Development may be direct or indirect. The Class Turbellaria contains mostly free-living forms ranging in size from a few mm to 50 cm. Most species are bottom dwellers in marine and freshwater environments that crawl over rocks, sand or vegetation. Smaller forms can swim by means of ventral cilia, but more often they move by laying down a sheet of mucus that aids in adhesion and helps the cilia gain traction.
Larger forms use powerful muscle contractions to crawl or swim. Unique to turbellarians are rod-shaped rhabdites found among the ventral epidermal cells of the body surface. These rhabdites secrete mucus that coats the animal's body, possibly for protection against predators or to prevent drying.
In terms of nutrition, most turbellarians are predators and scavengers. Epidermal mucous secretions trap and kill prey items.
A muscular pharynx everted though the ventral mouth is used to secrete digestive enzymes into prey, which is then sucked into the branched intestine that forms a gastrovascular cavity. In addition to a simple nervous system, turbellarians have light-sensitive eye spots called ocelli that help orient the animal to the direction of light. Touch and chemical receptors in some forms like the planarian seen in lab are concentrated in lateral projections from the head called auricles that look like ear lobes.
Reproduction in turbellarians can occur asexually through fission or sexually; all forms are monoecious but practice cross-fertilization. Planarians are also known for their tremendous powers of regeneration, and a planarian that has been cut into three pieces will give rise to three new complete individuals! The Class Monogenea contains animals called monogenetic flukes. Although most of species are ectoparasites on the skin or gills of fish, there a few forms found in the bladders of frogs and even one that lives in the eye of a hippopotamus!
The life cycle of a monogenetic fluke is direct, with a single host. Since they must depend on a single host for both reproduction and transmission, monogenetic flukes have evolved mechanisms that usually ensure that the parasites do not endanger the lives of their hosts, but in crowded conditions such as fish hatcheries , they can produce serious, damaging infestations.
The Class Trematoda contains about 8, species of leaf-like animals called digenetic flukes. The adults are endoparasites on vertebrates but many invertebrates serve as intermediate hosts, and many species of medical and economic importance! Development is trematodes indirect; not only adults but larvae reproduce and all species have at least two hosts, one for transmission and the other for reproduction.
The vast majority of flukes possess two large suckers that are used for attachment, an anterior one called an oral sucker, which surround the mouth and a posterior one called a ventral sucker, or acetabulum. Trematode Life Cycle In trematodes, one egg leads to the production of many progeny!
Eggs are typically deposited in water via the urine or feces of the definitive host. When they reach freshwater, the egg opens and a ciliated free-swimming larva called a miracidium swims out. The miracidium will then swim about until it finds a suitable intermediate host, which is usually an aquatic snail to which it is chemically attracted.
When the miracidium finds snail, it penetrates it, loses its cilia and develops into a sporocyst, which produces asexually either more sporocysts or a number of rediae that also produce asexually either more rediae or tailed forms called cercariae.
The cercariae emerge from the snail, swim around and penetrate a second intermediate host, the final definitive host or encyst on vegetation in the case of the sheep liver fluke , where they are transformed into metacercariae, which are juvenile flukes; the adult grows from the metacercariae when it is eaten by the definitive host. Trematode Infection in Humans Humans can be infected with a number of serious trematodes in a variety of ways.
In the case of the Oriental liver fluke Clonorchis sinensis , infection occurs by eating raw or poorly cooked fish which serve as the second intermediate host of the parasite containing the metacercariae of the trematode.
In the case of blood flukes Schistosoma , infection can occur when tailed cercariae burrow through exposed skin of people bathing or working in waters containing the cercariae such as Asian rice paddies.
Schistosomiasis is a chronic illness that can damage internal organs and, in children, impair growth and cognitive development. The urinary form of schistosomiasis is associated with increased risks for bladder cancer in adults, and the disease is the second most socioeconomically devastating parasitic disease after malaria!
The sheep liver fluke Fasciola hepatica is a common parasite of sheep and cattle, which become infected by eating aquatic plants containing encysted metacercariae juvenile flukes. Humans can acquire the parasite by eating raw watercress which grows naturally at the edges of lakes and ponds and is cultivated in many countries in Asia and Europe containing the metacercariae of the fluke.
The lung fluke Paragonimus westermani is a potential dangerous parasite found in Asia and South America that can cause death in human hosts. Their eggs are coughed up from the lungs of their host, swallowed and eliminated in feces Humans can become infected by eating raw or poorly cooked freshwater crabs the second intermediate host of the parasite containing the metacercariae of the fluke. The Class Cestoda contains about 4, species of tapeworms, all of which are highly modified endoparasites that live in just about every known vertebrate species.
The long, flattened body of a tapeworm which is referred to as the strobila is divided into segments called proglottids. Most forms have an organ called a scolex at the anterior end with suckers, hooks, etc. Tapeworms lack a digestive system and feed by absorbing nutrients directly from the host. The entire body surface is covered with minute projections called microtriches that greatly increase the absorptive surface area of the tapeworm. Tapeworms also secrete substances that inhibit the digestive enzymes of their host as well as lowering the pH around them to a level that they but not the digestive enzymes of their host can function.
In tapeworms, much of the strobila is given over to reproduction. Each proglottid is monoecious, and cross-fertilization or even self-fertilization is common. Proglottids can be filled with up to , eggs! The Tapeworm Life Cycle With few exceptions, all cestodes require at least two hosts, and the adult is the parasite in the digestive tract of vertebrates. Often one of the intermediate hosts is an invertebrate most often an arthropod such as a flea, louse or copepod that is eaten by the final host.
The eggs within the proglottids are shed daily in the feces into the soil where they may lie dormant for quite some time. Sometimes the egg-bearing proglottids crawl out of the anus by themselves and can be found wriggling about on an infected dog, cat or child or on infected clothing and bedding.
Once the eggs are released, they must be ingested by an intermediate host in order to hatch into hooked larvae called oncospheres, which bore through the intestinal wall and picked up by the circulatory system where they are transported to skeletal muscle, heart or even some other organ where they encyst as cysticerci bladder worms. Tapeworm Infection in Humans Humans can become infected with tapeworms by eating poorly cooked meat containing the cysticerci of the tapeworm. The most important tapeworms that infect humans are the beef tapeworm Taenia saginata and the pork tapeworm Taenia solium.
Another species of cestode that can infect humans is the broad fish tapeworm Diphyllobothrium latum , which is common in fish inhabiting the Great Lakes.
Again, infection occurs by ingesting cysticerci in raw or poorly cooked fish. In most cases, tapeworms found in the gut do not cause much damage to their human hosts, but occasionally they migrate to other organs such as the eyes or even the brain, where they can cause serious neurological problems and even death from cerebral cysticercosis!
The dog tapeworm Diplydium caninum is common in dogs but can be picked up by humans usually kids who ingest infected fleas that serve as intermediate hosts of the parasite. In contrast to radiate and acoelomate phyla in which the space between the body wall and the digestive tract is filled with mesoglea or with solid mesenchymal parenchyma, the remaining bilateral animals covered in the Zoo Lab website have a body cavity in which internal organs are located.
In the pseudocoelomates, the embryonic blastocoel persists as a body cavity. The Phylum Acanthocephala contains about 1, species of parasitic animals called spiny-headed worms, all of which are endoparasites in the intestinal tracts of vertebrates especially fishes. Two hosts are required to complete the life cycle, and the juveniles are parasites of crustaceans and insects. Most species are quite small less than 40 mm. Spiny-headed worms have an eversible proboscis covered with recurved spines that provides a means of attachment in the host's intestine.
Eggs pass out host and are eaten by certain insects or crustaceans where they hatch and go through several developmental stages. When the intermediate host is eaten by a bird, mammal or fish, the larva inside attaches to the intestinal wall with its spiny proboscis.
The Phylum Rotifera contains about 1, species of microscopic animals called rotifers that bear an anterior crown of cilia that give the appearance of a revolving wheel. Although cosmopolitan widely distributed , most are found only in freshwater environments. The general body plan of a rotifer is divided into three regions: a head, which bears a ciliated organ called a corona wheel organ , which creates currents that draw small planktonic forms into the mouth, which opens into a muscular pharynx called a mastax.
The mastax is equipped with intricate jaws composed of seven hard pieces called trophi that are used for grasping and chewing the prey. The trunk contains the visceral organs, and the foot when present is segmented and ringed into joints that can shorten or telescope.
Pedal glands on the foot secrete a sticky substance that anchors the animal to the substrate or allows it to creep along with leech like movements. From this point on, all animals that will be studied in the Zoo Lab website are eucoelomate, that is, they have a true coelom body cavity that is lined with a thin layer of mesodermal tissue called the peritoneum.
Note: The development of the coelom must be considered one of the most important steps in the evolution of larger and more complex forms for it provides plenty of space for organs that can be held in place by thin membranes called mesenteries! The Phylum Ectoprocta also called Bryozoa contains about 4, species of small colonial forms called moss animals that are found in shallow freshwater and marine environments.
Although bryozoans are also well represented in the fossil record, they are also quite abundant today. Modern marine forms exploit all kinds of firm substrates including shells, rocks, marine timbers, and ship bottoms. In fact, like barnacles, the ectoprocts are one of the most important groups of fouling organisms that need to be removed periodically from ship and boat hulls.
Each individual zooid consists of a feeding part and a case-forming part. The zoecium can be gelatinous, chitinous or calcareous, and sometimes it is impregnated with sand grains. The feeding portion of the animal contains the lophophore a ciliated feeding device that can also be used for gas exchange , digestive tract, muscles and nervous system. This is an ancient group that is well represented in the fossil record with some 30, described species but only about living species.
Brachiopods resemble bivalve molluscs, but unlike bivalves, they have shells that are located on the ventral and dorsal side rather than left and right. Brachiopods in the latter group are called lampshells because the larger ventral valve resembles a Roman oil lamp. Some brachiopods attach themselves to the substrate by a pedicel on the ventral valve while others just cement the ventral valve to the substrate like an oyster or burrow into the sediment.
Like bryozoans, brachiopods also have a lophophore surrounding the mouth that is used for feeding and gas exchange. Lab-5 This slide contains two specimens of the free-living turbellarian flatworm Planaria.
One specimen has been stained, while the other has been injected with carbon black to reveal the extent of the blind gastrovascular cavity, which is divided into three, many-branched trunks one anterior and two posterior.
Without an anus, food must first pass through the mouth into the gastrovascular cavity where it is digested after which waste products exit through the same opening. Note the large, eversible pharynx in each planarian that is used for feeding. In the head region are lateral projections called auricles not well developed on the specimens shown that contain touch and chemical receptors as well as light-sensitive ocelli eye spots.
This slide contains a cross section through the pharyngeal middle region of the free-living flatworm Planaria. Note the large muscular pharynx that lies within a space called the buccal cavity. During feeding, the pharynx can be everted through the mouth and used to suck up fluids and soft tissue from captured prey. Two branches of the extensive gastrovascular cavity can also be seen.
This cavity is lined with large, vacuolated cells that comprise the gastrodermis. On the outside of the flatworm is a ciliated epidermis that contains many gland cells as well as dark-staining rod-shaped bodies called rhabdites that can discharge their contents to form a protective mucous layer around the body. Reptiles and Amphibians.
Trees, Shrubs and Woody Vines. Wildflowers, Grasses and Other Nonwoody Plants. Scientific Name. Various families in class Turbellaria free-living flatworms in the phylum Platyhelminthes flatworms. Habitat and Conservation Turbellarians lack a respiratory and circulatory system, so they are extremely thin and require aquatic or very moist habitats. Food Unlike their parasitic cousins in the flatworm group the tapeworms and flukes , most turbellarians are free-living, and most are carnivores, eating tiny aquatic invertebrates such as rotifers, small crustaceans, and other worms.
Status There are many species of turbellarians in Missouri and in the world. Life Cycle Life Cycle. Human Connections Since they breathe through their skin, flatworms are sensitive to water quality and serve as indicators of reduced oxygen and other changes in their habitat.
Ecosystem Connections Ecosystems are based on the tiny plants and animals that form the base of food chains. Like many other cave-dwelling animals troglobites , the pink planarian lacks the ability to sense light. Right to Use. The rectangular end at upper left is the head, and the whitish part at that end is the brain. Pink planarians adhere to the bottoms of rocks under water. If the spaces between the rocks become clogged with dirt, their habitat is harmed. Similar Species. Horsehair Worms.
ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts.
While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control. Platyhelminthes flatworms Facebook. Animal Diversity.
Brown, Dubuque, IA. Read more Classification Kingdom Animalia animals Animalia: information 1 Animalia: pictures Animalia: specimens Animalia: sounds Animalia: maps Platyhelminthes: information 1 Platyhelminthes: pictures 29 Platyhelminthes: specimens 4. Moniezia expansa: information 1.
Trematoda: information 1 Trematoda: pictures
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