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Liver Sponge / Twilight Zone Expedition Team 2007, NOAA-OE

Liver Sponge, Plakortis sp.

Courtesy of the Twilight Zone Expedition Team 2007, NOAA-OE

When you look at a sponge, the category "animal" might not necessarily come to mind, but sponges are animals. There are over 5,000 species of sponges (Source: EOL), and most live in the marine environment, although there are freshwater sponges.

Sponges are classified in the phylum Porifera, a word that comes from the Latin words porus (pore) and ferre (bear), meaning "pore-bearer". This is a reference to the numerous holes (pores) on the sponge's surface. It is through these pores that the sponge draws in water from which it feeds.


Sponges come in a wide variety of colors, shapes and sizes. Some, like the liver sponge pictuerd here, look like a low-lying crust on a rock, while others can be taller than humans. Some sponges are in the form of encrustations or masses, some are branched, and some look like tall vases (e.g., see vase sponge image by clicking on the "more images" link above).

Sponges are relatively simple multi-celled animals. Sponges do not have tissues or organs like some animals do, but they have specialized cells to perform necessary functions. These cells each have a job - some are in charge of digestion, some reproduction, some bringing in water so the sponge can filter feed, and some for getting rid of wastes.

The skeleton, or structure of sponges is formed by spicules, which are made of silica (a glass-like material) or calcareous (calcium or calcium carbonate) materials, and spongin, a protein that supports the spicules. Sponge species may be most readily identified by examining their spicules under a microscope.

Sponges do not have a nervous system, so they don't move when touched.


Habitat and Distribution:

Sponges are found on the ocean floor or attached to substrates such as rocks, coral, shells and marine organisms.

Sponges range in habitat from shallow intertidal areas and coral reefs to the deep sea.


Most sponges feed on bacteria and organic matter by drawing water in through pores called ostia (singular: ostium), which are openings through which water comes into the body. Lining the channels in these pores are collar cells. The collars of these cells surround a hair-like structure called a flagellum. The flagella beat to create water currents. Most sponges feed on small organisms that come in with the water. There are also, a few species of carnivorous sponges that feed by using their spicules to capture prey such as small crustaceans.

Water and wastes are circulated out of the body by pores called oscula (singular: osculum).


Sponges reproduce both sexually and asexually. Sexual reproduction occurs by production of egg and sperm - in some species, this is from the same individual, in others, separate individuals produce eggs and sperm. Fertilization occurs when the gametes are brought into the sponge by currents of water. A larva is formed, and it settles on a substrate where it becomes attached for the rest of its life.

Asexual reproduction occurs by budding (when a part is broken off or one of its branch tips is constricted, and this small piece grows into a new sponge) or by producing packets of cells called gemmules.

Sponge Predators:

In general, sponges aren't very tasty to most other marine animals. They can contain toxins and their spicule structure probably doesn't make them very comfortable to digest. Two organisms that eat sponges, though, are hawksbill sea turtles and nudibranchs. Some nudibranchs will even absorb a sponge's toxin while it eats it, and use the toxin in its own defense.

Sponges and Humans:

Humans have long used sponges for bathing, cleaning, crafting and painting. Because of this, sponge harvesting industries developed in some areas, including Tarpon Springs and Key West, Florida.

Examples of Sponges:

There are thousands of sponge species, so it's difficult to list them all here, but here are a few:


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