Sponges are generally protected from predators by the presence of calcium and silica crystals. These crystalline structures are called

A) amoebocytes.
B) osculum.
C) choanocytes.
D) spicules.
E) spongin.

Calcium Crystals

Mineral deposits found in various tissues of the body, often in bones and teeth, contributing to their hardness.

Silica Crystals

Rigid, crystalline structures made of silicon dioxide (SiO2), found in nature as quartz and used industrially and scientifically for various applications.

Spicules

Small, spike-shaped structures found in certain animals like sponges, serving as a skeletal element.