Download The Cnidarians and Flatworms - General Biology II - Lab 9 | BIOL 1407 and more Lab Reports Biology in PDF only on Docsity!
Station 1
The Cnidarians – Phylum Cnidaria
Some of the most colorful marine organisms are the radially symmetrical cnidarians; they are sometimes known as the “flowers of the sea”. Only a few forms, such as Hydra , occur in aquatic habitats. While some forms are extremely dangerous (box jellies), most are important, harmless members of the marine ecosystems.
Members of the Phylum Cnidaria are diploblastic. Their bodies consist of the outer epidermis (derived from ectoderm) and the gastrodermis (derived from endoderm) which are held together by a non-cellular mesoglea. Cnidarians have an incomplete digestive system. With this type of digestive system there is a single opening, the mouth, in which food will enter and digestive waste will be eliminated. The gastrovascular cavity not only serves as the site of digestion but also is important in support (as it is filled with water), gas exchange, and the excretion of metabolic wastes.
The epidermis of a cnidarian contains contractile cells that will allow for movement. A simple nervous system, called a nerve net , coordinates these movements. These adaptations allow for a more active lifestyle than the sponges previously examined; cnidarians are predators!
To aid in their capture of prey (or in some cases self-defense from larger predators), cnidarians have cnidocytes located on their tentacles. Cnidocytes are stinging cells which contain a coiled thread called a nematocyst , which when discharged, deliver a venomous sting.
Cnidarian life cycles may include two growth forms: a polyp and/or medusa. Polyps consist of a body stalk, which terminates in a ring of tentacles surrounding the mouth. The polyp form is usually sessile and is not as well equipped for locomotion as the medusa. Medusae are free-swimming and are best described as being shaped like an umbrella or bell.
Reproduction in cnidarians can include sexual and asexual stages. Gonads develop in the epidermal tissue and release gametes into the water directly for external fertilization. A form of asexual reproduction called budding is common and consists of the production of buds which form as outgrowths of the polyp.
The Cnidarians and Flatworms
Laboratory
Examples of Cnidarians
Hydra – a solitary aquatic polyp
Hydra are small aquatic predators that feed on small zooplankton. They use their tentacles and cnidocytes to capture prey. Hydra lack a medusa stage in their life cycle and only exist as polyps reproducing sexually with gametes or asexually by budding. Hydra are fairly sessile attaching to an aquatic substrate and waving their tentacles waiting for prey. They are however, capable of locomotion using a somersault or inchworm approach to moving.
Observe the Hydra models and slide and use the laminated sheets to label your figures.
Label the epidermis, gastrodermis, gastrovascular cavity, mesoglea, tentacles, bud, mouth, gonads, nematocyst, cnidocyte
Observe the Hydra slide and sketch the Hydra in the space provided
Label the cnidocyte and the nematocyst
Coral – colonial polyps that secrete a calcareous cup
Hard and soft corals are important components of marine ecosystems. Corals exist as large colonies of polyps each of which is surrounded by a protective calcareous cup ( corallite ). When disturbed, the corallite allows the polyps to retract and seek refuge. These colonies are often quite large and when massed together can form reefs. Coral reef ecosystems rival the tropical rainforests with striking biodiversity.
Observe the coral specimens and examine the hard corals under the dissection microscope to see the corallite openings where the living polyps once resided.
Hard Corals Soft Coral – Sea Fan
Portuguese Man-O-War – a colonial polyp
Portuguese man-o-war drift on the ocean currents using their gas-filled float as a sail. These floats are modified polyps. Man-o-war have feeding polyps with long tentacles which dangle into the water column and capture fish and other prey using powerful nematocysts. The colorful man-o-war are common on Texas beaches and often deliver uncomfortable stings to unwary fisherman or
Portuguese Man-o-war
Review Questions
- Describe the difference between a polyp and medusa.
- What are gonads?
- Describe budding by Hydra.
- Where is the mesoglea?
- Which portion of the Obelia life cycle is capable of sexual reproduction?
- List two functions of cnidocytes.
- Describe the tissue layers of Hydra.
Jellies – free-swimming medusa stage dominates life cycle
Marine jellies (or jellyfish) are often encountered along beaches or bay systems. The large, free-swimming medusa move by pulsing actions of their bell. Many species have powerful nematocysts used to capture prey and can deliver an uncomfortable sting to potential predators as well. For example, the box jellies of the Pacific are known as some of the most dangerous, venomous animals on the planet. The tentacles are positioned along the margin of the bell-shaped medusa. Oral arms surround the mouth and hang under the bell. Four circular gonads can be seen in mature specimens during the breeding season.
The benthic (bottom-dwelling) polyp stage of the life cycle is tiny compared to the medusa.
Jelly medusa – label tentacles, oral arms, gonads, bell
wastes, planaria use protonephridia ( flame cells ). These protonephridia are scattered widely throughout the body so that wastes may be removed efficiently from the tissues.
Observe the planaria slide and use the models and laminated sheets to label the figures.
Dugesia slide- label the eyespots, auricles, mouth, pharynx, gastrovascular cavity
Dugesia model- label the eyespots, auricles, mouth, pharynx, gastrovascular cavity, brain, longitudinal nerves, transverse nerve, longitudinal muscle, transverse muscle, protonephridia
Tapeworms – parasitic flatworms
The tapeworms (or cestodes) are uniquely adapted as endoparasites (live inside a host). The adult tapeworms live in the small intestines of the final host (the host which harbors the adult stage) and do not have a digestive system. The tapeworm’s scolex (head- region) has an assortment of hooks or suckers for attachment to the final host’s small intestine. The remaining body is divided into segments known as proglottids. Each proglottid is a monoecious reproductive machine capable of producing an enormous number of fertilized eggs. Tapeworms can reach impressive sizes (some over 25m) due to the thousands of proglottids that form their body. The mature proglottids near the posterior are much larger as they are filled with fertilized eggs and may by passed from the host’s body in the feces.
The beef tapeworm ( Taenia ) is a common endoparasite of humans. To complete the life cycle, a ripe proglottid breaks free from the adult tapeworm and is passed with the host’s feces. If these feces are deposited in a grassy area, the tapeworm larvae attach to the blades of grass. The intermediate host (the host which harbors the larval stage) for the beef tapeworm is a bovine, which may ingest the larvae by consuming the grass. Once in the intermediate host’s body, a cyst surrounding the scolex develops in the muscle tissue. Humans can become infected by ingesting poorly cooked (temperature less than 60° C / 140° F) “ measly ” beef containing these cysts. The larval scolex is liberated from the cyst and attaches to the small iontestine where it remains for its adult life.
Examine the tapeworm specimen, slide and use the laminated sheet to label the life cycle.
Taenia slide – label the proglottid, scolex, hook, sucker
- Describe the sexual reproduction seen in planarians.
- What is negative phototaxis?
- Describe the function of the scolex of a tapeworm.
- Which organisms have proglottids? What is their function?.
- Why does a tapeworm lack a digestive system?
- How can a person ensure that if they consume beef, that they will not become infected by a tapeworm?
- Google the words “hydatid cyst” and use the space below to describe the medical significance.
Station 3
Observation of Live Planaria and Hydra
Observation of Hydra
Use a pipette to carefully transfer a Hydra from the culture to a depression slide and view under scanning power; you do not need to add a cover slip. Observe the way the Hyrda moves and look for the cnidocytes on the tentacles (they look like little ‘bumps’).
Now carefully take a dissection probe and touch the Hydra. Describe how it responded in the space below.
Now take a few of the brine shrimp larva from the seawater (about 4% NaCl) culture and transfer to a Petri dish with fresh spring water. This will take a steady hand because you do not want to transfer too much seawater. Allow the brine shrimp to swim for a moment to remove the seawater. Collect in the pipette once again and transfer to the depression slide. Observe the Hydra to see if it can capture a brine shrimp larva and consume it. Use the space below to record you observations.
Why did you rinse the brine shrimp?
Now take the 5% vinegar solution and carefully place one drop in the depression slide. As you do this, watch the Hyrda’s reaction through the microscope and record your observations below.
