hard
Brain coral is a type of coral that looks somewhat like a brain. It is a hard coral.
Lettuce Coral, brain coral, elkhorn coral, staghorn coral, star coral, fire coral, sea pen, scroll coral, golfball coral, mustard hill coral, rose coral, sea whips, maze coral, rigid cactus coral, orange cup coral.... and many more.
Whitewood is considered a soft type of wood.
Soft
http://www.wonder-okinawa.jp/006/english/hyakka/doubutu/sangorui/index.html Use that link to figure out which type of coral you need! If you just want the general name, though, use Cnidarians
Purpleheart wood is a hard type of wood.
The organism you are referring to is likely a type of crab, specifically a species with a soft body protected by two hard bluish-black shells. This type of crab typically consumes a diet consisting of both plants and animals, including plankton.
Black coral is a type of species belonging to the order Antipatharia, characterized by their black or dark-colored appearance. These corals are found in deep-sea environments and are known for their long, branching structures. Black coral is often harvested for use in jewelry and decorative items, although there are concerns about the sustainability of this practice due to overharvesting.
The rarest type of coral is the Elkhorn coral.
Plastic can be soft or hard, depending on its composition and processing. Some plastics are engineered to be flexible and soft, while others are rigid and hard.
Two types of coral that exhibit branching are fan coal and finger coral. Fan Coral: comes in many colors, has soft finger- like branching that is rounded at the ends. Finger Coral: distictively gray growing in thick colonies.
Zooxanthellae are a type of dinoflagellate that live in the "skin" of hard coral. It's a symbiotic relationship where the zooxanthellae are photosynthetic and produce nutrients for the host coral.