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Isolated spicular bodies of an extinct silicious sponge. (<em>Epistomella clivosa</em>).

Epistomella Clivosa

Isolated spicular bodies of an extinct silicious sponge. (Epistomella clivosa).

A modern sponge with silicious skeletal structure, and basal glass fibers for fixation (<em>Holtenia carpenteri</em>).

Holtenia Carpenteri

A modern sponge with silicious skeletal structure, and basal glass fibers for fixation (Holtenia…

Part of the skeletal structure of a lithisdid silicious sponge.

Jereiea Polystoma

Part of the skeletal structure of a lithisdid silicious sponge.

This illustration shows Quartz or Silica. Quarts is the most abundant mineral in the Earth's continental crust.

Quartz

This illustration shows Quartz or Silica. Quarts is the most abundant mineral in the Earth's continental…

A modern Radiolarian, showing the skeletal structure of silica and the extended fleshy threads or pseudopodia.

Radiolarian

A modern Radiolarian, showing the skeletal structure of silica and the extended fleshy threads or pseudopodia.

<em>Heliosphaera echinoides</em>, a modern Radiolarian.

Radiolarian

Heliosphaera echinoides, a modern Radiolarian.

A Cretaceous sponge with silicious skeleton retaining its form. (<em>Ventriculites simplex</em>).

A Cretaceous Sponge

A Cretaceous sponge with silicious skeleton retaining its form. (Ventriculites simplex).