Phylum platyhelminthes Ch. 36 Platyhelminthes Phylum platyhelminthes · Flatworms ·  3 cell (germ) layers · More complex than sponges, cnidarians and ctenophores Bilateral symmetry (left and right side)

3 Classes class: turbellaria *planaria (free living) class: trematoda *flukes (parasitic) class: cestoda *tapeworms (parasitic) These three classes make up 18,000 species

Structure and Function · Simplest animal with bilateral symmetry · Develops from 3 germ layers 1.   ectoderm (outer layer) 2.   mesoderm (middle layer) 3.   endoderm (inner layer) · In flatworm, all 3 germ layers are pressed against each other to form solid body Belong to group called acoelomate which means without body cavity

A. Respiration Since flat shape, all cells are in relative contact to its environment, so each cell exchanges gases by diffusion. It has no circulatory or respiratory system.

B. Digestion ·  Gastrovascular cavity is a gut with single opening. Food taken in, digested, and all waste back out same opening.

C. Nerves Located in anterior end, called cephalization.

1. Turbellaria: non parasitic ·  Majority live in ocean ·  Some in fresh water *Planaria dugesia (known as Planaria) · Move in water using wave like motion Move on ground by producing mucous and using cilia to glide on it

Planaria

Planarian Anatomy

A. Digestion · Feed on decayed plant or animal · Food ingested through pharynx (muscular tube) extended through middle of body · Goes to gastrovascular cavity · Cells here absorb nutrients draw p.710 36-2 a

Digestion

B. Excretion · Through network of excretory tubules * To get rid of waste · Through network of excretory tubules · Run length of body · Connects to flame cell which are enclosed tufts of beating cilia Draw p.710 36-2 b

C. Nerves · Ganglia receive information from sensory cells ·  2 clusters of nerve cells at anterior end called cerebral ganglia which serves as simple brain · Ganglia receive information from sensory cells ·  Transmit signals to muscles along nerves ·  Has ability to learn: moves from light · Uses eyespot near ganglia to sense environment Draw p.710 36-2 c

D. Reproduction · Hermaphrodites · When reproduce sexually, they simultaneously fertilize each other · Usually asexual in summer by regeneration They attach posterior end to something, anterior end moves until it splits. This is fission. Each half then regenerates into 2 complete planaria. Draw p.710 36-2 d

2. Class Trematoda · Leaf shape parasites · Flukes · Leaf shape parasites · Difference between free-living and parasitic is that parasitic flatworms have simpler structures Live inside host or outside on host

A. Digestion · Anterior sucker is around mouth · Attaches itself with anterior and ventral sucker (see fig. 36-3 p.711) · Anterior sucker is around mouth · Draws hosts body fluid into gastrovascular cavity Wastes go out the same opening

B. Nerves · No eyespots Entire external surface is covered by a sheet of fused cells called tegument which protects fluke against host

C. Reproduction ·  Hermaphrodites but sexual reproduction occurs ·  Human is the primary host (this is where harm can be done) ·  Adult worm lives in human blood vessels ·  Eggs and sperm fertilize · Some fertilized eggs make it to host’s bladder and intestines and get excreted in urine or feces

Reproduction · These eggs make it to fresh water and develop into ciliated larvae · These larvae find a particular species of snail. They burrow into snail’s tissue and asexual reproduction takes place. Snail is intermediate host (no harm is done here) · Larvae develop tails and leave · Enter skin of human and begin cycle again · Bad in Asia, Africa and S. America Draw life cycle transp. 149 also on p.712 fig. 36-4

3. Class Cestoda · Tapeworms · Parasitic · In intestines of most vertebrates · Up to 7 species can affect humans · Get through raw or undercooked food, which contains eggs or larvae Causes digestive problems, weight loss, lack of energy and anemia

Tapeworms

A. Digestion · No gastrovascular cavity · No digestive organs · No mouth · No gastrovascular cavity · No digestive organs Absorb nutrients directly from host’s digestive tract through its own tegument

B. Structure · Anterior is knob-shaped called scolex which has hooks and suckers · Short neck connects to proglottids (draw structure fig. 36-5 p. 713) · As tapeworm grows, it adds new proglottids behind scolex, and pushes others behind · Can be 30-35 ft. in length

C. Excretory Out same manner as absorption

D. Nerves · No eyespots · No light sensitive structures Have tegument which is close to environment

E. Reproduction · Hermaphrodites · Sperm from 1 proglottid fertilizes eggs from itself or another worm · Has 2 hosts *primary host is human *intermediate host is cow or pig Draw life cycle of tape worm transp. 150 or fig. 36-6 p. 714 · Hermaphrodites · Each proglottid contains both sex organs · Eggs stored in uterus Oldest proglottids have most eggs (up to 100,000)