include jellyfish, sea anemones, and corals. Cnidarians
are more complex animals than sponges in that they have
however, these tissues are not organized into organs. Cnidarians
have sac-like bodies with two cell layers separated by
a jelly-like layer (mesoglea). An outer layer of cells
encloses a sac-like body and extends into tentacles surrounding
a mouth at one end of the organism. The tentacles are equipped
with stinging cells (nematocysts). A layer
of cells (endoderm) lines the inner cavity (enteron) that
functions as a digestive cavity. Prey is disabled
by stinging cells (nematocysts) and pulled through the
into the cavity by the tentacles where it is digested.
Waste products exit out the mouth. In corals, the ectoderm
a skeletal material. |
Polyp & Medusa
have a primitive nervous system, muscular system, and a
system. Cnidarians alternate between polyp and medusa life
stages. Polyps are a sessile stage and reproduction is
though asexual budding. The buds become free-floating medusa.
Medusa release sperm
larvae through sexual
reproduction. The larvae eventually attach to a surface and
become a polyp. Jellyfish spend most of their life in the
medusa stage, while coral, hydra, and sea anemones spend
the majority of their life in the polyp stage.
are interested in corals
because they can be important reef builders, provide
clues to water conditions, water depth, climate, and
latitude. The orders of stony corals are of particular importance
to the paleontologist.
corals (order Tabulata) make their first appearance in
the early Ordovician. Tabulate corals were colonial, building
closely packed calcite tubes (corallites) with horizontal
dividers (tabulae). Favositid corallites are packed into
a honeycomb-like structure. Favositid corals were important
reef builders during the Silurian and Devonian. Halysitids
corallites were linked like chains and are often referred
to as chain corals. Halysites was an important
reef building coral during the Silurian. The tabulate coral
Lithostrotionella is the state gem for West Virginia.
corals (order Rugosa) make their first appearance in the
mid-Ordovician. Rugose corals are solitary or colonial.
Corallites of rugose corals are subdivided by vertical
walls (septa). The polyp lived in the cup-shaped top of
the corallite and grew upwards. Solitary rugose corals
are called horn corals. Hexagonaria is a colonial
rugose coral that was an important reef builder during
The Petoskey Stone is the state stone for Michigan and
represents the fossil Hexogonaria percarinata. Tabulate
and Rugose corals met with extinction in the Permian.
(order Scleractinia) may have evolved from a rugose coral.
They make their first appearance in the mid-Triassic and
have been major reef builders up to the present day. To
learn more about the history of reef building
visit the introduction to each time period
in our museum. Agatized coral, representing
a variety of fossil hexacorals from the Eocene,
is the state stone for Florida.
Science Olympiad Fossil Event
The 2011 Science Olympiad Fossil List the class
Scyphozoa (jellyfish), Horn and Colonial coral
and the following Cnidaria genera: Heliophyllum,
Favosites, Hexagonaria, Halysites,