As this happens, cells called sclerocytes start making long, spiny spicules. This species can reproduce without sex, by budding off a little packet of cells called a gemmule, which then develops into another sponge. The team studied a sponge called Ephydatia fluviatilis, which can be found growing on freshwater rocks and extending green, finger-like projections into the water. Now, Noriko Funayama’s group at Kyoto University has discovered how sponges build this skeleton, and his findings reiterate an important lesson about these creatures: they may look simple, but looks can be deceiving. The spicules act like an internal skeleton, giving the sponges shape and support. They come in a beautiful range of shapes: spines, grappling hooks, jacks, pollen-like spheres, and coralline branches. In fact, they can be sturdy and tough, because their jelly-like middle is often full of microscopic pieces of hard minerals, known as spicules. With such simple body plans, you might expect sponges to be flaccid and soft. And their bodies comprise just two layers of cells, sandwiching a jelly-like filling. They have no symmetry-no left or right, no front or back. They have no nervous, digestive, or circulatory systems. Sponges are animals that do incredible impressions of inanimate objects.
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