Hexactinellids

Hexactinellids, commonly known as glass sponges, are a class of marine sponges (phylum Porifera) distinguished by their skeletal framework of silica spicules with six rays, called hexactines, that interlock to form a three‑dimensional lattice. They are one of the earliest-diverging sponge lineages and are typically placed in Hexactinellida.

Most hexactinellids have a vase- or cup-shaped body, though forms range from slender to massive. Their tissues are syncytial, meaning many nuclei share a common cytoplasm, and their functional canal system lines a network of interconnected chambers through which water flows. The skeleton is transparent or glassy, often forming a delicate but strong lattice that supports the animal.

Habitat and distribution: Glass sponges occur mainly in deep marine environments worldwide, from polar to tropical regions, at depths commonly ranging from a few hundred to several thousand meters. They prefer hard substrates and are frequently found attached to rocks, coral reefs, or other structures; some form dense sponge reefs.

Reproduction and life history: Hexactinellids reproduce sexually, releasing sperm and eggs into the water column, with development leading to free-swimming larvae. Many species can also reproduce asexually by budding or fragmentation, especially after disturbance.

Ecology and fossil record: As filter feeders, hexactinellids play a role in deep-sea nutrient cycles and often contribute habitat complexity for other organisms. They have a long fossil record dating back to the early Paleozoic, with durable silica spicules preserved as fossils, providing important clues about early sponge evolution and ancient marine environments.