WORMS AND MOLLUSKS

Ms. Moore 10/18/12

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

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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