Life-cycle complicated, involves one or more hosts. Fertilization is internal.Development incomplete. In majority of forms, eggs are devoid of yolk but provided with special yolk cells and are covered by egg shell.Ĭross fertilization in trematodes and self-fertilization in cestodes is very common. Sexes are united, i.e., hermaphrodite with very few exceptions.Īsexual reproduction by fission occurs in many fresh water Turbellarians Sense organs are of common occurrence in Turbellaria but these are greatly reduced in parasitic forms. This type of nervous system is called ladder type of nervous system. The main nervous system consists of a pair of cerebral ganglia or brain and one to three pairs of longitudinal nerve cords connected to each other by transverse commisures. Respiratory & circulatory systems are absent.Įxcretory system consists of single or paired protonephridia with flame cells. It helps in transportation of food materials.ĭigestive system is totally absent in tapeworms but in other flatworms (Trematoda & Turbellaria) it consists of mouth, pharynx & blind intestine (anus absent). The space between the body wall, alimentary canal & other organs is filled with a peculiar connective tissue, called the parenchyma. However hooks, spines, suckers, teeths may be present which act as adhesive organs. The flat worms are mostly parasites but some are free living e.g., PlanariaĪcoelomate, triploblastic, bilaterally symmetrical and dorsoventrally flattened animals with organ system level of organisation.īody segmented (false segmentation) except in Class Cestoda.īody covered with a cellular, syncytial one-layered partly ciliated epidermis while in parasitic trematodes & cestodes epidermis is lacking & the body is covered with cuticle.Įxoskeleton & endoskeleton are completely absent.
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