Title: Worms and Mollusks
1Worms and Mollusks
2Flatworms
3What is a flatworm?
- Phylum Platyhelminthes
- No more than a few millimeters thick
- Have tissues and internal organ systems
- Have bilateral symmetry and cephalization
- Known as acoelomates (without coelem, which is
a fluid filled body cavity)
4Form and Function in Flatworms
- Feeding
- Digestive cavity with a single opening through
which both food and wastes pass - Parasitic worms obtain nutrients from foods that
have already been digested by their hosts
5Form and Function in Flatworms
- Respiration, Circulation, and Excretion
- Rely on diffusion to
- Transport oxygen and nutrients to internal
tissues - Remove carbon dioxide and other wastes from their
bodies - Have no gills or respiratory organs, heart, blood
vessels, or blood - Some have flame cells remove excess water and
filter wastes from the body
6Excretory System
7Form and Function in Flatworms
- Response
- A head encloses several ganglia (groups of nerve
cells) that control the nervous system - Have eyespots that look like eyes, but are groups
of cells that can detect changes in the amount of
light in their environment
8Form and Function in Flatworms
- Movement
- Two means of movement
- Cilia to help glide through water
- Muscle cells allow them to twist and turn
9Form and Function in Flatworms
- Reproduction
- Most are hermaphrodites that reproduce sexually
- A hermaphrodite is an individual that has both
male and female reproductive organs - Asexual reproduction takes place by fission, in
which an organism splits in two
10Groups of Flatworms
- Three main groups of Flatworms
- Turbellarians
- Flukes
- Tapeworms
- Most turbellarians are free-living
- Most other flatworm species are parasites
11Turbellarians
- Free-living flatworms
- Live in marine or freshwater
12Flukes
- Class Trematoda
- Parasitic flatworms
- Infect the internal organs of their host
13Tapeworms
- Class Cestoda
- Long, flat, parasitic worms
- Adapted to life inside the intestines of their
host - No digestive tract
- Absorb already digested nutrients from host
14Roundworms
15What is a Roundworm?
- Phylum Nematoda
- Slender, unsegmented worms with tapering ends
- Range in size from microscopic to a meter
- Most are free-living, inhabiting soil and water
- Others are parasitic
16What is a Roundworm?
- Have a pseudocoelom (false coelom)
- Have a digestive tract with two openings a
mouth and an anus
17Form and Function in Roundworms
- Have specialized tissues and organ systems
- Body systems of free-living roundworms are more
complex than parasitic ones
18Form and Function in Roundworms
- Feeding
- Predators that use grasping mouthparts to catch
and eat small animals - Respiration, Circulation, and Excretion
- Exchange gases and excrete metabolic waste
through their body walls - Depend on diffusion to carry nutrients and waste
through their bodies
19Form and Function in Roundworms
- Response
- Simple nervous systems
- Have several types of sense organs
- Movement
- Muscles extend the length of their bodies
- Reproduction
- Reproduce sexually, and most have separate sexes
20Roundworms and Human Disease
- Parasitic roundworms include
- Trichinosis-causing worms
- Filarial worms
- Ascarid worms
- Hookworms
21Trichinosis-Causing Worms
- Trichinosis terrible disease caused by the
roundworm Trichinella - Adult worms live and mate in the intestines of
their hosts - Humans usually get the disease from eating
undercooked pork
22Filarial Worms
- Threadlike worms that live in blood of birds and
mammals - Causes elephantiasis
23Ascarid Worms
- Serious parasite of vertebrate animals
- Causes malnutrition in more than 1 billion people
worldwide - Absorbs digested food from the hosts small
intestine
24Hookworms
- 25 of people in the world are affected with
hookworms - Live in hosts intestines
- Feed on blood, causing weakness and poor growth
25Annelids
26What is an Annelid?
- Phylum Annelida
- Worms with segmented bodies
- Each segment is separated by a septum
- Have a true coelom
27Form and Function in Annelids
- Feeding and Digestion
- Many get their food using a pharynx
- Food moves from the pharynx, into the esophagus,
the crop, the gizzard, and then to the intestine - Others obtain food by filter feeding
- Circulation
- Closed circulatory system blood is contained
within a network of blood vessels
28Form and Function in Annelids
- Respiration
- Aquatic annelids often breath through gills
- Land-dwelling annelids take in oxygen and give
off carbon dioxide through their moist skin - Excretion
- Digestive wastes pass through the anus at the end
of the digestive tract - Cellular waste is eliminated through nephridia
(excretory organs)
29Form and Function in Annelids
30Form and Function in Annelids
- Response
- Well developed nervous system consisting of a
brain and several nerve cords
31Form and Function in Annelids
- Movement
- Two groups of muscles that work together as part
of a hydrostatic skeleton - Reproduction
- Most reproduce sexually
- Some have separate sexes, others are
hermaphrodites
32Groups of Annelids
- Three classes of Annelids
- Oligochaetes
- Leeches
- Polychaetes
33Oligochaetes
- Class Oligochaeta
- Contains earthworms and their relatives
- Streamlined bodies
- Relatively few setae
- Most live in soil or freshwater
34Leeches
- Class Hirudinea
- External parasites that suck the blood and body
fluids of their host
35Polychaetes
- Class Polychaeta
- Contains sandworms, blood worms, and relatives
- Marine annelids that have paired, paddlelike
appendages tipped with setae (brushlike
structures)
36Ecology of Annelids
- Earthworms and many other annelids spend their
lives burrowing through soil, aerating and mixing
it - Earthworms help plant matter decompose
- Earthworm castings are rich in nitrogen,
phosphorus, potassium, micronutrients, and
beneficial bacteria
37Mollusks
38What is a Mollusk?
- Soft-bodied animals
- Usually have an internal or external shell
- Free-swimming larval stage called a trocophore
39Form and Function in Mollusks
- True coeloms
- Complex, interrelated organ systems
40Form and Function in Mollusks
- Body Plan
- Variation on four main parts
- Foot takes many forms
- Mantle layer of tissue that covers the
- mollusks body
- Shell made by glands in the mantle
- Visceral mass consists of internal organs
41Form and Function in Mollusks
- Feeding
- Can be herbivores, carnivores, filter feeders,
detritivores, or parasites - Snails and slugs feed using a tongue-shaped
structure called a radula
42Form and Function in Mollusks
- Feeding
- Clams, oysters, and scallops use gills
- Food enters through a siphon tubelike structure
through which water enters and leaves the body
43Form and Function in Mollusks
- Respiration
- Aquatic mollusks breathe using gills inside their
mantle cavity - Land snails and slugs respire through the moist
surface of their skin
44Form and Function in Mollusks
- Circulation
- Some have open circulatory systems works well
for slow-moving mollusks (snails and clams) - Others have closed circulatory systems works
best for fast moving mollusks (octopi and squid)
45Form and Function in Mollusks
- Excretion
- Nephridia remove wastes from the blood and
release it outside the body
46Form and Function in Mollusks
- Response
- Two-shelled mollusks have simple nervous systems
- Octopi and relatives have the most highly
developed nervous systems of all invertebrates - Octopus opening a jar
47Form and Function in Mollusks
- Movement
- Move in a variety of ways
- Snails secrete mucus and move over surfaces using
the foot - Octopi use a form a jet propulsion
- Reproduction
- Reproduce in a variety of ways
- Snails and two-shelled mollusks external
fertilization (sexually) - Tentacled mollusks and some snails internal
fertilization (sexually)
48Groups of Mollusks
- Three major classes
- Gastropods
- Bivalves
- Cephalopods
49Gastropods
- Class Gastropoda
- Shell-less or single-shelled
- Move using muscular foot on ventral side
- Includes pond snails, land slugs, sea
butterflies, sea hares, limpets, and nudibranchs
50Bivalves
- Class Bivalvia
- Have two shells held together by one or two
powerful muscles - Include clams, oysters, mussels, and scallops
51Cephalopods
- Class Cephalopoda
- Soft-bodied
- Head is attached to a single foot
- Foot is divided into tentacles or arms
- Includes octopi, squids, cuttlefishes, and
nautiluses
52Ecology of Mollusks
- Mollusks play many different roles in living
systems - Feed on plants
- Prey on animals
- Filter algae out of the water
- Eat detritus
- Some mollusks are hosts to symbiotic algae or to
parasites others are themselves parasites - Mollusks are food for many organisms