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Cnidarians!!!!!!!!!!!!!!. Jellyfish, Hydroids, Corals, & Sea Anemones. Basic Information. Radial symmetry Contain organisms such as jellyfish, hydroids, corals, and sea anemones

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Jellyfish, Hydroids, Corals, & Sea Anemones

basic information
Basic Information

Radial symmetry

Contain organisms such as jellyfish, hydroids, corals, and sea anemones

Cnidocytes- stinging cells in their tentacles that are used for protection and killing prey.

two different body plans
Two Different Body Plans
  • 1. Polyp- mostly benthic, cylindrical, mouth is at one end and is surrounded by a ring of tentacles.
    • Ex- corals and sea anemones
  • 2. Medusa- free floating stage that is commonly known as a jellyfish.
most of them do exhibit both during their life cycles except corals and sea anemones
Most of them do exhibit both during their life cycles, except corals and sea anemones
  • Both stages have the following:
    • Epidermis= outer layer of cells
    • Gastrovascular cavity that is rather large and is lined by cells called the gastrodermis.
    • Mesoglea- between the epidermis and gastrodermis and it’s a gelatinous material where jellies get their names from.

Stinging organelle-> called cnida and some function in locomotion while others function in capturing prey and defense.

Most are of the spearing type called nematocycts= which is hidden away in a tiny capsule inside the cell and when activated it shoots out like a harpoon.

When the cnidocil, a short bristle like structure, comes into contact with prey or another object, it gets activates and shoots out the nematocyst.

Some nematocysts have a thread like structure that wraps around the prey and strangles them.


  • Box Jellyfish- kills a person in minutes (3-20)
  • Portuguese Man of War
leatherbacks and nudibranchs
Leatherbacks and Nudibranchs
  • Leatherbacks use them as a toy to play with and to eat!
  • Feed on them and somehow store the nematocysts in their body and use them for their own defense.


Colonial and share food

Very small and usually inconspicuous

Some are sessile and some are motile.


Class Scyphozoan or true jellies

Swim by pulsating their bodies or floating in the currents (making them plankton).

Sense organs= photoreceptors allow them to determine if it is dark or light. Many species do not like bright sunlight so they only come to the surface when its cloudy or near dusk.



Flower animals (bright colors)- sea anemones, corals, gorgonians (soft corals)

Adults= sessile

Only polyp stage

sea anemones
Sea Anemones


Compartmentalized gastrovascular cavity

Deepwater / shallow

Sessile- some bury themselves in the mud like tube anemones

sea anemones continue
Sea Anemones Continue

Expand tentacles to feed

Contract their bodies when they are disturbed

Change locations by gliding on their base, by crawling on their side, or walking on their tentacles. Some species can detach and swim with brief contractions.

nutrition digestion feeding
Nutrition / Digestion / Feeding

Digest their prey in the central gastrovascular cavity

Two way digestive tract- food goes in and comes out the same way. Digestion and excretion are through the same crevice.

Sessile- suspension feeders / filter feeders (plankton and organic matter) such as corals and anemones.

Carnivorous- feed mostly on fish and larger invertebrates. Prey is paralyzed by the toxin in the nematocyst.

Upside down jelly-> Cassiopeia, feeds on plankton that gets stuck in mucus produced by modified tentacles.

ecological roles
Ecological Roles

Provide habitats like corals

Key predators of the ocean

Coral polyps: extremely important. They provide habitat for thousands of other organisms. The reefs provide a solid surface for sessile marine animals to attach to, place of refuge for fish, and they act as a buffer to protect coastal organisms from waves and storms.

host symbionts
Host Symbionts

Portuguese Man of War and the Nomeus (man of war fish). Fish just swims amongst the tentacles without getting stung while gaining protection from the jelly, but it also lures other fish into the tentacles .

host symbionts continues
Host symbionts continues

Zoozanthellae lives in corals and provides food to the coral as well as other reef fish.

Parrotfishes- eat large amounts of coral polyps.

sea anemones1
Sea Anemones


Cleaner Shrimp

Snapping Shrimp

Arrow Crabs

Brittle Stars

Young anemones will attach to crabs as a form of camouflage.

ctenophora the comb jellies 100 150 species known
Ctenophora- The Comb Jellies (100-150 species known)

No stinging cells

Hermaphroditic- release sperm and eggs into the water.

Planktonic , iridescent during the day and bioluminescent at night.

Eight rows of cilia plates for locomotion, the plates beat allowing the animal to move.

Carnivorous-> eats zooplankton, larval fish, and fish eggs.

Ecological Role-> managing zooplankton size, regulation of fish species, and they channel nutrients to other species that eat them.

ctenophore videos
Ctenophore videos

phylum mollusca
Phylum Mollusca
  • Snails, slugs, oysters, clams, octopuses, squid, cuttlefish
  • Four Main Body Parts:
    • 1. Head- foot= head, mouth, sensory organs, and foot used for locomotion.
    • 2. Visceral mass= circulatory, digestive, respiratory, excretory, and reproductive systems.
    • 3. Radula- ribbon of tissue that contains teeth (bivalves don’t have these). Unique to mollusks and helps in scraping, piercing, tearing, or cutting food.
    • 4. Mantle- protective tissue that covers all of the soft parts. Also responsible for forming the animals shell by excreting calcium. Also used for gas exchange in some species.
more characteristics
More Characteristics!!!!

Soft body enclosed in a calcium carbonate shell that is secreted by the mantle.

Shell can be modified-> squid= internal, octopus = none, snails = coiled.

Hemolymph- bathes / floods the organs, no vessels.

Complicated digestive system with a mouth in the head and the anus emptying into the mantle cavity.

characteristics continue
Characteristics Continue….
  • Complex nervous system (Cephalopoda has the most)
  • Gas exchange= gills, lungs, or through the body via diffusion.
  • Hermaphroditic and internal fertilization (separate sexes).
  • Shell is comprised of three layers:
    • 1. Periostracum= outermost layer /proteins
    • 2. Prismatic layer= middle layer / bulk of the shell and is made of calcium carbonate and protein
    • 3. Nacreous layer= innermost layer / thin, crystal prismatic sheets of calcium carbonate.

As the animal grows, new periostracum and prismatic layers form in the mantle. The nacreous layer is secreted continuously and is responsible for the thickness of the shell and cause the shell to have a prism look to it.

Pearls are formed in oysters when the nacreous material is layered over sand grains and other particles.

class polyplacophora chitons
Class Polyplacophora- Chitons

Flattened bodies with eight shell plates

Have a large flat foot that allows them to attach to rocks.

When removed they roll into a ball for protection.

Feed on algae with their radula

class scaphopoda tusk shells
Class Scaphopoda- Tusk Shells

Shell resembles an elephants tusk

Shell is open at both ends, and the animals foot protrudes from the larger end.

Water enters and exits at the small end.

Special tentacles on their head for feeding.

class gastropoda
Class Gastropoda

Means “Stomach Foot”

Snails, slugs, abalone, nudibranchs, etc


Coiled mass or organs is enclosed by the dorsal shell which rests on the central foot.

Some retract back into their shells by closing the opening or aperture with a hard covering called the operculum.


Some are carnivores and feed on clams, oysters, worms, and small fish (whelks and cone snails). Whelks can locate a food source as far as 30 meters ( 99 feet) away, but it takes days to get there.

Deposit feeders – feed on bottom sediment(mud snails)


Nudibranchs -> no shell, but they have colorful branches that represent the gut and exposed gills. They eat sponges and other inverts (cnidarians). Protect themselves by toxins.

(add in at bottom) Nudibranchs have projections all over their bodies that serve as areas of gas exchange called cerata (since they lack gills).

When they feed on Cnidarians they don’t digest the stinging cells, instead they leave the cells intact and move them along ciliated tracts in the digestive system that are then transferred to the cerata.

Remember bright colors = don’t mess with me 



Internal fertilization-> most males have a long flexible penis that allows them to deposit sperm into or near the female’s genital opening.

Egg cases of the female are usually surrounded by a jelly-like sac or a hard case (like a whelk egg case).

Some do shed their eggs into the sea = trochophore (free swimming larva).

class bivalvia bivalves
Class Bivalvia- Bivalves!!!

Clams, mussels, oysters, scallops

Two valve shell

Umbo = oldest part of the shell near the hinge.

Inhalant and exhalant openings / siphons -> obtain oxygen and also filter and sort food and waste particles.

Adductor muscles= large muscles that close the valves.

Foot function= burrowing and locomotion

Inhalant = carries food and oxygen, Exhalant= removes waste.

more about bivalves
More about Bivalves………….

Clams use their foot to burrow into the sand and then use a siphon to draw water in and out which allows them to breath and eat while under the sand.


Palps-> after the food is filtered through the gills, it forms a mass of paired structures that move the food to the bivalves mouth where it enters the digestive system.

bivalve adaptations
Bivalve adaptations

Different habitats but most are infauna = living beneath the sand.

Mussels byssal threads allow them to attach to rocks.

Pearls form when oysters secrete shiny layers of calcium carbonate to coat irritating particles that are loaded in the mantle and inner surface of the shell= nacreous layer.

Scallops-> swim by rapidly ejecting water (jet propulsion) from the mantle cavity and clapping the valves together using its adductor muscles.

Largest = geoduck (3 feet in length)



class cephalopoda
Class Cephalopoda

Octopuses, Squid, Cuttlefish, and Nautilus (only one covered in a shell)

Reduction or loss of external shell

“Head-footed”-> head pushes down toward the foot

Complex Nervous system

Foot= modified into arms and tentacles and equipped with suckers for catching prey.

Large eyes-> set on the sides of their head and can see shaped and colors

Thick muscular mantle = protection

Mantle forms a mantle cavity behind the head where 2-4 gills are located

Water enters at the free end of the mantle and leaves through the siphon.

Swim by forcing water out of the mantle cavity through the siphon= jet propulsion.

Siphon can move in any direction.

reproduction in bivalves add in
Reproduction in Bivalves (add in)

Separate sexes

Sperm and eggs are shed into the water and fertilization takes place in the water column.

Some are hermaphroditic like scallops and oysters.

Some oyster species brood the eggs in their gills and then suck in the sperm for fertilization.


Not octopi!

Eight arms

No shell

Crabs, lobsters, and shrimp= favs!!! Yummy 

Bite prey using beak like jaws and the radula helps clean away the flesh. Then they secrete a paralyzing substance, most are harmless

Live in crevices, bottles, rocks, corals

Distract predators with their ink sac, which produces a dark cloud of fluid.

Highly developed tactile sense and can discriminate objects in the basis of touch.


Elongated body and covered by mantle with two triangular fins

Can change directions because they have a siphon

Eight arms, two tentacles, which all have suckers that circle the mouth

Shell= pen = embedded in the mantle


Resemble squids in having eight arms and two tentacles

Flattened body

Fins run along the sides of the body

Have a calcified inner shell that allows them to be buoyant- the shell is the cuttlebone and is sold as a calcium source for birds in pet shops.

Swim over the bottom and feed on invertebrates such as crabs and shrimp

nautilus add in
Nautilus- add in

Coiled external shell

Series of gas filled chambers that allows it to maintain buoyancy

Has 60-90 short sucker like tentacles that are used to capture prey.

Scavenger and feeds on benthic organisms such as hermit crabs

all cephalopods add in
All Cephalopods – add in
  • All swim by jet propulsion via their siphon
  • Communicate by moving their arms, bodies, and changing color.
  • Specialized pigment cells called chromatophores
    • Pigment cells are dispersed = darker
    • Pigment cells are concentrated = lighter
the mimic octopus
The Mimic Octopus

Changes shape and color to mimic other organisms.

feeding and nutrition of cephalopods
Feeding and Nutrition of Cephalopods


Locate prey with their eyes and tentacles

The beak bites and tears prey

reproduction in cephalopods
Reproduction in Cephalopods

Separate sexes

Mating involves courtship displays.

Male squids have a modified arm that takes their sperm (spermatophore) and places it into the mantle cavity of the female (oviduct).

Some species lay eggs in shells, while others attach their eggs to rocks or objects.

Octopuses- lay eggs and incubate them until they hatch, while pumping water over them continuously so that they stay oxygenated. The mothers die afterwards because she eats little to nothing the whole time. She invests everything into her offspring.

arthropods animals with jointed appendages
Arthropods- animals with jointed appendages

Phylum Arthropoda- crabs, sea spiders, lobsters, horseshoe crabs, hermit crabs, etc.

Most successful group of animals, 75% of all animal species. Hard exoskeleton, jointed appendages, and sophisticated sense organs make it successful!

exoskeleton hard protective skeleton on the outside
Exoskeleton-> hard, protective skeleton (on the outside)

Made of thin chitin (proteins and sugars)

Calcium salts provide strength

Flexible- easy movement

Muscles attach to it- efficient movement

Drawbacks-> exoskeleton does not grow with animal, they molt, make them soft and susceptible to predators.

body of arthropods
Body of Arthropods

Segmented with jointed appendages

Function in locomotion

Efficient feeding

Sensory structures for monitoring the environment

Body ornamentation -> to attract a mate or for camouflage.

nervous system
Nervous System

Highly developed

Sense organs allow them to move quickly when environment changes

Capable of learning

subphylum chelicerates spiders ticks scorpions horseshoe crabs sea spiders
Subphylum- Chelicerates-> spiders, ticks, scorpions, horseshoe crabs, sea spiders

Six pairs of appendages

Chelicerae- one pair, and is modified for the purpose of feeding and takes the place of mouthparts.

horseshoe crabs
Horseshoe Crabs
  • Class- Xiphosura
  • Live in shallow waters, bays, estuaries
  • Living fossils and have not changed much
  • 3 basic body regions = entire body is carapace
    • Cephalothorax- largest, obvious appendages
    • Abdomen- gills are located
    • Telson- long spike, used for steering and defense
    • Carapace- hard outer covering
more horseshoe crabs
More Horseshoe Crabs
  • Movement-> walking and swimming
  • Feeding-> worms, mollusks, algae
    • Pick up food with chelicerae and pass it to the walking legs which crush the food before passing it to the mouth.
h crabs
H. Crabs

Males are smaller

Mating season-> one male or many males will attach to the carapace of a female and then they come to shore during high tide to mate and the female digs up the sand with the front of her carapace, depositing eggs in the depression. The male rides on the females back, shed his sperm onto the eggs before they are covered.

Pedipalp-> large set of claws on the males that help the males attach / grab onto the females shell.

subphylum crustacea
Subphylum Crustacea
  • Decapods, mantis shrimp, krill, copepods, amphipods, and barnacles
  • Mandibulates-> paired appendages on the head called mandibles (modified for feeding).
  • 3 Main body regions:
    • Head, thorax, and abdomen

Sensory antennae

Walking legs that are modified for swimming- also known as swimmerets. Chelipeds are used for reproduction and defense

Small ones exchange gas through the body and large ones have gills. The gills are feathery structures beneath the carapace.

Molting-> hide away because they are vulnerable. They hide until a new exoskeleton has hardened initiated by hormones in the head caused by changes in environmental conditions (temperature and photoperiod).

Mandible and maxillae are used for feeding

pistol shrimp
Pistol Shrimp

order decapoda
Order Decapoda

Crabs, lobsters, true shrimp

10 feet (five pairs of walking legs)

First pair= chelipeds= pincers used for capturing prey and for defense.

Largest is the giant spider crab (4 m and 40 pounds)

specialized behaviors
Specialized behaviors

Hermit Crabs- jump from shell to shell to accommodate body size

Decorator Crabs- attach bits of sponges and anemones to carapace for camouflage

Blue Crabs- most powerful and agile swimmers, last pair of legs are like paddles= propellers.

nutrition and digestion
Nutrition and Digestion

Chelipeds= capture prey

Mandibles= crush food

Plates in stomachs = grind food further

Alaskan King Crab-> sea stars and bivalves

Snowcrabs-> polycheates, crustaceans, bivalves

Hermit Crabs-> shrimp-> scavengers, detritus

Fiddler Crabs-> deposit feeders (scoop up mud) filter out organic matter and spit out mineral residue into round pellets.

Filter feeders-> mole crabs, porcelain crabs, pea crabs, burrowing shrimp


Usually separate sexes / internal fertilization

Males have special appendages for clasping the female and sperm delivery

They transmit sperm in packets= spermatophores

Brood their eggs into chambers

Shrimp-> shed their eggs into the water

mantis shrimp
Mantis Shrimp

The second pair of thoracic appendages is enlarged and has a moveable finger that can be extended rapidly to capture prey / defense-> smash or smear prey (blows can break an aquarium)


Pelagic Shrimp

Filter Feeders

Bioluminescent photophores attract mates in swarms.

Main diet of whales, seals, penguins, fish (blue whales eat a ton of krill in one feeding)

Literally jump out of their skins to molt


Bodies to resemble shrimp

Burrowers live in tubes that they build

Appendages are used for jumping, burrowing, or swimming.

Beach flea


Largest group of small crustaceans

The most abundant zooplankton

Feed on phytoplankton and detritus (filter feeders)


Sessile- only crustacean to be 

Class- Cirripedia

Attach to animals, rocks, boats, shells, corals, and any other solid object in the ocean


Echinodermata-> means spiny skinned animals

Sea stars, sea urchins, sea cucumbers,

Radial symmetry

Benthic- lives on the bottom


Endoskeleton- spiny covering, internal structure. Below epidermis is composed of calcium carbonate plates (ossicles) that project up = spiny skin

Pedicellarie- tiny, pincers at the base of the spines that project up= spiny skin (clean body and free of parasites)

Water vascular system – hydraulic system that functions in locomotion, feeding, gas exchange, and excretion.

structure continues
Structure Continues

Madreporite= water enters

Tube feet= hollow with ampulla (saclike structure)

Ambulacral groove- the sucker at the end of the ampulla

class asteroidea sea stars
Class Asteroidea- Sea Stars

Central disk with five arms

Mouth= underside

From each mouth radiates the ambulacral groove with tiny tube feet.

Aboral surface is rough / spiny and is on the opposite the mouth.


Water is pumped into the tube feet from the ampullae which cause them to protect the ambulacral groove. The suckers then hold firmly to solid surfaces while the muscles in the tube feet contract which forces water back in the ampullae and causing the tube feet to shorten. Very slow process.


Carnivores or scavengers

Eat fish and invertebrates

Locates prey chemically by kind of “smelling” the substances released by the prey

Mussels and bivalves- wrap around prey and pries the valves open

Sea Star- spits out a portion of its stomach out of its mouth and inserts it into the bivalves mouth and digests the prey. Also releases enzymes to breakdown the food and then retracts back.

reproduction and regeneration
Reproduction and Regeneration

Fragmentation- a piece breaks off as long as the gonads are in tact it can produce another

Some can produce a whole new species as long as part of the central disc is present.

Some species are capable of sexual reproduction

class ophiuroids
Class Ophiuroids

Brittle Stars, basket stars, serpent stars

Benthic organisms

Five arms-> slender / distinct

Lack pedicellarie (pincers)

Ambulacral grooves are closed

Tube feet are used to feeding and locomotion, no suckers

Avoid light



Brittle stars -> get their name because they detach one or more arms when disturbed-> arm undulates wildly distracting predators, while the brittle stars move away-> regenerate


Carnivores, scavengers, deposit feeders, suspension feeders, filter feeders

Brittle-> filter feeders and deposit feeders (eat organic matter on the bottom)

Filter- lift arm in the air and wave it -> releases strands of mucus that form around all of the arms= net= traps plankton

Basket stars= suspension feeders= zooplankton -> climb up corals at night and fan their arms toward the current -> coil the arms around it.


Cast off or automize (predators)

Divide in half


External / Internal fertilization

class echinoidea
Class Echinoidea

Means like a “hedgehog”

Sea urchins, heart urchins, sand dollars

Enclosed body by a hard endoskeleton called a test


Rocks / bury

Regular Echinoids-> sea urchins with long removable spines.

Bilateral irregular Echinoids-> heart urchins and sand dollars. They bury in the sand and the test is small spined (locomotion / cleaning)

echinoid structure
Echinoid Structure

Tube feet project from five pairs of ambulacral areas that are derived from the same embryonic structures as the arms of sea stars, spines from test

Spines function in protection

Sexes are separate, external fertilization


Most are grazers scraping the surface with their teeth

Sea urchin-> five teeth called Aristotle's lantern

Sand dollars and heart urchins -> tube feet to pick up food

Lift posterior half of its body projecting above the sand.

class holothuroidea
Class Holothuroidea

Sea cucumbers

Elongated bodies

Body wall is leathery

Move slowly using ventral tube feet and muscle contractions

Gas exchange- tubules called respiratory trees

Sexes are separate

Some brood their eggs in body cavity and larvae leaves via the anus


Deposit or suspension feeders

Around the mouth they have 10-30 tentacles that they trap food with. The tentacles are coated with a sticky mucus, so the organisms just get stuck on them and they retract their tentacles back into their mouth.


When disturbed some species release Cuverian tubules from their anus that looks like spaghetti. When it touches sea water it becomes sticky.

Eviscerate, which means they release some of their internal organs through either the mouth or anus.

crinoids class crinoida
Crinoids- Class Crinoida

Sea lilies, feather stars

Most primitive of Echinoderms, they are aged back to the Paleozoic era (80 species)

Free moving -> swim and crawl for short distances / escape

Cling to the bottom using a cirri

Nocturnal (shallow water)

Crawl out of tight spaces its time to feed

Suspension feeders-> filter small organisms with tube feet and by mucous nets of the ambulacral grooves (zooplankton / detritus)

Regeneration, external fertilization

Separate sexes

what are echinoderms ecological role
What are Echinoderms ecological role?

Provide food for humans -> we eat the gonads of sea urchins / sea cucumbers

They are predators of molluscs, other echinoderms, cnidarians, crustaceans, and kelp.

Sea cucumbers= medicinal. They produce a poison called holothurin which suppresses tumor growth and can aid in muscle and nerve problems.

Sea urchin roe (ovaries with eggs) sells to Japan for 100-150 per pound= sushi

Sea urchins destroy kelp beds and lobster pots

Control algae growth, especially on coral reefs.