Platyhelminthes

• General characteristics:– Known as “flat worms.”– Body plan: acoelomate, bilateral

symmetry

• Habitat: aquatic or in host’s body

Platyhelminthes• Nutrition:

• Parasitic - (blood, tissue, or predigested materials from host’s intestines) OR

• Scavengers and Saprobes

Platyhelminthes• Feeding:

• Planarians extend pharynx from mouth

• Parasites have specialized mouth parts to attach to their host.

Platyhelminthes

• Digestion: – Extracellular: food is pumped

into digestive cavity or gut and cells digest and absorb nutrients, digested food is then diffused into the other body tissue

• Excretion: diffusion through the body wall– planarians have flame cells to

excrete water and wastes through pores

Platyhelminthes

• Respiration and Circulation: Diffusion of gases through the skin, skin must remain moist

Platyhelminthes

• Nervous: most have ganglia (mass of nervous tissue), eyespots, sensory lobes and respond to touch and chemicals– Demostrates

cephalization, nervous tissue is concentrated in the head region.

Platyhelminthes

• Reproduction: – Sexual Reproduction:

• Hermaphrodites• Parasitic worms require

hosts to reproduce• Sexual reproduction

exchange sperm, internal fertilization

Section 27-1

Flukes mature and reproduce sexually in the blood vessels of human intestines. Embryos are released and passed out with feces.

Once in the water, embryos develop into swimming larvae that infect an intermediate host (snail).

After asexualreproduction, newlarvae are releasedfrom the snail into the water. They then infect humans, the primary host, by boring through their skin.

Primary host (human)

Intermediate host(snail)

Humanintestine

Adultfluke

Embryo

Ciliatedlarva

Tailedlarva

Schistosome Life CycleSchistosome Life Cycle

Shistosomiasis

Tapeworm Life Cycle

DON’T DO THIS!! GROSS!

Platyhelminthes

• Reproduction:– Asexual reproduction through

fragmentation or fission.

Platyhelminthes• Mobility:

– Cilia for gliding– Muscle cells controlled by nervous system to react

to stimuli

Freshwater flatworms have simple ganglia and nerve cords that run the length of the body. The excretory system consists of a network of tubules connected to flame cells that remove excess water and cell wastes.

Most flatworms are hermaphrodites, having male reproductive organs (testes) and female reproductive organs (ovaries) in the same organism.

Flatworms use a pharynx to suck food into the gastrovascular cavity. Digested food diffuses from the cavity into other cells of the body. Eyespots in somespecies detect light.

Eyespot

Head

Gastrovascularcavity

Ganglia

Nervecords

Excretorysystem

Mouth Pharynx

Ovary

Testes

Excretorytubule

Flame cell

The Anatomy of a Flatworm

Platyhelminthes

• Common Examples: – Turbellaria (Planarian)– Trematoda (Fluke)– Cestoda (Tapeworm)

Nematoda• General characteristics:

– Known as “round worms”.– Pseudocoleomate – long and slender, tapered at both

ends– protostomes– bilateral symmetry– Body is covered in a complex cuticle

Nematoda• Habitat/Nutrition:

– Parasites• Feeding

– Both mouth and anus connected by digestive tube• Digestion: takes place in digestive cavity, digested food

diffuses into other body tissue. – May also have digestive sacs that food is pumped into for

digestion.

Nematoda

Nematoda

• Circulation and Respiration: Diffusion of gases through the skin

• Excretion: Canal system, diffusion through body wall or out through mouth

• Nervous: simple nervous system, with a main ventral (belly) nerve cord and smaller dorsal (back) nerve cord

Nematoda

• Reproduction:– Sexual

– usually dioescious (separate sexes)

– internal fertilization– genders differ in size,

shape and color– Parasitic worms require

host

Life Cycle of Hookworm

Life Cycle of Whipworm

Nematoda• Mobility: Muscles along body wall for

movement

Nematoda• Examples:

– Hookworms– Pinworms– Guinea worms

Annelida• General characteristics:

– Known as “segmented worms”– Coelomates

• Habitat: aquatic and moist soil

Annelida

• Nutrition: heterotrophic, filter feeders, parasites, scavengers, and saprobes

• Feeding: Pharynx used to obtain food– Carnivorous species have two or more sharp jaws

Annelida• Excretion:

– Digestive wastes pass out through the anus

– Cellular wastes containing nitrogen is passed out by the nephridia (simple kidney)

Annelida

• Digestion: extracellular, takes place in intestine– Earthworm: pharynx →

esophagus→ crop (storage) → gizzard (ground) → intestines (absorption)

Annelida

• Circulation: – closed (blood contained in vessels)

Annelida

• Respiration:– Aquatic: breathe

through gills– Land dwellers: diffusion

through skin (must stay moist) typically secrete a mucus to keep skin moist

Annelida

• Nervous:– Best developed sense

organs in free living marine organism

– Well developed nervous systems consisting of brain and spinal cord

– Two or more pairs of eyes, sensory tentacles, chemical receptors and statocysts that help detect gravity

Annelida

• Reproduction– Most sexually– Some use external

fertilization and have separate sexes

– Earth worms and leeches are hermaphroditic, but rarely fertilize their own eggs

Annelida• Mobility

– Two major groups of muscles that function as part of the hydrostatic skeleton

– Longitudinal and circular muscles, move by alternating contractions

– Earthworms have hair-like structures called setae that allow them to easily grip a surface.

– Marine worms have parapodia to use for swimming and crawling

Section 27-3

Anus

Clitellum

Circular muscle

Longitudinalmuscle

Nephridia Ganglia Ringvessels

Reproductiveorgans

Ventralblood vessel

Ganglion

Brain

Mouth

Dorsalblood vessel

CropGizzardBody segments

Setae

Annelida

• Examples:– Earthworms– Leeches– Marine worms