Planaria eat living or dead small animals that they suck up with their muscular mouths. Food passes from the mouth through the pharynx into the intestines where it is digested by the cells lining the intestines. Although very thin and delicate, flatworms are active carnivores and scavengers, using their proboscis to feed on dead or injured animals and colonial animals such as bryozoans and soft-corals.
Each flatworm is different in terms of food consumption, but most platyhelminthes absorb nutrients by consuming them through a mouth. Food travels into a gut-type structure that holds and digests it.
Once the food is broken down, the digestive system passes it all through the body. Are flatworms dangerous? While New Guinea flatworms pose a potential health threat, they are no more dangerous than the native species of invertebrates that can carry the rat lungworm parasite.
Humans are unlikely to be affected by the rat lungworm parasite since transmission of the parasite can only occur through ingestion. Are flatworms poisonous? Polycladid flatworms are often brightly colored - a toxic warning to predators. Flatworms can be identified easily because, unlike nudibranchs, they do not have gills on their backs or other appendages. Moving the sides of its body in a rippling motion, a flatworm crawls over corals. How do flatworms infect humans? The infection occurs when humans consume T.
The result is that the eggs hatch and develop into a larval form that is capable of penetrating the intestinal wall and migrating through the body to form cysts in various tissues. Why are flatworms important to humans? Flatworms provide new insight into organ regeneration and the evolution of mammalian kidneys. Summary: Our bodies are perfectly capable of renewing billions of cells every day but fail miserably when it comes to replacing damaged organs such as kidneys.
What are some examples of flatworms? Flatworm species include: Turbellaria. Girardia tigrina. What are three examples of flatworms? 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. The monogeneans are ectoparasites, mostly of fish, with simple lifecycles that consist of a free-swimming larva that attaches to a fish to begin transformation to the parasitic adult form.
The parasite has only one host and that host is usually only one species. The worms may produce enzymes that digest the host tissues or simply graze on surface mucus and skin particles. Most monogeneans are hermaphroditic, but the male gametes develop first and so cross-fertilization is quite common. The trematodes, or flukes, are internal parasites of mollusks and many other groups, including humans. Trematodes have complex lifecycles that involve a primary host in which sexual reproduction occurs, and one or more secondary hosts in which asexual reproduction occurs.
Small flatworms use waves of ciliary action for locomotion to glide over surfaces, whereas larger species use muscular movements of their entire body to creep, swim, twist or somersault along the substrate. If a flatworm is starved it is capable of shrinking to hatching size and when fed it has the ability to grow back to its original size.
Flatworms are hermaphroditic having both male and female sex organs and they typically reproduce both sexually and asexually. The majority of sexual reproduction is through cross-fertilization where both individuals fertilize each other.
The fertilized eggs are frequently stored for a period of time within the flatworm, and are either retained in the parent or laid as egg masses. Some freshwater flatworms produce special overwintering eggs, which are retained within the parent until spring. Asexual reproduction occurs under environmentally stressful conditions or when mating partners are scarce. This usually occurs by one of two methods;. The first method is through budding; the buds grow out along the length of the parent's body, forming chains until they are ready to separate into new individuals.
The second method is called transverse fission; the posterior half of the worm attaches itself to the substrate while the anterior half continues to move forward until the two halves pull apart. Each half regenerates to form a complete worm. A few species can actually fragment themselves into several pieces, each of which regenerates to form several small worms. The flatworm's lifespan is uncertain, but in captivity members of one species lived from days.
Flatworms may regulate population dynamics of zooplankton in ponds. They are also consumers of protozoans, rotifers, and algae, and help to regulate populations of these organisms. Animal Life Resource Available here. Brusca, R.
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