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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
• 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