Worms and Mollusks
Chapter 27:
3 Phylums of Worms
1. Flatworms (phylum Platyhelminthes)
Turbellaria (free-living)
Trematoda (flukes),
Cestoda (tape worms)
2. Round Worms (phylum Nematoda)
Trichinella (trichinosis)
filarial worms (elephantiasis)
Ascaris and hookworms
3. Segmented Worms (phylum Annelida)
Oligochaeta (earthworms)
Hyrudinea (leeches)
Polychaeta (sandworms, bloodworms)
Classes of Mollusca Phylum
1. belly-footed (class Gastropoda)
“gastro means belly
&
pod means foot”
snails and slugs
2. double-shelled (class Bivalvia)
“bi means 2
&
valve means shell”
clams,mussels, oysters and scallops
3. head-footed (class Cephalopoda)
“cephalo means head
&
pod means foot”
octopus, squid, cuddlefish, nautilus
“Coelum - fluid filled body cavity line with tissue from mesoderm”
“No Coelum”
“False Coelum”
“True Coelum”
FLATWORMS
Flatworms
• Phylum Platyhelminthes
• Soft, flattened animals with
cephalization and bilateral symmetry
• Acoelomates: 3 germ layers with no true
body cavity (coelom)
• Most are parasitic
• Terms: pharynx, flame cells, ganglia,
hermaphodite
• Sexual and asexual reproduction
• Examples: flukes, planaria, tapeworms
Flatworms
• Acoelomate: flatworms
are without a coelom
• Coelom: fluid-filled
body cavity lined with
mesoderm
• The digestive cavity is
the only body cavity
Platyhelminthes Feeding
• Free-living flatworms
– Carnivores that feed on tiny aquatic animals
– Scavengers that feed on recently dead animals
• Parasitic flatworms
– Feed on blood, tissue fluids, or pieces of cells
within a host’s body (Example: tapeworm)
Respiration, Circulation, & Excretion
in Platyhelminthes
• Rely on diffusion
• Flame cells: remove excess
water and metabolic wastes
from the body
Platyhelminthes Response
• Ganglia: group of nerve
cells that controls the
nervous system; in the head
region
• Eyespot
Platyhelminthes Movement
• Cilia
• Muscle cells
• Flap to swim
Reproduction: Sexually and Asexually
in Platyhelminthes
Free-living
• Sexually: hermaphrodites
during sexual reproduction,
two worms join in a pair,
delivering sperm to each
other
• Asexually: fission
Reproduction: Sexually and Asexually
in Platyhelminthes
Parasitic
• A complex life
cycle including
both sexual
and asexual
reproduction
Groups of Flatworms: Platyhelminthes
•Turbellarians - free-living;
most live in marine or fresh
water (class Terbellaria)
• Flukes - parasitic; infect the
internal organs of their host
(class Trematoda)
•Tapeworms - Long, flat, parasitic;
adapted to life inside the intestines
of their host (class Cestoda)
Groups of Flatworms: Platyhelminthes
Class: Turbellarians
• Free living Flatworms
• Most live in freshwater or marine environments
• Bottom dwellers living in sand or mud
• Most are carnivores or detritus
• Example: Planarians
Groups of Flatworms: Platyhelminthes
Class: Trematoda (Flukes)
• Parasitic Flatworms
• Most flukes infect the internal organs of their host
• Some are external parasites that live on the skin,
mouth, gills of their host
• Many have complicated life cycles that involve two
or more animal hosts
• They are usually less than a centimeter long
• They cause serious pain to millions of humans and
animals
• The most destructive live in the tropics.
Liver Fluke Life Cycle
•
Groups of Flatworms: Platyhelminthes
Class: Trematoda (Flukes)
• Flukes of the genus Schistosoma infect about
200 million people per year
• The Schistosoma fluke causes schistosomiasis
in humans
• A serious disease in which the eggs clog blood
vessels which can cause swelling and tissue
decay in the lungs, liver, spleen, or intestines
Blood Flukes
Groups of Flatworms: Platyhelminthes
Life Cycle of Schistosoma
• Larvae enter humans through skin
• Reproduce sexually in blood vessels of intestines
• Release eggs into water
• Larvae enter snails and reproduce asexually
• Burrow out and infect humans again
– More prevalent with no sewage treatment
Blood Fluke Life Cycle
•
Groups of Flatworms: Platyhelminthes
Class: Cestoda (tapeworms)
• Parasitic worms
• Adapted to live inside the intestines of their hosts
• Food is digested directly through the body walls
• Rarely kill but cause weakness & weight loss
Groups of Flatworms: Platyhelminthes
Class: Cestoda (tapeworms)
• Structure of a tapeworm
• Scolex
– Structure that contains suckers or hooks
Groups of Flatworms: Platyhelminthes
Class: Cestoda (tapeworms)
• Proglottids
–
–
–
–
Segments that make up most of the worms body
Proglottids contain male and female reproductive parts
They can contain as many as 100,000 eggs.
They can produce as many as half a billion eggs in a
year
Tapeworm Life Cycle
Groups of Flatworms: Platyhelminthes
Class: Cestoda (tapeworms)
• Taenia saginata, the Beef Tapeworm
ROUNDWORMS
Roundworms
• Phylum Nematoda
• No segments
• Many free-living, some Parasitic
• Pseudocoelomate: 3 germ layers
with false cavity(coelom)
• Digestive system with two
openings: mouth and anus
• Inhabit the soil, salt flats, aquatic
sediments and water from polar
regions to the tropics
• Hookworms, trichinella, ascaris
“A rotting apple may contain 100,000 nematodes!”
Roundworms
Nematode Feeding
Free-living roundworms
Carnivores that use
grasping mouth parts
and spines
Respiration, Circulation, & Excretion
in Nematodes
• Exchange gases and excrete metabolic waste
through their body walls
• No internal transport system
• They rely on diffusion to carry nutrients and
waste throughout their bodies
Nematode Response
• Simple nervous systems, consisting of
several ganglia
• Run from the head to the tail
• Nerves transmit sensory information and
control movement
Nematode Movement
• Hydrostatic skeleton
• Aquatic roundworms move like snakes
• Soil-dwelling roundworms push their way
through by thrashing around
Nematode Reproduction
• Sexually
• Separate males and females
• Internal fertilization
• Male deposits sperm inside the female’s reproductive
tract
• Parasitic roundworms have complex life cycles
involving two or three different hosts or organs within
a single host
Nematode Reproduction
Roundworms and Human Disease
Trichinosis-causing worms
• Adult worms live and mate in the intestines of their
host (humans, pigs and other mammals)
Filarial worms
• Found primarily in tropical regions of Asia,
threadlike worms that live in the blood and lymph
vessels of birds and mammals, including humans,
transmitted by biting insects, causes elephantiasis
Roundworms and Human Disease
Ascarid worms
• Serious parasite of humans and many other
vertebrates, causes malnutrition; spread by eating
vegetables or food that are not washed properly
Hookworms
• Hatch outside the body of the host and develop in the
soil, can enter a barefoot and travel through the
bloodstream to the intestines
Roundworms Causing Human Disease:
Trichinosis - Causing Worms
• Trichinosis is a terrible disease caused by the
roundworm Trichinella
• Adult worms live and mate in the intestines of
their hosts which include:
– Humans, pigs, and other animals
Warning… Very Graphic Images! (next 11 slides)
Roundworms Causing Human Disease:
Trichinella Worm - Trichinosis
Humans get
Trichinosis by eating
raw or incompletely
cooked pork.
Roundworms Causing Human Disease:
Filarial Worms
• Found primarily in tropical regions of Asia
• Threadlike worms live in blood and lymph vessels of
birds and mammals…including humans
• Transmitted through bitting insects especially mosquitos
• Large numbers of filarial worms may block the passage
of fluids within the lymph vessels
• This causes what is known as elephantiasis
Roundworms Causing Human Disease:
Filarial Worms - Elephantiasis
Roundworms Causing Human Disease:
Ascarid Worms
• Ascaris lumbricoides is a serious parasite of
humans and other vertebrate animals
• Causes malnutrition to more than 1 billion
people worldwide including many people
living in the southeastern United States
– Cause: by eating vegetables and other foods that
are not washed properly
Roundworms Causing Human Disease:
Ascarid Worms
Roundworms Causing Human Disease:
Ascarid Worms
This is why
we have to
have puppies
“wormed”
Ascarids
affect many
other animals
Video: Worms in
a dog’s heart
Roundworms Causing Human Disease:
Hookworms
• As many as one quarter of the people in the
world are infected with hookworms
• They suck the hosts blood causing
weakness and poor growth
• See chart for life cycle!
Roundworms Causing Human Disease:
Hookworms
Roundworms Causing Human Disease:
Hookworms
•
Roundworms Causing Human Disease:
New Guinea Worms
Research on C. elegans
• Free-living roundworm
Caenorhabditis elegans, C.
elegans
• Feeds on rotting vegetation
• First multicellular animal whose
DNA was fully sequenced
• Helps understand genes and how
eukaryotes became multicellular
ANNELIDS
Segmented Worms
•
•
•
•
Phylum Annelida
Annelid means “little ring”
True coelom coelomates
Embryonic similarity to
mollusks because of larval
stage called trocophore
• Ecology: aeration of soils,
castings increase nutrients in
soil, food source
Annelids
• True coelom that is lined
• Segmented bodies
• Septa: internal walls
between each segment
• Setae: bristles that are
attached to each segment;
used in respiration
Form and Function in Annelids
• Have complex
organ systems
• Segmented body
Form and Function in Annelids
Annelid Feeding and Digestion
• Filter feeders to predators
• Get their food using a pharynx
• Crop: in earthworms; part of the digestive system
in which food can be stored
• Gizzard: in earthworms; part of the digestive
system in which food is ground into smaller pieces
Annelid Circulation
• Closed circulatory system: blood is contained within
a network of blood vessels
• Blood circulates through two major blood vessels
that run from head to tail
• Blood in dorsal vessel moves blood toward the
head of the worm
• Blood in ventral vessel runs from head to tail
• Dorsal blood vessel functions like a heart because it
contracts and helps pump blood
Annelid Respiration
• Aquatic annelids: gills
• Land-dwelling annelids: diffusion through
their moist skin
Annelid Excretion
• Two kinds of waste (digestive & nitrogen)
1. Digestive waste passes out through the anus
at the end of the digestive tract
2. Nephridia: excretory organs that filter fluid
in the coelom (nitriogen waste)
Annelid Response
• Well-developed nervous system consisting
of a brain and several nerve cords
• The sense organs are best developed in freeliving marine annelids
• Also have adaptations for detecting stimuli
•
•
•
•
Sensory tentacles
Chemical receptors
Statocysts (help to detect gravity)
Two or more pair of eyes
Annelid Movement
• Hydrostatic skeleton
• Longitudinal muscles and circular muscles
• Moves by alternating contracting these two
sets of muscles
Annelid Reproduction
• Sexually, external fertilization or have separate sexes
• Earthworms and leeches are hermaphroditic
– Exchange sperm
• Seminal vesicles – produce sperm
• Seminal receptacles – receive sperm
– Clitellum: a band of thickened, specialized segments
that secretes a mucus ring into which eggs and sperm
are released and fertilization occurs
– The ring slips off the body and form a protective
cocoon for the worms that hatch a week later
Annelid Reproduction
Annelid Reproduction
Groups of Annelids
• Class Oligochaetes (Ahl-il-goh-keets) earthworms
– streamlined and have relatively few setae compared
to polychaetes, live in soil or water
• Class Hirudinea (hir-yoo-DIN-ee-uh) leeches
– External parasites that suck the blood and body
fluids of their host
• Class Polychaeta (pahl-ih-keets) sand and bloodworms
– Marine annelids that have paired, paddlelike
appendages tipped with setae
Groups of Segmented: Annelida
Class: Oligochaeta
• Earthworms
– Annelids that have few setae
– Live in soil or fresh water
– Spend most of lives hidden underground
• Can see evidence of an earthworm above
ground in CASTINGS
– Castings: Indigestible particles of sand, clay,
and grains that are passed out of the worm
through the anus
Groups of Segmented: Annelida
Class: Oligochaeta
Anus
Setae
Body segments
Gizzard Crop
Dorsal
blood vessel
Clitellum
Mouth
Brain
Ganglion
Circular muscle
Longitudinal
muscle
Nephridia Ganglia
Ring
Reproductive
vessels
organs
Ventral
blood vessel
Groups of Segmented: Annelida
Class: Hirudinea
• Leeches
– Live in moist, tropical countries
– External parasites that suck the blood
and body fluids of their host
– Have powerful suckers at both ends of their bodies
– Leeches are sometimes used after surgery
• Can reduce swelling when a body part is reattached
• Also secrete a fluid that prevents blood from clotting
• They can suck up to five times their weight in blood!
MEDICAL
LEECHES
LEECH
SUCKERS
Groups of Segmented: Annelida
Class: Polychaeta
• Sandworms, Bloodworms
– Marine annelids that have paired, paddle-like
appendages tipped with setae
– Live in cracks in coral reefs, in sand, mud or open
water
Groups of Segmented: Annelida
Class: Polychaeta
FANWORMS
Groups of Segmented: Annelida
Class: Polychaeta
SANDWORMS
Ecology of Annelids
• Provide passageways for plant roots and
water and allow the growth of beneficial,
oxygen requiring soil bacteria
• Important in the diet of many birds, moles,
skunks, toads and snakes
• In the sea they participate in a wide range of
food chains
MOLLUSKS
Mollusks
• Soft-bodied with internal
or external shell
• Foot, mantle, visceral mass, shell
• Uses a radula to feed
• Water enters and leaves through a
siphon
• Gastropods: snails and slugs
• Bivalves: clams, mussels, scallops
• Cephalopods: squid, octopi,
• Food source, research, filter-feeders
•Trochophore: free-swimming larval stage of aquatic mollusk
Mollusks
• All seem very different, but grouped together
because they share very similar developmental
stages
– Aquatic mollusks have free-swimming larval stage
called trochophore
Form and Function in Mollusks
• True coeloms
• Have complex organ
systems
Mollusk Body Plan
• Foot: muscular part
of a mollusk
• Mantle: thin layer of
tissue that covers
most of a mollusk’s
body
Mollusk Body Plan
• Shell: structure in
mollusks made by
glands in the mantle
that secrete calcium
carbonate
• Visceral mass: area
beneath the mantle of a
mollusk that contains
the internal organs
Mollusk Body Plan
Squid
Snail
Shell
Clam
Early
mollusk
Mantle cavity
Foot
Gills
Digestive tract
Mollusk Feeding
•
•
•
•
•
Herbivorous
Carnivores
Filter feeders
Detritivores
Parasites
• Radula: flexible, tongue-shaped structure used to
capture food by snails and slugs
• Siphon: tube-like structure through which water
enters and leaves the body, capturing plankton in
the process
Mollusk Feeding
Octopi and some sea
slugs use sharp jaws to
eat prey
To subdue prey, some
octopi also produce
poison
Mollusk Feeding
Clams and oysters filter feed using feathery gills
Draw in water using their SIPHON
Mollusk Respiration
• Gills inside their mantle cavity
• Land snails respire using a mantle cavity
lined with blood vessels
• Typically live in moist places to keep this
lining wet
Mollusk Circulation
• Open circulatory system: blood is pumped through
vessels by a simple heart
– Works well for slow-moving mollusks such as
snails and clams (demands for oxygen are low)
– Blood passes from sinuses to the gills, where
they exchange O2 and CO2 and back to heart
• Closed circulatory system: can transport blood
through an animal’s body much more quickly
Mollusk Excretion
• Cells of the body release nitrogencontaining waste into the blood in the form
of ammonia
• Nephridia remove ammonia from the blood
and release it out of the body
Mollusk Response
• Complexity of the nervous system varies
greatly between mollusks
• Clams and other two-shelled mollusk lead
inactive lives simple nervous system
Mollusk Response
• Octopi and their relatives are
active and intelligent
predators  most highly
developed nervous system of
all invertebrates
• Capable of complex behavior,
such as opening a jar to get
food inside
Mollusk Movement
• Move in many different speeds
• Snails secrete mucus and move
slowly over the surface using a
rippling motion of the foot
• Torsion – twist guts into bag
• Octopus uses a form of jet
propulsion, drawing water into
its mantle and forcing it out the
siphon (octopus squirts bird)
Mollusk Reproduction
• Reproduce in many different ways
• Most have separate males and
females (octopi hatch from eggs)
• Snails and two-shelled mollusk
reproduce sexually by external
fertilization
• octopi and squid reproduce
sexually by internal fertilization
• Fertilized egg develops into free
swimming trochophore larva
• Some mollusk are hermaphrodites
Groups of Mollusks
• Gastropods (belly footed)
– Shell-less or single-shelled mollusks that move by using a
muscular foot located on the ventral side
– Ex: snails, slugs, sea butterflies, nudibranchs, and conch
• Bivalves (2 shells)
– Have two shells that are held together by powerful muscles
– Ex: clams, oysters, mussels and scallops
• Cephalopods (head footed)
– Soft-bodied mollusks in which the head is attached to a single
foot; the foot is divided into tentacles or arms
– Ex: octopi, squids, cuttlefishes and nautiluses
Groups of Mollusks: class Gastropoda
Slugs!
Groups of Mollusks: class Gastropoda
Snail
Groups of Mollusks: class Gastropoda
Sea Slug
Groups of Mollusks: class Gastropoda
Conche
Groups of Mollusks: class Bivalve
Groups of Mollusks: class Bivalve
Groups of Mollusks: class Bivalve
Giant Clam
Groups of Mollusks: class Cephalopoda
Squid
Groups of Mollusks: class Cephalopoda
Caribbean Octopus
Groups of Mollusks: class Cephalopoda
Squid
Groups of Mollusks: class Cephalopoda
White Horned
Octopus
Groups of Mollusks: class Cephalopoda
Sea Butterfly
Groups of Mollusks: class Gastropoda
Cuddlefish
Groups of Mollusks: class Cephalopoda
Groups of Mollusks: class Cephalopoda
Ecology of Mollusks
• Feed on plants, prey on animals, and clean
up their environment by filtering algae out
of the water or by eating detritus
• Filter-feeding bivalves can be used to
monitor water quality
• Serve as subjects of biological research