Worms- Phylum Platyhelminthes

Worms- Phylum PlatyhelminthesLINK TO VIDEO

Flatworms - General Information

3 phyla in Ch. 14 – We are going to focus mainly on Phylum Platyhelminthes Symmetry: Bilateral Cephalization- head end concentrated with sense organs and nervous control Tripoblastic- has a middle germ layer (mesoderm) as well as ectoderm and endoderm

Parasitic in nature Examples of Flatworms include: planaria, flukes, and tapeworms 4 Classes : Turbellaria(Planarians), Trematoda (Flukes), Monogenea and Cestoda(Tapeworms)

Class: Turbellians - Body Form •Ciliated epidermis •Rod- shaped Rhabdites- swell and form a protective mucous sheath around the body •Dual gland adhesive organs in the epidermis

Class Monogenea, Tremotoda, and Cestoda – Body form Parasitic Non-ciliated body covering Ciliated covering is lost once a host is contacted

Digestive System: Includes a mouth, pharynx, and an intestine

GVC- Gastrovascular cavity present

Mainly carnivorous – feed on small crustaceons, nematodes, rotifers, and insects

Flatworms have a system called: protonephridia/ can be used for osmoregulation or excretion

System is mainly osmoregulatory ( regulates the water inside and outside of the body)

Flame Cells- cup shaped cell that has flagella extending out

Nervous System-

Simple nervous system (found in turbellarians) – Subepidermal Nerve Plexus similar to the nerve net in cnidarians

•May also have one to five pairs on longitudinal nerve cords lying under the muscle layer

•Have ganglia and neurons

•SENSE ORGANS:

•Ocelli: light sensitive eyespots

•Tactile Cells -touch

•Chemoreceptive cells -

•Statocysts for equilibrium

•Rheorecptors- sensing direction in water currents

Reproduction and regeneration: Reproduce both sexually and asexually (fission) same as budding like the hydra

Almost all flatworms are monoecious Some have spiral determinate cleavage typical of protostomes

Class Turbellaria – extra information Often distinguished on the basis of the form of the gut ( present or absent? , simple or branched?, pattern of branching? ) •Creeping forms that combine muscular with ciliary movements to move

Class Trematoda All parasitic flukes

Leaflike in form

Penetration glands / organs for adhesion to hosts like suckers and hooks

Increased reproduction capacity

Sense organs are poorly developed

EX: Liver Fluke in Humans ( common in regions of east Asia, especially China, Southeast Asia, and Japan; also common in cats, dogs, and pigs.)

Blood Fluke (causes schistosomiasis)

Life cycle of a fluke

Class Monogenea Are all parasites ( on fish, frogs, turtles, and one on the eye of a hippopotamus) Cause little damage to hosts Can be serious if many hosts are crowded together (farm-raised fish)

Class Cestoda- Tapeworms

Long, flat bodies

Has a scolex(for attachment to host)- has suckers/ tentacles for attachment , and proglottids ( linear series of reproductive units)

No digestive system

Well-developed muscles

Excretory system is similar to other flatworms as well as nervous system

No special sense organs

No head

Examples of Cestoda : Beef Tapeworm, Pork Tapeworm, Fish tapeworm, Dog Tapeworm

Phylum Nemertea Often called ribbon worms

Long muscular proboscis

Bilateral

Triploblastic

1000 species; all marine