Cnidaria Quiz

The Triploblastic, Acoelomate Body Plan

Platyhelminthes 34,000+ Species

    Platyhelminthes Characteristics

         -Usually have flat bodies

         -Unsegmented

         -Bilateral symmetry

         -Incomplete Gut (they do not have an anus)

               -Food enters a gut, where the nutrients is absorbed and then the remainder is spit out the same opening. 

         -Somewhat Cephalized (this means they somewhat have a head)

         -Protonephridia as excretory/osmoregulatory structures

         -Have a central nervous system

         -Simple brain (Aggregation of nerve cells in the brain)

         -Has an actual mesoderm (they are triploblastic meaning they have 3 layers)

         -No anus

Platyhelminthes Classes

     Turbellaria

         -Most common marine species

        -Free living carnivores (Free living means they are not parasites)

        -Aquatic

        -Mostly hermaphroditic

The Planarian is an example of a fresh water Turbellarian

Turbillarian Anatomy

    -Flatworm anatomy is very simple. The flatworms have an organ called protonephridia. The protonephridia is a series of folds that absorb small molecules. In this manner they act like simple kidneys.

    -The flatworm has a pharynx in the middle of its body. It uses the pharynx as both a mouth and an anus.

Class Monogenea (Flukes)

          -Monogentic Flukes

          -Flukes are a parasite. Most flukes have multiple hosts with many life cycles. The monogenea flukes are called monogenea because they only have one life cycle and only one host (mono = one)

    Class Trematoda (Flukes)

          -Another type of fluke that has many life cycles and multiple hosts

          -Have complicated life cycles

          -In most species, the fluke will hatch from an egg as a larva. The larva will then go infect an intermediate host. The larva will grow in that host and then become a sporocyst. This is a dormant stage where the fluke is waiting to enter its primary host. If an animal eats the intermediate host, the fluke will awaken from its sporocyst stage and now infect the main host. In the main host, the fluke will reproduce. The main host will release the eggs in its feces causing the cycle to repeat.       

        The Chinese Liver Fluke is an example of a trematode

There are other ways to catch Flukes

-One way a person can catch a fluke is by simply walking barefoot in a pond that has flukes. The fluke eggs hatch in the pond. The fluke larva enters a snail where the snail will be the intermediate host. The fluke will live off the snail and grow. Once the fluke is large enough it will leave the body of the snail looking for a main host. When a person walks into the pond the fluke will enter the skin of the person and then travel through their blood stream entering either their lungs or some other home where they will reproduce.

        Cestoidea (Tapeworms)

                -Tapeworms have a strange life cycle as well. They do not only have a host but they also have an intermediate host

                -The adult tapeworm has a head called a scolex

                    -The head attaches to the intestines and then starts to grow proglottids

                    -Cestoides are not segmented they are strobilated (Strobila)

                         -A strobila is when an organism clones itself creating cloned segments

                    - Each proglottid is a new juvenile tapeworm

                    -The tapeworm releases these in the feces of its host so the cycle can start over

The Beef tapeworm

                    -The intermediate host for a beef tapeworm is the cow

                        -The tapeworm burrows into the muscle of the cow and lays dormant as a sporocyst

                        -The sporocyst awakens once the muscle meat is eaten by another animal

                        -The tapeworm then grows into an adult tapeworm in the new host's intestines

Scratch Model