Classification of Phylum Platyhelminthes

Phylum Platyhelminthes is divided into three classes: The following classification is done by Hymen based on Platyhelminthe's characteristics.

• CLASS I - TURBELLARIA
• CLASS II - TERMATODA
• CLASS III - CESTODA

CLASS I: TURBELLARIA:

1. Mostly free-living forms found in fresh or sea waters or on land.
2. Body is unsegmented and is dorsoventrally flattened.
3. Epidermis is cellular or syncytial.
4. Intestine is either absent (Acoela) or simple and sac-like (Rhabdocoela) or branched.

Order (1): Acoela:

They are marine and small. The mouth and pharynx are simple or absent. Oviducts 2 yolk glands are absent. Ex: Convoluta.

Order (2): Rhabdocoela:

They are small. A digestive bad is present and the 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. The intestine is simple or branched. They are mostly marine. Ex: Otoplana, Bothnoplana.

Order (4): TricIadlda:

A dorsoventrally flat body is seen. The intestine has two lateral limbs and one median limb Genital aperture is single. Ex: Bipalium. Planaria.

Order (5): Poiyciadida:

These are leaf-like turbellarians. The intestine shows several branches Genital apertures are separate. Ex: Thysanozoan, Planocera.

CLASS II: TERMATODA:

These are commonly known as flukes. These are ectoparasitic or endoparasitic forms. The body is unsegmented and elongated. Adhesive organs are one or two suckers without hooks and spines. The digestive tract is bifurcated and highly diverticulated. Anus is absent.

Order (1): Monogenea (Heterocotyloa):

These are ectoparasitic forms. An oral sucker may be present, absent, or poorly developed. A posterior end with adhesive discs with hooks is common. Ex: Monocells, Polystomum.

Order (2): Aspidobothria:

These are endoparasites. The 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. The life cycle is complicated. Ex: Fasciola, Opiathorchis.

CLASS III: CESTODA:

Endoparasitic forms. Body covered with thick cuticle. The 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: Amphibian.

Order (2): Gyrocotylidea:

The 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 the ovaries. Vitellaria are scattered. The common genital atrium is marginal. Parasitic in the intestine of elasmobranchs. Ex: Phyllobothrium, Acanthobothrium.

Order (2): Lecanicephaloidea:

Scolex is divided by a transverse groove into 2 parts, the upper part shows the 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. The ovary is bilobed. Live as parasites in freshwater 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 is in the form of a continuous layer in the cortical parenchyma. These are endoparasites of fish. Ex: Tetrarhynchus.

Order (6): Pseudophyllidea (or) Dibothriocephaloidea:

Scolex shows 2 or 6 grooves like suckers without hooks. The neck is indistinct. Testis are numerous and scattered. The 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 a single apical sucker. Progiottids are few, endoparasites of fish. Ex: Nippotaenia.

Order (8): Taenioidea or Cyclophyllidea:

Scolex has four suckers and a hooked rostellum. The 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, and yolk glands are absent. Parasites in birds. Ex: Gastrotaenia.