Flatworms have no body cavity other than the gut and the smallest free-living forms may even lack that! They neither have a distinctive skeleton nor digestive, nervous, circulatory and respiratory systems. Parasitic flatworms attach to their hosts via sucker-like mechanisms called holdfasts. Since flatworms have the ability to regenerate themselves, the lost parts develop and each of the fragment grows into a separate individual. Imagine a flatworm as being like a snake: The head half is awfully different from the tail half, but drawing a line down the middle will create two symmetrical halves. As we mentioned previously, there are three parasitic groups of platyhelminthes, and one non-parasitic one. The phylum consists of four classes: Trematoda , Cestoda , planarians , and. They can be microscopic, and they can lack a chest cavity or circulatory system.
It should be noted that some authorities consider Monogenea, which contains the order Aspidogastrea, to be a subclass within the class Trematoda. Trematoda and cestoda are total parasites. Life without a coelom : The image at left is a fluke possibly a species of Probolitrema. Reproduction A flatworm reproduces by splitting in two. They can be gray, brown, or black with stripes, spots, or mottled.
The main types of flatworms are flukes, tapeworms, cestoda and trematoda. Head Distinct head is present at the anterior end of the body. But sense cells are found in the body wall of turbellarians and are able to respond various stimuli. In other words, both the male and female reproductive organs are present in a single flatworm. In the tapeworms, the tapelike body is generally divided into a series of segments, or proglottids, each of which develops a complete set of male and female genitalia. Parasites in immature stages larvae can cause serious damage to the host.
Atti della Societa Italiana di Scienze Naturale e Storia Naturale, Milano, 129 2-3 : 139-145. Most flatworms take in food via their mouth, then move it into a digestive gut that attaches to the digestive structures. When disturbed they can swim for a considerable period of time by throwing the sides of their body into undulating waves. Several ganglionated longitudinal cords arise from the brain. On the other hand, there are other flatworms that require cross-fertilization for reproduction. They find their food through sensors that function like antennae.
In Paramphistomum the sucker is posterior-most in position, in Echinostoma and Fasciola the position is shifted more anteriorly. The parasitic worms bear hooks, scolex, suckers and other features for attaching to the host organisms. Most of this protein comes from the vitellaria. Very small head or scolex which is provided with sucker and hooks for attachment to host. Introduction to the Platyhelminthes Introduction to the Platyhelminthes Life in two dimensions. Liver fluke photo provided by , and used under conditions. Mode of life Free living aquatic forms.
The tapeworm can get into a persons digestive tract and grow to enormous lengths. Circulation A flatworm has a gastrovascular cavity with one opening. Because of the lack of any other body cavity, in larger flatworms the gut is often very highly branched in order to transport food to all parts of the body. Development may be direct eggs hatch into tiny worms that resemble the adults or indirect with a ciliated larval form. Appearance A flatworm can be microscopic or many feet long and is generally very thin.
Development of Platyhelminthes : Though hermaphrodite, the practice of cross-fertilization is the rule. The host contracts this disease by eating undercooked meat that harbors the larvae of the trichinella worm. Space between body wall and internal organs is filled up with parenchyma. Some flatworms parasitize plants, including soybeans, potatoes and pine bark. The flatworms can reproduce in both ways, sexually as well as asexually. The flatworm has three distinct cell layers - The ectoderm, the mesoderm and the endoderm and is considered to be the first organism to exhibit this factor.
The development of directional movement is correlated with cephalization. There are about 20,000 species in this group. In some groups, particularly those that live primarily in water or have an aqueous phase in the life cycle, the eggshell consists of a hardened known as , or tanned protein. The hard parts in Platyhelminthes are the hooks and spines. Reproduction occurs sexually but in few forms such as freshwater form asexual reproduction occurs by fission. The Polyclads are broad leaf-like while the tapeworms are flat and ribbon-like.