WORMS – Chapter 27

A) Flatworms: Phylum Platyhelminthes

Soft and Flat Tissues and Internal Organ

Systems 3 embryonic germ layers Bilateral symmetry Cephalization Acoelomates-without coelom (no

fluid-filled body cavity)

Feeding

Food enters Mouth/anus, then travels to pharynx, then to Gastrovascular cavity for digestion/absorption

•Carnivore

•Scavenger

•Parasitic

Respiration, Circulation, Excretion

Diffusion of O2 and nutrients through body walls

Flame cells/Nephridia – remove excess water and metabolic waste Connected to pores in the skin

Response

Ganglia – controls N.S. (nerve cell cluster)

Eyespot – detects light changes Some have specialized cells to detect

chemicals, food, etc.

Movement Cilia on epidermal

cells for gliding Muscle cells for

twisting/turning

Reproduction Hermaphrodites Sexual by 2 worms

exchanging sperm, and each lay eggs

Internal fertilization Asexual by fission

(organism splits in 2 and each half grows new parts)

Classes of Flatworms:

Turbellaria (ex: planarian) Trematoda (ex:Flukes) Cestoda (ex: Tapeworms)

A1) Class Turbellaria: Turbellarians Free-living Marine or fresh

water Not Parasitic

Ex. Pseudobiceros gloriosusTropical free-living flatworm (non-parasitic)

Ex. Planaria Cross-eyed; fresh water free-living flatworm

(non-parasitic)

A2) Class Trematoda: Flukes Parasitic Infect internal

organs of hosts Intestines; blood

vessels Some have

Multiple Hosts Snails as

intermediate hosts

Ex. Blood Fluke (not free-

living)

Parasite that matures in human blood vessels

Schistosoma mansoniLife CycleBlood Fluke

(has multiple hosts:Snail=intermediate hostHuman=primary host)

A3) Class Cestoda: Tapeworms

Parasitic Lives in intestines Long and flat Scolex-head with

suckers (hooks) Proglottids-body

segments

1) Cow/Fish/Pig (intermediate host) consumes food or water w/ zygotes (fecally contaminated)

2) Hatch to larvae and burrow into muscles as cysts (protected)

3) Human eats meat not fully cooked and larvae activated to grow to adult in human intestines

4) Eggs passed in human feces

Tapeworm Life Cycle

B) Roundworms: Phylum Nematoda Unsegmented Most are free-

living Digestive tract

with two openings – mouth and anus

Pseudocoelom-false body cavity

Feeding Most are carnivores Use mouth parts and

spines to catch food

Hook Worms

Respiration, Circulation, Excretion

Diffusion through body walls

Response Simple nervous system Nerves run body length from

Ganglia in head Simple sense organs to detect

chemicals from prey or hosts

Movement Hydrostatic skeleton Muscles and fluid in the

pseudocoelom work together to produce movement

Reproduction Sexual Internal fertilization Separate genders

Human Disease --Parasitic Roundworms Trichinosis-Causing Worms Filarial Worms Ascarid Worms Hookworms

B1) Trichinella Trichinosis Cysts are ingested

from eating animal muscle tissue

Females burrow into intestinal wall

Larvae travel to organs via bloodstream and form cysts

2 common hosts Rats and pigs

Humans affected by eating undercooked pork

B2) Filarial Worms Live in blood and

lymph vessels Transmitted by

mosquitoes Can block the

movement of fluids

Elephantiasis

B3) Ascaris

1. Eggs hatch in intestines2. Larvae burrow into

bloodstream to lungs3. Travel to air passages,

coughed up and then swallowed

4. Carried to the intestines and mature

5. Eggs released via feces

• Spread by eating improperly washed vegetables (foods)

Male vs. Female

B4) Hookworms ¼ of the human population infected with

hookworms Eggs hatch outside body and develop in

soil Use sharp toothlike plates and hooks to

burrow into skin and enter bloodstream Travel to lungs and then intestines Suck blood causing weakness Don’t walk barefoot outside!!!

--Segmented worms with a coelom (body cavity) that is lined with mesoderm

C) Annelids: Phylum Annelida

Feeding and digestion Filter feeders to predators Earthworm

Full Digestive Tract: mouth pharynx esophagus crop gizzard intestine anus

Crop- store food Gizzard- grind food Anus – removal of solid undigested

waste

Circulation Closed system, 2 major blood

vessels Dorsal blood vessel: tail head

(pumps like heart) Ventral blood vessel: head tail

Response Ganglia Ventral nerve cord

Respiration and Excretion Respiration-

Skin (moist due to mucus secretion) - land

Gills - aquatic Excretion-

Nephridia - filter out fluid/liquid metabolic waste

Movement- Hydrostatic skeleton

Longitudinal muscles – short and fat Circular muscles – long and thin

Setae- brush hair-like projections

Reproduction- Mostly sexual, some hermaphrodites,

some separate sexes Clitellum-thick band secretes mucus ring

after 2 worms exchange sperm for fertilization

Mucus ring slips off and forms protective cocoonhatching

Classes of Annelids

C1) Class Oligochaeta: Oligochaetes- Earthworms

Few setae on each segment Soil or fresh water

C2) Class Hirudinea: Leeches

External parasites Suck blood and body fluids of host Medicinal Uses

Reduces swelling and prevents clotting

C3) Class Polychaeta: Polychaetes Sandworms,

bloodworms Marine Paired paddle-like

appendages w/ setae

Live in coral reefs, sand, mud

What do you think caused this marking?

Worm? Bacteria? Virus? Fungus? Hickey?

Ringworm Not caused by a worm! Fungal infection Can occur on any part of body Contact with infected people,

animals, soil, etc. Medically called Tinea

Ecology of Annelids

•Burrowing through soil builds tunnels for plants roots and water•Help plant matter decompose as they digest the soil•“mine” minerals from deep soil layers•Earthworm castings are rich in N, P, K, and bacteria•Food for birds

Earthworm Dissection

External View

Internal Structure

Pharynx

Aortic Arches

Seminal Vesicle

Seminal Receptacle

Septum

Crop

Gizzard

Intestine

Ventral Nerve Cord

Dorsal Blood Vessel