Sea Pickle

Sea pickles are light-emitting colonies of small stationary animals found underwater.

Obtaining
A sea pickle colony will break instantly and drop itself as an item if broken using anything, or if the block below it breaks, dropping as many pickles as there are on the block.

Natural generation
Sea pickle colonies generate on the bottom of warm oceans. They can also be found on top of coral blocks.

Usage
Sea pickles can be placed on top of most solid blocks, as well as non-solid blocks, up to four per block, similarly to turtle eggs. Only the first sea pickle can be placed while aiming against an adjacent block; placing additional pickles within the space while aiming at such a block will completely refuse to place the pickle, a completely intentional feature. They produce light when underwater, and each additional pickle adds 3 light levels. When they produce light, there is a pale green glow at the end of the pickle.

Bone meal can be on sea pickles if they are underwater, and planted on living coral blocks. This will increase their number on that block, and spread to empty areas underwater above other living coral blocks. They can spread to the original sea pickle's level or one level below, out to a horizontal taxicab distance of 2. Bone meal can be used on sea pickles planted on other blocks, or outside of water, but nothing will happen and the bone meal will still be consumed.

Trivia

 * They appear to be based on Pyrosomes, real-life tunicates with blue-green bioluminescence. They are also commonly called sea pickles, which is where the name likely came from.
 * If played on "moody" brightness setting (or low brightness percentage such as 30%), Sea Pickles at the bottom of the ocean will give off red-orange light.
 * Sea Pickles have a stem when placed in water while when placed on land, they have no stem