Where is a planarians mouth

Turbellarians are hermaphrodites, meaning that each individual animal possesses both male and female anatomy, and when two turbellarians mate, they inseminate one another. Some species lay eggs encased in round capsules on short stalks.

Turbellarians are also famous for their ability to regenerate when cut into pieces, and some species reproduce by splitting their bodies into two of these clones. 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.

Many people know planarians from watching them regenerate from cut pieces in biology class, a wonderful thing to witness. Ecosystems are based on the tiny plants and animals that form the base of food chains. Turbellarians are an important link between the tiny, sometimes microscopic animals they eat and their own, larger predators, such as small fish, crayfish, and aquatic insects.

Turbellarians Planarians; Free-Living Flatworms. Field Guide Aquatic Invertebrates. Butterflies and Moths. Land Invertebrates. 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. These larvae leave the snail and are present on the ground in areas of poor sanitation. The immature stages enter humans by burrowing through the skin of a human host. The immature flukes enter blood vessels and mature there.

They can cause anemia and damage to the liver, bladder, and brain. Tapeworms Class Cestoda are also parasite flatworms. Humans can become infected with tapeworms by ingesting uncooked or undercooked pork or beef. Larval immature stages of the tapeworm present in the muscle of pigs or cows are ingested.

The tapeworm attaches to the intestine while passing through the digestive tract using hooks or suckers. The tapeworm matures and grows in the intestine, a food-rich environment. The tapeworm grows longer by budding. Each proglottid contains reproductive structures and eggs are produced and become fertilized within each segment.

The oldest proglottids break off of the tapeworm and leave the host with feces. In areas of poor sanitation, pigs or cows ingest the zygotes. The immature stages burrow into the muscle tissue of the pig or cow and the cycle repeats. The impact the Phylum Platyhelminthes has on humans is the fact that several animals within the phylum are human parasites.

The Phylum Nematoda roundworms or nematodes includes harmless, soil-dwelling roundworms nematodes that eat decaying organic material or small soil animals. The phylum also includes plant parasites that infect the roots of plants. These parasitic nematodes decrease the productivity of many human crops. The phylum includes several human parasites see below. Like the Phylum Platyhelminthes, the Phylum Nematoda consists of bilaterally symmetrical animals that have the organ system level of organization.

The Phylum Nematoda differs from the Phylum Platyhelminthes in two significant ways. First, roundworms have a complete digestive system.

This means that there are two opening to the digestive system. The mouth at the anterior ingests or swallows food, and the anus at the posterior releases digestive waste. A complete digestive system is much more efficient than a cul-de-sac gut. The complete digestive system allows continuous processing of food. A roundworm can eat continuously, food digestion can occur continuously, and waste material can be released continuously.

Animals with a cul-de-sac gut must wait until a meal has been digested, release digestive waste from the mouth, and only then swallow the next meal. The second significant difference between the Phylum Nematoda and the Phylum Platyhelminthes is that the roundworms have a fluid filled body cavity.

The presence of this structure allows space and cushioning for organs, provides the roundworm with a hydraulic skeleton, and aids in the distribution of food from the digestive tract to the other cells of the worm. Several human parasites are roundworms. Many people in tropical countries are infected with hookworm. Immature stages of this parasitic worm burrow through the skin, travel through the blood vessels to the lungs, enter the air spaces of the lungs and crawl into the esophagus.

The immature stage is then swallowed. The worm attaches to the intestine with hooks and matures into an adult. Fertilized eggs are released with feces, and the zygotes develop into immature stages on soil. When people walk barefoot over the soil, they become infected.

The mature hookworm drinks blood and lymph juices. They cause anemia due to blood loss. The human roundworm is common where human feces is used as plant fertilizer. People ingest eggs when they eat plant material. The immature stages travel through the human body in blood vessels.

Mature human roundworms live in the intestine where they produced eggs that are released with feces.

The free-living species of flatworms are predators or scavengers. Parasitic forms feed on the tissues of their hosts. Most flatworms, such as the planarian shown in Figure 1, have a gastrovascular cavity rather than a complete digestive system.

Some species also have an anal opening. The gut may be a simple sac or highly branched. Digestion is extracellular, with digested materials taken in to the cells of the gut lining by phagocytosis. One group, the cestodes, lacks a digestive system. Flatworms have an excretory system with a network of tubules throughout the body with openings to the environment and nearby flame cells, whose cilia beat to direct waste fluids concentrated in the tubules out of the body.

The system is responsible for the regulation of dissolved salts and the excretion of nitrogenous wastes. The nervous system consists of a pair of nerve cords running the length of the body with connections between them and a large ganglion or concentration of nerves at the anterior end of the worm, where there may also be a concentration of photosensory and chemosensory cells. Figure 1. The planarian is a flatworm that has a gastrovascular cavity with one opening that serves as both mouth and anus.

The excretory system is made up of tubules connected to excretory pores on both sides of the body. The nervous system is composed of two interconnected nerve cords running the length of the body, with cerebral ganglia and eyespots at the anterior end. There is neither a circulatory nor respiratory system, with gas and nutrient exchange dependent on diffusion and cell-cell junctions.

Most flatworm species are monoecious, and fertilization is typically internal. Asexual reproduction is common in some groups. Platyhelminthes are traditionally divided into four classes: Turbellaria, Monogenea, Trematoda, and Cestoda Figure 2.

As discussed above, the relationships among members of these classes is being reassessed, with the turbellarians in particular now viewed as a paraphyletic group, a group that does not have a single common ancestor.

Figure 2. Phylum Platyhelminthes is divided into four classes. Dactylogyrus , commonly called a gill fluke, is about 0. The class Turbellaria includes mainly free-living, marine species, although some species live in freshwater or moist terrestrial environments.

The ventral epidermis of turbellarians is ciliated and facilitates their locomotion. Some turbellarians are capable of remarkable feats of regeneration in which they may regrow the body, even from a small fragment.