Transcript Worms - walker2014

Worms
Chapters 26.3, 26.4, and 27.2
Animal Classification
Invertebrates
Sponges
Cnidarians
Worms
Mollusks
Arthropods
Enchinoderms
- Phylum
Platyhelimenthes
- Phylum Nematoda
- Phylum Annelida
Animals
(cold-blooded)
Fishes
Amphibians
Reptiles
Endotherms
Birds
Mammals
Ectotherms
Vertebrates
(warm-blooded)
Flatworms

Phylum Platyhelimenthes






(Greek) platy = flat
helmins = worm
The least complex worm
Acoelomates
About 14,500 species exist found in marine,
freshwater, and land
The most commonly studied flatworm is the
planarian
Nervous Control


Most of the nervous system is located in its
head
The nervous system consists of two nerve
cords that run the length of the body
Nerve cords
Nervous Control


Eyespots can detect the presence or
absence of light
Sensory cells can detect chemicals and
movement in water
Sensory cells
Eyespots
Sensory cells
Nervous Control

Ganglion


A small swelling of the nerve cord
Receives messages from the eyespots and
sensory pits, then communicates with the rest of
the body
Ganglia
Reproduction



Most flatworms are hermaphroditic
Can reproduce sexually and asexually
Sexual reproduction



Two planarians will exchange sperm
Internal fertilization occurs
Zygotes are then released in water where they will
hatch
Reproduction

Asexual reproduction

Planarians can regenerate when damaged

Regeneration – The replacement or regrowth of missing
body parts
Feeding and Digestion in Planarians

A planarian feeds on dead or slow-moving
organisms


Planarians are not parasitic
To eat, a planarian extends its pharynx from
its mouth

Pharynx – a tube-like, muscular organ (also
known as the throat)
Extended
pharynx
Feeding and Digestion in Planarians



Enzymes breakdown the food outside the
body, and then food particles are sucked into
the digestive tract
Food is digested in individual cells
Waste leaves through its one opening
(mouth)
Planarian’s Pharynx
http://www.youtube.com/watch?v=ecCgCwKRZnM
Feeding and Digestion in Planarians


Excretory system – eliminates waste from the
body
Flame cells – excess water is removed from
the body
Feeding and Digestion in Parasitic
Flatworms

Parasitic flatworms
have mouthparts with
hooks that keep them
attached to their hosts
Hook
Sucker
Feeding and Digestion in Parasitic
Flatworms

Parasitic flatworms
don’t need a digestive
system because they
obtain nutrients from
food that has been
digested by their host
Hook
Sucker
Tapeworm


Scolex – a knobshaped head
Proglottid – detachable,
individual sections that
contain muscles,
nerves, flame cells, and
reproductive organs
Hook
Sucker
Tapeworm


Each proglottid can
contain up to 100,000
eggs
Can reach up to 33 ft in
length and contain over
2,000 proglottids
Hook
Sucker
Fluke larva can bore
through the skin,
enter the
bloodstream, and
move to the intestines
Eggs are passed out
the intestines
Adult flukes
Embryo
develops in
human
waste
Second larval stage
The larva will enter
the snail host for
further development
First larval stage
are found in
water
Roundworms

Phylum Nematoda




Greek word nema = thread
Found in soil, animal, freshwater, and marine
environments
More than 12,000 species exist
Nearly all plant and animals are affected by
parasitic roundworms



Pseudocoelomate
Have a complete digestive system with two
openings (mouth and anus)
Free-living species have well-developed
eyespots whereas parasitic species have
underdeveloped eyespots
Roundworm Parasites of Humans



Ascaris is the most common roundworm
infection in humans worldwide
More common in subtropical areas
Children become infected more often than
adults

Timmy plays in a sandbox…
Roundworm Parasites of Humans



Pinworms are the most common roundworm
parasites in the U.S.
Children are the commonly infected
Eggs can survive two weeks on the surface
Roundworm Parasites of Humans


During night, female pinworms lay eggs
around the anus of host
Taping the anus before bedtime is one
method used to eliminate pinworms
Roundworm Parasites of Humans


Trichinella can be ingested in raw or
undercooked pork or wild game (turkey)
Trichinella can be controlled by properly
cooking meat
Roundworm Parasites of Humans


Hookworms are common in warm climates
where people walk on contaminated soil in
bare feet
Hookworms cause people to feel weak and
tired due to blood loss

Hookworm infection from dogs and cats
Segmented Worms

Phylum Annelida



Latin term anellus = “little ring"
Examples: Earthworms, bristleworms, and
leeches
Coelomates with two body openings
Segmented Worms


Can be found in most environments, except
in frozen soil and dry, compact sand
15,000 species of segmented worms
Earthworm
Bristleworm
Leech
External Anatomy of an Earthworm





Prostomium – a tongue-like lobe above the
mouth
Clitellum - the swelling of the earthworm near
its anterior side
Setae - Tiny bristles that help earthworms
and britleworms move through soil
Mouth
Anus
Nervous System



Segmented worms have simple nervous
systems
Some species have eyes and brains
All species have nerve cords and ganglia
Internal view of an earthworm
Circulatory

Segmented worms have a closed circulatory
system – blood flows through vessels to
reach all parts of the body

Open circulatory system – blood is not enclosed in
vessels throughout the entire body

Examples: flatworms and roundworms
Internal view of an earthworm
Respiration

Segmented worms must live in water or wet
areas because they are able to exchange
gases directly through their moist skin
Digestion


Annelids have a complete digestive system
Have a crop and a gizzard


Crop – a sac that holds soil temporarily before it
moves into the gizzard
Gizzard – a muscular organ that grinds food
Internal view of an earthworm
Excretion

Annelids have two nephrida in almost every
segment that collect waste products and
transport them out of the body
Internal view of an earthworm
Reproduction





Earthworms and leeches are hermaphrodites
During sexual reproduction, worms exchange
sperm
Eggs are fertilized and laid in the soil
The eggs hatch in 2-3 weeks
Bristleworms have separate sexes and
reproduces sexually
Internal view of an earthworm
Leeches


Many species are
parasites that suck
blood or other body
fluids from their hosts
Front and rear suckers
enable leeches to
attach themselves to
their hosts
Leeches

The saliva contains chemicals that act as a
anesthetic



Example – Novocain
Other chemicals prevent the blood from
clotting
Leeches are used medically to remove
decaying tissues of patients
Leeches


A leech can ingest 2-5 times its own weight in
one meal
A leech will drop off its host when its full and
may not eat again for months