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Marine Invertebrates
Main Ideas
Classification and Comparison of all
invertebrates
Sponges are asymmetric, sessile animals
that filter food from the water circulating
through their bodies.
Sponges provide habitats for other animals.
Main Ideas
Cnidarians and ctenophores exhibit radial
symmetry.
Cnidarians posses a high specialized
stinging cell used to capture prey and for
protection.
Main Ideas
Marine Worms exhibit bilateral symmetry.
Turbellarians are free living flatworms;
flukes and tapeworms are parasitic.
Nematodes are abundant and important
members of the meio-fauna
Main Ideas
Several other worm-like animals like ribbon
worms, spiny headed worms, peanut
worms, acorn worms and beard worms play
important ecological roles in the marine
environment.
What are animals?
Multi-cellular
Eukaryotic cells with no cell walls
Cannot produce their own food
All animals, with the exception of adult
sponges can actively move.
Classification of Animals
Living creatures inhabit almost every
part of our waters and land, and they
exist in an astonishing variety of shapes
and sizes.
Over a million kinds of animals and
plants are known, and probably millions
more are yet to be discovered and
described.
Classification of Animals
To study this vast number of life forms,
biologists classify organisms into groups
and subgroups that have similar
anatomy (body parts) and physiology
(the workings of those parts).
Classification of Animals
All animals are members of the animal
kingdom.
A kingdom is divided into smaller groups, the
most inclusive being the phyla (the singular is
phylum).
A phylum is successively divided into classes,
orders, families, genus, and species.
Each group may be further divided into
subgroups, such as subphyla or subclasses.
Classification of Animals
Kingdom- Phylum-Class-Order-FamilyGenus-Species
When talking about an animal you are just
naming the genus and species.
Use Latin and Greek roots for unfamiliar
names.
Example: lobster is Homarus (genus)
gammarus (species)
Invertebrates: Spiny Lobster
Classification System
Using this classification system, we can
study the characteristics of one kind of
organism or compare the common
characteristics of several groups.
Classification System
In the phylum Chordata is a subphylum
Vertebrata, which includes all animals with
backbones.
Among its members are animals such as fish,
frogs, lizards, birds, and humans.
Animals are often divided into two groups,
vertebrates and invertebrates. Although this
division is convenient, it is confusing because
invertebrates do not make up a formal
scientific group.
Classification System
The term invertebrate does not refer to a
strictly defined scientific group, it is a handy
term meaning “any animal without a
backbone.”
All kinds of animals except vertebrates are
invertebrates.
Invertebrates are far more abundant in the
ocean and on land than vertebrates are.
Invertebrates: Tube Sponges and
Coral
Invertebrates: Long Spined Sea
Urchin hiding in Coral
Sponges or Porifera
Come in an variety of colors and an
amazing array of shapes.

The shapes are determined by the bottom
sediment, the material they are growing in
and ocean currents.

Red, yellow, green, orange and purple are
extremely common.
Green
Sponge
Sponges
They are predominantly marine

Exception family of Spongillidae who live in
freshwater.
Sponges are benthic creatures, found at
all latitudes beneath the world's oceans,
and from the intertidal to the deep-sea.
Natural Dead Sponges- Lose
their color when dead
Sponges
They are sessile- means doesn’t move
much.
It has been shown that some younger
sponges are able to move slowly (up to 4
mm per day).
Sponges
Some sponges bore into the shells of
bivalves (mussels and clams) gastropods,
and the colonial skeletons of corals by
slowly etching away chips of calcareous
material.
Sponge
covering a
shell of bivalve
Sponges
A sponge can settle on a snail shell that is
being used by a hermit crab; an unusual
association can be formed.
This sponge/crab association results in a
mobile sponge.
Sponge and Crab
Generalized Anatomy of a
Sponge
Body is built around a system of water canals.
Body full of tiny pores called ostia in which water
passes through.
Water is source of nutrients and oxygen, and
carries away wastes.
Water is like the blood of the human body,
circulating food and nutrients throughout the
sponge.
Generalized Anatomy of a
Sponge
Water comes in through ostia, and enters
large cavity called spongocoel.
Water exits out the osculum.
See handout: Anatomy of a sponge.
Sponge Size and Body Forms
Asconoid sponge: the simplest form, tubular
and small.

Usually found in clusters.
During evolution, sponges found it helped
out if they could grow by folding over areas
of the sponge.

This increased the amount of volume of water it
could filter (thus get nutrients)
Asconoid Sponge- Magnified
Sponge Size and Body Forms
Syconoid Sponges: has body wall folding to
it, but only a small amount.
Leuconoid Sponges: many folds to these
types of sponges.

Largest type of sponges.
Syconoid Sponges
Leuconoid Sponges
Nutrition and Digestion
Suspension Feeders: feed on food suspended in water.
Filter feeders: because they filter their food from the
water.
Collar cells trap the food that is flowing in with the
water.

Collar cells have flagella, which will push the water through
the cells.
Flowing water also takes out wastes produced by the
sponge.

Water: digestive system
Collar Cells in Sponges
Sponge Reproduction
Depends on type of sponge.
Sexually: egg and sperm released into the water
and hope to god that they combine.

Sponges are hermaphrodites, thus producing both
sperm and egg cells.
Asexually: budding
Commercially sold sponges cut the buds off the
sponge, thus leaving more in the stead of the adult
one they killed.
Asexual
Reproduction:
Budding
Ecological Role of Sponges
Compete for space with other bottom
dwelling organisms.
Need good material to attach to- if a
fertilized baby sponge doesn’t get it, it dies.
Produce chemicals to kill other species
around them to make room.
Ecological Role of Sponges
Few animals eat sponges- eating the spicules is
like eating needles.
Chemicals to kill off other species from settling
next to them, also kill deter grazing.
Only Sea Turtles and a couple other animals are
brave enough to eat them.


Sea Turtle Poop is composed of 95% of spicules.
Has a toughly lined digestive tract.
Hawksbill Sea Turtle eats Sponges
Sponges and Symbiotic
Relationships
Sponge houses bacteria, that provide food
for sponge while the bacteria gains nutrients
and a house.

Cyanobacteria is a photosynthesizer, which
produces its own food and shares with the
sponge.
Sponges and crabs: the sponge grows on the
crab becoming motile. The crab gets
camouflage.
Sponge and Hermit Crab
Introduction to Cnidarians:
Stinging Celled Animals
Sea Anemone
Jellyfish
Cnidarians
Cnid: nettle
Includes Corals, Sea Anemones and Jellyfish
Corals: located near tropical islands
Sea Anemones: Cold artic waters to the equator
Hydra: microscopic cnidarians in freshwater
Jellyfish: float near surface of ocean

Can also exist in streams
Brain Coral
Elk Horn Coral
Common Characteristics
Jelly-like materials
Carnivorous
Capture small drifting animals w/ tentacles
Some brightly colored
Graceful movement w/ tides
Giant Sea Anemone
Sea Plume (Soft Coral)
Body Structure
Outer layer: ectoderm has cells that capture
food and secrete mucus
Jelly-like material between two layers:
MESOLGLEA
Surround central cavity: gastrovasular
cavity which extend to tentacles
2 Forms
Medusa: body shaped like an umbrella, w/
tentacles hanging.


Not sessile
Jellyfish
Polyp: top has tentacles, with a hollow cylinder
that opens and closes at the top.


Sessile: so can only eat what ever comes in contact w/
mouth.
Corals and Sea Anemones
Polyp Body
Medusa Body
Body Symmetry
Radial Symmetry: extend from a central
axis.
Radial structure allows them to sting and
capture organisms in any direction.
Most sessile organisms have radial
symmetry.
Radial Symmetry
Food Capture
Unique long stinging cells called:
Cnidocytes
Long harpoon like tubes called: Nematocyst
When the Nematocyst senses food is fires
venom outward to stun the prey.
Barbs line the harpoon-tube to attach prey.
Stings
Jellyfish sting to paralyze and capture food.

All others do also.
Potency of venom varies
Portuguese Man of War: painful sting for
human
Sea Wasp (Australian jelly fish) will kill
you.
Sea Wasp
Stings
Some marine organisms are immune
Clownfish and Anemone mutualism
Shell-less mollusk Glaucus is a predator of
man-of-war, eating it, and using the
Cnidocytes for its own defenses.
Turtles eat jellyfish w/ no problems
Venom
Is a protein
Some people are allergic thus having a
worse reaction.
Treat a sting by breaking down the protein
Chemically: meat tenderizer
 Thermally: apply heat to denature proteins

Hydrostatic Skeleton
Unlike sponges, sea anemones and jellyfish have
no skeletal structure to support their soft tissue.
They fill their gastrovascular cavity with water
and close mouth tight.


This puts the water under pressure like a balloon.
If the Cnidarian contracts its body hard it loses water.
It takes several minutes to pump the water back in.
Propulsion
When a ring of muscles contract, a jet of water is
forced out.
The jelly fish relaxes and then the umbrella
reforms.
Alternating muscles contract creating pulsating
movements.
Jellyfish are such poor swimmers that they are
classified as plankton because they can not swim
against a current.
Digestion
Tentacles move the food into their mouths.
Prey is swallowed into the gastrovascular cavity
and digested.
Ectoderm cells produce enzymes, which break
down the food.
Can consume anything from plankton to small reef
fish.
Indigestible material is expelled through the
mouth.
Respiration and Nutrient
Absorption
Have neither respiratory or circulatory
systems.
Get Oxygen directly from water.
Nutrients pas through the liquid between the
cells, wastes pass out by the same route.
Nervous System/Muscular
System
Consists of cells with long, thin fibers that
respond to stimuli.
Nerves send impulses to muscle cells.
In the sea anemone muscular system
consists of muscle cells lying in bands up
and down the body wall and in a circle
around the mouth.
Body shortens when contractions occur.
Nervous System/Muscular
System (cont.)
If one side contracts the anemone moves that
direction.
Mechanoreception- the ability to respond to a
stimulus of touch or pressure.
When something touches it…it moves
Chemoreception – the ability to respond to
chemical stimuli

Crucial to finding foods, detecting harmful substances,
and in some organisms selecting, attracting mates.
Nervous System/Muscular
System (cont.)
Photoreception- ability to respond to
changes in light intensity.
Positive response – organism moves
towards the stimulus.
Negative response- organism moves away
from the stimulus
Reproduction
Reproduce both sexually and asexually
Sexual reproduction begins with the production of
eggs and sperm
Eggs in ovaries, sperm in testes.
Fertilization occurs when the egg and sperm unite.
Some species fertilization happens in the water, in
others fertilization happens in the female.
Reproduction (cont)
New organism grows into a larva
Larva swim by the use of cilia- small hair like
structures.
 Because they can not swim against currents
they are classified a plankton.
 Can drift for hundred of miles
 Attaches to a hard surface and grows into an
adult

Asexual Reproduction
Asexual Reproduction
Reproduction without eggs and sperm.
Budding- like growing a new branch on a tree
Cells on the side or base of the parent begin to
bulge out.
If many attached buds are produced , they form a
large colony.
In some organisms the bud detaches and settle
down nearby.
Regeneration
Replace lost or damaged parts.
Small damaged chunks may even regenerate
into new organisms.
Worms
Display a great range in size, efficiency,
complexity, and body structure.
Long thin creatures that get around efficiently
without legs.
Different phyla = different degrees of complexity
Flatworms – simple – barely more complex than a
cnidarian
Some may rival more advance organisms such as
mollusks, snails, and oysters.
Spaghetti Worms
Fan Worms (gills visible)
Worms
Degree of complexity depends on different
body features and systems.
Have a Bilateral symmetry

Like fish they have a definite front and rear.
Organs for sensing light, touch and smell
are in their heads
Can detect the different environments they
encounter.
Organization
Front of the worm is called the anterior
end.
Rear is called the posterior end.
Under part is called ventral surface
Upper part is called the dorsal surface.
Six features and systems
a) mesoderm, an intermediate body layer that forms muscle
tissue
b) central nervous system guided by a “brain”
c) excretory system to eliminate some kinds of waste
products
d) complete digestive system, from an anterior mouth to a
posterior anus
e) coelom, a body cavity between the digestive tube and the
external body wall
f)
circulatory system consisting of a series of tubes
(vessels) filled with fluid (blood) to transport dissolved nutrients,
oxygen, and waste products around the body rapidly and
efficiently
Flatworm
Simple Worms: The Flatworms
Least Complicated
Live on land, in fresh water, in the ocean,
and in or on other animals
Symbiotic parasites (ex. Tapeworms)
 Can make humans or animals sick or kill them

Marine flatworms are just a few centimeters
long.
Flatworms
Some live symbiotically with crabs, clams,
oysters, shrimp, and barnacles.
Some brightly colored, other are drab and
blend in.
A three-layered body with no
Coelom
More complex then cndarians
Flatworms have 3 layers ectoderm,
endoderm, and mesoderm.
Mesoderm is between the two other layers
 Cells specialize into a muscular system that
enables the animal to move around.

Flatworms
Have a digestive system with only a single
opening
Cavity branches into all parts of the body.
This feature is the source of the name for
some marine flatworms (polycladida)
These feed through a long, tubular pharynx
Cells lining digestive cavity finish digesting
food.
Flatworms
Undigested food come out the mouth as in
Cndarians
Have a CNS




Mass of brain cells called a brain
Sensory cells in the head detect changes in the
environment.
Sensory cells that detect light are clustered into two
eyes in the head
Sensory cells that detect water currents , solid objects,
and chemicals are in two flap like projections on the
head called auricles
Living without a Circulatory
System
Flatworms have no circulatory system
Get nutrients by diffusion.
Body shape and constant contact with water
facilitates absorption
All their cells are wither close to their outer
surface of digestive cavity.
Flatworms: Excretory system
Network runs the length of the animal and
opens to the outside through small pores in
the posterior region of the body.
Have flagella that force the food down and
out.
Because this movement looks like a
flickering fire, the structure is called a flame
bulb.
Fireworm
Complex Worms: The Annelids
Typically have segemented bodies
Divided into repeating sections called
segments with many internal orgains
Earthworms are familiar members of this
phylum
Some annelid worms (earthworms) are
important as fishing bait.
Complex Worms: The Annelids
Most marine annelid worms are poly-chaetes
(Poly=many; chaeta=bristle)
Polychaete worms are so named because most of
their segments have muscular flaps called
parapodia (para=near; podia=feet)
Setae – stiff bristles on parapodia


May dig them into sand for locomotion
Fireworms have stinging bristles on their parapodium
Polycaetes
Some have a proboscis that can extend from
their mouths to catch prey.
Feeding organ armed with small teeth or
jaws on the tip.
Can make a living in many habitats: mud,
sand, sponges, live corals, and algaw
Tubeworms
Polychaetes that live in tubes they secrete
Tubes attach to rocks
Feed by extending feathery tentacles
Food moves along groves in tentacles to the
mouth.
Some retract them when food lands
Use parapodia to create currents of water that flow
through the tubes

Aid in respiration and helps clean tubes
Segmented Worms with a
Coelom
Annelid worms have evolved body features not found
in flatworms. These features appear in some form in
all larger, more complex animals:
a)
complete digestive system, from an anterior
mouth to a posterior anus
b)
coelom, a body cavity between the digestive
tube and the external body wall
c)
circulatory system consisting of a series of
tubes (vessels) filled with fluid (blood) to transport
dissolved nutrients, oxygen, and waste products
rapidly and efficiently
Segmented Worms with a
Coelom
Like flatworms annelids have a mesoderm
with muscle, a CNS, and an Excretory
system. More advanced
Complete digestive system has:
1. mouth at one end,
 2. a long tube with specialized parts in the
middle
 3. An anus at the other end.

Digestive advantages
Eat while previous meal digests
Specialization digesting foods in stages
As food move along nutrients are digested
by cells.
Coelom
Fluid filled cavity lying between the digestive tube
and outer body.
Surrounded by mesoderm.
Digestive tube lies inside the outer body tube
“Tube within a tube construction”
Fluid in the coelom: supports soft tissues of the
body wall (like a cnidarins hydrostatic skeleton)
Coelom
Muscles in the wall of body tube and
digestive tube can put pressure on the fluid
to aid in movement
Muscles come from mesoderm tissue.
Types of muscles
Circular – when contracted the segment gets
longer and narrower
 Longitudinal – when contracted the segment
gets shorter and fatter.

Annelid’s CNS
Found in anterior end of annelids, dorsal to
digestive tube there is a pair of nerve cluster
which are the brain.
Nerves link the brain to sense organs
Polychaetes have eyes that can detect light
differences.
A cluster of nerve cells called a ganglion
operates the organs in each segment
Annelid’s Excretory system
Consists of a pair of small tubes in each
segment
Tubes are called nephridia
(nephrus=kidney)

Filter coelomic fluid which contains useful
nutrient molecules along with waste molecules
Annelid’s circulatory system
Closed system where blood is pumped
along by muscles in blood vessels.
Blood flows through microscopic
capillaries.
Parapodia increase the surface area of the
skin for respiration
System allows organisms to grow large
unlike flatworms.