EarthLabs > Corals > Lab 2: Anatomy of Coral > 2A: Coral's
Cousin Hydra  Anatomy of Coral  Part A: Coral's Cousin Hydra
Hydra viridis at 100x magnification. Image courtesy of
Wikipedia.  Although it is extremely difficult to obtain and
study live coral polyps in the classroom, hydras, freshwater
cousins of corals, are readily available. Luckily, there are
many similarities between these two animals, so studying hydras
can help us understand more about corals. Hydras belong to the
phylum Cnidariacnidaria: an animal phylum characterized by
stinging cells called nematocysts, which also contains stony
(hard) corals, anemones, sea fans, sea pens, hydras, and
jellyfish.("nī-DARE-ee-ah"), which comes from the Greek word for
"stinging needle". These coral relatives are found in most
unpolluted freshwater ponds, lakes and streams in temperate and
tropical regions. They are typically only a few millimeters long
and are therefore best studied under a microscope.    1. Using a
medicine dropper, carefully place a live hy