Anthozoa - Corals
and Anemones
Anemones
Corals
Corals
Anthozoa
• Sea anemones and most corals
• Polyp is dominant and only life
form
– NO MEDUSA
– Presents evolutionary question:
• Were the original cnidarians all
medusae and pelagic, with the
medusa being lost in the
anthozoans and most hydrozoans?
• OR is the polyp and a benthic
existence the primitive state with
the pelagic medusa evolving later?
Anthozoa
• Reproduction
– Asexual
• Longitudinal or transverse fission
• Pedal laceration
– Parts of pedal disk detach and differentiate
into new animal
– Sexual
• Gametes produced by polyp
• Planula larvae produce another polyp
Anthozoa
• Defense and territoriality
– Acrorhagi: special stinging cells used to
defend territory against neighboring
anemones
– Also have capture tentacles
– Sweeper tentacles in corals and some
anemones
acrorhagi
Feeding
tentacles
Sweeper
Tentacles
Sweeper Tentacles
Sweeper Tentacles
Anthozoa
• Feeding
– Carnivorous
• Use nematocysts on tentacles
– Anatomy differs from hydrozoan polyps
• Food enters mouth and then goes through tubular
pharynx before entering the gastrovascular cavity
• Ciliated grooves called siphonoglyphs extend down
the pharynx from the mouth
• Gastrovascular cavity is partitioned by mesenteries
– Infoldings of gastrodermis
– Increases surface area for secreting digestive
enzymes and for nutrient absorption
siphonoglyph
gonads
Anthozoa
• Muscles and movement
– Longitudinal and circular muscles
– Sea water in gastrovascular cavity acts as
hydrostatic skeleton
– Some anemones can “crawl” slowly
– Others are carried around by other
invertebrates
– A few can swim
– Most are sessile
Sea Anemones
• Symbioses
– Zooxanthellae
• “Anemone fish”
– Percula clown fish in aquarium
– These fish have substituted the mushroom
corals for sea anemones
• Anemones are too dangerous in a reef tank
• They will sting other corals and kill many of the
hard and soft corals and polyps
Corals and Coral Reefs
• Types of corals
– Subclass Hexacorallia
• Tentacles in multiples of 6 around mouth
• Solitary forms are the sea anemones
• No special protective covering
• Colonial species are the true or “stony” corals
• Found in warm, clear water
• Largest reefs are found in tropical areas of the
Indo-Pacific
• One of the largest reefs is the Great Barrier Reef
off the northeast coast of Australia
– 2000 km long
– 145 km wide
Sublcass Hexacorallia
(=Zoantharia)
• True anemones: Order Actiniaria
• Mushroom corals: Order
Corallimorpharia
• Zoanthis polyps: Order Zoanthidea
• True corals: Order Scleractinia
Order Actiniaria
Order Corallimorpharia
Order
Corallimorpharia
Order Zoanthidea
Order Zoanthidea
Hexacorallia
• Corals are carnivorous but usually occur where
plankton is not abundant
– Coral polyps have zooxanthellae
• Endosymbiotic dinoflagellates
• Require high amounts of light for photosynthesis
• Therefore silty deposits from land can suffocate a reef
• Zooxanthellae are very sensitive to heat so global
warming is another danger for reefs as sea
temperatures rise
• Zooxanthellae provide photosynthate to coral polyp
and use the metabolic wastes from the animal for its
own growth
Zooxanthellae in Xenia
Hexacorallia
• Formation of coral skeleton
– Rate of reef growth is higher in light than in dark
• Therefore: implies zooxanthellae play a role
– Mechanism?
• Have an effect on availability of bicarbonate ion
which is essential for calcification process
• Contribute some critical component of the organic
matrix that allows for calcium carbonate deposits to
form
• Localized removal of dissolved phosphates (nutrient
for algae) which can inhibit formation of calcium
carbonate
• Generate extra oxygen through photosynthesis which
speeds up rate of coral metabolism
Hexacorallia
• Subclass Octocorallia (Alcyonaria)
– 8 tentacles
– Tentacles are pinnate
– Some have no support other than the thick
mesoglea
• These are the soft corals
– Others have proteinaceous or calcareous
internal skeletons
• These are the gorgonians and pipe corals
Subclass Octocorallia
(AKA Alcyonaria)
• Xenia – pulse corals
• Sea Pens
• Gorgonians – see lab samples
Miscellany
• Corals have medical uses
– Tiny pieces of coral are used for some
bone grafts especially face and jaw
• Tiny pores are rapidly infiltrated by capillaries
and bone forming osteoblasts
– Used to make artificial eyes move!
• Blood vessels and muscles invade coral
fragment and then patient can use their own
muscles to move the fake eyeball
Emerging Patterns in
Evolution
• Skeleton (Hydrostatic
Skeleton)
• Contractile tissues/locomotion
• Nervous system
• Gut
• Gastrulation
• Radial Symmetry
• Two embryonic tissues
3 Germ Layers
Ectoderm forms epidermis and central
nervous system
Endoderm forms the lining of gut and
associated organs
– It is argued that the early embryo may
have more than just these two
• Mesoderm forms all the stuff in between
gut tube and skin, such as, muscle,
bone, connective tissue, blood, etc.
The Cnidaria are good
candidates as the crossroad
of metazoan evolution.
• Sponges are the living proof of how a protozoan
colony can become a metazoan, without
reaching a level of organisation involving a
recognisable body form, real tissues and a
nervous system.
• The Cnidaria are the first animals with tissue
layers, muscles, and sense organs.
– They lie at the base of the tree because they are
diploblastic, have radial symmetry, and do not have a
real brain.
Cnidaria and Metazoan
Evolution
• They are present in the fossil record since the
Precambrian, when animals similar to modern
forms were absent.
• The strange creatures of the Precambrian,
besides cnidarians, apparently did not pose
the foundations of future metazoan
organisations, whereas these are evident in
the Cnidaria.
•
Boero, Bouillon, and Piraino. 2005. The role of Cnidaria in evolution and
ecology. It. J. Zool. 72:65-71
Cnidaria and Metazoan
Evolution
• From an ecological point of view, the cnidarians
probably play roles that are much more
important than usually perceived.
– Both Cnidaria and Ctenophora feed on the eggs and
larvae of most benthic, planktonic and nektonic
organisms
• Might be keystone species
• Maintain high biodiversity, by feeding on potentially
highly competitive, resource monopolizing species.
• During periodic outbreaks of their populations
– serious effects on fisheries yields and other problems
Myxozoa
Myxozoa
Phylogenomic Analyses Firmly
Place Myxozoa in Cnidaria
• All Myxozoa possess polar capsules that are
similar to nematocysts of Cnidaria in
ultrastructure and ontogeny and are used for
host attachment
• Presence of a minicollagen gene
– Minicollagens are cnidarian-specific
constituents of nematocyst walls.
• Phylogenetic analyses placed Myxozoa as
sister group of Medusozoa within Cnidaria
Maximilian P. Nesnidal, Martin Helmkampf, Iris Bruchhaus, Mansour El-Matbouli, B. Hausdorf.
Agent of Whirling Disease Meets Orphan Worm: Phylogenomic Analyses Firmly Place Myxozoa in Cnidaria. PLOS
One Published: January 30, 2013 DOI: 10.1371/journal.pone.0054576
Phylogenetic tree based on a
dataset including 128 genes
Myxozoa
• Myxozoa ("slime animals") are so unusual
that they were long believed to be protozoa entirely the wrong kingdom - until molecular
analysis proved a direct relationship with the
jellyfish, corals and other cnidaria. It's an
understandable mistake, considering these
"jellies" can consist of as little as a single cell
and live as parasites in other animals; jellies
who evolved into germs.
Myxozoa
• Most slime animals pass through two different
hosts in their life cycle.
Actinospores
Myxospores
Myxozoa
– Actinospores
• Work the same way but attack larger hosts;
• Most species attack fish, but a few are known to favor
amphibians or aquatic reptiles, and at least one
invades shrews.
• In larger hosts, the plasmodium can become visible to
the naked eye, a concentration of thick, clear slime
growing and feeding in the host's tissues.
• Some attack the muscles, some attack the heart, some
even dwell within the spinal column, causing severe
skeletal deformities and neurological damage.
• Thousands of spores are released once the host dies,
with some species killing more than 90% of infected
fish.
The newly-discovered parasite which creates
mysterious holes in the Greenland halibut was
discovered by Greenlandic fishermen, and
researchers have yet to figure out how prevalent
this parasite is. (April 7, 2012)