Hexacorallia

Actiniaria
Scleractinia
Antipatharia
Elkhorn coral Acropora palmata
Photo: James St. John · CC BY 2.0
These branching structures belong to an animal, not a plant. Elkhorn coral grows in shallow Caribbean waters; thickets shelter fish and other creatures.
Rough-skinned Sea Anemone Actinostola callosa
Photo: Mutsu-sango · CC BY-SA 2.5
A seafloor anemone. A study off eastern Canada found a diverse range of small food items in its digestive cavity.
Venus flytrap sea anemone Actinoscyphia aurelia
Photo: Image courtesy of Aquapix and Expedition to the Deep Slope 2007, NOAA-OE · Public domain
A deep-sea anemone observed on sandy and muddy seafloors during a Gulf of Alaska survey.