Spicula of sponge, Atlantic mud.
"The Student's Elements of Geology"
Sir Charles Lyell
Leaves are porous, and admit air and light more or less freely into their substance; they are generally smooth and even glazed on one surface; they are usually covered on one or both sides with Spicula, and they very commonly present one or more acuminated points in their outline-all circumstances which tend to augment their power of emitting heat by reflection or radiation.
"The Earth as Modified by Human Action"
George P. Marsh
He was put into cold Water, and immediately the icy Spicula were discharged from all Parts of his Body, so that he seemed covered with an icy Crust.
"An Account of the Diseases which were most frequent in the British military hospitals in Germany"
Donald Monro