PLATYHELMINTHES

PLATYS HELMINTHES

FLAT WORMS

General CharacteristicsFree-living or parasiticThe simplest animals that are bilaterally

symmetrical, First animals with 3 germ layers - triploblastic◦Ectodermis◦Mesodermis◦Endodermis

Epidermis has cilia or cuticleCoelom lacking (acoelomate).The phylum Platyhelminthes

represents all flatworms in the kingdom Animalia.

CLASSES

Class Turbellaria - Free Living Worms

Class Trematoda - FlukesClass Monogenea - FlukesClass Cestoidea - Tapeworms

Turbellaria(e.g., Planaria)They are mostly free-living, and range

from 1 mm (0.039 in) to 600 mm (24 in) in length.

Most are predators or scavengers, and terrestrial species are mostly nocturnal and live in shaded, humid locations, such as leaf litter or rotting wood. 

Turbellarians have no cuticle (external layer of organic but non cellular material). 

 In a few species, the skin is a syncytium, a collection of cells with multiple nuclei and a single, shared, external membrane. However, the skins of most species consist of a single layer of cells. 

Non parasitic animals.

Some species also have a protrusible pharynx that captures food and transfers it into the mouth

Can be carnivores or scavenge on dead animals and detritus.

On the anterior end (head) are eyes.The anterior end possesses lateral

projections called auricles.A ciliated epidermal layer covers the body.

Phylum Platyhelminthes 8

• Loosely connected mesenchyme cells surrounds the gut.

• LocomotionSwim or crawl by cilliary population.• Feeding & DigestionMouth is an opening located on the mid ventral line. • Food goes through this mouth and pharynx

like tube into gastro vascular cavity.

When the animal is feeding pharanyx is projected out of the mouth.

There is no anus, so undigested food particles are ejected through mouth.

ExcretionConsists of an interconnecting series of

excretory canals.

Cillia containing flame cells are found at the end of the side branches of these canals.

These flame cells are most important for water balance.

ReproductionAsexually – Transverse fissionSexually – Copulation

Nervous systemTwo longitudinal nerves that extend the

length of each side of the body.It forms a brain in the anterior region.Series of transverse nervous can be

seen.

Parasites ???

Class TrematodaLive as endoparaeyte/ endoparacyte.Size is less than 1mm to more than

8cm.Oval or elongate shapedDigestive system, nervous system

redused compared to Turbellaria.(e.g., Fascioloaris, Clonorchis)

Reproduction

Class MonogeneaFree-living flatworms are predators.Live in water or in shaded ,humid terrestrial environment such as leaf litter.

Ciliated larvae.

Most distinguishing feature is the presence of a large attachment organ called an opistohaptor

Have a single host.

Class CestodaEndoparasites (E.g. Tapeworms)The anterior end has scolex. It used to

attach to the hosts body.Near scolex there is rostrellum that

contains hooks, scolex also include suckers.

Hooks can withdraw or extend.

From strobila makes up body. Strobila is a collection of proglottids.

Most are adapted to live inside the gut of the host.

4ft to 10ft ( Sometimes 40 feets)Body is covered by protective cuticle.Digestive system absentReproduction

They are hermaphroditic.

Body planOuter Body Covering

• The body of some Platyhelminthes (e.g., turbellarians )

is covered by a ciliated epidermis

• Epidermal cells contain rod-shaped structures called

rhabdites that when released into the surrounding water,

expand and form a protective mucous coat around the

animal.

• The outer body covering of other platyhelminthes

(e.g., parasitic forms) is a non-ciliated tegument

• The tegument is referred to as a syncytial

epithelium

BODY CAVITYAcoelomates

SYMMETRY Bilaterally symmetrical Dorsoventrally flattened

Digestive System

• Some of the Platyhelminthes possess a

digestive system, with a mouth, pharynx, and

a branching intestine from which the nutrients

are absorbed

• The intestine, with only one opening, is a

blind system.

NERVOUS SYSTEMAnterior cerebral ganglia,

longitudinal nerve cords, nerve cords, and some lateral nerve

Sensory organs ( e.g. Eye spots,

statocytes )

Reproduction Platyhelminthes reproduction

occurring types

Asexual reproduction Sexual reproduction

Excretory System

Flame cells, the beating of their flagella extract water that contains wastes and some reusable material, and drive it into networks of tube cells which are lined with flagella and microvilli.

The tube cells flagella drive the water towards exits called nephridiopores

Combinations of flame cells and tube cells are called protonephredia.

Distinguished feature of phylum Platyhelminthes

Flame cells.

Diseases cause by Platyhelminthes for fish

Intense monogenean infections induce respiratory and osmoregulation dysfunctions.

Metacarcarial infection It may affect the growth and survival or disfigure fish so they lose their market value as a food or ornamental profucts.

CestodiasisLow number of pleurocercoides

may be located in vital organs such as the brain, heart, spleen, kidney or gonad and have a devastating affects on the fish.

Presence or absence of ciliaFree living adult have ciliaLarval stage of parasitic animals

have cilia