From the Super Mario Wiki
A Preying Mantas is a Jellyfish found underwater in Super Mario World 2: Yoshi's Island and its remake Yoshi's Island: Super Mario Advance 3. They move up and down in a small area, and therefore do not pose much of a threat to the Yoshis. The Yoshis can simply defeat them by shooting a torpedo at them in their Yoshi Submarine forms.
It is possible that the Preying Mantases are related to the salt-water dwelling Jellyfish from Yoshi's Story.
Preying Mantases also appear in Super Mario Galaxy in the Deep Dark Galaxy and the Bigmouth Galaxy. They are found in groups of four swimming around, hurting Mario if he touches them. They can be defeated with a Spin or a Koopa Shell and give one Coin when defeated. They also appear in Super Mario Galaxy 2 in the Cosmic Cove Galaxy.
They appear again as enemies in Yoshi's New Island.
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