Denbigh Baptist Christian School
Middle School Life Science
Invertebrates I: Sponges, Jellyfish, and Worms
15A What is an Invertebrate?
“in” – not or without
“vertebrate” – one of the bones along the back of an animal
Therefore – animal w/o a backbone
Skeleton – provides mechanical support to attach muscles; also provides for consistent
shape
Some skeletons internal; others external
15B Sponges
“pore” animals – body consists of numerous pores through which they pump water
Phylum – Porifera
All live in water, most in oceans though SOME live in fresh water
Adult sponges permanently attached to solid objects – unable to move
Embryonic (baby) “can” swim for a short time
Skeletons made of SPONGIN (flexible fibrous protein) and SPICULES (stiff pointed
spikes of calcium carbonate)
Hollow central cavity and large opening near top
Lining central cavity are collar cells with flagella to cause water to flow inward through
small pores and exit through the large upper opening
FILTER FEEDERS – because they “filter” water in order to obtain food
Cells along lining of central cavity capture microscopic food and absorb O2 in addition to
releasing “waste”
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Denbigh Baptist Christian School
Middle School Life Science
15C The Jellyfish: A Cnidarian
Phylum Cnidaria
Tentacles with stinging cells
Usually found in oceans; occasionally in fresh water
15C.1 The Body of a Jellyfish
Primary support is “jelly” like mass that fills space between two layers of tissue
Hydrostatic skeleton – similar to a water balloon; water provides support
Large central cavity surrounded by two layers of tissue
Tentacles surround the “mouth” (only body opening)
Ectoderm – outer tissue layer
Endoderm – inner tissue layer
Gastrovascular cavity – inside where jellyfish digests food
Food enters mouth and waste leaves
Network of nerves throughout the body but no brain to coordinate reactions
15C.2 Jellyfish Activities
Tentacles contain NEMATOCYSTS – special cells in the ectoderm
Nematocysts contain a “trigger” which causes a thin tube to be forced out
Poison is forced through this tube
Weak muscle fibers can push food into the mouth and into gastrovascular cavity
Enzymes are released in the endoderm to break down food
Food enters vacuoles
Waste expelled through the mouth
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Denbigh Baptist Christian School
Middle School Life Science
Jellyfish can “swim” by squeezing out water like a water jet resulting in slow jerky
motion
15C.3 Other Interesting Cnidarians
Hydras
Corals
Sea anemones
Portuguese man-of-war (up to 50 ft long)
Cnidarians have radial symmetry along length of body – no defined left/right side
though they do have a definite TOP and BOTTOM
15D The Planarian: A Flatworm
The term “plane” comes to mind … flatworm
Bilateral symmetry – prefix “bi” implies 2; lateral  length wise
Mirror images along center-line
Phylum Platyhelminthes
Free-living – often found in freshwater streams and in soil
Implies NOT a parasite
15D.1 The Planarian’s Nervous System
Most animals control bodies via neurons
NEURONS – long, thin nerve cells that carry impulses from one point to anther
Kind of like computer communication cables or phone lines
Nervous systems become complex, some sort of “director” required
GANGLION – director or coordination center
Planarians have longitudinal nerves (two of them) running down the length of the body
Across (tranverse) the body is additional nerves.
The appearance of nerves is like a ladder
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Denbigh Baptist Christian School
Middle School Life Science
Like humans, planarian’s ganglia coordinate response to stimuli (something an organism
can sense).
There is keen sense of smell and light.
Smell likely important for location of food
15D.2 The Planarian’s Digestive and Excretory Systems
Cilia on underside help planarian to “glide” over underwater surfaces.
Mouth located on underside
Inside mouth is long branching cavity – intestine
Intestine lined with layer of cells – GASTRODERM
“Eating” is accomplished by extending PHARYNX through mouth and “sucking” food
into intestine.
Enzymes are excreted to begin digestion of food
Gastroderm absorbed small pieces of food after enzyme effect. Cellular digestion
completes the process.
Non-digested material – expelled from intestine through mouth
Intestine extends to all portions of body
Planarian is about thickness of a sheet of paper
Size allows for exchange of O2 and CO2 directly with environment
15D.3 Other Interesting Flatworms
Tapeworms, flukes and marine flatworms
Tapeworms – common parasite of animals and humans
Found in digestive tract (attaches itself) “sucks/absorbs” digested food
Many segments (reproductive in nature) fill with eggs.
Exit body via waste excrement
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Denbigh Baptist Christian School
Middle School Life Science
Parasitic worms in humans are unpleasant and harmful
15E Roundworms
Phylum Nematoda
Round, tubular bodies with tapered ends
Some are parasites
15E.1 Ascaris – A Common Roundorm
Often found in intestines of various animals
Release eggs into animal’s intestines that exit via feces
Tiny eggs are often swallowed by grazing animals beginning the process again
15E.2 Other Interesting Roundworms
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Hooksworms
Pinworms
Trichina worms
Vinegar eel
15F Segmented Worms
Earthworm has long, slender body with a series of segments
Phylum Annelida
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Leeches
Tubeworms
Scale worms
Sandworms
Fireworms
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Denbigh Baptist Christian School
Middle School Life Science
15F.1 The Body of an Earthworm
Epidermis covers body
Epidermis exchanges gases (CO2 and O2) with environment
Secretes a thin outer coating – cuticle which protects from parasites and “stuff”
Two muscles layers for support and motion
One is “circular” and changes the diameter of the worm
When diameter changes, length necessarily changes with it
Second muscle layer is longitudinal which can lengthen/shorten the worm
Movement is in multiple steps
Bristles in “rear” are extended to anchor the rear
Circular muscles contract causing diameter to decrease AND lengthening worm
Bristles in “front” extended to anchor and bristles in rear are retracted
Longitudinal muscles contract causing diameter to increase and length to shorten
15F.2 The Earthworm’s Nervous System
Sensory receptor – structure that can sense a stimulus and start an impulse along a
neuron
Located over the body of an earthworm
Sensitive to
 Chemicals
 Light
 Temperature
 Other
More receptors at “front” than anywhere else
Since “leads” with front, helps to distinguish between food and danger
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Denbigh Baptist Christian School
Middle School Life Science
Two large ganglia located in 3rd segment (diagram 15F-3 page 278)
Nerve cord (bundle of nerves) located in lower half of earthworm
Small ganglia located in each segment along the cord
Ganglia interpret impulses and worm decides what to do
Interprets and decides – however this doesn’t imply intelligence as very little is present
Ganglia takes input from sensory receptors and “informs” muscles, bristles and other
structures
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Denbigh Baptist Christian School
Middle School Life Science
15F.3 The Earthworm’s Digestive System
Often eats “soil” as it forms tunnels
Most of soil is indigestible and or non-food
Some of the ingested soil contains decaying leaves, fungi and small creatures
Digestive tract is long, straight
Enlargements, constrictions, infoldings and glands along the way … each with own
function in digestion process
Mouth scretes fluids to moisten soil
Upper lip forces food into mouth
Connected to mouth is pharynx (FEHR inks)
Glands secrete fluid into pharynx to lubricate food passing through
Muscle fibers contract to help “pull” food into earthworm
Esophagus (ih SAHF uh gus)– tubular passageway to carry food from pharynx to crop
CROP -- temporary storage chamber
Food passes from crop to “gizzard” … yet another “bulge” in digestive tract
Muscles in gizzard walls contract and relax pushing gizzard walls in/out
Gizzard performs mechanical digestion by “grinding” food particles against sand and grit
particles
Ground-up food passes to intestine of earthworm
Digestive enzymes in intestine (from cells in intestinal tract) continue digestion “outside”
the cell breaking food down into soluble materials
Inner intestinal wall has folds with ridges to provide extra surface area for absorbing of
food
Food molecules are absorbed through intestine into blood vessels
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Denbigh Baptist Christian School
Middle School Life Science
Blood vessels carry food to all the cells
Indigestible “food” passes through intestines and exit via the anus frequently
accumulating in “piles” outside tunnels. Piles are called castings.
15F.4 The Earthworm’s Circulatory System
Continuous network of blood vessels
Blood remains “inside” vessels
Closed circulatory system – blood never leaves blood vessels
Large dorsal blood vessel (along the back; dorsal – back) acts like the heart
Dorsal blood vessel “pumps” blood to 5 sets of aortic arches which essentially makes
this “function” like a heart and controls blood pressure
Blood passes through aortic arches to ventral blood vessel (ventral – belly)
Ventral blood vessel carries blood along “bottom” to every segment
Smaller arteries branch from ventral blood vessel
From the smaller arteries blood travels to CAPILLARIES
Walls of capillaries are very thin and allow substances to pass between blood and
earthworm’s tissues.
Blood flows from arteries through capillaries to VEINS.
VEINS – carry blood toward the heart
This type of system is known as “closed circulatory”
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Denbigh Baptist Christian School
Middle School Life Science
15F.5 The Earthworm’s Respiratory and Excretory Systems
No special respiratory structures
O2 and CO2 exchange through moist skin
O2 received through skin transfers to blood in capillaries
In an emergency, earthworm CAN go w/o new O2 for several hours
During heavy rainstorm – burrows fill causing earthworm to come to the surface to get
O2
All but first and last few segments have EXCRETORY TUBULES through which waste
is excreted through tiny pores on the surface of earthworm
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