Sponge

Sponges, or sea sponges, are interesting animals that live in the water. They belong to a group called Porifera, meaning "pore bearer." These animals are mostly found in the sea and stay attached to the seabed. They are very old and have been around for a long time, helping to build reefs that many sea creatures depend on.

Sponges are made of many cells that can change and move. Unlike other animals, they do not have systems for nerves, digestion, or blood flow. Instead, they use water to get food and oxygen and to remove waste. Water moves through their bodies using tiny hair-like structures called flagella on special cells.

Scientists think sponges might be one of the earliest types of animals, but they are still learning more about them. Fossils of early sponges have been found that are about 800 million years old. The study of sponges is called spongiology.

Etymology

The word "sponge" comes from an ancient Greek word spóngos. The scientific name for sponges is Porifera, which means "pore bearing" in Latin. This name describes the many tiny holes in a sponge's body.

Overview

Sponges are simple animals that live mostly in the ocean. They are not like other animals because they do not have true tissues or organs. Instead, they have a body full of tiny holes and channels that let water flow through them. This water brings food and oxygen to the sponge.

Sponges have a soft, jelly-like middle layer surrounded by thin layers of cells. Most sponges stay in one spot on the sea floor their whole lives, but when they are very small, they can move around. Some sponges make their own skeletons from special tiny sticks, while others use a soft, stretchy material. Scientists think sponges might be the oldest animal group on Earth, and they have been around for more than 580 million years.

Distinguishing features

Further information: Cnidaria and Ctenophore

Sponges are a group of animals called Porifera. They are special because they stay in one place and have many tiny holes. These holes let water flow through them. Most sponges have cells with tiny parts that help move the water.

Sponges have a soft middle layer between two thin layers of cells. They do not have a nervous system like we do, but they have many different kinds of cells that can move inside their bodies.

Basic structure

A sponge's body is hollow and is held in shape by the mesohyl, a jelly-like substance made mainly of collagen. Sponges have many different types of cells that help them live. Some cells, called choanocytes, have tiny hair-like structures called flagella that move water through the sponge's body. This water brings food and oxygen.

Sponges also have other special cells. Some cells make collagen, while others make tiny "spines" called spicules that help protect the sponge. Most sponges take in water at the bottom and push it out at the top, which helps them get food and oxygen from the water.

Vital functions

Sponges are simple sea creatures that stay in one place. They get food from the water by pulling it through their bodies. Unlike more complex animals, sponges do not have special systems for breathing, digesting, or getting rid of waste. The flow of water through their bodies helps them with all these tasks.

Some sponges can move slowly across the sea floor. Others can close their openings to protect themselves. They can also reproduce without needing another sponge, either by breaking into pieces or by making special survival pods called gemmules. Most sponges can reproduce by releasing eggs and sperm into the water. Even though sponges do not have brains or nerves, they can coordinate movements and reactions in their bodies.

Ecology

Sponges live in many parts of the world's oceans, from cold polar waters to warm tropical seas. They like calm, clear water because too much dirt can block their pores and make it hard for them to eat. Sponges are often found on hard surfaces like rocks, but some can stick to softer surfaces using a root-like base.

Sponges are important in their homes. Some sponges work with tiny plants that make food from sunlight, making extra oxygen and organic matter for where they live. They also protect themselves from other sea creatures by shedding tiny sharp pieces or by making substances that keep others away.

Sponges are eaten by some animals, like certain fish and turtles. Some tiny insects called spongeflies live in freshwater sponges, with their young feeding inside the sponge. Sponges can also harm coral reefs by breaking down the rocks and corals they live on.

Sponges often work together with other sea creatures. For example, some small shrimp live inside sponges and help protect them from predators. Sponges also host many tiny microbes that live with them and help make important substances. These friendships help keep the sponge and its home healthy.

Systematics

Taxonomy

Carl Linnaeus once thought sponges were plants. Later, scientists put them in a group called Parazoa, different from other animals. Today, sponges are in the phylum Porifera.

Sponges are sorted into classes by their skeletons. Some have glass-like parts, others have skeletons made of a special kind of stone, and many have soft, flexible pieces.

Classes

Sponges were once split into three groups, but scientists found a fourth group that is very different from the others.

Phylogeny

Scientists are still learning how sponges connect to other animals. Some think sponges might be very close to the beginning of all animal life, while others think another group might hold that spot. Studies help us learn how different sponge groups relate to each other.

Evolutionary history

Fossil record

See also: Huainan biota

Sponges may have lived long before a big change in life called the Cambrian explosion, but we only find clear sponge fossils from the Cambrian period onward. Some old reports said they found sponge pieces in rocks from about 750 million years ago, but this is not proven. Well-preserved sponge fossils from about 580 million years ago are from the Ediacaran period, found in the Doushantuo Formation. These fossils include several types of sponge parts.

Fossils of glass sponges are found from about 540 million years ago in Australia, China, and Mongolia. Early Cambrian sponges from Mexico show signs of smaller pieces joining to make bigger ones. Calcium carbonate sponge fossils are seen from about 530 to 523 million years ago in Australia. Other early sponge-like fossils come from the Chengjiang fauna, from 525 to 520 million years ago. Some possible sponge fossils from 890 million years ago in Canada might change what we think about when the first animals lived, if proven.

Freshwater sponges appear to be a newer group, with their earliest fossils from the Mid-Eocene period, about 48 to 40 million years ago. Most modern sponges belong to one group, but their fossils are rare because their skeletons do not preserve well.

Relationships to other animal group

In the 1990s, scientists thought all sponges came from one common sponge ancestor and were the closest relatives to all other animals. But newer studies tell a more complex story. Some suggest that more complex animals are closer to certain sponge groups than to others, meaning sponges may not all share one single ancestor. Recent studies using DNA comparisons support that sponges are the closest group to the ancestors of all multi-celled animals.

One big study in 2017 showed that sponges form a natural group and are the closest relatives to all other multi-celled animals. Other work suggests that a group called comb jellies might be the closest instead. More research is needed to fully understand sponge family ties.

The debates continue, but sponges remain important for understanding how animals first evolved.

Notable spongiologists

Here are some scientists who studied sponges:

• Céline Allewaert
• Patricia Bergquist
• James Scott Bowerbank
• Maurice Burton
• Henry John Carter
• Max Walker de Laubenfels
• Arthur Dendy
• Édouard Placide Duchassaing de Fontbressin
• Randolph Kirkpatrick
• Robert J. Lendlmayer von Lendenfeld
• Edward Alfred Minchin
• Giovanni Domenico Nardo
• Eduard Oscar Schmidt
• Émile Topsent

Use

By dolphins

In 1997, scientists found that bottlenose dolphins in Shark Bay use sponges as tools. A dolphin holds a marine sponge on its rostrum to protect itself while searching for food on the sandy sea bottom. This behavior, called sponging, is mostly done by female dolphins. A study in 2005 showed that mother dolphins teach this skill to their daughters. All dolphins that use sponges are closely related, which suggests this behavior started not too long ago.

By humans

Skeleton

Some sponges have rough skeletons made of calcium carbonate or silica, but two types, Hippospongia and Spongia, have soft, fibrous skeletons. People in the past used these soft sponges for many things, like padding for helmets, drinking cups, and water filters. Before synthetic sponges were invented, they were also used for cleaning, applying paints, and making ceramic glazes. But by the middle of the 1900s, too many sponges were caught, and both the animals and the industry nearly disappeared.

Today, many sponge-like objects are made from materials that are not from real sponges. These synthetic sponges are used for cleaning, in personal care, and in medical applications. Common materials include cellulose foam, polyurethane foam, and sometimes silicone foam.

The luffa “sponge,” also called loofah, is not from an animal. It comes from the fibrous part of the sponge gourd plant.

Sponges may help with medicine because they or the tiny organisms that live with them can make chemicals that might fight viruses, bacteria, tumors, and fungi. Sponges have developed many unusual compounds to protect themselves since they cannot move or hide. One group of these compounds, called oxylipins, can stop the growth of cancer cells, bacteria, and fungi. For example, a compound called plakoridine A from Okinawa’s Plakortis sponges has shown promise in fighting certain cancer cells.