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WORMS AND MOLLUSKS
Ms. Moore 2/11/13
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: fissionorganism 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 passageselephantiasis
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
