A Guide to Sea Sponges

Spawning Sea Sponge, Osprey Reef, Coral Sea, Australia
Spawning Sea Sponge, Osprey Reef, Coral Sea, Australia. Daniela Dirscherl/WaterFrame/Getty Images

When you look at a sponge, the word animal might not be the first that comes to mind, but sea sponges are animals. There are over 5,000 species of sponges and most live in the marine environment, although there are also freshwater sponges.

Sponges are classified in the phylum Porifera. The word porifera 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, 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, like the one shown here, look like tall vases.

Sponges are relatively simple multi-celled animals. They 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 are used for getting rid of wastes.

The skeleton of a sponge is formed from 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 enters 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 the production of egg and sperm. In some species these gametes are 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 to the rest of its life. in the image shown here, you can see a spawning sponge.

Asexual reproduction occurs by budding, which happens when a part of a sponge is broken off or one of its branch tips is constricted, and then this small piece grows into a new sponge. They may also reproduce asexually 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 then 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: