Studied by 5 people
A look into the phylogeny of corals, sea anemones, jellies, and others.
radiates
animals displaying radial or biradial symmetry
diploblastic (ectoderm and endoderm)
no cephalization
The radiates clade of animals contains…
phylum Cnidaria and Cnetophora
phylum Cnidaria
sea anemones, jellyfish, corals, etc.
have cnidocytes for defense and/or offense
ancient group of animals, with fossils from 700 mya
mostly marine and sessile
sometimes lives symbiotically with other organisms
cnidocytes
defensive cells seen in phylum Cnidaria
has discharging organelles
cnidocyte type example
nematocyst
nematocyst
a type of cnidocytes
injects toxin for prey capture or defense through hollow filament
sometimes has barbs to latch into victim
usually triggered by cnidocil
Are nematocysts single use or reuseable structures?
single-use
once they have been launched, they cannot go back in
cnidarians can shed these cells and make new nematocysts
phylum Cnidaria classes and description of what’s included
Hydrozoa - hydras
Scyphozoa - the true jellies
Cubozoa - box jellies, sea wasps
Anthozoa - anemones, corals, and other related things
Staurozoa - very few species of medusa-like animals (not much focus in this course)
Myxozoa - highly modified parasitic forms (very different from rest of the phylum)
phylum Cnidaria body plans
dimorphic: polyp and medusa forms
physical relationship of polyp and medusa form
polyp is the sessile, “upright” form
medusa is the free moving, “downward” form
can show with your hand: polyp form is palm facing up, medusa form is palm facing down, and your fingers are the tentacles.
dimorphic
an animal having two separate forms
polyp
typically tubular
blind gut
sessile
reproduces asexually
colonies may have several morphologically distinct polyps
medusa
the “jelly” form
bell or umbrella shaped
usually free-swimming
mouth is directed downwards
tentacles may extend down
sensory structures for sensing orientation and light
sexually reproduce to make polyps
linked to motor response via nerve ring at the base of the bell
Are medusa forms dioecious or monoecious?
dioecious
general life cycle of cnidarians
zygote → motile planula larva → planula larva settles, metamorphosis → polyp → asexually form medusa → mature medusa → sexually reproduce with other medusae and form a zygote
Polyps may form other polyps via…
asexual reproduction
planula larva
the larval stage between zygote and polyp in cnidarians
ephyra
a baby medusa that still needs to grow into a full size medusa
variations in life cycle in cnidarians
drifting polyp colony, or polyp/medusae colony
life cycles without medusae
cnidarian cell layers
two cell layers:
inner layer - gastrodermis
outer layer - may have cnidocytes with nematocysts
has mesoglea between layers
gastrodermis
AKA inner layer or endoderm
digestion layer on the inside of the cnidarian
epidermis
AKA ectoderm
may have cnidocytes with nematocysts in cnidarians
mesoglea
gelatinous, buoyant filling between cell layers
supports the body
organ systems of cnidarians
feeding and digestion
nerve net
feeding and digestion in cnidarians
both stages carnivorous
coral also get carbon from algal symbionts
nerve net
example of diffuse nervous system, not central
in medusae, nerve net and nerve ring function like a central nervous system, but not quite
important landmark in evolution of nervous systems
nerve ring
ring of nerves near the end of the bell
Class Hydrozoa
mostly marine, colonial (freshwater forms do exist!)
has polyp and medusa forms
typical hyzroid colonies look like:
base, stalk, one or more terminal zooids
hydranths
gonangia
may have perisarc
zooids
individual polyps found in hydroid colonies
hydranths
feeding zooids that capture prey in a hydroid colony
gonangia
reproductive polyps that form medusa buds in hydroid colonies
perisarc
non-living chitinous covering found “shrink-wrapped” around hydroids
hydroid medusae
small (mm or cm across)
velum
gastrovascular cavity - continuous from mouth to tentacles
bell margin has:
many sensory cells (detecting light and other things)
nerve rings
velum
shelf-like lip in the medusa form of hydroids
helps with trapping water in order to propel itself farther
freshwater hydras
solitary polyps
can flop around and move
no medusa stage
nematocysts capture prey
some species with symbiotic algae
sexual and asexual reproduction
other examples of hydrozoans
Physalia (Portuguese man-of-war)
polymorphic colonies with both polyps and medusae
acts as one individual
mutualistic relationship with some fish
Class Scyphozoa
most of the larger jellyfish in this class
mostly in open sea
bells vary in shape and size
most less than 1/2 m across
scalloped margin
true jelly body plan
no velum
many nematocysts
thick layer of mesoglea
dioecious
internal fertilization
examples of true jellies
moon jellies
cosmopolitan distribution
upside down jellyfish
tissues have symbiotic dinoflagellates
acts like a polyp so the dinoflagellates make sugar
uses bell to suction cup itself to the bottom
Scyphozoa life cycle
zygote → cilicated planula larva → planula attaches to form scyphistoma → scyphistoma under goes strobilation → strobila forms ephyrae → break loose to form
scyphistoma
the name of strobilating polyps in class Scyphozoa
strobilation
the asexual reproduction of medusae
Class Staurozoa
no medusa stage
solitary polyp on a stalk
polyp top resembled a medusa
reproduce sexually
very few species
not much is known about this class
Class Cubozoa
box jellyfish, sea wasps
dominant medusa form
polyp form inconspicuous or unknown
voracious predators
box jelly body plan
mostly small (2-3 cm)
umbrella square, tentacles at the corners
pedalium at base of each tentacle
has velarium at edge of umbrella
has potent toxins: can kill a human in a couple of minutes
pedallium
flat blade at the base of each tentacle in class Cubozoa
velarium
umbrella edge turns in in class Cubozoa
increases swimming efficiency
like the velum in hydrozoa
Class Myxozoa
newer class in Cnidarians
obligate parasites
structurally, are highly reduced cnidarians
extremely small genome for an animal
Class Myxozoa body plan
tiny - just a couple of cells big
has polar capsules
Class Myxozoa examples
those that cause whirling disease
annelid worms
polar capsules
found in class Myxozoa
homologous to nematocysts
Class Anthozoa
no medusa stage
all marine
large gastrovascular cavity and divided into different parts
has three subclasses
Anthozoa subclasses
Hexacorallia
Ceriantipatharia
Octocorallia
subclass Hexacorallia
part of class Anthozoa
sea anemones, hard corals
hexamerous (6) body plan
polyps larger, heavier than hydrozoan polyps
resides in costal areas
glide on pedal discs
oral discs
carniverous
some can swim
pedal disk
found in subclass Hexacorallia
lets it attach to shells, rocks, etc.
oral disk
found in subclass Hexacorallia
surrounds the open mouth and where the tentacles attach to
sea anemone behavior
can contact and withdraw tenacles into their oral disk
mutualistic relationships:
many harbor symbiotic dinoflagellates (algae)
some live on crab shells
some provide shelter for anemone fish
sea anemone reproduction
sexual reproduction:
some dioecious, some monoecious
monoecious species are protandrous
asexual reproduction:
occurs via pedal laceration
occurs via longitudinal fission, but also transverse fission and budding
protandrous
produce sperm first, then eggs later
found in sea anemones
pedal laceration
type of asexual reprduction
pieces of pedal disk break off and regenerate
found in sea anemones
true (stony) corals
looks like tiny sea anemones in calcareous cups
secretes exoskeleton
in colonies, exoskeleton can becomes massive, but the living coral forms thin layer over that exoskeleton
subclass Ceriantipatharia
part of class Anthozoa
few species
tube anemones
solitary, buried in soft sediments
thorny corals
colonial, attach to form substrates
tough, spiny exoskeleton
hexamerous (6) body plan
subclass Octocorallia
part of class Anthozoa
soft and horny corals (sea fans, sea pens, sea pansies, etc.)
octomerous (8) body plan
eight pinnate tentacles
eight complete septa
all are colonial, with some varied forms
soft & horny coral body plan
gastrovascular cavities communicate through solenia
have coenenchyme
skeleton secreted within the coenenchyme
solenia
tubes found connecting gastrovascular cavities in soft and horny corals
coenenchyme
tissue consisting of mesoglea and solenia, connecting cavities together
found in soft and horny coral
coral reefs
productive, diverse ecosystems
limestone deposited over 1000s of years
living plants and animals limited to the top layer
Coral reefs need _________________ corals for reef formation, but other species may be involved.
hermatypic (hard)
(class Hexacorallia)
coral reef requirements
warmth, light, salinity of undiluted sea water (basically can’t be next to a river mouth or other body of fresh water)
limited to shallow waters between 30 N and 30 S
relationship of zooxanthellae and coral tissues
zooxanthellae live inside the cells of coral, and gives food to coral during the day
coral gives zooxanthellae a place to live, and the zooxanthellae can take in phosphorous and nitrogen excreted by the coral
threats to coral reefs
nutrients from fertilizer and sewage → excessive algae growth
overfishing of herbivorous fishes → excessive algae growth
pollution (pesticides, oil, sediment, etc.)
global warming → warm water causing coral bleaching
higher atmospheric CO2 → acidifies oceans water, making precipitation of CaCO3 by corals more difficult
coral bleaching
caused by global warming
coral expels zooxanthellae, causing the coral to turn white
usually results in the death of the coral
phylum Ctenophora
comb jellies
about 150 species
all marine, mostly preferring warm waters
8 rows of comb-like plates for locomotion
nearly all free-swimming
biradial symmetry
comb jelly body plan
some relatively large (1 m)
no definite head, but do have oral and aboral ends
translucent body with gelatinous layer
most have two extendable tentacles
comb jelly behavior
some feed on cnidarians, incorporating cnidocytes as defensive mechanisms
bioluminescent
comb jelly reproduction
monoecious in most species
cydippid larva somewhat resembles adult
medusae and polyp are both monoecious, not different like other cnidarians
cydippid larva
comb jelly larva
phylogeny of the diploblasts
ctenophores and cnidarians have typical diploblastic characteristics,
but the cells within the gelatinous layer are problematic…
are they really triploblastic organisms?
in short - diploblastic with some added features (from what we know)
Note
Flashcard