The document discusses the phylum Cnidaria, including corals. It notes that corals are colonies of tiny polyps that can reproduce both asexually through budding and sexually by releasing gametes. Corals secrete calcium carbonate skeletons and have complex life cycles involving larval and polyp stages. They are found in tropical oceans where they form important reef ecosystems.
2. Phylum Cnidaria
Includes organisms such as jellyfish, hydra, sea
anemones, and corals.
Are radially symmetric.
Have two basic body forms, Medusae and Polyp.
Have complex life cycles with asexual polyp stages and
sexual medusae stages.
Organisms in phylum Cnidaria also have colonial forms.
3. Characteristics of Corals
Are colonies of tiny polyps which reproduce both asexually
and sexually.
Have a colonial form that allows for sharing of nutrients
Can produce exoskeletons to protect against predators.
Do not form medusa unlike other Cnidarians.
4. Types of Corals
Hard corals (hermatypic): secrete a
limestone exoskeleton around itself as
protection. The exoskeleton or shell of
the coral remains even after the
organism dies.
Soft corals (ahermatypic): are tree-like and
flexible with a skeleton within their
bodies giving them shape but allowing
movement with the waves
5. Life History
Corals first appeared during the Cambrian period, 542 million
years ago
Didn’t build reefs but existed as small solitary organisms
During the Ordovician period 488 million years ago, tabulate
corals become widespread
Corals were very abundant. Like modern corals, these
ancestors built reefs, some of which ended as structures in
sedimentary rocks
A coral reef exoskeleton found in the
Coloured Canyon in Sinai, Egypt.
6. Reproduction
Corals reproduce either asexually by budding or by sexually
releasing gametes (sperm and eggs).
Asexually, budding occurs when a new zygote grows onto
another one and remains attached, separating only when
mature.
Sexually, fertilization can occur within a coral known as
“brooding” or outside of a coral known as “broadcasting”
7. Life Cycle
For brooders, internal fertilization occurs with
gametes within the coral
For broadcasters, fertilization occurs outside of the
coral
The zygote formed then enters the stage as a free-
swimming larva until it matures and becomes a polyp
Once it becomes a polyp it remains rooted and when
matured, releases gametes
8. Consumption
Polyps feed on organisms from microscopic plankton
to small fish.
Polyps release nematocysts from their calices to stun
and kill their prey
9. Habitat and Niche
Corals are found in all oceans from tropical to polar
regions, but coral reefs are formed mostly in tropical
oceans near the equator.
Coral reefs, which are consolidated limestone coral,
provide shelter, spawning, nursery, and feeding area for
marine organisms. They even act as physical barriers to
protect the shores from waves.
