Category: Invertebrate Unit
Invertebrate Crossword
Unsegmented Worm
Unsegmented Worms
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Phylum Platyhelminthes
Characteristics
- Called flatworms because bodies are flattened dorso-ventrally
- Acoelomate – solid bodies without a lined body cavity
- Have 3 body layers — outer ectoderm, middle mesoderm, & inner endoderm
- Bilaterally symmetrical
- Show cephalization (concentration of sensory organs at anterior or head end)
- Body cells exchange oxygen & carbon dioxide directly with environment by diffusion
- Single opening into gastrovascular cavity; two-way digestive tract
- Some are parasites & others are free-living
- Parasitic worms have thick cell layer called tegument covered with a nonliving cuticle covering their bodies as protection inside hosts
- Includes 3 classes — Turbellaria (planarians), Trematoda (parasitic flukes), & Cestoda (parasitic tapeworms
Class Turbellaria
- Most are marine but includes freshwater planarian (Dugesia)
Planarians
- Spade-shaped at the anterior end & have two, light-sensitive eyespots
- Can sense light, touch, taste, & small
- Have 2 clusters of nerve cells or ganglia to form a simple brain
- Nervous system composed of a nerve net
- Capable of simple learning
- Move by tiny hairs or cilia over a mucus layer that they secrete
- Feed by scavenging or protozoans
- Have a single opening or mouth located at the end of a muscular tube called the pharynx which can be extended when feeding
- Flame cells help remove wastes to excretory pores
- Hermaphrodites that cross-fertilize eggs that are then deposited into a capsule until hatching in 2-3 weeks
- Reproduce asexually by fragmentation
Class Trematoda
- Includes parasitic flukes
- About 1 cm long & oval shaped
- Require a host to live
- Have both oral & ventral suckers to cling to host & suck blood, cells, & body fluids
- Oral sucker around mouth at anterior end sucks blood
- May be endoparasites (live inside a host) or ectoparasites (live on the outside of host
- Covered in tough, unciliated tegument
- Nervous & excretory systems like turbellarians
- Hermaphrodites
- Have a long, coiled uterus that stores & releases 10,000+ eggs
- Eggs released through genital pore & develop into larva
- Show complex life cycles
- Life cycle of sheep liver fluke:
* Adult liver flukes live in sheep liver & gall bladder where they mate & form eggs
* Eggs enter intestines, pass out with feces, & hatch in water
* Larva enter snails, asexually multiply, then leave snail & form cysts
* Cysts (dormant larva with hard, protective covering) clings to grass
* Sheep ingest cysts when they eat grass
* Cysts hatch in digestive tract & bore through intestines into bloodstream
* Mature & reproduce in the liver
- Schistosomiasis (disease caused by parasitic blood flukes) infects people in Asia, Africa, & South America causing intestinal bleeding & tissue decay that can result in death
Class Cestoda
- Includes tapeworms
- Adapted for parasitic life
- Tough outer tegument prevents being digested by host
- Anterior end called scolex contains hooks & suckers for attachment to intestine of host
- Long, ribbon-like bodies up to 12 m in length
- Nervous system extends length of body but lacks sense organs
- Lacks mouth & digestive tract but absorbs digested nutrients from host
- Grows by making body segments called proglottids
- Each proglottid produces eggs & sperm that cross-fertilize with other segments & also self-fertilize (hermaphrodites)
- Oldest, mature proglottids containing eggs at posterior end break off & pass out with feces
- Life cycle of beef tapeworm:
* Cattle eat grass with proglottids containing fertilized eggs
* Eggs hatch into larva & bore through cow’s intestine into bloodstream
* Larva burrow into cow’s muscle & form cysts
* Humans eat beef (muscle) & cysts travels to intestines
* Cyst breaks open & adult beef tapeworm forms
BEEF TAPEWORM LIFE CYCLE
Phylum Nematoda
Characteristics
- Called roundworms
- Includes Ascaris, hookworms, Trichinella, & pinworms
- Pseudocoelomates have fluid-filled body cavity partially lined with mesoderm
- Pseudocoelom contains the body organs & provides hydrostatic skeletal support for muscles
- Have long slender bodies that taper at both ends
- Covered with flexible cuticle
- Digestive tract with anterior mouth & posterior anus; called one-way digestive tract
- Separate sexes in most species
- Most are free living
- Some are parasites on plants & animals
- Ascaris is a parasitic roundworm living in the intestines of pigs, horses, & humans
- Ascaris life cycle:
* Enter body in contaminated food or water & hatch in intestines
* Larva bore into bloodstream & carried to lungs & throat
* Larva coughed up, swallowed, & return to intestines to mature & mate
* Block the intestine causing death
- Hookworm eggs hatch in moist soil & larva bore through bare feet of new host
- Trichinella are human parasites caused by eating undercooked pork containing the cysts
* Cause disease called trichinosis
* Cysts cause muscle pain & stiffness
CYSTS IN CONTAMINATED PORK
Phylum Rotifera
Characteristics
- Known as rotifers or wheel animals
- Transparent, free-swimming microscopic animal
- Freshwater & marine
- Have a ring of cilia around mouth that rotates like a wheel to bring in food
- Feed on unicellular algae, bacteria, & protozoa
- Have a muscular organ called the mastax behind the pharynx to chop food
- Nervous system composed of anterior ganglia & 2 long nerve cords
- Show cephalization (head end)
- Have 2 anterior, light-sensitive eyespots
Sponge & Cnidarian Study Guide
Study guide for Sponge, Cnidarians, & Ctenophores
· Know relatives of the jellyfish
· How are sponges different from other animals
· Know characteristics of all invertebrates
· Know characteristics of sponges
· What is the function of collar cells in sponges
· What are spicules
· Know characteristics of adult sponges
· Be able to explain skeletal support of sponges
· How do sponges obtain their food
· What helps draw water into a sponge
· What is the function of amebocytes in sponges
· How does excess water leave a sponge
· What is the purpose of gemmules in sponges
· What is a hermaphrodite
· How can sponges reproduce
· Know animals that capture prey by using nematocysts
· What are the 2 distinct life stages of cnidarians
· Describe nematocysts
· What organisms have tentacles with stinging cells
· Know examples of cnidarians
· Describe the life of a planula larva
· Know the life stage that is dominant in sea anemones
· What organisms would be anthozoans
· Know the dominant life stage of jellyfish
· Know the main characteristics of ctenophores
Sponges & Cnidarian
Sponges, Cnidarians, & Ctenophores
Phylum Porifera
Characteristics
- Includes marine & freshwater sponges
- Found in the kingdom Animalia & subkingdom Parazoa
- Sessile as adults
- Simplest of all animals
- Contain specialized cells, but no tissue
- Asymmetrical
- Bodies filled with holes or pores for water circulation
- Marine sponges are larger & more colorful than freshwater sponges
- Range in size from 2 centimeters to 2 meters
- Osculum is single, large body opening at the top for water & wastes to leave
- Spongocoel is the body cavity of sponges
- Have only 2 cell layers (ectoderm & endoderm) separated by jellylike material
- Flagellated cells called choanocytes or collar cells line their internal body cavity
- Flagella of choanocytes beat & pull in water containing food which the collar traps
- Spongin is a network of flexible, protein fibers making up the sponge’s skeleton
- Spicules are tiny, hard particles shaped like spikes or stars in the skeleton of some sponges
- Spicules are made of calcium carbonate or silica
Feeding
- Sponges are filter feeders that remove plankton (food) from the water that is brought in through pores lined with collar cells
- Flagella pull in bacteria, protozoans, & algae that sticks to collar of choanocytes where it is digested
- Amebocytes are specialized cells in sponges that can roam to pick up food from choanocytes & distribute it to all other parts of the sponge
- Amebocytes also transport carbon dioxide & wastes away from sponge cells
- Excess water & food leaves through the excurrent osculum
Reproduction
- Sponges can reproduce asexually by external buds that break off & form new sponges or stay attached to form sponge colonies
- Gemmules are specialized, internal buds formed by sponges during cold or dry weather that can survive harsh conditions
- Gemmules consist of a food-filled ball of amebocytes surrounded by a protective coat with spicules & released when adult sponge dies
- Gemmules break open when conditions improve & the cells form new sponges
- Sponge can also asexually regenerate missing parts or a new sponge from a small piece of sponge
- Sponges are hermaphrodites (produce both eggs & sperm), but they exchange sperm & cross-fertilize eggs during sexual reproduction
- Planula is the flagellated, free-swimming larva that forms from the zygote
- Planula larva eventually settles to the bottom & attaches to develop into an adult, sessile sponge
Classes of Sponges
- Calcarea are chalky sponges with calcium carbonate spicules
- Hexactinella includes glass sponges & the Venus flower basket with silica spicules
- Demospongiae include horny & bath sponges with only spongin or spongin & silica spicules
- Sclerospongiae are coral sponges & have spongin & silica and calcium carbonate spicules
Phylum Cnidaria
Characteristics
- Includes marine organisms such as jelllyfish, Portuguese man-of-war, coral, sea anemone, & sea fans
- Hydra is a freshwater cnidarian
- All carnivorous
- Have 2 cell layers (epidermis -outer & gastrodermis-inner) with a hollow body called gastrovascular cavity
- Contain a jelly-like layer between epidermis 7 gastrodermis called mesoglea
- Single opening (mouth/anus) to gastrovascular cavity where food & water enter & wastes leave; called two-way digestive system
- Have tentacles around mouth to pull in water & capture food
- Have a simple nerve net with to help with movement & senses
- Sessile members include corals, sea anemones, & sea fans
- Have radial symmetry as adults
- Contain stinging cells called cnidocytes in their tentacles that contain coiled stingers called nematocysts that can shoot out & paralyze prey
Body Forms
- Have 2 basic body forms —polyp & medusa
- Polyp forms are usually sessile with upright tentacles arranged around the mouth at the top and with a thin layer of mesoglea
- Polyps are the asexual stage
- Corals, hydra, & sea anemones exist in the polyp form as adults
CORAL POLYPS
- Medusa forms are usually free-swimming, bell-shaped animals with tentacles that hang down around the mouth and with a thick layer of mesoglea for support
- Medusa are the sexual stage
- Jellyfish & Portuguese man-of-war are medusa form as adults
- Some cnidarians are dimorphic or go through both polyp & medusa stages in their life cycle
JELLYFISH LIFE CYCLE
- Some are solitary (Hydra) others are colonial (corals)
- Three classes include Hydrozoa (hydra), Scyphozoa (jellyfish), & Anthozoa (sea anemones & corals)
Hydrozoa
- Includes freshwater, sessile hydra (exists only as polyps)
- Portuguese man-of-war (exists as colony of polyps & medusa)
- Group of cells called basal disk produces sticky secretion for attachment & can secrete gas bubbles to unattach & let hydra float
- Hydra also move by somersaulting (tentacles bend over to bottom as basal disk pulls free)
- Tentacles pull food into gastrovascular cavity where enzymes digest it
- Reproduce asexually by budding during warm weather & sexually in the fall
- Hermaphrodites that release sperm into water to fertilize eggs of another hydra
HYDRA
Scyphozoa
- Includes bell-shaped jellyfish
- Medusa stage is dominant in the life cycle
- Tentacles may be meters in length & carry poisons that cause severe pain or death
- Have both asexual polyps & sexual medusa stages in their life cycles
- Adult medusa stage releases eggs & sperm into water
- Fertilization produces ciliated planula larva that settles to the bottom, attaches, & forms tentacles
- New medusa bud off of reproductive polyps & form adult jellyfish
Anthozoa
- Include corals in a limestone case & sea anemones
- Called “flower animals”
- All marine
- Sea anemone is a sessile, polyp-form that uses its tentacles to paralyze fish
- Some anemones in the Pacific Ocean live symbiotically with the clownfish sharing food & protecting each other
- Corals are small, colonial polyps living in limestone cases
- Coral reefs form as polyps die & provide a home and protection for other marine animals
- Reefs form in warm, shallow water & only the top layer has living polyps
- Algae may live symbiotically with coral supplying them with oxygen
Phylum Ctenophora
Characteristics
- All marine
- Includes comb jellies
- Have eight rows of fused cilia called “comb rows”
- Largest animal to move by cilia
- Move by beating cilia
- Lack cnidocytes but have cells sticky cells called colloblasts that bind to prey
- Colloblasts located on two ribbon-like tentacles
- Have sensory structure called apical organ to detect direction in the water
- Most are hermaphrodites (make eggs & sperm)
- Produce light by bioluminescence
Squid Dissection
Objectives:
As a result of this lesson, students will be able to:
Materials:
Procedure
Place the squid with the dorsal (back) side up in the dissecting pan. This means put the side with the funnel down and the fin side up. Make sure the tentacles and arms are towards you. Locate the head, eyes, beaks (mouth), arms (8), two longer feeding tentacles, fins, mantle, and skin. Use the hand lens to examine the suckers on the tentacles and arms as well as the spots on the skin, which are chromatophores.
What are the differences between arm and tentacle suckers? Where are the suckers located on the feeding tentacles as compared to the location of the suckers on the arms?
How do you account for the different locations of the suckers on the tentacles and the arms? What are chromatophores?
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Starfish Dissection
Starfish Dissection |
Introduction:
Echinoderms are radially symmetrical animals that are only found in the sea (there are none on land or in fresh water). Echinoderms mean “spiny skin” in Greek. Many, but not all, echinoderms have spiny skin. There are over 6,000 species. Echinoderms usually have five appendages (arms or rays), but there are some exceptions.
Radial symmetry means that the body is a hub, like a bicycle wheel, and tentacles are spokes coming out of it (think of a starfish). As larvae, echinoderms are bilaterally symmetrical. As they mature, they become radially symmetrical.
Most adult echinoderms live on the bottom of the ocean floor. Many echinoderms have suckers on the ends of their feet that are used to capture and hold prey, and to hold onto rocks in a swift current.
Sea Stars
- Asteroideas are the true sea stars and sun stars.
- Ophiuroideas are brittle stars and basket stars.
The differences between the two sub-types lies in how the arms connect to the central disk. Ophiuroids have arms that do not connect with each other. There is a distinct boundary between arm and central disk. Asteroids have arms that are connected to each other. Also, it is harder to tell with asteroids where the central disk ends and the arms begin.
The sea star’s top surface (or skin) looks spiny if you examine it. If you look very closely you will notice that there are different types of growths on the surface. Some bumps are used to absorb oxygen, they are called dermal branchiae. Pedicellaria are pincher-like organs used to clean the surface of the skin. Barnacle larvae could land on a sea star and start growing if it were not for these organs.
How Do Sea Stars Move?
Each ray of a sea star has a light sensitive organ called an eyespot. Though it can not see nearly as well as we do, sea stars can detect light and its general direction. They have some idea of where they are going.

Can Sea Stars Grow New Arms?
Given enough time, sea stars can grow back arms that have been damaged or removed. For a few species, the severed arm can grow back into a complete sea star! For most sea stars, however, a severed limb dies.
What Do Sea Stars Eat?
Sea stars eat many things. A sea star’s diet can include: barnacles, snails, sea urchins, clams, and mussels. A few species, such as the spiny star of the North Atlantic, eat other sea stars! Many sea stars eat mussels and clams in an interesting way. They surround the shell and use the suckers on their feet to pull the two shells (or valves) apart. The sea star has enough force in its arms to actually bend the shell! This creates an opening between the two shells that is only .01 inches wide. Using this tiny gap, the sea star puts its stomach into the clam’s shell and eats its insides. When it is done, nothing is left but an empty shell.
Materials:
Preserved starfish, dissecting pan, scissors, scalpel, forceps, T-pins, pencil, lab apron, safety glasses
Procedure:
Dorsal view of starfish showing external anatomy
Ventral view of starfish showing external anatomy
Dorsal view of a dissected starfish showing rectal cecum, anus, madreporite, pyloric stomach, pyloric duct
Dorsal view of a dissected starfish showing madreporite, stone canal, cardiac stomach, and ampullae
Dissection showing where cardiac stomach opens into the mouth
Close up of madreporite and stone canal
Dorsal view of a dissected starfish showing pyloric caecum and pyloric ducts
Dorsal view of a dissected starfish showing gonads and ampullae
Ventral view of starfish showing external anatomy
Starfish Prelab
Starfish Prelab | ![]() |
1. In what phylum are starfish found?
2. What is the habitat for starfish?
3. On what do starfish feed?
4. What system in their body helps them catch & hold their food?
5. What does echinoderm mean in Greek? Why is this a good name for this group?
6. Name 2 classes of echinoderms & a member of each class.
7. Where does water enter a starfish? Where does it leave?
Pzsol Mollusks
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Mollusk
Mollusks
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Phylum Mollusca
Characteristics
- Soft-bodied invertebrate covered with protective mantle that may or may not form a hard, calcium carbonate shell
- Includes chitons, snails, slugs, clams, oysters, squid, octopus, & nautilus
- Second largest animal phylum
- Have a muscular foot for movement which is modified into tentacles for squid & octopus
- Complete, one-way digestive tract with a mouth & anus
- Have a fully-lined coelom
- Cephalization – have a distinct head with sense organs & brain
- Have a scraping, mouth-like structure called the radula
- Go through free-swimming larval stage called trochophore
Trochophore Larva
- Body organs called visceral mass lie below mantle
- Have circulatory, respiratory, digestive, excretory, nervous, & reproductive systems
- Bilaterally symmetrical
- Most have separate sexes that cross-fertilize eggs
- Gills between the mantle & visceral mass are used for gas exchange
- Includes 4 classes — Polyplacophora (chitons), Gastropoda (snails, slugs, nudibranchs, conchs & abalone), Pelecypoda or Bivalvia (clams, oysters, & mussels), & Cephalopoda (squid, octopus, & nautilus)
SNAIL, CLAM, CHITON, & SQUID
Class Polyplacophora
Characteristics
- All marine
- Have a shell divided into 8 over-lapping plates
- Live on rocks along seashore feeding on algae
CHITON
Class Gastropoda
Characteristics
- Head has a pair of retractable tentacles with eyes located at the ends
- Have a single shell or valve (snails) or none (slugs)
- Known as univalves
- Snails
* May be marine, freshwater, or terrestrial
* Aquatic snails breathe through gills & use their radula to scrape algae for food
* Terrestrial snails use their mantle cavity as a modified lung & saw off leaves
* Retreat into shell in dry periods & seals opening with mucus
* Have open circulatory system
* Secrete mucus & use muscular foot to move
* Land snails are hermaphrodites
* Aquatic snails have separate sexes
* Use internal fertilization
- Slugs
* Live in moist terrestrial areas
* Lack a shell
SLUG
- Pteropods
* Called “sea butterflies”
* Marine
* Have a wing-like flap for swimming
“SEA BUTTERFLY”
- Oyster Drills
* Radula modified to drill into oyster shells
OYSTER DRILL
- Nudibranch
* Marine slug
* Lacks shell
NUDIBRANCH
Class Bivalvia or Pelecypoda
Characteristics
- Sessile or sedentary
- Includes marine clams, oysters, shipworms, & scallops and freshwater mussels
- Filter feeders
- Have two-part, hinged shell (2 valves)
- Have muscular foot that extends from shell for movement
- Scallops clap valves together to move
- Shell secreted by mantle & made of 3 layers — outer horny layer protects against acids, middle prismatic layer made of calcium carbonate for strength, & inner pearly layer next to soft body
- Mantle secretes substance called “mother of pearl” to surround irritants like grains of sand
- Oldest, raised part of shell called umbo
- Powerful anterior & posterior adductor muscles open & close shell
- Lack a distinct head
- Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen
INTERNAL CLAM ANATOMY
- Have heart & open circulatory system
- Nervous system made of 3 pairs of ganglia, nerve cords, & sensory cells that detect light, chemicals, & touch
- Separate sexes with external fertilization of eggs
Class Cephalopoda or Amphineura
Characteristics
- Includes octopus, squid, cuttlefish, & chambered nautilus
- All marine
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NAUTILUS | OCTOPUS | SQUID |
- Most intelligent mollusk
- Well developed head
- Active, free swimming predators
- Foot divided into tentacles with suckers
- Use their radula & beak to feed
- Closed circulatory system
- Lack an external shell
- Highly developed nervous system with vertebrate-like eyes
- Separate sexes with internal fertilization
- Squid
* Largest invertebrate is the Giant Squid
* Large, complex brain
* Ten tentacles with longest pair to catch prey
* Use jet propulsion to move by forcing water out their excurrent siphon
* Chromatophores in the skin can help change squid color for camouflage
* Can squirt an inky substance into water to temporarily blind predators
* Have internal shell called pen
* Female lays eggs in jellylike material & protects them until hatching
GIANT SQUID
- Octopus
* Eight tentacles
* Similar to squid
* Crawls along bottom looking for prey
OCTOPUS
- Chambered Nautilus
* Has an exterior shell
* Lives in the outer chamber of the shell
* Secretes gas into the other chambers to adjust buoyancy
NAUTILUS
Economic Importance of Mollusks
- Used by humans for food
- Pearls from oysters
- Shells used for jewelry
- Do crop & garden damage
- Serve as intermediate hosts for some parasites such as flukes