Flatworms, Roundworms, & Rotifers Chapter 34

Phylum Platyhelminthes Section 34.1

General Structure: 3 germ layers – ectoderm, mesoderm, and endoderm acoelomates Bilateral symmetry Anterior and posterior ends Dorsal and ventral surfaces only Flat body plan Flatworms!

General Functions: Exchange oxygen and carbon dioxide directly with the environment to cells by diffusion No circulatory system or respiratory system needed Only one opening where food and wastes pass through! Cephalization

Turbellaria - non-parasitic Classification: Four Classes: Turbellaria - non-parasitic Trematoda- parasitic Monogenea - parasitic Cestoda –parasitic

1. Class Turbellaria: 4,500 species Mostly marine Swim in wavelike motion Glide over solid surfaces on layer of mucus Example: Planarian Dugesia freshwater Video

Planarian Body Plan:

Planarian Organ Systems: Digestive System: Scavengers & predators Decaying plants & animal matter Prey on smaller organism Pharynx – throat that extends to the middle of body video Pharynx

Planarian Organ Systems: Excretory System: Flame Cells – enclosed tufts of cilia that draw excess water together and excretes it through pores video Flame Cells

Planarian Organ Systems: Nervous System: Cerebral ganglia: two clusters of nerve cells at anterior “Brain” Can learn Eyespots: sense direction and intensity of light Other senses: touch, water currents, chemicals

Planarian Organ Systems: Reproductive System: Sexual: Hermaphrodites Eggs laid in protective capsule Hatch in 2-3 weeks Asexual: Regeneration

2. Class Trematoda & 3. Class Monogenea: Both are parasitic flukes Leaf-shaped flatworms Endoparasites: Live in blood, intestines, lungs, liver, etc. Ectoparasites: Live on external surfaces of aquatic hosts

Structure of Flukes Anterior & ventral suckers for attachment to host Nervous system like planarian Except NO eyespots Tegument – outer layer that protects from host’s immune and digestive system

Liver fluke

Reproduction of flukes: Most are hermaphroditic May release 10,000+ eggs at a time! Complicated life cycle (p. 692)

Life Cycle: Primary host: adult parasite gets nourishment from this host Sexual reproduction Intermediate host: larvae derive nourishment here Asexual reproduction

Fluke Diseases in Humans Swimmer’s itch: minor skin irritation and swelling Small brown fluke in lakes (in Ohio) Dies within skin because humans are not ideal hosts

Swimmer’s itch

Schistomiasis (blood fluke): disease that causes tissue damage, bleeding, tissue decay and possible death Lungs, intestine, bladder, & liver 200 million people affected worldwide Human- Primary host Snail- Secondary or Intermediate host Animation!

WHO Info.

4. Class Cestoda 5,000 species of tapeworms Can live in intestines of most vertebrates Enter through undercooked food with eggs or larvae Symptoms of infection: Digestive problems Weight loss Lack of energy anemia

Structure: Tegument to protect from host Also absorbs nutrients from host Scolex: knob-shaped organ with hooks and suckers to attach to host Proglottids: body sections after a short neck Up to 2,000 per tapeworm!

Reproduction: Hermaphrodites Each proglottid has ovaries and testes Filled with 100,000+ eggs each! Eggs fertilized by sperm of different proglottid

Life Cycle: Cysts: dormant larvae surrounded by protective covering in animal muscle

Phylum Nematoda & Rotifera Section 34.2

General Characteristics: Bilateral symmetry Fluid filled body cavity pseudocoelomate Holds internal organs Stores sperm & eggs Supports body Structure that muscles can contract against

Phylum Nematoda Roundworms 1mm to 4ft Digestive tract with 2 openings Long, slender bodies that taper at both ends 1mm to 4ft Digestive tract with 2 openings Anterior – mouth Posterior – anus One directional movement

Continued… Most have separate sexes Cuticle – protective covering Free-living on land, salt and freshwater 15,000 species known 150 species parasitic to plants and animals Humans are host to 50 species!

Ascaris: Roundworm parasite that lives in intestine Pigs, horses, & humans Can totally block host’s intestine Up to a foot in length Female produces 200,000 eggs/day

Video

Life Cycle: Eggs leave with feces and enter soil Enter humans with contaminated food and water Larvae enter intestines and move to blood stream, then lungs, coughed up and swallowed back to intestines where they mate and reproduce

Hookworms: Another intestinal parasite Mouth has cutting plates that clamp onto intestine wall Feed on host’s blood which may lead to anemia May cause slow mental and physical development in children Affects 1 billion people in tropical and subtropical regions

Hookworm Enter host by boring through the feet Video

Life Cycle: Eggs leave with feces Larvae develop in soil Enter host’s feet Hitch a ride with blood to the lungs Coughed up and swallowed to intestines where adult develop

Trichinella: Video Infect humans and pigs Adults embed in walls of intestine Larvae travel via blood to muscles Form cysts Humans get it from eating undercooked pork Causes disease trichinosis Muscle pain & stiffness Can cause death Video

Pinworm – most common in U.S. Live and mate in lower intestine Female crawls out at night and lays eggs around anus Person scratches during sleep and spreads eggs to everything touched Eggs ingested and hatch

Pinworm

Filarial worms – 250 million people infected in tropics Found in lymphatic system (collects excess fluid from blood vessels) Can cause elephantiasis Swollen limbs, skin hardens & thickens Can cause heartworm in dogs and cats Spread by mosquitoes

Phylum Rotifera Most are transparent (see-through) Free-living in freshwater 100 to 50 micrometers No water = dry up and look like grains of sand; when water is present again they go back to normal Cool adaptation!

Rotifer Structures: Cilia – sweep food into mouth Mastax – breaks down food Stomach Intestine – absorbs nutrients Cloaca – digestive, reproductive, and excretory systems empty here Universal hole Flame cells – pull excess water together Anus – hole to the outside

Body Parts: video

Have cerebral ganglia and eyespots Reproduction by: Parthenogenesis – unfertilized eggs become adult females