MARINE INVERTEBRATES

Marine Invertebrates
 Vertebrates: animals with a
backbone
 Invertebrates: animals
without a backbone
 At least 97% of all species
of animals are
invertebrates

Sponges
 Sponges belong to the phylum Porifera or “pore
bearers”
 aggregations of specialized cells
 do not form true tissues or organs
 nearly all marine

Sponges
 sessile: living permanently attached to the bottom
or some other surface

Sponges
 ostia: numerous tiny pores on the surface of the
sponge
 allows water to enter and circulate through a series of
canals where plankton and other organic matter are
filtered out and eaten
 sponge cells are very plastic
 if separated, the cells can even regroup and form a new
sponge

Sponges
 water is pumped into a
larger feeding chamber
lined with collar cells or
choanocytes
 water leaves through
osculum: large opening
on the top of the
sponge

Sponges

Sponges
 most have spicules:
transparent siliceous or
calcareous supporting
structures of different
shapes and sizes
 many have a skeleton of
spongin: tough elastic fibers
made of protein

Sponges
 amoebocytes: wandering cells, that secrete
spicules and spongin

Sponges
 suspension feeders: animals that eat food particles
suspended in water
 filter feeders: actively filter the food particles in the
suspension
 deposit feeders: eat detritus that settles on the bottom

Sponges

Sponges
 Most produce
asexually
 budding of
new sponge
 Some use
gemmules:
survivor pods

Sponges
 Found almost
everywhere in the world
 largest number are found
in tropical waters
 encrusting sponges:
form thin sometimes
brightly colored growths
on rocks or dead coral

Sponges – Economic Importance
 bath sponges
 still harvested in a few locations of the Gulf of Mexico
and the eastern Mediterranean
 some produce potentially useful chemicals

Cnidarians
 Phylum Cnidaria
 Also called coenlenterates
 over 9,000 species including sea anemones, jellyfish,
corals

Cnidarians
 display radial symmetry: similar parts of the body are
arranged and repeated around a central axis
 look the same from all sides
 no head, front, or back

Cnidarians
 cnidocytes: specialized cells used mainly for capturing
prey

Cnidarians
 oral surface: where
the mouth is
located
 aboral surface:
located in the
opposite site of
the mouth

Cnidarians

Cnidarians
 centrally located
mouth
surrounded by
tentacles: slender
finger-like
extensions used to
capture and
handle food
 mouth opens into
a gut where food is
digested

Cnidarians
 capture food (small prey) by discharging nematocysts
(or cnidae): unique stinging structures found within
cells in the tentacles

Cnidarians
 Occur in two basic forms - polyp or medusa

Cnidarians
 Polyp: a sac-like attached stage with the mouth and
tentacles oriented upward
 sessile
 Ex. sea anemone

Cnidarians
 Medusa: Bell-like structure that resembles an upside-
down polyp and is adapted for swimming
 motile, swimming
 Ex. jellyfish

Types of Cnidarians
 Hydrozoans
 Scyphozoans
 Anthozoans

Hydrozoans (polyps)
 Feathery bushy colonies of tiny polyps
 drifting colonies of hydrozoans are called
siphonophores
 example: portuguese man-of-war (blue bubble or blue
bottle) (Physalia physalis)

Portuguese Man-of-War

Scyphozoans
 True jellies with medusa shapes that can reach up to 6
feet in diameter
 True Nematocysts are only found in Hydrozoans and
Scyphozoans

Anthozoans
 lack medusa stage
 consists of solitary colonial polyps
 anemones
 corals
 seapens
 sea pansies

Worms
 bilateral symmetry: the arrangement of the body
parts in such a way that there is only one way to cut
the body and create two identical halves
 ex. humans

Flatworms
 Phylum: Platyhelminthes
 dorsoventrally flattened (flat bellies and backs)
 20,000 species of flatworms

Flatworms
 Turbellarians
 most common marine
flatworms
 mainly live in or around
the surface of other
invertebrates (mollusks,
crabs, etc)

Flatworms
 Flukes (trematodes)
 largest group of flatworms
 6,000+ species
 all are parasites
 adults always live in a vertebrate
 larvae may inhabit invertebrates or smaller vertebrates
such as fish

Flatworms
 Tapeworms (cestodes)
 parasitic
 long body made of
repeating units
 live in the intestines of
vertebrates

Ribbon Worms (Nemertean Worms)
 Phylum: Nemertea
 outwardly resemble
flatworms, slightly more
complex
 more advanced intestinal
system
 circulatory system
 proboscis: long fleshy tube
used to entangle prey

Nematodes (roundworms)
 Phylum: Nematoda
 most are parastic
 a layer of muscles in the body wall pushes and
squeezes against the fluid creating a hydrostatic
skeleton
 Hydrostatic Skeleton: A system that uses water
pressure against the body wall to maintain body
shape and aid in locomotion
 provide support and aids in locomotion

Nematodes (roundworms)
 live in the flesh or muscle
tissue which used to make
sashimi, sushi, and cerviche
 if the fish is served raw or
undercooked, human
infection is possible

Segmented Worms (annelids)
 Phylum: Annelida
 earthworms and many marine
worms
 Display segmentation
 segments act as a hydrostatic
skeleton
 efficient crawlers and
burrowers

Polychaetes (Bristle worms)
 Phylum: Annelida Class: Polychaeta
 each body segment has a pair of flattened
extensions called parapodia “beyond/beside feet”
 which have stiff, often sharp bristles called setae
 Used for movement and breathing through gills on
parapodia

Polychaetes (Bristle worms)

Oligochaetes
 Oligochaetes
 small worms found in mud and sand
 feed on detritus
 lack parapodia

Oligochaetes
 Leeches
 Class: Hirudinea
 live mainly in fresh water
 marine species can be found
attached to marine fishes and
invertebrates
 highly specialized annelida with a
sucker at each end and no parapodia

 Echiurans
 all marine
 similar to peanut worms in size and
shape
 have a non-retractable, spoon-like
(forked) proboscis
 deposit feeders
 Peanut Worms
 sipunculans
 1 to 35 cm long (.4 to 14 inches)
 soft unsegmented bodies
 burrow in the bottom or move into
empty shells
 when it becomes compact it
resembles a large peanut

Clams, Octopuses, and Snails

Molluscs
 Phylum: Mollusca
 more species of mollusca than any other animal
group
 around 200,000 living species

Molluscs
 most have soft bodies encased in a calcium
carbonate shell
 live in marine, freshwater and terrestrial
environments

Molluscs
 cephalopods (squid, cuttlefish, octopus) most
neurologically-advanced of all invertebrates
 gastropods (snails and slugs) are the most numerous
division
 giant or colossal squid are the largest known invertebrate
species

Molluscs
 The body is covered by a
mantle: a thin layer of
tissue that secretes the
shell
 usually bilaterally
symmetric
 ventral, muscular foot
usually used for
locomotion

Molluscs
 most have a head with eyes and additional sensory
organs
 Radula: a ribbon of small teeth (unique to
molluscs) or rasping tongue
 made mainly of chitin

Molluscs
 gas exchange occurs through paired gills
 shell is modified (internal for squid, octopod; external for
gastropods)

Gastropods
 class - Gastropoda
 largest, most common, and most varied group
 includes snails, periwinkles, limpets, abalones

Gastropods
 a coiled
collection of
organs
enclosed by a
dorsal shell
 shell rests on
a ventral foot
 varied shell
structure and
size

Gastropods
 carnivorous gastropods prey on clams, oysters worms
and even small fishes
 other gastropods are detritivores

Gastropods
 Nudibranchs or sea slugs - gastropods that have lost
their shell entirely
nudibranchs

Bivalves
 class - Bivalvia
 includes clams,
mussels,
oysters,
scallops

Bivalves
 have two-part shells each part is called a valve
 symmetric along the hinge line
 no head no radula
 inner surface of the shell is lined by the mantle

Bivalves
 gills are used for gas exchange and filter feeding
 strong muscles in the mantle cavity are used to
open and close the valves

Oysters
 Most commercially
valuable for pearls
 Form when the oysters
secrete layers of calcium
carbonate coat an irritant
or parasite lodges
between the mantle and
the inner surface of the
shell

Clams
 Use foot to bury in sand or mud
 Draw water in and out of mantle through siphons
 Feed and maintain oxygen while still buried

Mussels
 Live mainly in the intertidal zone
 Attach to surface using strong, byssal threads (beard)

Scallops
 Highly prized food source
 100 simple blue eyes around the valves

Cephalopods
 class-cephalopoda
 specialized for locomotion
 adapted mollusc body plan for an active way of life
(nearly all agile swimmers)
 include octopuses, squids, cuttlefish, nautilus

Cephalopods
 complex
nervous system
 reduced inner
shell or no
shell at all
 all are marine
or brackish
 no radula, but
do have a two
part beak

Cephalopods
 foot is modified into arms and tentacles
 large eyes usually set on sides of the head
 thick, muscular mantle

Cephalopods
 2 to 4 gills
 water enters through the free edge of the mantle and
leaves through the siphon or funnel a muscular tube
formed by what remains of the foot

Nautilus
 the chambered nautilus is considered the most
primitive living cephalopod, because of its shell
 dates back 450 million years

Nautilus
 shell is thin, double layered
and pearly white inside
with a dull white with
reddish zebra stripe outside
 the shell is separated into
chambers by the septa,
made of shell material
 as it grows it creates new
larger chambers
 1 chamber every few weeks
until it reaches 38
chambers

Nautilus
 occupies one body chamber
 strong, beak-shaped crushing jaws
 eat algae , fish, crabs, shrimp and other
invertebrates

Nautilus
 large collection
of tentacles
arranged into
two circles, an
inner and an
outer.
 the female has
twice as many
tentacles in its
inner circle
than the male

Squid
 has only a thin shell remnant (pen) within it’s mantle
 strengthened outer collagen sheath to maintain the
mantle’s shape and size

Squid
 to swim, the squid fills the mantle cavity with water
and then forces it outward through the funnel in a jet-
propulsion like manner
 normally swims backwards, can swim forward by
bringing all 8 arms together
Humboldt Squid

Squid
 fins along the body help with stabilization
 large squids can reach speeds of 15-20 mph
 many species swim in schools

Squid
 8 arms, 2 long tentacles covered in suckers: adhesive
discs used for suction between the squid an another
object
 tentacles only have suckers on the flattened end

Octopus
 has lost shell entirely
 bag-like mantle located above the head
 also has a strengthened collagen sheath surrounding
the mantle

Octopus
 does not normally swim
 prefers to remain in
contact with a solid
surface
 uses suckers on its 8 legs
to push and pull itself
along the surface
 most have 240 suckers
on each arm
 Crawling

Octopus
 usually a solitary animal that lives in a permanent den
or cave under rocks
 ink
 chromatophores: specialized cells used to help an
organism change color
 Chromatophores in action

Feeding and Digestion
 separate mouth and anus
 all cephalopods are
carnivores
 involves salivary and
digestive glands to help
break down food
 varied diets and
complexity of digestive
systems based on diet
Hungry octopus

Feeding and Digestion
 crystalline style: an
enzyme secreting rod
found in the stomach of
bivalves continually
rotates food and helps in
digestion

Feeding and Digestion
 most molluscs have an open circulatory system
 cephalopods have a closed circulatory system

Nervous System
 gastropods and bivalves
do not have a single
brain but several sets of
ganglia
 cephalopods most
complex
 allows for learning to
occur
 and for rapid movement
and color changing to
avoid predation

Reproduction
 most reproduce sexually, some hermaphroditic
 cephalopods use a spermatophore
 cephalopods lack larva and have large yolk-filled eggs
 octopus protect eggs and female usually dies
protecting young because she does not leave to eat
herself

Reproduction
Octopus mating

Arthropods
 Phylum: Arthropoda
 largest phylum of animals
 insects are dominant
terrestrial group
 crustaceans are more
common in marine
environments

Arthropods
 segmented, bilaterally symmetric
 possess an exoskeleton: large, non-living external
skeleton
 composed of chitin and secreted by the underlying
layer of tissue

Arthropods
 provides protection, support and increased surface
area for muscle attachment
 to grow, arthropods must molt

Crustaceans
 chitinous skeleton hardened by calcium carbonate
 appendages specialized for swimming
 possess 2 pairs of antennae

Small Crustaceans - Copepods
 small, important to plankton
 use enlarged pair of antennae for swimming
 many are parasitic

Small Crustaceans - Barnacles
 filter feeders
 live attached to surfaces,
including other living
organisms
 covered in calcareous
plates
 have feather-like
filtering appendages
called cirri
 actually legs used to
sweep water

Small Crustaceans – Amphipods
 small curved body and flattened sideways
 less than 2 cm in length
 some live under larger organisms skin like lice, parasites

Small Crustaceans - Isopods
 about the same size amphipods
 dorsoventrally flattened
 ex. terrestrial pill bugs
 many are parasitic

Small Crustaceans - Krill
 Also called euphausids
 planktonic, shrimp-like
 up to 6 cm long (2.5 in)
 most are filter feeders
 swim in groups of billions of individuals

Decapods
 five pairs of
legs or
pereiopods
 the first is
heavier -
usually claws
for feeding
and defense

Decapods
 three pairs of maxillipeds near the mouth
 turned forward, and specialized to sort food and push it
towards the mouth

Decapods
 well developed carapace
 encloses the part of the body called the cephalothorax
 the rest of the body is known as the body

Decapods
 shrimp and lobsters have laterally compressed bodies with
distinct and elongated abdomens (the “tail”)

Decapods
 Decapods use their
chelipeds for feeding
and fighting
 Therefore they often
lose a claw
 They are able to
regenerate lost
chelipeds

Decapods
 Also most arthropods have two distinct claws
 The larger is called the crusher claw
 And the thinner, more serrated one, is called the
pincer or tearing claw

Decapods
 In many arthropods, such as lobsters, there are major
structural difference between males and females
 1. Claw size (larger in males)
 2. Tail width (wider in females)
 3. Texture of swimmerets (harder in males)

Decapods
 Reproduce sexually, using internal fertilization

Decapods
 Also in crabs, a male has a v shaped abdomen and a
female has a u shaped abdomen

Shrimp
 Typically scavengers
 Varied life environments
 Mutualistic relationships
with other organisms
Shrimp 1 Shrimp 2

American Lobster (Homarus
americanus)
 also known as the northern lobster, Atlantic
lobster or Maine lobster
 family Nephropidae, commercial lobsters
 bottom dweller
 found in colder waters off the Atlantic coast of
North America
 New England and Canada

Lobsters
 scavenger and predator
 solitary in rocks or caves, also nocturnal
 exoskeleton, which molts 2-3 times a year as a
juvenile and once a year as an adult
Blue Lobster Molt

Lobsters
 Heavy bodied with a large abdomen and huge
chelipeds
 one is lost in an accident or a fight it will regenerate
 sold with one claw -“cull”
 Sold with no claws – “bullet”

Lobsters
 4 pairs of walking
legs (pereiopods)
 4 sets of swimmerets
(pleopods), extend
across the body
 harder in males
 softer in females used
to protect eggs

Lobsters
 feathery gills located on either side of the cephalothorax

Hermit Crabs
 hermit crabs are not true
crabs
 scavengers
 hide in empty gastropod
shells

Crabs
 abdomen is small and tucked under a compact and
broad cephalothorax
 largest and most diverse group of decapods

Crabs
 highly mobile -
much faster than
lobsters
 move sideways when
they’re in a hurry
 sideways movement
can also be used to
indicate mating
 ex. fiddler crab

Horseshoe Crabs
 not true crabs
 “living fossils”
 eyes being
researched to
improve vision
errors in humans

Sea spiders

Lophophorates
 Have a lophophore - feeding structure made of a set of
ciliated tentacles arranged in a horseshoe-like shape

Lophophorates
 Three main types:
 Bryozoans - lace-like
 Phoronids - worm-like
 Lamp Shells - clam-like

Echinoderms
 Phylum: Echinodermata
 Pentamerous Radial symmetry: Five-way symmetry

Echinoderms
 Water-vascular
system: A
network of
water-filled
canals
 sea stars sea
urchins connect
to a madreporite:
a porous plate on
the aboral
surface

Echinoderms
 Tube feet: muscular extensions of the water-vascular
system that often end in a sucker
 ampullae: muscular sacs that sometimes aid in the
extension of tube feet

Echinoderms
 small nerve net similar to cnidarians
 ability to regenerate
 Comet: a sea star with one large regenerated arm

Echinoderms
 many spines and bumps - part of the endoskeleton
 give the nickname “spiny-skinned”

Echinoderms
 Four main types:
 Sea stars
 Brittle Stars
 Sea Cucumbers
 Sea Urchins

Sea Stars
 Class: Asteroidea
 five arms that radiate around a central disk

Sea Stars
 hundreds of
tube feet
extend from
the oral
surface along
radiating
channels on
each arm call
ambulacral
grooves

Sea Stars
 the aboral surface of most sea stars is covered with spines
modified into pincer like organs called pedicellariae
 most are predators of bivalves

Brittle Stars
 Class: Ophiuroidea
 star shaped body
 very long flexible arms
 lack an anus
 are detritivores

Sea Cucumbers
 Class: Holothuroidea
 superficially wormlike
 lack spines
 no radial symmetry

Sea Cucumbers
 oral and aboral surfaces
are located on the ends
 deposit feeders
 move using five rows of
tube feet
 use branched tentacles
to gather food

Sea Cucumbers
 defense
 some secrete toxic substances
 some discharge, sometimes toxic, filaments from the
anus to discourage predators
 some eviscerate: discharge the gut and other organs
through the anus

Sea Urchins
 endoskeleton is round
and rigid with movable
spines and pedicellariae
 movement is based on
tube feet and the
movable spines joined
to sockets of the
exoskeleton

Sea Urchins
 grazers - sea weeds and
grasses
 mouth has an intricate
system of jaws and
muscles called
aristotle’s lantern
 used to bite off pieces

Sea Urchins
 live in rocky shores
 also includes sand dollars

Chordates without a backbone
 Phylum Chordata
 divided into three major groups (subphyla)
 two lack a backbone, one does not
 Protochordates: the invertebrate chordates, chordates
without a backbone

Chordates without a backbone
 4 characteristics needed to be a chordate:
 1. single, hollow nerve chord that runs along the dorsal
side of the body

Chordates with a backbone
 2. pharyngeal gill slits - small openings along the
anterior end of the gut
 pharynx in humans

Chordates without a backbone
 3. notochord - flexible rod for support that lies between
the nerve chord and the gut

Chordates Without a Backbone
 4. post-anal tail - a tail that extends beyond the anus
(coccyx in humans)

Chordates without a backbone

Chordates without a backbone

Chordates without a backbone
 also have a ventral heart
 in vertebrates the notochord is replaced by the backbone
(vertebral column)

Tunicates
 Subphylum:
Unichordata
 best known are sea
squirts
 the notochord and
tail are absorbed
during
metamorphosis

Tunicates
 difference between sponge is the protective tunic
 tunic: leathery or gelatinous outer covering not found
on sponges
 filter feeders

Lancelets
 Subphylum
Cephalochordata
 almost 3 in long
 laterally compressed and
elongated body like a fish
 bottom dwellers
 filter feeders