Ms. Moore
2/11/13
WORMS AND MOLLUSKS
What is a flatworm?
 Phylum: Platyhelminthes
 Flatworms are soft, flattened worms that have
tissues and internal organ systems.
 They are the simplest animals to have 3
embryonic germ layers, bilateral symmetry,
and cephalization.
 Acoelomates: without coelom (fluid-filled body
cavity, lined with tissue from mesoderm
Flatworms: Form and Function
 Feeding:
 Carnivores or Scavengers ; can be parasitic
 Digestive cavity with single opening (mouth)
 Pharynx: extends outside the mouth and pumps
food into digestive cavity (gut)
 Food diffuses from the digestive cavity into all
other body tissues
 Respiration, Circulation, and Excretion:
 Since their bodies are so flat and thin, many
flatworms do not need a circulatory system to
transport materials (use diffusion).
 No gills or respiratory organs; no heart, blood
vessels, or blood.
 Flame cells: specialized cells that remove excess
water from the body; filter and remove ammonia
and urea using pores of the skin
 Response:
 Ganglia: groups of nerve cells that control the
nervous system (no brain)
 Eyespot: group of cells that can detect changes in
the amount of light in their environment
 Movement:
 Cilia on the epidermal cells help glide through the
water.
 Muscles controlled by the nervous system help to
twist and turn to react to environment.
 Reproduction:
 Hermaphrodite: both male and female
reproductive organs
 Sexual: two worms join in a pair and they deliver
sperm to each other
 Asexual: fissionorganism splits in two and each
half grows new parts to become a complete
organism
Groups of Flatworms
 Turbellarians
 Flukes
 Tapeworms
Turbellarians
 Free-living flatworms
 Most live in marine or fresh water
 Bottom dwellers: living in sand or mud
 Planarians: “cross-eyed” freshwater worms
Flukes
 Class: Trematoda
 Parasitic flatworms that infect internal organs
of their host; can also be external parasites.
Tapeworms
 Class: Cestoda
 Long, flat, parasitic worms that are adapted to life inside
the intestines of their hosts.
 Scolex: contains suckers or hooks; attaches
 Proglottids: segments that make up most of worm’s body;
contain male and female reproductive organs
 Youngest proglottids are at the anterior end and the largest and
most mature are at t he posterior. After eggs have been fertilized,
proglottids break off and release zygotes that are passed out of
the host in feces/
 Testes: fertilize eggs of other tapeworms or of self
What is a Roundworm?
 Phylum: Nematoda
 Roundworms are slender, unsegmented worms with
tapering ends; Range in size from microscopic to a
meter in length
 Pseudocoelom: false coelom (only partially lined with
mesoderm
 Digestive tract with two openings—mouth and anus
(posterior opening of digestive tract)
 “tube within a tube”: inner tube is digestive tract and outer
tube is body wall
 Food moves in one direction
Roundworms: Form and Function
 Feeding:
 Carnivorous: eat small animals by latching on to
them with grasping mouth parts and spikes
 Scavengers: eat algae or decaying mater
 Consume bacteria and fungi
 The free living roundworms
tend to be more complex
than parasitic roundworms.
 Respiration, Circulation, and Excretion
 Diffusion through body walls
 Response
 Simple nervous systems with several ganglia; sense
organs that detect chemicals given off by prey or host
 Movement
 Muscles extend length of body; function as hydrostatic
skeleton
 Reproduction
 Sexually with male and female worms
 Internal fertilization
Roundworms and Human Disease
 Trichinosis-Causing Worms
 Caused by Trichinella roundworm
 Worms burrow into intestine walls
and females release larvae that travel
through the bloodstream and live in
organs and tissues of host’s body
 Filarial Worms
 Found in tropic regions of Asia; live in blood and
lymph vessels of birds and mammals (humans)
 Transmitted host-to-host by biting insects like
mosquitoes
 Large numbers could block lymph
passageselephantiasis
 Ascarid Worms
 The cause of malnutrition of more
than 1 billion people worldwide.
 Ascaris lumbricoides usually spread by
eating vegetables that are not washed
properly.
 Hookworms
 25% of the world’s population is
infected with these worms
 Eggs hatch outside the body and
mature in the soil
 Use tooth-like plates to burrow into
skin of an uncovered foot and live in
bloodstream
 Suck blood and cause weakness and
poor growth
Research on C. elegans
 DNA sequence has been mapped out (97
million bp)
 Help us find out how eukaryotes become
multicellular and how multicellular animals
are similar and different
What is an Annelid?
 Phylum: Annelida; “little ring”
 Septa: internal walls between each body segment
 Setae: bristles attached to each segment
 Annelids are worms with segmented bodies
 Have true coelom that is lined with tissue derived
from mesoderm.
 Like roundworms, annelids have a tube within a
tube system with an anus.
Annelids: Form and Function
 Feeding and Digestion
 Range from filter feeders to
predators
 Use a pharynx that hold two or
more sharp jaws used to attack
prey.
 Earthworms: pharynx pumps
food into esophagus moves
to crop (storage) through
gizzard (ground into smaller
pieces) intestine
 Circulation
 Closed Circulatory System: blood is contained
within a network of blood vessels
 Earthworm: blood circulates through two major
blood vessels
 Dorsal runs to head; ventral runs to tail
 Dorsal functions as a heart due to contractions =
pump blood
 Respiration
 Aquatic annelids breathe through gills
 Land-dwelling annelids take in oxygen and give
off carbon dioxide through moist skin; mucus
 Excretion
 Digestive waste passes through the anus
 Cellular waste eliminated by nephridia (excretory
organs that filter fluid in the coelom)
 Response
 Brain and nerve cords
 Marine annelids are more developed:
sensory tentacles, chemical receptors, statocyts,
two or more pairs of eyes
 Movement
 Hydrostatic skeleton
 Longitudinal muscles: front to rear; muscles
contract to make worm shorter and fatter
 Circular muscles: contract to make worm longer
and thinner
 Marine annelids: paddle like appendages
(parapodia)
 Reproduction
 Sexually: external fertilization
 Hermaphrodites: two worms
exchange sperm and store them in
special sacs
 Clitellum: band of thickened,
specialized segments, secretes a
mucous ring into which sperm and
egg are released; rings slips off and
forms a cocoon; worms hatch weeks
later
Groups of Annelids
 Class: Oligochaetes
 Annelids that typically have streamlined bodies
and relatively few setae; soil or freshwater
 Castings: mixture of sand, clay and undigested
food that an earthworm expels from its anus.
 Class: Hirudinea
 Leeches
 External parasites that suck the blood and body




fluids of their host
¼ are carnivorous that that feed on soft-bodies
invertebrates
Suckers at both ends of body
Proboscia: muscular extension that can be forced
into tissue of host
Can release a substance that anesthetizes wound
and prevents blood from clotting.
 Class: Polychaeta
 Polychaetes
 Marine annelids that have
paired , paddle like
appendages tipped with setae
Ecology of Annelids
 Earthworms (and other
annelids) burrow through soil,
aerating it and mixing it to
depths of two meters or more
 Mine minerals from deeper
soil layers
 Diets of many birds and other
vertebrates
What is a Mollusk?
 Phylum: Mollusca
 Mollusks are soft-bodied
animals that usually have an
internal or external shell.
 Ex: snails, slugs, clams, squids,
and octopi.
 Trochophore: free-swimming
larval stage
 Characteristic of Annelida =
related 550 m.y.a.
Form and Function: Mollusks
 True coeloms and organ systems
 Body Plan (4 basic parts):
 Foot: muscular structure used for crawling, burrowing, and
capturing prey
 Mantle: thin layer of tissue that covers the body (cloak)
 Shell: glands in mantle secrete calcium carbonate; reduced or
lost in slugs and other mollusks
 Visceral Mass: beneath mantle; consists of internal organs
(Figure 27-21)
 Feeding:
 Can be herbivores, carnivores, filter feeders,




detritivores, or parasites
Radula: flexible tongue-shaped structure used by
snails and slugs; 100s of teeth are attached
Octopi use sharp jaws and tentacles to feed
Clams, oysters, and scallops filter feed with their
gills and mucus
Siphon: tube like structure where water enters
and leaves the body
 Respiration:
 Use gills inside their mantle cavity
 Land species have no gills, but they do have thin blood
vessels in mantle that stay moist for oxygen passage.
 Circulation: open or closed
 Open circulatory system: blood is pumped through
blood vessels by a simple heart; the blood makes way
through body to the gills, then back to the heart;
found in slow moving mollusks
 Closed circulatory system: used in fast-moving
mollusks bc it moves blood through body faster
 Excretion:
 Cells release wastes into blood and nephridia remove
it from the body
 Response:
 Slugs use simple ganglia and octopi use complex
brain
 Complex brain allow them to remember things
and be trained for reward or avoid punishment
 Movement:
 Slugs secrete mucus and use their foot to glide
 Octopi use jet propulsion
 Reproduction:
 Sexually by internal or external fertilization
 Can be hermaphrodites, but do not fertilize own
eggs
Groups of Mollusks
 Gastropods
 Class: Gastropoda
 Gastropods are shell-less or single-shelled
mollusks that move by using a muscular foot
located on the ventral side
 EX: snails, land slugs, sea butterflies, and sea
horses
 Protection: some can retract back into their shell
or use ink to make a smoke screen; some produce
chemicals that make them taste bad; nudibranchs
can recycle nematocysts and use them
 Bivalves
 Class: Bivalvia
 Bivalves have 2 shells held together by one
powerful muscle
 EX: clams, oysters, mussels, and scallops
 Most stay in one spot for long periods of time,
except scallops (move to run from predators)
 Eat through filter feeding or sifting through the
mud.
 Cephalopods
 Class: Cephalopoda
 Cephalopods have a head that is attached to their foot




which is divided into tentacles or arms (8+).
EX: octopus, squids, cuttlefishes, nautiluses
Nautiluses are the only ones with external shells;
they have over 90 tentacles; control water depth by
amount of gases in their mantle
Octopi have lost shells completely
Cuttlefishes have small shells inside their body
Ecology of Mollusks
 Mollusks can be used to detect water quality
 Filter algae out of the water
 Live symbiotically with other organisms
 Major food source for humans