UNIT 6 INVERTEBRATES
PART 1
SPONGES; CNIDARIANS;
CTENOPHORES; PLATYHELMINTHES;
NEMERTEA; NEMATODA; ANNELIDA;
SIPUNCLA; ECHIURANS; MOLLUCS;
 The following is a website that I found of
photographs, videos, and species
identification of organisms around Australia.
 http://www.julianrocks.net/index.htm
 Animals classified into two main groups:
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Vertebrates: those having backbones
Invertebrates: those that do not have a
backbone (97% of all animal species)

Most marine or aquatic except for the insects
SPONGES (Phylum Porifera)
 Most simple multicellular animal
 Organized on the cellular level- no true
tissues or organs; the cells are independent
of each other
 Almost all marine
 All are sessile (permanently attached to a
surface)
 video
 Suspension feeder- eat food particles
suspended in water
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Filter feeder- filter food particles
 The basic body form of all sponges is a sac-like
structure consisting of three layers –
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an outer layer of epidermal cells
an inner layer of cells, many of which are flagellated
cells called choanocytes
a middle layer of amoeboid cells that form skeletal
structures of various sorts. These layers are perforated
by a large number of small pores (thus the name
Porifera). The cavity of this sac is called the
spongocoel and has at least one opening to the
outside, called an osculum
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The skeletons of sponges can be composed of
an organic substance called spongin (the stuff
of an ordinary bath sponge), or they may have
calcareous or siliceous skeletons composed of
chambers, or more commonly rod-like
branched elements called spicules. After
death, spicules are scattered across the sea
floor and may be found as disarticulated
microfossils.
link
 The poriferans (sponges) are characterized by cell
groups that are independent of each other and have
the ability to change their function during their life
cycle.
 The skeletons of sponges can be composed of an
organic substance called spongin (the stuff of an
ordinary bath sponge), or they may have calcareous
or siliceous skeletons composed of chambers, or
more commonly rod-like branched elements called
spicules.
 After death, spicules are scattered across the sea
floor and may be found as disarticulated microfossils.
3 basic types of sponges
 The Asconoid Sponges
example: Leucoselenia (Class Calcispongiae)
 Asconoid sponges have the simplest
organization. Choanocytes line the
spongocoel, drawing water through small
ostia and expelling it through the osculum.
 The Syconoid Sponges
example: Scypha (Class Calcispongiae)
 Syconoid sponges have a tubular design
similar to the ascon sponge, but the body wall
is folded. The "folds" form radial canals.
Choanocytes line the radial canals rather
than the spongocoel.
This shows the
radial canals
 The Leuconoid Sponges
example: the "bath sponge" (Class Demospongiae)
.
 Leuconoid sponges represent the most complex body
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form.
The canal system is extensively branched. Small
incurrent canals lead to flagellated chambers lined
by choanocytes. Flagellated chambers discharge
water into excurrent canals that eventually lead to an
osculum.
Usually there are many oscula in each sponge.
The skeleton of this sponge is made of a soft protein,
called spongin, rather than calcium carbonate or
silica
Link to sponge photos
REPRODUCTION
 ASEXUAL: branches or buds break off
 SEXUALLY: produce gametes in specialized
collar cells or amebocytes
 MOST HERMAPHRODITIC
 BROADCAST SPAWNING- release of sperm
into the water; eggs remain inside the body
and fertilization is internal
 Development inside sponge; a planktonic
larva called a parenchymula larva
 metamorphosis
CNIDARIANS
video
Basic characteristics
 Tissues evolved to perform certain functions
 Also called coelenterates
 Ex: sea anemones, jellyfishes, coral
 Radial symmetry (similar body parts arranged
and repeated around a central axis)

Looks the same from all sides; no head, front
or back
 Oral surface = where mouth is
 Aboral surface = side without mouth
Basic characteristics cont.
 Centrally located mouth surrounded by
tentacles that capture and handle food
 Mouth opens into a gut where food is
digested
 Have nematocysts (or cnidae) that are
specialized cells that discharge poison to help
maintain food
 Feeding and digestion: carnivores; initial
phase of digestion is said to be extracellular
because it takes place outside cells;
intracellular digestion within cells lining the
gut complete the food breakdown
http://undersea.com.au/corals/coral_structure.htm
 Behavior- have specialized nerve cells which
interconnect to form a nerve net that
transmits impulses in all directions
 Medusaes have a statocysts that give them a
sense of balance

Small calcareous bodies in fluid-filled
chambers with small hairs
2 basic forms
 1. Polyp= sac-like life stage with mouth and
tentacles
 2. Medusa= bell-like; jellyfish; upside down
polyp
 Some animals exhibit both stages in their life;
others exhibit only 1 kind throughout their life
 Larvae = planula- a cylindrical ciliated stage
made of two cell layers; planktonic until it
settles on the bottom
Cell layers of Cnidaria
 2 layers form the body wall
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Epidermis- external
Gastrodermis- lines the gut
 Mesoglea- narrow; gelatinous middle layer
that contains no cells

In a medusa, the layer is expanded to form a
gelatinous, domed bell
CLASSES OF CNIDARIANS
 10,000 known species
 1. Hydrozoans- wide range of forms
 A. Siphonophores- form drifting colonies of polyps
 Ex: Portuguese man-of-war; some of the colony are
specialized as floats
 Some contain droplets of oil
 Some form long tentacles to capture prey
 Reproduction- varies; some have specific reproductive
polyps that release gametes and fertilization takes
place and develops into swimming planulae that
settles on the bottom and develops into a polyp which
divides into interconnected polyps
Marrus orthocanna, a deep sea
siphonophore. The combined
digestive and circulatory system is
red; all other parts are
transparent.
www.siphonophores.org/images/2729_600.jpg
Physophora hydrostatica
Man-o-war
www.alienstingers.com/.../group_siphono_b.gif
image48.webshots.com/.../377734356ljKMfl_ph.jpg
Most Hydrozoans are feathery or bushy colonies of tiny polyps.
 2. Scyphozoans- larger jellyfish
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Large medusa dominant life stage
Reproduction: polyps are small; release
juvenile medusas
Some bell’s may reach a diameter of 2 m; a
just discovered one that is 3 m
Swim w/a rhythmic contraction of the bell;
easily carried by currents
Can be very dangerous; fatal stings
Aurelia aurita (moon jelly)
 3. Cubozoa- most toxic
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Ex: sea wasp- box jellyfish
Death due to heart failure
There is an antivenom
The box jellyfish, or sea wasp (Chironex)
that swims in tropical waters off the coast of
Australia with a width of approximately 25
cm can kill a person within minutes!
bioweb.uwlax.edu/.../Lab_3a-07a.jpg
Carybdea
 4. Anthozoans- solitary or colonial polyps
that lack a medusa
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Largest number of Cnidarian species
More complex body
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Gut has several thin partitions called septa that
increase the surface area for digestion and
provide support allowing the polyp to be larger
Ex: sea anemones; corals
www.anthozoa.com/Photos/Welcome/Anthozoans.jpg
CORALS HERMATYPIC- corals where the polyps
produce calcium carbonate skeletons; form
reefs
 AHERMATYPIC- corals who do not help to
build reefs
 Scleractinian corals- most important reef
builders; also known as stony or “true” corals
 Contain symbiotic zooanthellae
(dinoflagellates) that help the corals make
their calcium carbonate skeletons
The coral polyp
 Reefs are colony of polyps connected with a
thin layer of tissue
 Starts when a planktonic coral larva, called a
planula, settles on a hard surface and
metamorphoses into a polyp which divides
over and over to produce the colony
 Digestive systems remain connected and
share a common nervous system
 Only living tissue is a thin layer on the surface
 Hard Corals
limestone skeletons
multiple tentacles
 Soft Corals
soft skeleton with spicules
8 tentacles
chemical repellents
 Gorgonians- sea fans; colonial anthozoans

Precious corals and black corals are made
into jewelry
carlsafina.files.wordpress.com/2009/01/a-shal...
CTENOPHORES
COMB JELLIES-video
 All marine
 100 species
 Radially symmetry and gelatinous body
 Swim with 8 rows of CILIARY COMBS, long
cilia fused at the base that beat in waves
reflecting light
 In warm and cold waters
 COLLOBLASTS- long tentacles armed with
sticky cells
Comb jelly
www.mwra.state.ma.us/.../graphic/ctenophore.jpg
BILATERALLY
SYMMETRICAL WORMS
FLATWORMS, RIBBON WORMS,
NEMATODES, SEGMENTED WORMSVIDEO
FLATWORMS
 Phylum- Platyhelminthe
 Dorsoventrally flat
 Simplest animals with tissues organized into
real organs and organ systems
 Have a central nervous system
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Simple brain- bundle of nerve cells
Several nerve cords the length of the worm
Only one opening for gut/anus
 Embryos have a middle layer of tissue called
the MESODERM (1st animal to have it)- which
gives rise to muscles, the reproductive
system, and other organs
 20,000 species
 Most common marine ones are the
TURBELLARIANS- free living carnivores
www.daviddarling.info/images/flatworm_section.jpg
Polyclad flatworm, Pseudoceros sp,
Egyptian Red Sea.
Photo © Mike Keggen
FENCING
http://www.julianrocks.net/flatworms/PseudobicerosBedfordi.html
 Flukes or TREMATODES- largest group of
flatworms; 6000 species; all parasitic
 Tapeworms or CESTODES- long body with
repeating units; live in intestines of
vertebrates; don’t have a gut or mouth but
absorb nutrients
RIBBON WORMS
 Or NEMERTEAN
 More complex organization
 Complete digestive tract with gut, mouth, and
anus
 Circulatory system
 Proboscis-long fleshy tube used to entangle
prey
 Predators that feed on worms and
crustaceans
 900 species mostly marine
http://rydberg.biology.colostate.edu/Dissections/Nemertea/Nemer
teawh.JPG
Nematodes
 Roundworms
 Found mostly in sediment or intestinal tracts;
most parasitic; small, with slender body that is
pointed at one end
 Gut and anus
 Has a hydrostatic skeleton- a system that
uses water pressure against the body wall to
maintain body shape and aid in locomotion
 Anywhere between 10,000 to 25,000 species
 Larvae found in raw or poorly cooked fish
http://www.diplectanum.dsl.pipex.com/sim/anisak.jpg
SEGMENTED WORM OR
ANNELIDS
 About 20,000 species
 More complex body systems
 Has segmentation- identical body segments
 Has a coelom-body cavity found in
structurally complex animals- completely
surrounded by tissue developed from the
mesoderm
Classes of Annelids
 1)Polychaetes- most of the marine
annelids;made of body segmetnns that have
a pair of flattened extensions called
parapodia that have setae (sharp bristles)
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Have a closed circulatory system that
transports nutrients, oxygen, and carbon
dioxide
Have gills on the parapodia that contain
capillaries to help with the absorption of
oxygen
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10,000 species almost all marine
Live in temporary or permanent tubes made of
mucus, protein, seaweed bits, mud, etc.
Mostly carnivores but some are suspension
feeders
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Proboscis ensnares prey
Life history of Polychaetes
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Have a trochophore- a planktonic larval stage
with cilia
Some such as the Tomopteris are planktonic for
entire life
Nereis
http://www.esu.edu/~milewski/intro_biol_two/lab__12_a
nnel_arthro/images/nereis.jpg
An assemblage of polychaetes (Photo by H. Torres)
 2) Pogonophorans or beard worms
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Lack a mouth and gut
Has food absorbing tufts
135 species
Deep water
Another group called the vestimentiferans
are much longer
Some found at hydrothermal vents
www.nematodes.org/.../pogonophora/pogo
1.gif
 3)Oligochaetes- found in mud and sand; eat
detritus;marine relatives of earthworms; no
parapodia
http://www.mpi-bremen.de/Binaries/Binary7687/Oalg_7_RGB_small.jpg
 4.) Leeches- some marine species; parasitic;
sucker at one end; no parapodia
Tracy Clark
8/11/2006
La Jolla Shores
Hornyhead Tubot
Pleuronichthys verticalis
Leech
Unidentified
Nikon D70
60mm lens
PEANUT WORMS
 Phylum: Sipuncula
 Unsegmented bodies
 Burrowers; shallow water; deposit feeders
 All marine
 Long, anterior portion has a mouth a a set of
small lobes of branching tentacles
 320 species
http://www.livewild.org/CostaRica/Pics/a5751.jpg
ECHIURANS- phylum Echiura
 135 species all marine
 Look like peanut worms but with a non-
retractable, spoon-like or forked proboscis
 Deposit feeders
 Some live in U-shaped tubes in the mud
http://farm4.static.flickr.com/3089/2922855838_a3df563b1e.jpg?v=1223412990
Molluscs: The Successful
Soft Body
BASIC MOLLUSK
CHARACTERISTICS
 Most have a soft body enclosed in a calcium
carbonate shell
 Body covered with a mantle- a thin layer of
tissue that secretes the shell
 Bilaterally symmetrical
 Ventral, muscular foot
 Head with sensory organs including eyes
 Have a radula- ribbon-like band of teeth
made of chitin used for feeding
 Have paired gills
3 major classes of Mollusks
 Gastropods (class Gastropoda)
 Bivalves (class Bivalvia)
 Cephlapods (class Cephlapodia)
 2 minor classes of Mollusks:
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Chitons
Tusk shells
Gastropods “stomach footed”
 Largest and most common class
 Snails, limpets, abalones and nudibranches
 75,000 species mostly marine
 Has a hard dorsal shell
 Use radula to scrape algae from rocks
 Some are deposit feeders; some are
carnivores
 Nudibranches or sea slugs have no shell
Nudibranch
Limpet
www.barwonbluff.com.au/.../limpet%20smooth.jpg
http://birdhouse.org/blog/wpcontent/uploads/2008/05/nudibranch.jpg
limpet
coneshell
www.theseashore.org.uk/theseashore
http://www.scuba-equipmentusa.com/marine/JUN05/images/Conus_texti
le.jpg
Violet snails
http://www.floridastateparks.org/bahiahonda/images/BAH-violet-snail.jpg
BIVALVES
 Clams,mussels,oysters etc.
 Body is laterally compressed and enclosed in
a shell with two parts
 No head, no radula
 Gills larger and used for obtaining oxygen
and to filter food particles
 Inner surface of shell lined by mantle;
therefore whole body is in the mantle cavitya large space between the two halves of the
mantle
 Siphons-tube-like extension through which
water flows in and out of the mantle cavity in
bivalves, cephlapods, and tunicates
 Mussels have byssal threads to attach to
submerged surfaces such as rocks etc.
Pearl diving video
Pearl oyster
 http://www.japan-hopper.com/wp-
content/photos/pearl_oyster.jpg
www.waterworxbali.com/.../giant-clam-diver.jpg
Giant sea clam…largest bivalve can be up to
3ft in length
 Some bivalves bore into coral, rock or wood
 Ex: shipworm– known as a fouling organism
because they settle on the bottom
CEPHLAPODA- “head-footed”
 Predators
 Octopuses, squids, cuttlefishes
 Reduced or absent shell
 Foot modified into arms and tentacles with suckers
 Round bodies- octopus
 Elongated bodies- squid
 Bodies protected by thick, muscular mantle
 Mantle cavity behind head contains 2-4 gills
 Siphon = funnel- a muscular tube from the foot