Invertebrate Groups
Purpose: to supplement teacher information on select groups of invertebrate taxa.
Grade Level: any elementary
Sponges
No tissue organization
Suspension feeders (filter water for food)
Larvae that swim
Skeletal Structure - spicules
Marine and Fresh water
Very common in cold marine ecosystems (off Washington, Alaska, Antarctica)
and in Coral Reefs
Come in many colors (bright lavender, blue, yellow, red, white, etc.)
Grow to conform with environment (no specific shapes usually)
Hollow-bodied Animals (Cnidaria)
Two tissue layers only (inside, outside)
Radial Symmetry (cut into several equal parts, like a star)
All have stinging cells (jellyfish stings) - for catching food
Only one opening that acts as both mouth and anus
No head, central nervous system, gills, circulatory system
Two main life stages - medusa (jellyfish), polyp (anemone)
Most species have both stages but one is dominant
Medusa - tentacles down, mouth down
Polyp - tentacles up, mouth up
Examples - jellyfish (sea nettle, portugese man-of-war, cannonball jellyfish, lion's
mane (very poisonous), box jelly (most poisonous)), sea anemones, corals,
sea fans
Marine and Freshwater
Worms
3 tissue layers (inside, middle, outside)
3 kinds - segmented, round, flat
Breathe through their skins (oxygen and carbon dioxide diffuse through)
Organs and Organ systems present
Earthworms
Closed Circulatory system (5 hearts with blood vessels)
Segmented
Both male and female reproductive parts, exchange sperm
Eggs laid in a cocoon
Eat dirt (good for gardens because can break down things into small pieces)
Crop and gizzard to help grind food
Roundworms
Pin worms, nematodes, heart worms
Medically important
Not segmented
Move by whipping back and forth
Tube within a tube (digestive tract within a tube-like body)
Flatworms
Not truly segmented
Many parasitic (tapeworm, liver flukes)
Mouth only (no anus)
Arthropoda (means jointed legs)
Arachnids
Scorpions - primitive arachnid
Deserts, tropical rain forests
Nocturnal
Some can reach 18 centimeters in length
Stinger at end of abdomen
Spiders - predacious, many eat insects
Two body parts (cephalothorax and abdomen)
8 eyes
Produce silk (for webs, moving, egg cases)
Not all make webs - some are sit and wait predators and pounce on their
prey
Mites and Ticks
Parasitic - eat blood (often of mammals)
Crustacea
head plus trunk (thorax and abdomen), segmented, articulated legs
gills for gas exchange (need to be moist/wet)
complex life-cycle with larva
primarily aquatic
head with 2 pair of antennae, mandibles (primary feeding appendage), 2 pair
maxillae (accessory feeding appendages)
compound eyes stalks usually
hard, calcified carapace usually covers trunk
appendages adapted for different functions (eating, walking, swimming, etc.)
Decapods (crabs, crayfish, lobsters and shrimp)
5 pairs of legs
Crabs have a reduced abdomen that is folded underneath the thorax
Shrimp, Lobsters and Crabs have the abdomen extended behind
Very diverse group - some semi-terrestrial (still need to keep gills
wet)(hermit crabs, ghost crabs) but mostly are aquatic
Barnacles
Swimming larvae
Only in marine ecosystems
Do not move around (sessile)
Attach to rocks, shells, coral, whales, turtles, boats
Larvae settle to bottom head down and cement themselves and form a
shell made of 2-5 plates
Legs are used to filter feed (like a dip net)
Stalk on gooseneck barnacles is muscular and attaches them to rock, etc.
Most are sessile and cement the plates directly to surface
Pillbugs (Rolypolys)
Terrestrial but there are many related species that are aquatic
Eyes not on stalks
One species of deep sea isopod gets up to 42cm long (I will try to bring
one in)
7 pairs of walking legs
need to stay where it is moist (under logs, rocks, leaf litter)
Roll in a ball to conserve water
Brine Shrimp (Sea Monkeys) and Fairy Shrimp
Some can live in very salty water
Lay very dessication tolerant eggs (can be dried out for long periods of
time)
Live in temporary pools
Used as food for fish
Trunk with 11-18 segments and pairs of legs
No carapace
Many other groups that are less well-known (copepods, fairy-shrimp,
amphipods, …)
Millipedes
2 pair of legs on each segment
Terrestrial
Live underneath leaves, stones, soil (moist areas)
Over 10,000 species in world
A tropical species can get to 30 cm long
Walking appears as a wave in leg movement down the body (first pair,
second pair, third pair, etc)
Feed on dead plant material
No gills
Have spiracles (like insects) for gas exchange
Centipedes
1 pair of legs per segment, terrestrial
one species can grow to 30cm length (tropical)
poison claws for protection and killing prey
no gills, do have spiracles for gas exchange
live under leaves, stones, soil (moist areas)
often find in houses
Insects
largest group of animals
flying has allow insects to inhabit so many different habitats and diversify
(that's why there are so many species)
3 pairs of walking legs
usually 2 pairs of wings
single pair of antennae
pair of compound eyes
Head, thorax and abdomen
Gas exchange through spiracles
Development is complex (stages) - some have larva, pupa and adult while
others go through several nymph stages (look very much like adult but
without wings) before the adult stage
Mollusks
All have a sheet of skin called a mantle that produces a calcareous shell
Open circulatory system (have a heart but not complete blood vessels)
Large, muscular foot
Second largest group of animals (behind insects)
Use gills to exchange gas except in land snails and slugs
Very good fossil record because of shells
Snails and Slugs
Single shell (coiled), lost in slugs
Fresh and marine water and terrestrial
Terrestrial ones have lost the gills and have a chamber, formed by the
mantle, that acts as a lung for gas exchange
Have a head
Can pull their body way back in the shell and cover the opening to prevent
loss of water
Use mucus under their foot to allow them to move across surfaces
Eat by scraping with a hard tooth-like organ (radula)
Some are herbivores, some are carnivores
Clams, mussels, oysters, scallops
Two shells hinged at back
No head (but have a mouth)
Most are filter feeders (take food from water as passed between shells)
Gills are used for gas exchange and as a sieve for feeding
Foot is very large and strong for digging (often people call this the tongue)
Sessile (don't move around much) although some can swim by clapping
shells together (scallops)
Oysters and freshwater mussels produce pearls by secreting shell material
around an irritant (piece of sand) that has gotten in between the shells
Squid, Octopus
Head and foot
Very well developed nervous system with eyes that see almost as good as
mammal eyes do
Usually a reduced, internal shell as an adaptation for swimming (hard to swim
with a big "rock" on your back)
Foot is modified into tentacles (arms)
Largest invertebrates in world are squid and octopus
Giant squid have been seen to get up to 16 meters long
Swim by jet propulsion (pull water in and expel it quickly out pushing them
forward)
Octopus - 8 appendages
Squid - 10 appendages
Arms have suckers - to help hold prey
Most are carnivorous
Have an ink-gland that they shoot out as a decoy when they are trying to get
away from a predator (confuses predator)
Have a hard beak to help in feeding
Spiny Skinned Animals (starfish, sand dollars, sea cucumbers, sea urchins)
All are marine (no freshwater, no terrestrial)
Mostly bottom dwellers - crawl to move
Bodies are made up of 5 parts that are very similar to each other
Have an internal skeleton made up of calcareous material
Often have projecting spines
Have a system of water canals that help in moving around (like suction cups)
Have only one opening to stomach
Some can evert their stomachs and digest their food (stick stomach in clam and
digest)
Others scrape algae and eat it (herbivores, grazers)
Amazing regeneration abilities
Clammers wanted to get rid of starfish eating their clams so they caught
them, cut them up and threw them back thinking they were dead but the next
year there were up to 5 times as many starfish. Why? As long as there is a
portion of the central disk of the starfish attached to the arm, the starfish can
regenerate everything else.