Sponges are usually found on the beach after their soft parts have decomposed, leaving only the skeleton which is usually made of a brown horny material. This contrasts with the brilliant colours that characterise many of the living sponges. When they die, the once-living parts rot away, leaving the skeleton.
Though they live attached to the substratum as plants do, they are actually simple animals. Sponges are a collection of cells that cooperate to pump water through the whole animal so that they can filter out tiny living things for food and extract oxygen from the water. They have a system of tubes for this purpose, but don’t have any organs like heart, nerves, muscles or stomach. Scientists have pushed live sponges through a sieve to separate the cells, and amazingly they re-assemble themselves into a complete sponge again!
This sponge skeleton is composed of a horny material. Sponges are many-celled animals but lack distinct organs and tissues. They are sedentary filter feeders living mostly in deep water or sea caves and have few predators. There are free-standing sponges and encrusting sponges. Living sponges are often brilliantly coloured.
This beautiful photo of a sponge by John Terni won our 2007 Flotsam photo competition.
These two sponges are relatively fresh and are still showing their colour.
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