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CHAPTER 5
Protozoan Groups Unicellular Eukaryotes
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Emergence of Eukaryotes
 Protozoa
Lack a cell wall
Have at least one motile stage in life cycle
Most ingest their food
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Form and Function
Locomotion
 Cilia and flagella
 Contain 9 pairs of microtubules arranged around a
central pair
Cilia
Propel water parallel to the cell surface
Flagella
Propel water parallel to the flagellum axis
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Form and Function
How Pseudopodia Work
Endoplasm
Contains nucleus and cytoplasmic organelles
Ectoplasm
More transparent (hyaline)
Contains bases of cilia or flagella
Often more rigid
Appears granular
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11-8
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Form and Function
Functional Components of Protozoan Cells
• Nucleus
– Membrane bound organelle
– Contains DNA in the form of chromosomes
– Chromatin often clumps irregularly leaving clear
areas
– Nucleoli are often present
– Macronuclei of ciliates
• Compact or condensed with no clear areas
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Form and Function
• Mitochondria
– Involved in energy production
 Golgi apparatus
Part of the secretory system of the endoplasmic
reticulum
 Plastids
Organelles containing a variety of photosynthetic
pigments
Perhaps added when a cyanobacterium was
engulfed but not digested
Chloroplasts contain different types of chlorophylls
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11-11
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Form and Function
 Extrusomes
General term applied to membrane-bound
organelles used to extrude material from cell
All not believed to be homologous
Ciliate trichocysts are examples
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Form and Function
Nutrition
 Holozoic nutrition implies phagocytosis
Infolding of cell membrane surrounds food
particle
Invagination pinches off
Food particle contained in intracellular vesicle
Food vacuole (phagosome)
Lysosomes fuse with phagosome and release
enzymes
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Form and Function
Digested products absorbed across vacuole
membrane
Undigestible material released to outside by
exocytosis
 In ciliates, site of phagocytosis called a cytostome
Many have a point for expulsion of wastes
Cytopyge or cytoproct
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11-15
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Form and Function
Excretion and Osmoregulation
 Excretion of metabolic wastes is by diffusion
 Primary end product of nitrogen metabolism
Ammonia
 Contractile vacuoles fill and empty to maintain
osmotic balance
No known lipid bilayer that retains water against a
gradient
A proton pump may actively transport H+ ions and
cotransport bicarbonate into vacuole
Water enters by osmosis
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Form and Function
Reproduction
 Asexual Processes
Fission
Produces more individuals than other forms of
reproduction
Binary fission is most common
Two identical individuals produced
Budding
Occurs when a small progeny cell (bud) pinches off
from parent cell
Bud grows to adult size
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Form and Function
Multiple fission (schizogony)
Cytokinesis preceded by several nuclear divisions
May individuals formed simultaneously
If union of gametes precedes multiple fission
Called sporogony
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Form and Function
 Sexual Processes
 All protozoa reproduce asexually
Some exclusively
 Sexual reproduction also occurs widely among
protozoa
Meiosis
May occur during or just before gamete
formation
In other groups, meiosis occurs after
fertilization (zygotic meiosis)
All individuals produced asexually in life cycle up to
next zygote are haploid
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Form and Function
 Encystment and Excystment
Unicellular forms amazingly successful in
extremely harsh conditions
Related to the ability to form cysts
Dormant forms that shut down metabolism
and have a resistant external covering (secreted
by Golgi apparatus)
Encystment is not found in Paramecium, rare
or absent in marine forms
Excystment
Escape from cysts when environmental
conditions are favorable
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Major Protozoan Taxa
Clade Viridiplantae
Unicellular and multicellular green algae,
bryophytes, and vascular plants
Phylum Chlorophyta
Flagellated, autotrophic, single-celled algae
such as Chlamydomonas, as well as colonial
forms like Gonium and Volvox
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11-23
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Major Protozoan Taxa
Phylum Euglenozoa
Have a series of longitudinal microtubules
Stiffen the cell membrane into a pellicle
Subphylum Euglenida
Chloroplasts surrounded by a double
membrane
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11-25
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Major Protozoan Taxa
Subphylum Kinetoplasta
• Zooflagellates
– Holozoic or saprozoic nutrition
– Most are symbiotic
– Trypanosoma
• Important genus of protozoan parasites
– Some not pathogenic
– T. brucei gambiense and T. b. rhodesiense
» Cause African sleeping sickness in humans
– T. cruzi
» Causes Chagas disease
» All transmitted by tsetse flies
» Transmitted by “kissing bugs”
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Major Protozoan Taxa
Clade Alveolata
Three traditional phyla united by the shared
presence of alveoli
Membrane-bound sacs beneath cell membrane
Function varies with phylum
Phylum Ciliophora
Phylum Dinoflagellata
Phylum Apicomplexa
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Major Protozoan Taxa
Phylum Ciliophora
Ciliates are the most diverse and specialized
protozoans
Larger than most other protozoa
Most free-living, some commensal and parasitic
Usually solitaire and motile
Most free-living in freshwater or marine habitats
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Major Protozoan Taxa
Multinucleate
Macronuclei
Metabolic and developmental functions
Divides amitotically
Micronuclei
Involved in sexual reproduction and give rise
to macronuclei afterwards
Divide mitotically
Trichocysts and toxicysts in some
Expel long thread-like structures when
stimulated
Believed to be defensive mechanism
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11-31
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Major Protozoan Taxa
Paramecium may be studied as a typical free-living
ciliate
Slipper-shaped
Asymmetrical appearance caused by oral
groove
Pellicle may be ornamented, have ridges, or
papillalike projections
Trichocysts present
Cytostome leads to a tubular cytopharynx
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Major Protozoan Taxa
Fecal material discharged from the cytoproct
2 contractile vacuoles
Kidney-shaped macronucleus with smaller
micronucleus alongside
Some species have up to seven micronuclei
Holozoic
Body is elastic
Can bend and squeeze through spaces
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Major Protozoan Taxa
Phylum Dinoflagellata
– About half are photoautotrophic
– Chloroplasts possibly acquired by endosymbiosis
– Some among the most important primary producers in
marine environments
– Commonly have two flagella
– Body naked or covered by cellulose plates
– Many have a mouth region through which they can ingest
prey
– Many are bioluminescent
– Zooxanthellae
• Live in mutualistic association with corals and other invertebrates
• Only corals with symbiotic zooxanthellae form coral reefs
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Major Protozoan Taxa
Phylum Apicomplexa
– Plasmodium: The Malarial Organism
» Most important infectious disease of
humans
» Four species infect humans
» Each produces different clinical
symptoms
» Anopheles mosquitoes carry all forms
» Female injects the Plasmodium present
in her saliva
» Migrate to the mosquito’s salivary gland
where they are injected into a human
host
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11-37
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Major Protozoan Taxa
Amoebas
Found in fresh and salt water, and moist soils
Some planktonic, some require a substratum
Most reproduce by binary fission
Nutrition is holozoic
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Major Protozoan Taxa
Limestone and chalk deposits have been laid
down by foraminiferan accumulations
Chalk deposits of many areas of England,
including White Cliffs of Dover, formed in this
way.
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Major Protozoan Taxa
Radiolarian
Refers to marine testate amoeba with intricate
skeletons
Oldest known protozoa
Pelagic and live in shallow water
Shell surface fused with spines
Cytoplasm around the capsule extends
axopodia to catch prey
Reproduce by binary fission & budding
Useful for determining the age of rock strata
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11-42
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CHAPTER 6
Sponges
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Phylum Porifera
General Features
• Sessile sponges are filter feeders
• Porifera means “pore-bearing”
– Sac-like bodies perforated by many pores
• Use flagellated “collar cells”, or choanocytes, to
move water
• Body is efficient aquatic filter
• Approximately 15,000 species of sponges
– Most are marine
• Few live in brackish water, 150 in fresh water
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Phylum Porifera
 Marine sponges found in all seas at all depths and
vary greatly in size
 Many species are brightly colored because of
pigments in dermal cells
 Embryos are free-swimming, adult sponges always
attached
 Some appear radially symmetrical but many are
irregular in shape
 Some stand erect, some are branched, and some are
encrusting
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Phylum Porifera
Form and Function
• Body openings consist of small incurrent pores
or dermal ostia
• Incurrent pores: Average diameter of 50 μm
• Inside the body
– Water is directed past the choanocytes where food
particles are collected
– Choanocytes (flagellated collar cells) line some of the
canals
• Keep the current flowing by beating of flagella
• Trap and phagocytize food particles passing by
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Phylum Porifera
• Sponges non-selectively consume food particles
sized between 0.1 μm and 50 μm
– The smallest particles are taken into
choanocytes by phagocytosis
– Protein molecules may be taken in by
pinocytosis
– Two other cell types, pinacocytes and
archaeocytes, play a role in sponge feeding
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12-49
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Phylum Porifera
• Types of Canal Systems
– Asconoids: Flagellated Spongocoels
• Simplest body form
• Small and tube-shaped
• Water enters a large cavity, the spongocoel
– Lined with choanocytes
– Choanocyte flagella pull water through
– All Calcarea are asconoids
» Leucosolenia
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Phylum Porifera
– Syconoids: Flagellated Canals
• Resemble asconoids but larger with a
thicker body wall
• Wall contains choanocyte-lined radial
canals that empty into spongocoel
– Water enters radial canals through tiny
openings called prosopyles
• Spongocoel is lined with epithelial cells
rather than choanocytes
• Food is digested by choanocytes
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12-53
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Phylum Porifera
• Leuconoids: Flagellated Chambers
– Most complex and are larger with many oscula
– Clusters of flagellated chambers are filled from
incurrent canals, and discharge to excurrent
canals
– Most sponges are leuconoid
– System increases flagellated surfaces
compared to volume
• More collar cells can meet food demands
• Large sponges filter 1500 liters of water per day
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Phylum Porifera
• Types of Cells
– Sponge cells are arranged in a gelatinous matrix,
mesohyl
• Connective “tissue” of sponges
• Absence of true tissues or organs requires that all fundamental
processes occur at the level of individual cells
– Only visible activities of sponges are
• Slight alterations in shape, local contraction, propagating
contractions, and closing and opening of incurrent and excurrent
pores
• Movements occur very slowly
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12-57
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Phylum Porifera
–Pinacocytes
• Form pinacoderm
• Flat epithelial-like cells
• Somewhat contractile
• Some are myocytes that help regulate flow
of water
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Phylum Porifera
– Choanocytes
• Oval cells with one end embedded in mesohyl
• Exposed end has one flagellum surrounded by
a collar
• Collar consists of adjacent microvilli
– Forms a fine filtering device to strain food
– Particles too large to enter collar are trapped in
mucous
– Moved to the choanocyte and phagocytized
– Food engulfed by choanocytes is passed to
archaeocytes for digestion
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Phylum Porifera
–Archaeocytes
• Move about in the mesohyl
• Phagocytize particles in the pinacoderm
• Can differentiate into any other type of cell
– Sclerocytes secrete spicules
– Spongocytes secrete spongin
– Collencytes secrete fibrillar collagen
– Lophocytes secrete collagen
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Phylum Porifera
Class Calcarea
• Calcareous sponges with spicules of calcium
carbonate
• Spicules are straight or have three or four rays
• Most are small with tubular or vase shapes
• Many are drab in color, but some are bright
yellow, green, red, or lavender
• Leucosolenia and Sycon are marine shallowwater
• Asconoid, syconoid and leuconoid body forms
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Phylum Porifera
Class Hexactinellida
 Glass sponges with six-rayed spicules of silica
 Nearly all are deep-sea forms
 Most are radially symmetrical
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Phylum Porifera
Class Demospongiae
 Spicules are siliceous but not six rayed
 Absent or bound together by spongin
 Leuconoid body form
 All marine except for Spongillidae, the freshwater
sponges
 Freshwater sponges
 Widely distributed in well-oxygenated ponds and springs
 Marine demosponges
 Highly varied in color and shape
 Bath sponges
 Lacks siliceous spicules
 Have spongin skeletons
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12-64
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CHAPTER 7
Radiate
Animals
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Phylum Cnidaria
 Over 9,000 species in the phylum Cnidaria
 Equipped with specialized cells: cnidocytes
 Contain a specialized stinging organelle, the nematocyst
 Fossil specimens dated to over 700 million years ago
 Extant species
 Most common in shallow marine environments
 Some freshwater
 None are terrestrial
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Phylum Cnidaria
 Some ctenophores, molluscs and flatworms eat
hydroids and use the stinging nematocysts for their
own defense
 Four classes of Cnidaria
Hydrozoa
Scyphozoa
Cubozoa
Anthozoa
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Phylum Cnidaria
Characteristics of Phylum Cnidaria
All are aquatic and mostly marine
Symmetry
Radial or biradial
Two body types
Free-swimming medusae
Sessile polyps
Diploblastic
Epidermis and gastrodermis
Mesoglea: extracellar matrix that lies between
ectodermis and gastrodermis
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Phylum Cnidaria
 Incomplete gut: gastrovascular cavity
 Extracellular digestion in gastrovascular cavity
 Intracellular digestion in gastrodermal cells
 Tentacles usually encircle mouth or oral region
 Muscular contractions via epitheliomuscular cells
 Outer layer of longitudinal fibers and an inner layer of
circular fibers
 Sense organs for balance (statocysts) and
photosensitivity (ocelli)
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Phylum Cnidaria
 Nerve net
 Asexual reproduction
 Budding in polyps
 Sexual reproduction
 By gametes in all medusae and some polyps
 No excretory or respiratory system
 Acoelomate
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Form and Function
Phylum Cnidaria
• Cnidaria have two basic body plans:
polyp and medusa
– Polyp
• Hydroid form
• Adaptation to a sedentary life
• Tubular body with the mouth directed upward and
surrounded by tentacles
• Mouth leads into a blind gastrovascular cavity
• Aboral end attached to substratum by pedal disc
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Phylum Cnidaria
– Medusa
•
•
•
•
Bell or umbrella-shaped
Usually free-swimming
Mouth directed downward
Tentacles may extend down from rim of umbrella
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Phylum Cnidaria
Life Cycles
• Polyps and medusae play different roles in the
cnidarian life cycle
• Typically, zygote develops into a motile planula
larva
• Planula settles, and metamorphoses into a polyp
– Produce other polyps asexually
– Polyps eventually produce a free-swimming medusa by
asexual reproduction
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Phylum Cnidaria
Body Wall
 Cnidarian body
 Outer epidermis
 Inner gastrodermis
 Layers separated by mesoglea
 Mesoglea
Gelatinous (at least 95% water)
Continuous in polyps, extending through body and
tentacles
Supports body
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Phylum Cnidaria
Epitheliomuscular cells
Form most of epidermis and cause muscular
contraction
Undifferentiated interstitial cells
Develop into cnidoblasts, sex cells, buds, or
nerve cells, but not epitheliomuscular cells.
Gland cells
On the adhesive disc secrete an adhesive and
sometimes a gas bubble for floating
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Phylum Cnidaria
Mechanism of Nematocyst Discharge
 When stimulated, water to rush into the capsule
 The operculum opens and rapidly launches the
filament
 Barbs inject venom into prey
 Only a few jellyfish and the Portuguese man-of-war
can seriously harm humans
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13-79
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Phylum Cnidaria
Nerve Net
• Nerve net of cnidarians one of the best
examples of diffuse nervous system
– Two nerve nets, one at the base of epidermis and one
at the base of gastrodermis, interconnect
• Nerve action potentials transmitted across
synapses by neurotransmitters
• Unlike higher animals,
– Nerve nets have neurotransmitters on both sides of
the synapses
– Allowing transmission in either direction
– No myelin sheath on axons
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Class Hydrozoa
 Most marine and colonial with both polyp and
medusa forms
 Hydra is not typical
 Colonial Obelia is more exemplary
In Obelia, the medusae buds are formed by a
reproductive polyp called a gonangium
Hydroid medusae
Usually smaller than schyphozoan medusae
Typically also bears statocysts, specialized sense organs
that function in equilibrium, and light-sensitive ocelli
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Phylum Cnidaria
• Other Hydrozoans
• In Physalia, the float, pneumatophore
– Thought to have expanded from the original
larval polyp
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Phylum Cnidaria
Class Scyphozoa
 Most of the larger jellyfishes belong to this class
 Nearly all float in open sea
 Bells vary in shape and size
 Composed mostly of mesoglea
 Mouth located beneath the umbrella
 Manubrium forms four oral arms
 Capture and ingest prey
 Tentacles, manubrium, and often entire body may
have nematocysts
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Phylum Cnidaria
 Sexes are separate
Fertilization is internal in the gastric pouch of the
female
Zygote develops into a ciliated planula larva
Attaches and develops into a scyphistoma
Scyphistoma undergoes strobilation
Form buds called ephyrae that break loose to form
jellyfish medusae
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Phylum Cnidaria
Class Staurozoa
•
•
•
•
Commonly called stauromedusans
No medusa stage
Solitary polyp body that is stalked
Uses adhesive disk to attach to seaweeds, and
objects on sea bottom
• Polyp top resembles a medusa with eight
extensions (“arms”) ending in tentacle clusters
surrounding mouth
• Reproduce sexually
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Phylum Cnidaria
Class Cubozoa
 Medusa form is dominant
 Polyp is inconspicuous or unknown
 Umbrella is square
 One or more tentacles extend from each corner
 Umbrella edge turns inward to form a velarium
 Increases swimming efficiency
 Strong swimmers
 Feed mostly on fish in nearshore areas
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Phylum Cnidaria
Class Anthozoa
• Lack a medusa stage
• All marine, in both deep and shallow water, and
vary in size
 The mesoglea is mesenchyme containing ameboid
cells
 No special organs for respiration or excretion
Sea Anemones
 Polyps larger and heavier than hydrozoan polyps
 Attach to shells, rocks, timber, etc. by pedal discs
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Phylum Cnidaria
Hexacorallian Corals
• Members of the order Scleractinia
• Also called true or stony corals
• Described as miniature sea anemones that live in
calcareous cups they have secreted
• Sheet of living tissue forms over the coral surface
– Connects all gastrovascular cavities
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Phylum Cnidaria
Octocorallian Corals
• Octomerous symmetry,
– Eight pinnate tentacles
– Eight unpaired complete septa
• All are colonial
– Gastrovascular cavities communicate through tubes
called solenia
– Solenia pass through an extensive mesoglea
• Show great variation in form of colony
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Phylum Ctenophora
• Phylum composed of about 150 species
• All marine, most prefer warm waters
• Ctenophores
– Eight rows of comb-like plates used for locomotion
• Nearly all free-swimming, few creep or are
sessile
• Body structure (ellipsoid or spherical shape)
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Phylum Ctenophora
• Tentacles
– Two tentacles are long, solid and extensible
– Retract into a pair of tentacle sheaths
– Surface bears colloblasts or glue cells that secrete
sticky material to hold animals
• Body wall resembles cnidarians with a
gelatinous collenchyme in the interior
• Muscle cells are distinct and not part of the
epitheliomuscular cells
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Phylum Ctenophora
 When ctenophore contacts an unfavorable stimulus
 Cilia reverse their beat
 Moves organisms backward
 Comb plates are sensitive to touch
 Withdraw into the animal when touched
 Most ctenophores are bioluminescent at night
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