1. A minute needle-like body, siliceous or calcareous, found in invertebrates.
2. A small pointed structure serving as a skeletal element in various marine and freshwater invertebrates; such as, sponges and corals: "Small needlelike structures or spicules include the silicates or calcium carbonate processes supporting the soft tissue of certain invertebrates; especially, sponges."

"Rigidity is given to the sponge by an internal skeleton of shkort rods or spicules that are embedded in the soft tissue."

"The spicules have a wide variety of shapes; such as, stars, needles, crosses, etc."