Linked from
The 7 pages that link to Spicule, each with the reason it gives.
SpongeBroader topic: Spicules support the body and can deter predators.
ChromosphereBroader topic: These jets carry mass and energy upward from the chromosphere.
AplacophoraBroader topic: Calcareous spicules cover aplacophoran bodies in place of a shell.
Calcareous spongeBroader topic: Calcium carbonate spicules form the defining skeleton of Calcarea.
HexactinellidNarrower topic: Hexactinellid skeletons are assembled from specialized spicules.