Sponge

Sponges, or sea sponges, are fascinating animals that live in the water. They belong to a group called Porifera, which means "pore bearer." These animals are found mostly 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 up of many cells that can change and move around. Unlike other animals, they do not have complicated systems for nerves, digestion, or blood flow. Instead, they use water to get food and oxygen and to get rid of waste. Water moves through their bodies using tiny hair-like structures called flagella on special cells known as collar cells.

Scientists think sponges might be one of the earliest types of animals, but they are still learning about their exact place in the animal family tree. Fossils of early sponges, like Otavia, 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 reflects the many tiny holes or pores 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 are stuck to 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 belong to a group of animals called Porifera. They are special because they are usually stuck in one place and have many tiny holes and channels that let water flow through them. Most sponges have special cells with tiny hair-like parts that help move the water.

Unlike many other animals, sponges have a soft, jelly-like middle layer between two thin layers of cells. They do not have a nervous system like we do, but they still have many different kinds of cells that can move around 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. Some cells can even change into other types of cells when needed. 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. They can change their shape to catch the best water currents.

Vital functions

Sponges are simple sea creatures that stay in one place. They filter 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. Instead, the flow of water through their bodies helps them with all these tasks.

Some sponges can move slowly across the sea floor, while 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 also 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 prefer calm, clear water because too much sediment can block their pores and make it hard for them to feed. Sponges are often found on hard surfaces like rocks, but some can attach to softer surfaces using a root-like base.

Sponges play an important role in their environments. Some sponges work with tiny plants that make food from sunlight, producing extra oxygen and organic matter for their habitats. 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 produce important substances. These relationships help keep the sponge and its environment healthy.

Systematics

Taxonomy

Carl Linnaeus once thought sponges were plants. Later, scientists placed them in a group called Parazoa, separate from other animals. Today, sponges belong to the phylum Porifera.

Sponges are grouped into classes based on their skeletons. Some have glass-like structures, others have skeletons made of a special kind of stone, and many have soft, flexible parts.

Classes

Sponges used to be split into three groups, but scientists discovered a fourth group that is quite different from the others.

Phylogeny

Scientists are still learning about how sponges relate to other animals. Some think sponges might be very close to the start of all animal life, while others think a different group might hold that place. Studies help us understand how different sponge groups are related to each other.

Evolutionary history

Fossil record

See also: Huainan biota

Sponges may have existed long before the big burst of life known as the Cambrian explosion, but we only find clear sponge fossils from the Cambrian period onward. Some old reports suggested finding sponge pieces in rocks from around 750 million years ago, but these are not proven. Well-preserved sponge fossils from about 580 million years ago come from the Ediacaran period, found in the Doushantuo Formation. These include several types of sponge parts.

Fossils of glass sponges are found from around 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 our ideas about when the first animals lived, if confirmed.

Freshwater sponges seem 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 learned that bottlenose dolphins in Shark Bay use sponges as tools. A dolphin can hold a marine sponge on its rostrum, which helps protect it 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, and all dolphins that use sponges are closely related. This suggests the behavior is a new idea that 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.