Phyla Porifera, Cnidaria, and
Ctenophora
Chapter 9
Phylum Porifera (Sponges)
• Poriferans are mostly marine animals.
• Characteristics include:
– Asymmetrical or radial symmetry
– Three types of cells
– Central cavity for water circulation
– No tissue or organs
– Mostly sessile
Poriferan Cell Types
• Pinacocytes
– Thin, flat cells that line the outer surface of sponges
– Some specialized into porocytes that regulate water circulation
• Amoeboid cells
– Contained in jellylike mesohyl layer
– Function in reproduction, secreting skeletal elements,
transporting and storing food, and forming contractile rings
around openings in the wall
• Choanocytes
– Collar cells lining inner chamber
– Flagellated with microvilli surrounding each flagellum
– Flagella create water current and the collar of microvilli filters
food particles
http://www.waycross.edu/faculty/gcook/ecology/animalia/zoa.html
Sponge Skeleton
• Sponge skeletons may be made of
needlelike spikes called spicules.
– Spicules are made of calcium carbonate or
silica and are formed by amoeboid cells.
• Some sponges have skeletons made of
spongin which is made of collagen
– Spongin skeletons are used as commercial
sponges
http://www-biol.paisley.ac.uk/biomedia/graphics/jpegs/SPICULES.gif
Ascon Body Form
• Vaselike shape
• Outer openings of porocytes are called
ostia (singular-ostium)
– Ostia lead directly to inner chamber called the
spongocoel which is lined with choanocytes
• Water is drawn in through ostia and exits
through large opening at the top of the
sponge called the osculum.
http://mac01.eps.pitt.edu/geoweb/c
ourses/GEO1200/lab3/structure.htm
Sycon Body Form
• Outer wall appears folded
• Water enters through openings called dermal
•
•
•
pores which are openings of incurrent canals
(infolded invaginations).
Incurrent canals are connected to radial canals
through pores.
Radial canals are lined with choanocytes and
lead to the spongocoel.
Spongocoel has an osculum.
http://mac01.eps.pi
tt.edu/geoweb/cour
ses/GEO1200/lab3/
structure.htm
Leucon Body Form
• Leucon body forms contain an extensively
•
•
•
branched canal system.
Water enters through ostia and enters incurrent
canals.
Incurrent canals lead to choanocyte chambers
and leaves chambers through excurrent canals.
No spongocoel is present and there are multiple
oscula.
http://mac01.eps.pitt.edu/geoweb/courses/GEO1200/lab3/structure.htm
Nutrition and Gas Exchange
• Sponges feed on bacteria, microscopic algae, protists, and other
microscopic organisms.
• Some deep water sponges (Genus Asbestopluma) are carnivorous
and feed on small crustaceans.
• Sponges serve the ecosystem by filtering water and reducing turbity
(cloudiness).
– A 1 cm by 10 cm sponge can filter 20 liters of water every day.
• Food is filtered and trapped by choanocyte cells and then trapped
by food vacuoles where digestion by enzymes begins.
– Amoeboid cells distribute digested food products to other cells.
• Nutrients can also be phagocytized by pinacocytes along incurrent
canals or absorbed by active transport.
• Gas exchange and excretion of nitrogenous wastes occur by
diffusion
Asbestopluma
http://scilib.ucsd.edu/sio/nsf/fguide/porif
era26.html
Cellular Communication
• Sponges do not have a nervous system for cell
•
to cell communication
Cells respond to stimuli in the environment to
regulate activities.
– Example: Sunlight inhibits constriction of ostia
keeping them open, thus maintaining maximum water
circulation during sunlight hours.
• Some cellular communication may be present
due to observations of activity changes with no
external stimulus.
– Method of communication is unknown.
Reproduction
• Most sponges are monoecious meaning both sexes occur in one
organism.
– Egg and sperm are produced at different time to prevent self
fertilization.
– Egg and sperm are derived from meiotic choanocytes.
– Eggs are stored in mesohyl.
– Sperm exit one sponge through its osculum and enter another with
incurrent water.
– Sperm are transferred to egg by amoeboid choanocytes.
• Asexual reproduction occurs in some marine sponges and
freshwater sponges.
– Gemmules containing amoeboid cells are released during winter when
the parent dies. The gemmules release the amoeboid cells during the
spring which organize into a sponge.
http://www.puk.ac.za/lifesc/zol/zol121/spong1.htm
Life Cycle of Sponges
• Earliest development occurs in the mesohyl.
• The zygote cleaves and forms a flagellated larva.
• Larva break free of the mesohyl and exit the
•
sponge through water currents.
The larva free swims for 2 days and finally
settles on a substrate and develops into an adult
sponge.
Porifera Classification
• Class Calcarea
– Calcium carbonate spicule skeletons
– All three body forms represented
– All marine
– Also known as calcareous sponges
– Examples:
• Grantia
• Leucosolenia
http://www.bscd.uchicago.edu/classes/biosci184/Imag
es/Grantia.html
http://www.dscc.e
du/kjones/bio2ani
mal.htm
http://www.olympusmicro.com/micd/galleries/darkfield/grantia.html
http://www.mareco.org/KML/sponges/pa
ges/leucosolenia%20species_jpg.htm
http://www.mareco.org/KML/sponge
s/pages/leucosolenia%20eleanor_jp
g.htm
http://www.biol.rug.nl/onderwaterbiologie/f
oto10.jpg
Classification (cont.)
• Class Hexactinellida
–
–
–
–
–
–
–
Silica spicule skeletons
Spicules often form intricate lattice
Cup or vase shaped
Sycon or leucon body form
Found in tropical West Indies and eastern Pacific
Also called glass sponges
Example: Euplectella
http://www.biology.ualberta.ca/courses.
hp/zool250/Labs/Lab03/Euplectella.gif
http://evylmyke.ca/musings/Seasponge.htm
Classification (cont.)
• Class demospongiae
–
–
–
–
–
Colorful sponges
Silica spicule skeletons or spongin skeletons
Leucon body forms
Can grow very large (1 m in height and diameter)
Examples
• One family of freshwater sponges (Spongillidae)
• Cliona
• Spongilla
http://www.dpo.uab.edu/~acnnnghm/
BY255L/BY255LImages/BY255LImage
s-Porifera/Spongilla-01.jpg
http://www.mareco.org/KML/sponge
s/images/cliona%20celata2_jpg.jpg
http://www.swan.ac.uk/biodiv/gower/Gower%20Rocky%20shore%20cryptic%20h
abitats.htm
Phylum Cnidaria (Coelenterata)
• Mostly marine animals that possess radial
or bilateral symmetry
• Diploblastic organization with true tissues
• Gastrovascular cavity present
• Nerve net present
• Cnidocyte cells with nematocysts for
defense, feeding, and attachment
Body Structure of Cnidarians
• Ectoderm gives rise to epidermis (outer body
•
•
•
layer)
Endoderm gives rise to gastrodermis (inner body
layer)
Each tissue layer possesses specialized cells that
function in protection, feeding, coordination,
movement, digestion and absorption.
Mesoglea is a jellylike layer between the
epidermis and gastrodermis.
http://www.waycross.edu/faculty/gcook/ecology/animalia/cnido.jpg
Cnidocytes
• Cnidocytes are specialized cell that
produce nematocysts.
– A nematocyst is a fluid filled capsule with an
coiled, hollow tube
– Operculum is a lidlike structure that caps the
capsule
• Cnidocyte possesses a cnidocil (modified
cilium) that acts as a sensor to open the
operculum and discharge the coiled tube.
http://www.wm.edu/act2online/projects/fahey03/cnidaria.html
Nematocysts
• Nematocysts used for feeding and defense have
spines that penetrate prey.
– The spines discharge paralyzing toxins.
• Other nematocysts may have unarmed tubes for
•
grasping or stick secretions for anchoring the
animal.
30 types of nematocysts have been observed
with single individuals having six or more
different types.
http://faculty.shc.edu/cchester/BIO205/Labs/Lab%2004/cnidocytes.htm
http://virtual.yosemite.cc.ca.us/randerson/marine%20invertebrates/nematocy.htm
Alternation of Generations
• The life cycle of most cnidarians includes two
body forms.
– Polyp-asexual, sessile stage that is attached to a
substrate and has a cylindrical body and a mouth
surrounded by food gathering tentacles.
– Medusa-dioecious, free swimming stage that is
shaped like a bowl with tentacles dangling down.
• Mouth is located in the center of the body and faces down.
• Movement occurs through pulsations of the body.
Medusae contain much more mesoglea than polyps
making them more jellylike.
http://www.wormguy.com/galimg/uw/pag
es/polyp.htm
http://antedoonsub.bravehost.com/t.b
orras/pages/medusa.htm
Feeding and digestion
• Most cnidarians feed on small crustaceans.
– Nematocysts capture prey and tentacles are shortened to draw
food towards the mouth.
• Gastrodermis lines the gastrovascular cavity where
digestion occurs.
– Gastrodermal gland cells secrete mucus and enzymes to reduce
the food to a broth
– Nutritive-muscular cells phagocytize food and incorporate into
food vacuoles where digestion is completed.
• These cells also cause peristaltic contractions that cause the
movement of food through the vascular cavity and expelling
undigested material through the mouth.
http://www.waycross.edu/faculty/gc
ook/ecology/animalia/anemone%20%20st.%20andrew%27s.gif
http://www.earthguide.ucsd.edu/hughes2001/acct/lzace/jellyfish.htm
Support
• Water buoyancy provides most support
needed by cnidarians.
• Cnidarians also possess a hydrostatic
skeleton-fluids are confined in a cavity
against which contractile cells of the body
act for movement.
– Epithelio-muscular cells aid movement
Movement
• Polyps
– Somersault from base to tentacles
– Wormlike movement using tentacles for attachment
– Glide on base or walk on tentacles
• Medusae
– Swim and float
• Horizontal movement-floating
• Vertical movement-swimming through pulsations of the body
Nerve Net
• Nerve cells are interconnected forming a nerve
•
net below the epidermis near the mesoglea.
Nerve nets conducts impulses in response to
local stimuli
– Strength of stimulus determines distance and speed
of impulse
• Example: Weak stimulus at a tentacle may cause tentacle to
retract while strong stimulus in same spot may cause entire
organism to move.
• Sensory receptors are distributed throughout the
body and can perceive touch and chemicals.
Gas Exchange
• Large surface area of the cnidarian allows
all gas exchange and waste elimination to
occur by diffusion through the body
surface.
Reproduction
• Most cnidarians are dioecious.
• Sperm and egg are released either into the gastrovascular cavity or
•
•
•
•
into the water.
After fertilization the zygote develops into a blastula tissue
separation begins.
The blastula elongates into a planula which is a free swimming larva
which attaches to a substrate.
The gastrovascular cavity forms and a young polyp develops.
Body wall of the polyp buds to form either a medusa form or
another polyp.
– Some buds may stay attached to the polyp to form a colony of polyps.
Jellyfish Life Cycle
Classification of Cnidarians
• Cnidarians are classified in one of 4
classes
– Hydrozoa (Obelia, Gonionemus, Physalia)
– Scyphozoa (true jellyfish, Aurelia)
– Cubozoa (Chironex)
– Anthozoa (corals, anemones)
Hydrozoa
• Small, mostly marine, some freshwater
• Alternation of generations present
• Nematocysts only on epidermis
• Gametes released to water rather than
gastrovascular cavity
• Mesoglea is acellular (no specialized cells
present)
Obelia
• Colonial polyp
– asexual
• Medusa stage
– sexual
Gonionemus
• Medusa stage predominates
• Lives in shallow marine waters
• Clings to seaweed
• Short polyp stage
• Gametes released into the water
Hydra
•
•
•
•
Freshwater
Hangs from plants
No medusa stage
Polyp reproduces
both sexually and
asexually
Physalia
• Portuguese man-of•
•
•
war
colonial
Cannot swim
Lethal to small
vertebrates,
dangerous to humans
Scyphozoa
• Marine
• “True Jellyfish”
• Aurelia
•
• Mastigias
•
because dominate
stage is medusa
Mesoglea contains
cells
Cnidocytes on
epidermis and
gastrodermis
– common in Pacific and
Atlantic waters of N.
America
quinquecirrha
– Stinging nettle,
Atlantic
Aurelia & Mastigia quinquecirrha
Cubozoa
• Cuboidal
• Tentacles hang from
corners
Warm tropical waters
•
• Chironex fleckeri
– Sea wasp or box jelly
– Off Australian coast
has caused many
human deaths
Anthozoa
• Colonial or solitary
• No medusa stage, only polyps
• Anemones
• Corals
• All marione
Anemones
• Solitary
• Large and colorful
• Attached or buried in
•
•
a substrate
Feed on invertebrates
and fish
Sexual and asexual
reproduction
Corals
• Colonial
• Sexual and asexual
•
•
reproduction
Stony corals hard
calcium carbonate
exoskeleton forms
coral reefs
Soft corals-sea pens,
sea fans
Phylum Ctenophora
• Comb jellies
• Diploblastic
• Nerve net
• Colloblasts (adhesive structures)
• 8 comb rows used in locomotion
– Class Tentaculata-with tentacles
(Pleurobrancia)
– Class Nuda-Without tentacles (Beroe)
Pleurobranchia
Beroe