Exercise 3 - The Radiate Animals: Cnidaria

• Cnidarians include some of nature’s most beautiful and dangerous aquatic creatures such as jellyfishes, hydroids, anemones and corals.
• The Cnidarians are diploblastic in that they have only two well-coordinated tissue layers:

  1. an ectoderm, which forms the epidermis and
  2. an endoderm, which forms the gastrodermis that lines a simple sac-like gut
• Cnidarians do not have true muscle tissues and their nervous system is actually a diffuse nerve net.
• Despite their relatively simple organization, more than 9,000 species of cnidarians exist today. The phylum takes its name from unique stinging cells called cnidocytes which make these animals very effective predators of animals even more organized and faster than them.
• All cnidarian forms fit into one of two body types: a polyp or a medusa.
• Some colonial members  even  display  polymorphism.
• What are the four classification of Cnidaria?

  Class Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa.
• Class Hydozoa – Cnidocytes in epidermis only, gametes epidermal, velum usually present in medusa, polyps without septa, marine with some freshwater representatives.
• Class Scyphozoa – Medusa dominant in life history, gametes endodermal, scalloped bell margin without velum, cnidocytes present in gastrodermis and epidermis, marine, gametes endodermal.
• Class Cubozoa – Medusa dominant life stage, cuboidal bell with velarium with tentacles that hang from each corner of the bell, marine.
• Class Anthozoa – Medusa stage absent, solitary or colonial polyps with a gastrovascular cavity divided by septa, marine.
• What are the samples under Class Hydrozoa?

  Hydra, Obelia, and Aglaophenia (sea fern)
• Hydra - This small, solitary freshwater cnidarian can be found attached to parts of aquatic plants such as Hydrilla and lily pads. The mouth is located at a colonial elevation called the hypostome and is encircled by 6 to 10 tentacles.
• Obelia - This small colonial cnidarian is found in the marine environment.  It also displays two types of polyps and is therefore polymorphic. The medusa of Obelia lacks a velum that is normally present in other members of its class.
• Aglaophenia (sea fern) - This colonial animal superficially resembles a fern although the stings of its polyps are quite potent and irritating to divers. It is common in coral reefs in the Philippines.
• What are the samples under Class Scyphozoa?

  Aurelia (moon jellyfish) and Cassiopea (upside-down jellyfish)
• Aurelia (moon jellyfish) - The moon jellyfish feeds on small marine planktonic animals and a cosmopolitan on distribution.
• On the underside (subumbrella) of the jellyfish is a projection that forms four frilly oral arms that are used for prey capture.
• Cassiopea (upside-down jellyfish) -This jellyfish is found in seagrass and coral reefs with its mouth oriented towards the surface. It actually has symbiotic algae in its arms hence its orientation to maximize exposure to sunlight.
• Class Cubozoa

  Box Jellyfish - The box jellyfishes are considered among the most venomous marine animals. These tentacles hang down from a flattened blade called pedalium.
• What are the samples under Class Anthozoa?

  Sea anemone

  Acropora (staghorn coral)

  Fungia (mushroom coral)

  Goniopora (daisy coral)

  Tubiopora (organ pipe coral)

  Pteroeides (sea pen)

  Xenia (hand coral)

  Gorgonian (sea fan)
• Sea anemone - is a solitary cnidarian that lives in tidepools, sandy areas, and coral reefs.
• Acropora (staghorn coral) - This is a genus of stony coral (scleractinian) that is common in Indo-Pacific coral reefs. It is one of the fastest growing corals and serves as a habitat for many marine invertebrates and fishes.
• Live stony corals are often colourful because of symbiotic algae called zooxanthellae living in the tissue of the polyps.
• Acropora is easily distinguished from other genera of branching scleractinians by the presence of an axial corallite, which is a single corallite found at the tip of each branch of the corallum.
• The other corallites surrounding the branches are called radial corallites.
• Fungia (mushroom coral) - Fungia is an example of a free-living (i.e., unattached to the  substrate),  solitary  scleratinian.  Its skeleton is basically a large single corallite that is either circular or elongated.
• Many solid partitions called sclerosepta with serrated margins are found radiating from the edge of the corallite.
• Goniopora (daisy coral) - It is a massive (hemi-spherical) scleractinian often traded in the aquarium industry. Live Goniopora colonies have long-stemmed polyps that are crowned with 24 tentacles.
• Tubiopora (organ pipe coral) - The organ pipe coral is found in coral reefs and is used as material for ornaments and jewelry.
• Pteroeides (sea pen) - The sea pen is a colonial cnidarian commonly found in sandy marine areas. It has a single large polyp that forms the central axis wherein the base is used to anchor the colony into the seafloor.
• Xenia (hand coral) - This is one genus of soft coral (coral that produce spicules instead of a solid skeleton) consisting of many polyps with 8 pinnate tentacles. One of the popular corals traded in the aquarium industry.
• Gorgonian (sea fan) -The sea fan is normally found on deep reef slopes where currents are strong.
• Gorgonian (sea fan) -  Its branching fan-like skeleton is actually composed of a horny material called gorgonin. Live sea fans have numerous tiny polyps with 8 pinnate tentacles.