Anatomy of Coral

Part B: Coral Polyps

1. Now that you are familiar with the basic structure of hydra polyps, let's take a look at how closely they actually compare to coral polyps.
   
   
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   Show me the details of coral polyp anatomy
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   Image source: NOAA. Click image to enlarge.

   From NOAA: Polyps are made of an outer cell layer called epidermis ("ep-ih-DERM-iss") and an inner cell layer called gastrodermis ("gas-tro-DERM-iss"), with a jelly-like substance called mesoglea ("mez-oh-GLEE-uh") in between. Each polyp makes its own cup-shaped skeleton called a calyx ("KAY-lix)" from limestone (calcium carbonate). The base of the calyx is called the basal plate, and the outer walls of the calyx are called the theca ("THEE-kuh"). Vertical partitions called septa (plural form of septum) extend part-way into the cup from the inner surface of the theca. The outer surface of the theca is covered by the soft tissues of the coral. Polyps have a mouth surrounded by a ring of arms called tentacles. The tentacles have stinging cells called nematocysts ("nee-MAT-oh-sists") that polyps use to capture food. Most corals are carnivorous, and feed on small floating animals or even fish. Many corals also feed by collecting very small bits of floating material on strings of mucous, which they pull into their mouths. Food is digested by digestive filaments in the stomach. Waste is expelled through the mouth. Most reef-building corals have very small polyps, about one to three millimeters in diameter. Individual polyps in a coral colony are connected by a thin band of living tissue called a coenosarc ("SEE-no-sark").
   
   
   
   
   
   

   Checking In

   • What physical characteristics does the hydra share with a coral polyp? Identify any common body parts.
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     Hydras and coral polyps both have: symmetric tube-like structure, tentacles, nematocysts, a single mouth/waste opening, a gastrovascular cavity (stomach), epidermis, mesoglea, gastrodermis, and a basal disc/plate for attaching to hard surfaces.
   • What are the key differences between the anatomy of coral polyps and hydra.
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     The calyx, theca, and coenosarc, which are not found in hydra, are responsible for connect individual polyps and creating skeletal reef-building material.
2. Build a simple physical model of a single coral polyp using the following everyday materials:
   • One 3" x 3" sticky note (i.e. Post-It© notes)
   • pencil or pen
   • Transparent tape
   • Scissors
   • 1 egg carton cup (1/12 of an egg carton)
3. Working with a partner or in a small group, come up with a creative way to model a full day in the life of a polyp. Demonstrate the details of how it gets nutrients in the daytime and in the nighttime. Use available craft materials to modify, reinvent, or extend your coral polyp model. Include as many details as you can to fully describe each process.
4. Keep your model in a safe place so you can use it again later in the unit.

Optional Extension

Learn more about Coral Polyp Anatomy with the interactive at the bottom of this link.