hexactines

Hexactines are six-rayed siliceous spicules that serve as a principal skeletal element in certain sponges, most notably within the class Hexactinellida, commonly known as glass sponges. They arise from specialized cells that secrete hydrated silica and are often organized into a three-dimensional lattice that provides structural support and forms part of the sponge’s water-filtering framework.

Morphologically, a hexactine typically features six rays radiating from a central point. The rays are usually straight, though they can be curved or fused near their bases, and they vary in length and thickness. Spicules may occur individually or interlock with others to create rigid networks, contributing to the distinctive latticework characteristic of many hexactinellid species.

Hexactine spicules are a diagnostic feature of Hexactinellida and are central to understanding their biology. They are predominantly associated with deep-water habitats, where the silica-based skeletons aid in maintaining structural integrity in flowing currents. Their siliceous composition also aids preservation, resulting in a fossil record that helps paleontologists identify ancient glass sponges.

In addition to hexactines, other spicule types exist, including triactines (three rays), tetractines (four), and pentactines (five). The arrangement and combination of these spicules determine the sponge’s external form and skeletal rigidity. The study of hexactines informs taxonomy, functional morphology, and the evolutionary history of siliceous sponges.