TentaclesA ring of soft arms round the mouth. The polyp uses them to catch small animals for food, to defend itself and to clear away debris.
MouthThe only opening of the body. Food goes in through it, and waste comes out the same way.
StomachA hollow that fills most of the body. It opens only at the mouth. Thin filaments inside it digest the food. It is also called the gastrovascular cavity.
Stinging cells (nematocysts)Tiny stinging cells in the outer tissue of the tentacles. Each holds a coiled thread that shoots out when prey touches it.
ZooxanthellaeTiny cells that live inside the tissues of most reef-building corals. They make food from sunlight, share it with the polyp and give the coral its color.
The cup and the skeleton 5
CoenosarcA thin band of living tissue that lies over the skeleton. It joins each polyp to its neighbors. It makes the coral one colony.
Calyx (cup)The cup of skeleton that a polyp builds and sits in. When it is disturbed, the polyp pulls itself down into the cup. This one is drawn empty.
Wall of the cupThe side of the cup. It stands round the lower part of the polyp like the wall of a well.
Basal plateThe floor of the cup. From time to time the polyp lifts itself and lays a new floor above the old one, and so the coral grows upward.
SkeletonThe hard part of a stony coral, made of calcium carbonate. The polyps lay it down under themselves, and over many years it builds a reef.
How this list was compiled: Every name checked on 2026-09-30 in two sources. NOAA National Ocean Service, Corals tutorial (What are corals?, Polyps up close, What is zooxanthellae?, How do stony corals grow?), https://oceanservice.noaa.gov/education/tutorial_corals/coral01_intro.html. Wikipedia, Coral, Corallite, Polyp, Zooxanthellae and Cnidocyte, https://en.wikipedia.org/wiki/Coral. Animal Diversity Web, University of Michigan Museum of Zoology, Anthozoa and Cnidaria, https://animaldiversity.org/accounts/Anthozoa/. Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work
How it works
On this coral polyp diagram to label, write a name on each numbered line: 1 to 5 are on the polyp, 6 to 10 on the skeleton and the tissue over it.
Read the full guide
Coral polyp worksheet word bank
Ten names, in alphabetical order: basal plate, calyx (cup), coenosarc, mouth, skeleton, stinging cells (nematocysts), stomach, tentacles, wall of the cup, zooxanthellae.
The numbers that get swapped
Four lines end on the hard skeleton: 7 inside the empty cup at the right, 8 on the upright wall beside the cut polyp, 9 on the flat floor under it, 10 on the large block under everything. On the arms, 1 ends on a whole tentacle and 4 on the dots along a bent one. Inside the body, 3 ends in the open space and 5 on a small ring in the wall. 6 is the thin band that joins the cut polyp to the smaller one at the left, which has no number.
When marking, gastrovascular cavity is right on line 3, cnidocytes on line 4, corallite on line 7 and theca on line 8.
The stacked lines under number 9 are older floors, left below as the polyp grew upward. They have no number.
Questions and answers
How big is a coral polyp?
Small. The polyps of hard, or stony, corals average 1 to 3 millimeters across. The drawing on the worksheet is much enlarged and is not to scale.
How many tentacles does a coral polyp have?
It depends on the kind of coral. A soft coral polyp has eight, each with small side branches. A stony coral polyp, the kind on this sheet, is built on a plan of six, and its tentacles are plain and taper to a point.
What is coral bleaching?
When corals are stressed, the polyps push out their zooxanthellae, number 5 on the sheet, and the colony turns stark white. If it goes too long without the food they supply, the coral can starve.
Is a coral polyp a cnidarian?
Yes. Corals are anthozoans, in the phylum Cnidaria with the sea anemones, sea fans and sea pens. Cnidarians are the stinging animals, and the stinging cells are number 4 on the sheet.
Is there a coral polyp diagram to label test?
The printed worksheet works as one: it carries the numbered drawing and ten blank lines, and no word list. The answer key prints the same drawing over the ten names in order, tentacles first and skeleton last.