BY255L - Invertebrate Zoology Lab > Phylum Cnidaria (pronounce)

Phylum Cnidaria Contents

Notes
Class Hydrozoa (pronounce)
Class Scyphozoa (pronounce)
Class Anthozoa (pronounce)
Links

Cnidaria notes

Microscope reminder - no stop on 40x. Use the fine focus only. Starting Lab 2 broken slides cost $10. Bring rubber gloves for dissection Lab 3.

Be able to answer questions 1, 2, 4, 5 (polyp only) on pages 78 and 79. These may be on the first test.

Cnidaria general characteristics

Tissue level of organization, no true organs
Tissue layers - epidermis, mesoglea (gelatinous/fibrous may have wandering amebocytes), gastro/endodermis
Characteristic is the cnidocyte (nettle cell which contains a capsule, the nematocyst, which can eject a stinging harpoon-like structure.
Usually has alternation of generations between polyp and medusa. Either form may be dominant.

Jellyfish article (handout) - Jellyfish blooms possible causes

natural cycle
global warming
introduced species from ballast water
oil platforms

Class Hydrozoa (pronounce)

Order Hydroida

Polyp example - Hydra (no medusa stage)

Note that the gastrovascular cavity is filled with water so it acts as a hydrostatic skeleton.
Gastrovascular cavity extends into arms, but digestive function is in upper body.
Nematocysts batteries are mainly on the tentacles. (note military analogy).
Dioecious (separate sexes), but they cannot be reliably differentiated by appearance. Also reproduces by budding. (In living Hydra look for buds. The green color is from a symbiotic alga, zoochlorella.).
Hydra - budding reproduction
Hydra - spermary or ovary

Colonial polyps

Example - Pennaria

Branching polyp structure
Reproductive polyp, gonophore, connects directly to feeding polyp (hypostome and mouth)
Chitinous perisarc
Coenosarc - three tissue layers and gastrovascular cavity
Pennaria

Obelia

Separate gonozooid and gastrozooid.
Perisarc covers these with a cup-like structure.
This type of perisarc is termed thecate.
BY255L Obelia page

Hydractinia

Hydractinia

Example with dominant medusa - Gonionemus

Gonionemus page

Craspedacusta

Freshwater jellyfish - two articles (handout)
Blooms of freshwater jellyfish on rare instances occur in Alabama ponds and have also occurred in Lay Lake and Logan Martin Lake.
Indiana University of Pennsylvania (sic) web article

Order Chondrophora

Velella - By-the-wind-sailor

Velella page

Order Siphonophora

Colonial free-living polyps

Physalia - Portuguese man-of-war

Cormidium includes feeding and reproductive and structures for movement (there are many cormidia) and tentacles with batteries of nematocysts
Chitinous sail can be raised or lowered. Chitinous secretion also supports the pneumatophore which is filled with nitrogen and carbon dioxide released at the gas gland.
Physalia - Portuguese man of war

Order Stylasterina

Millepora

Called stinging coral or fire coral
Resembles a true coral, but it has specialized feeding and reproductive polyps connected by epithelium. In true corals all polyps are buds from a single individual.
It is a calcareous milleporinid hydrocoral.
Millepora

Class Scyphozoa (pronounce)

True jellyfish
No velum
Cellular mesoglea

Order Semaeostomae

Aurelia

Most common jellyfish in America and Europe
exumbrella and subumbrella
oral arm of manubrium and mouth, gonads, tentacles, statocyst of rhopalium, ocellus
Life cycle - Explain whole cycle, but students identify strobila and ephyra only
Aurelia
Aurelia page

ephyra

Order Rhizostomae

Cassiopeia

Lives up-side-down
Contracts to draw in prey and oxygen and remove wastes
Benthic (lives mostly on the sea bottom)
Frilly oral arms with many tiny mouths
mucus and nematocysts trap plankton
Symbiotic zooxanthellae live in the mesoglea.
There are 3 Cassiopeia in the classroom aquarium.
Cassiopeia - Upside-down jellyfish

Stomolophus meleagris

Stomolophus meleagris - Cannon ball jellyfish

Class Anthozoa (pronounce)
Flower animals: sea anemones, sea fans, and corals

This is the largest class of Cnidarians, containing over 6,000 species.
Sessile polyps
No medusa (i.e. no jellyfish stage)
Flattened oral disk instead of hypostome of Hydrozoa
Radial symmetry
There are both hermatypic (these build reefs) and ahermatypic (these do not build reefs) species. Most Anthozoa are hermatypic.
True corals have radial symmetry in multiples of six.
Tropical hermatypic corals have symbiotic zooxanthellae which give the polyps a golden-brown color. Zooxanthellae are photosynthetic dinoflagellates. Corals offer protection and zooxanthellae fix carbon that is transferred to the polyps for energy.
Anthozoans can be either colonial or solitary organisms.
There are living anemones from St. Joseph's Bay, Florida in the classroom aquarium.

Subclass Zoantharia (Hexacorallia) - Stony or true corals

Characteristics of stony or true corals

Hexameric (six-fold) symmetry
Polyps are identical.
Gastrovascular cavities are connected on top of skeleton
They have a limestone (calcium carbonate - CaCO₃) skeleton.
Subclass includes both solitary and colonial forms.

Metridium dissection

peristome and mouth
tentacles
pedal disk
oral disk
pharynx
mesenteries
gonads
acontia

Metridium

More Hexacorals

Subclass Alcyonaria (Octocorallia)

Characteristics of Alcyonaria

Each polyp has eight pennate tentacles.
Gastrovascular cavities are connected by solenia
Solenia are in a thickened mesoglea called coenenchyme.
The skeleton is proteinaceous (gorgonin).

Alcyonaria specimens

Gorgonia (A is a living gorgonian in the class aquarium. The tissue layers are gone from the tips of some parts and you can see the tough protein secretion, gorgonin, that gives gorgonians their shape.)
Sea fan
Sea pen
Sea whip
Organ pipe coral

Fossil Cnidarians

Horn coral fossil (Order Rugosa)