma , will be our example of the Phylum Chordata. Remember that YOU are an example as well. Look at the whole specimen mounted on a slide and note the form of the segmentation. A stiff rod runs the length of the body; this is the notochord. Its elasticity opposes the contractions of the muscles.

Notice that some of the anterior segments bear gill slits. These segments become part of the head in the vertebrates, which probably descended from an ancestor much like the lancelet. Review the other chordate specimens on display. Fill in the characteristics on the chart. The last phylum to be examined is also the most peculiar, the Phylum Echinodermata. A starfish is a typical example. What kind of symmetry does it have? Examine other specimens available in this group.

Fill in the chart for this phylum. Your final activity today is to make up a dichotomous key, similar to the one you used several weeks ago, that could be used to identify the eight animal phyla you have just studied. In evolutionary terms, this simple form of symmetry promoted active mobility and increased sophistication of resource-seeking and predator-prey relationships. Bilateral symmetry : This monarch butterfly demonstrates bilateral symmetry down the sagittal plane, with the line of symmetry running from ventral to dorsal and dividing the body into two left and right halves.

Animals in the phylum Echinodermata such as sea stars, sand dollars, and sea urchins display radial symmetry as adults, but their larval stages exhibit bilateral symmetry. This is termed secondary radial symmetry. They are believed to have evolved from bilaterally symmetrical animals; thus, they are classified as bilaterally symmetrical.

Secondary radial symmetry in echinoderms : The larvae of echinoderms sea stars, sand dollars, and sea urchins have bilateral symmetry as larvae, but develop radial symmetry as full adults.

Only members of the phylum Porifera sponges have no body plan symmetry. There are some fish species, such as flounder, that lack symmetry as adults.

However, the larval fish are bilaterally symmetrical. Animals may be characterized by the presence of a coelom, formation of the mouth, and type of cell cleavage during embryonic development. Most animal species undergo a separation of tissues into germ layers during embryonic development. Animals develop either two or three embryonic germs layers. Radially-symmetrical animals are diploblasts, developing two germ layers: an inner layer endoderm and an outer layer ectoderm.

Diploblasts have a non-living layer between the endoderm and ectoderm. Bilaterally-symmetrical animals are called triploblasts, developing three tissue layers: an inner layer endoderm , an outer layer ectoderm , and a middle layer mesoderm. Germ development in embryogenesis : During embryogenesis, diploblasts develop two embryonic germ layers: an ectoderm and an endoderm. Triploblasts develop a third layer, the mesoderm, between the endoderm and ectoderm. Each of the three germ layers in a blastula, or developing ball of cells, becomes particular body tissues and organs.

The endoderm gives rise to the stomach, intestines, liver, pancreas, and the lining of the digestive tract, as well as to the lining of the trachea, bronchi, and lungs of the respiratory tract. The ectoderm develops into the outer epithelial covering of the body surface and the central nervous system.

The mesoderm, the third germ layer forming between the endoderm and ectoderm in triploblasts, gives rise to all muscle tissues including the cardiac tissues and muscles of the intestines , connective tissues such as the skeleton and blood cells, and most other visceral organs such as the kidneys and the spleen.

Differentiation in triploblasts : Triploblasts may be a acoelomates, b eucoelomates, or c pseudocoelomates. Acoelomates have no body cavity. Eucoelomates have a body cavity within the mesoderm, called a coelom, which is lined with mesoderm.

Pseudocoelomates also have a body cavity, but it is sandwiched between the endoderm and mesoderm. Triploblasts that do not develop a coelom are called acoelomates: their mesoderm region is completely filled with tissue.

Flatworms in the phylum Platyhelminthes are acoelomates.