Spicule (noun)

1. A small, needle-like or rod-like structure, especially one found in the skeleton of a sponge.
2. A small, pointed crystal or mineral in a rock or mineral deposit.
3. A small, slender, stiff, bristle-like projection or process on some invertebrate animals, such as certain sponges.

Origin:

Early 19th century: from latin spiculum "a pointed weapon", diminutive of spicus "a spike".

Examples:

1. Spicules provide structural support for the soft body of a sponge.
2. The rock sample was found to contain many small spicules of quartz.
3. Spicules are involved in the defense mechanism of some invertebrates.
4. The spicules of the jellyfish can cause a painful sting to predators and humans.
5. Spicules can be used as a tool to identify different species of sponges.