The document provides an introduction to the phylum Platyhelminthes. Some key points: 1) Platyhelminthes includes flatworms and are the most primitive bilateral animals, with some being free-living and others being parasites. 2) They have a triploblastic, bilaterally symmetrical body without organs for locomotion but with adhesive organs like suckers. 3) Their nervous system is ladder-like with a brain ring and longitudinal nerves connected by transverse commissures. They lack circulatory and respiratory systems.

1. ANIMAL KINGDOM
PLATYHELMINTHES

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4. Introduction, Other features, Body layers, Nervous
system, Digestion, Circulation and skeleton, Respiration,
Excretion, Reproduction
Synopsis

5. Introduction

6. INTRODUCTION
◈ Gegenbour suggested the name Platyhelminthes.
◈ Included flat worms most primitive bilateral animals.
◈ Free living (terrestrial, fresh water or marine) or
parasite.
◈ Study of worms causing parasitic infestation in human
is Helminthology.
◈ Most members of this phylum are the parasites of
vertebrate. Some are found in aquatic habitat.

7. Other features

8. OTHER FEATURES
◈ Body organisation is of tissue organ grade.
◈ Body is Triploblastic i.e. body is formed from three germinal
layers i.e. Ectoderm, Endoderm & Mesoderm.
◈ Body is bilaterally symmetrical.
◈ Locomotary organs are absent in these animals but adhesive
organs are present like suckers, hook etc
◈ These are acoelomate. In between various organs a solid,
loose mesodermal tissue called Mesenchyma or Parenchyma
is present.

10. Body layers

11. BODY LAYERS
◈ Epidermis is syncytial and is some time ciliated. On
the body wall of parasitic animals a thick cuticle is
present i.e. Tegument.
◈ This cuticle protects the parasite from the digestive -
enzymes of the host. It is secreted by the epidermis.
◈ Muscles in the body-wall are mesodermal. Below the
epidermis, longitudinal, circular and oblique muscles
are present.

13. Nervous system

14. NERVOUS SYSTEM
◈ Nervous system is ladder
like having brain ring and
two main longitudinal
nerves connected at
intervals by transverse
commissures. Sense
organs occur in free living
form.

15. Digestion

16. DIGESTION
◈ In Turbellaria and Tramatoda class an incomplete
(blind sac body plan) and without anus digestive
system is present.
◈ In animals of class Cestoda, digestive system is
completely absent.

17. Circulation and
Skeleton

18. CIRCULATION AND SKELETON
◈ Skeleton and circulatory systems are absent.
Turgidity of the fluid in the parenchymal meshes
maintains the form of the body (Hydroskeleton).

19. Respiration

20. RESPIRATION
◈ Animal respire through body surface. Anaerobic
respiration in internal parasite like Taenia.

21. Excretion

22. EXCRETION
◈ Excretory organs are protonephridia or flame-cells.
◈ Flame-cells are also termed as the Solenocytes.They
also help in osmoregulation.

23. Reproduction

24. REPRODUCTION
◈ All animals of this phylum are bisexual.
◈ Reproductive system is complex and well-developed.
◈ Fertilization may be self or cross and internal.
◈ Cleavage is spiral & determinate.
◈ Development may be direct or indirect.
◈ In indirect development, larva may be one of more
types. In these animals yolk/vitelline glands are
present which provide nutrition to the eggs.

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