Phylum Platyhelminthes is divided into three classes: The following classification done by Hymen based on Platyhelminthes characteristics
CLASS I - TURBELLARIA
CLASS II - TERMATODA
CLASS III - CESTODA
CLASS I: TURBELLARIA:
- Mostly free - living forms found in fresh or sea waters or on land.
- Body is unsegmented and is dorsiventrally flattened.
- Epidermis is cellular or syncytial.
- Intestine is either absent (Acoela) or simple and sac like (Rhabdocoela) or branched.
Order (1): Acoela: They are marine and small. Mouth and pharynx are simpleor absent. Oviducts 2 yolk glands are absent. Ex: Convoluta.
Order (2): Rhabdocoela: They are small. A digestive bad is present and intestine is sac like. Many are free swimming. Reproductive organs are present. Ex: Microstomum, Temnocephala.
Order (3): Alloeocoela: Small sized worms are included in this order. Intestine is simple or branched. They are mostly marine. Ex: Otoplana, Bothnoplana.
Order (4): TricIadlda: Dorsiventrally flat body is seen. Intestine has two lateral limbs and one median limb Genital aperture is single.Ex: Bipalium. Planaria.
Order (5): Poiyciadida: These are leaf like turbellarians. Intestine shows a number of branches Genital apertures are separate. Ex: Thysanozoan, Planocera.
CLASS II: TERMATODA:
These are commonly known as flukes. These are ectoparasitic or endoparasitic forms. Body is unsegmented and enlongated. Adhesive organs are, one or two suckers without hooks and spines. Digestive tract is bifurcated and highly diverticulated. Anus is absent.
Order (1): Monogenea (Heterocotyloa): These are ectoparasitic forms. An oral sucker may be" present, or absent or poorly developed. Posterior end with adhesive discs with hooks is common. Ex: Monocells, Polystomum.
Order (2): Aspidobothria: These are endoparasites. Oral sucker is absent. Hooks are absent. Development is direct. Ex: Aspidogaster.
Order (3): Digenea (or) Malacocotylea: Endoparasites are included. Suckers are present without loops. Life cycle is complicated. Ex: Fasciola, Opiathorchis.
CLASS III: CESTODA:
Totally endoparasitic forms. Body covered with thick cuticle. Mouth,digestive tract and sense organs are absent. Fertilization is internal. It is divided into 2 sub-classes.
Sub class I: Cestodaria or Monozoa: These are simple fish parasites. Body without a scolex and strobila.
Order (1): Amphilinidea: No suckers or bothria. Frontal glands are present. Male and vaginal pores are present. Ex: Amphilian.
Order (2): Gyrocotylidea: Anterior end has a cup like sucker. Uterus straight and runs directly up-to pore. Endoparasites in chimaeroid fishes. Ex: Gyrocotyle.
Sub class II: Eucestoda (or) Merozoa: Scolex with adhesive organs. More than one set of reproductive organs. Larva has 6 hooks.
Order (1): Tetraphyllidea or Phyllobothridea: Scolex shows four bothria, often with hooks. Testis is placed in front of ovaries. Vitellaria are scattered. Common genital atrium marginal. Parasitic in the intestine of elasmobranchs. Ex: Phyllobothrium, Acanthobothrium.
Order (2): Lecanicephaloidea: Scolex divided by a transverse groove into 2 parts, upper part shows disc, lower part shows 4 suckers. Intestinal parasites of elasmobranch fishes. Ex: Lecanicephalum, Ploypocephalus.
Order (3): Protencephalidea: These are segmented tapeworms. Scolex has 4 suckers. Ovary is bilobed. Live as parasites in fresh water fishes. Ex: Protocephalus.
Order (4): Diphyllidea: Scolex has two bothria and a spiny head stalk. These are intestinal parasites of elasmobranch fishes.Ex: Echinobothrium.
Order (5): Trypamorphyncha (or) Tetrarhynchoidea: Scolex shows 2 or 4 sessile bothria and bears four retractile tentacles. Vitellaria are in the form of continuous layer in cortical parenchyma. These are endoparasite of fishes. Ex: Tetrarhynchus.
Order (6): Pseudophyllidea (or) Dibothriocephaloidea: Scolex shows 2 or 6 groove like suckers without hooks. Neck is indistinct. Testis are numerous and scattered. Ovary is bilobed. Genital apertures are mid ventral in position. Intestinal parasites of teleost fish or man. Ex: Diphyllobothrium (Dibothriocephaius)
Order (7): Nippotaenidea: Scolex has single apical sucker. Progiottids are few, endoparasites of fish. Ex: Nippotaenia.
Order (8): Taenioidea or Cyclophyllidea: Scolex has four suckers and hooked rostellum. Neck is well marked. Genital pores are on one or both margins. Endoparasites. Ex: Taenia solium, Echinococcus granulosus.
Order (9): Aporidea: Scolex with 4 suckers, unsegmented ootype, yolk glands are absent. Parasites in birds. Ex: Gastrotaenia.