Transcript Worms and Mollusks

Worms and Mollusks
Biology I: Chapter 27
FLATWORMS
Flatworms
• Phylum Platyhelminthes
• Simplest animals to have:
• Soft, flattened worms
• 3 embryonic germ layers
• Tissues and internal organs • Bilateral symmetry (a
right and a left)
• Cephalization
Flatworms
• Acoelomate: flatworms
are without a coelom
• Coelom: fluid-filled
body cavity lined with
mesoderm
• The digestive cavity is
the only body cavity
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
• Rely on diffusion
• Flame cells: remove excess
water and metabolic wastes
from the body
Response
• Ganglia: group of nerve
cells that controls the
nervous system; in the head
region
• Eyespot
Movement
• Cilia
• Muscle cells
Reproduction: Sexually and Asexually
Free-living
• Sexually: hermaphrodites
– during sexual reproduction, two
worms join in a pair, delivering
sperm to each other
• Asexually: fission
Reproduction: Sexually and Asexually
Parasitic
• A complex life cycle
including both sexual and
asexual reproduction
Groups of Flatworms
• Turbellarians
– Free-living; most live in marine or fresh water
• Flukes
– Parasitic; infect the internal organs of their host
• Tapeworms
– Long, flat, parasitic;
adapted to life inside
the intestines of their host
ROUNDWORMS
Roundworms
• Phylum Nematoda
• Slender, unsegmented
worm
• Pseudocoelom
• Digestive system with two
openings: a mouth and an
anus
Feeding
Free-living roundworms
• Carnivores that use
grasping mouthparts
and spines
Respiration, Circulation, & Excretion
• Exchange gases and excrete metabolic waste
through their body walls
• No internal transport system
• Depend on diffusion
Response
• Simple nervous systems, consisting of
several ganglia
• Run from the head to the tail
• Nerves transmit sensory information and
control movement
Movement
• Hydrostatic skeleton
• Aquatic roundworms move like snakes
• Soil-dwelling roundworms push their way
through by thrashing around
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
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
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
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
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
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
Respiration
• Aquatic annelids: gills
• Land-dwelling annelids: diffusion through
their moist skin
Excretion
• Two kinds of waste
• Digestive waste passes out through the anus at the
end of the digestive tract
• Nephridia: excretory organs that filter fluid in the
coelom
Response
• Well-developed nervous system consisting
of a brain and several nerve cords
• The sense organs are best developed in freeliving marine annelids
Movement
• Hydrostatic skeleton
• Longitudinal muscles and circular muscles
• Moves by alternating contracting these two
sets of muscles
Reproduction
• Sexually
• Some use external fertilization or have separate sexes
• Others, such as earthworms and leeches, are hermaphrodites
– Exchange 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
Groups of Annelids
• Oligochaetes
– Streamlined bodies and have relatively few setae compared
to polychaetes, live in soil or fresh water
• Leeches
– External parasites that suck the blood and body fluids of
their host
• Polychaetes
– Marine annelids that have paired, paddlelike appendages
tipped with setae
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
• Phylum Mollusca
• Soft-bodied animals
• Internal or external shell
• Include snails, slugs, clams, squids and
octopi
• Trochophore: free-swimming larval
stage of an aquatic mollusk
Form and Function in Mollusks
• True coeloms
• Have complex organ
systems
Body Plan
• Foot: muscular part
of a mollusk
• Mantle: thin layer of
tissue that covers
most of a mollusk’s
body
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
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
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
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)
• Closed circulatory system: can transport blood
through an animal’s body much more quickly
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
Response
• Complexity of the nervous system varies
greatly between mollusks
• Clams and other two-shelled mollusk lead
inactive lives simple nervous system
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
Movement
• Move in many different speeds
• Snails secrete mucus and move
slowly over the surface using a
rippling motion of the foot
• Octopus uses a form of jet
propulsion, drawing water into
its mantle and forcing it out the
siphon
Reproduction
• Reproduce in many different ways
• Snails and two-shelled mollusk
reproduce sexually by external
fertilization
• Some mollusk are hermaphrodites
Groups of Mollusks
• Gastropods
– Shell-less or single-shelled mollusks that move by
using a muscular foot located on the ventral side
• Bivalves
– Have two shells that are held together by one or two
powerful muscles
• Cephalopods
– Soft-bodied mollusks in which the head is attached to a
single foot; the foot is divided into tentacles or arms
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