Sponges are an animal phylum consisting of around 5000-8000 known species (4,6)—and perhaps as many as 15,000 to 24,000 including those not yet described (2,6)—that live all around the world (5). They can be found in both marine and freshwater environments at any depth, though especially in coral reefs, mangrove habitats, and seagrass ecosystems (2). These creatures come in a huge array of colors and sizes (2,5,6)—measuring anywhere from 0.5 inches (1.3 cm) to 70 inches (178 cm) (6)—and can have bodies with shapes that resemble trees, cups, tubes, fans, balls, shapeless blobs, and more (2). Despite this great diversity in appearance, all sponges share a physical feature unique among animals: they have cells that can move freely and change forms, allowing the sponges to continuously reshape their bodies(1,2). Also, nearly all sponges have a body-plan that enables a simple lifestyle known as filter-feeding (2,6). (The exceptions are a group of sponges which are carnivorous, feeding on small crustaceans (5,7)). A filter-feeding sponge pumps water through pores in the outer layer of cells that surrounds its body and draws small food particles such as bacteria out of the water that comes in (1,2,4,5,6). The water keeps flowing in the same direction through a network of canals until it exits the sponge via one or more holes in the sponge’s body (1,2). Although early animal lineage patterns are still unresolved (2), the very simplistic animals of the sponge phylum may in fact have been the first multicellular animals to appear on Earth (2,6), probably descending from organisms similar to modern choanoflagellates 635-750 million years ago (2,3).
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