Feather stars are colorful sea creatures that have been described as "flowers of the coral seas." Sometimes called sea lilies and found in their highest concentrations around Indonesia, the Philippines and Australia's Great Barrier Reef, they are echinoderms, a phylum that includes starfish, sea urchins and sea cucumbers. There about 600 species of feather star. Crinoid is their scientific name. [Source: Fred Bavendam, National Geographic, December, 1996]

Some species of crinoid reach three feet in diameter and have 200 or more feathery arms. Found in reefs, shallow pools and deep sea trenches, they come in a rainbow of colors, including yellow, orange, red, green and white. In 1999, a colony of crinoids was found nine kilometers below the ocean surface in Izu-Ogasawara Trench off Japan.

Modern crinoids look almost exactly like their 250-million-year-old ancestors. They evolved from creatures that first appeared 500 million years ago. Crinoids have no brain or eyes but their well developed nervous system allows them to sense movement, light and food. On the arms of most species are dozens of tube feet covered with sticky mucus that traps food that moves down grooves toward the mouth. The tube feet also absorb oxygen from the water.

Crinoid fossil
Sea lilies can attach themselves to a rock like a plant or swim freely in the sea. Most species hide under rocks, in crevices and under coral ledges, coming out out only at night and slowly across hard surfaces to find good places to feed. A few species swim is manner described as a dance of "undulated sweeps of alternate arms.”

Crinoids are filter feeders that wait for plankton, algae, small crustacean and other organic materials to be pushed their way by currents. During the day they keep all their arms bound tightly together in a tight ball. At night they crawl slowly from their daytime hiding places, taking as long as half an hour to make the march, and then unfurl their arms, ideally positioning themselves at right angles to the current, so a lot of food comes their way, and swaying gently while feeding.

Crinoids are rarely are attacked by fish. They are composed of few edible parts and their spiny surfaces emit mucus that is sometimes toxic to fish. Crinoids sometimes provide homes for small fish and shrimp, often colored the same as their hosts. Some species like the Merlet's scorpionfish have lacy fringes that mimic crinoid arms.


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Mostly anchored to reefs or other hard surfaces, sponges are plant-like animals that live in water and survive by drawing water through small pours of their tubelike walls and expelling it through openings at the top, in the process filtering out the plankton it feeds on. Sponges can grow to the size of barrels. For a long times they were thought to be plants. [Source: Henry Genthe, Smithsonian]

Sponges are colonies of single cells with a porous structure. There are several thousand species of marine and freshwater sponge, many of which form spectacular, bright colored masses on reefs around the world. Most sponges live in salt water but a few species live in fresh water. Sponges belong to the phylum porifera, meaning "pore-bearing animals.” These are animals with porous bodies and specific cells for extracting plankton from seawater.

Sponges are among the world's oldest creatures. Along with jellyfish they first emerged between 800 million and 1 billion years ago. They are more primitive than coral, sea urchins and jellyfish in that they don't have stomachs or tentacles and are regarded as the simplest of all living animals. Sponges are immobile, living attached to solid surface. Instead of organs or tissues that have colonies of cells that perform specific tasks.

There are around 5,000 species of marine sponge. They include glass sponges, with fragile but delicate matrixes of spicules; calcareous sponges, the only sponges with spicules made of calcium carbonate; demosponges, that compete with coral to dominate reefs and make up 90 percent of all sponges; Venus-flower baskets, one of the most beautiful glass sponges; bath sponges, used to make shingles; and horny sponges that you should keep away from your girlfriend. Deep sea sponges gave been found at deep sea vents and in the Southern Ocean abyss.

Some sponges have symbiotic relationships with crabs and shrimp that extract food as they clean algae and parasites and tend and prune the sponges themselves. Most sponges contains toxins to protect them from grazing fish and mobile invertebrates. Without the toxins the sponges are vulnerable and perfect food for many fish to munch on. Sponges also defend themselves with tough layers of skin and sharp spicules.

650-Million-Year-Old Sponges May Be World’s Oldest Animals

feather star
Discover News reported in August 2010, “Sponges are just about the simplest animals on the Earth. And they might be the oldest ones we know, too. Adam Maloof and colleagues published a study in Nature Geoscience this week about their find that could push back the oldest known animal life by 70 million years. In Australia, Maloof says, the team found remains of ancient sponges dating to about 650 million years ago. The prior oldest known hard-bodied animals were reef-dwelling organisms called Namacalathus, which date to approximately 550 million years ago. Disputed remains for other possible soft-bodied animals date to between 577 and 542 million years ago. [Discovery News, August 2010]

At 650 million years old, the sponges would predate the Cambrian Explosion — a huge blossoming of diversity in animal life — by 100 million years. These organisms would also predate an intense moment in our planet’s history known as “Snowball Earth,” according to paleobiologist Martin Brasier. It’s even possible that they helped cause it. However, there may be controversy to come on this finding. The Australian reports on geologists from that country pooh-poohing the find by their American rivals and saying they have better and older fossils.

A few million years after the sponges were around a glaciation extended to the equator, wiping out large swathes of life. Brasier argues that in the absence of more complex creatures that can recycle debris, like worms, the carbon in early life forms got buried in a constantly growing carbon sink, sucking carbon dioxide out of the air and causing global cooling. Sponges would have contributed to such a cooling sink, he says [New Scientist].

According to Maloof, his team found the fossils by sheer accident: They were digging around in Australia for clues about the climate of the past, and first wrote off the finds as mere mud chips. “But then we noticed these repeated shapes that we were finding everywhere — wishbones, rings, perforated slabs and anvils. By the second year, we realised we had stumbled upon some sort of organism, and we decided to analyse the fossils. No-one was expecting that we would find animals that lived before the ice age, and since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the “snowball Earth?” [BBC News].

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white tine sponge
The analysis itself was no picnic. To perform an x-ray or CT examination of fossils, you need to be looking at a fossil that has a different density than the surrounding rock. But the sponges were essentially the same density, forcing Maloof’s team to get creative. To get around this problem, the researchers used what Maloof called a “serial grinder and imager.” One of 32 collected block samples from the formation was shaved off 50 microns at a time — about half the width of a human hair — and then photographed after each minute shaving. The images were then stacked to create complete three-dimensional models of two of the sponge fossils [Discovery News].

Sponge Characteristics

Sponges have cells that carry out specialized functions but they do not form true tissues or organs. They have no sense organs or nerves but they can feel water through mechanisms in their cells.

Sponges feed by filtering tiny particles from the water, which are directed to pores on the animal’s surface by flagella. After entering the pores the water travels through a system of canals with specialized cells that strain food particles from the water and expel the water through large vents. Most sponges are tubes, closed at one end, but they can also take other forms such as spheres or branching structures.

The canal system is supported by an internal skeletons made of spicules (bits of silica and calcium carbonate) embedded in a strong protein known as spongin. Some sponges create incredible sophisticated lattices that seem beyond the means of colonies of single cells. How the cells orient themselves to create these structures is not known.

Contrary to what most people think, sponges are not completely stationary. They can crawl across the sea floor. Some species move around four millimeters a day by extending a flat foot-like appendages and dragging the rest of the body behind, often leaving pieces of their skeleton on their wake. Scientists have studied sponge mobility in tanks by outlining the position of sponges and measured how far they moved.

Feeding, Reproducing and Merging Sponges

Passion Flower feather star
Most sponges depend on ocean currents to carry food their way and feed on diatoms, detritus and various kinds of plankton but some species eat tiny crustaceans. Sponges play an important role in the reef community by filtering matter suspended in the water, ensuring life-supporting sunlight can reach the reef's life forms. Because they are largely immobile the are dependent on their environment to bring them food.

Sponges reproduce in many different ways. Many species release clouds of eggs and sperm into the water from their large central cavity. The eggs and sperm unite, forming larvae that drift into the sea until finding a place to attach themselves and metamorphose.

Sponges can become quite large. Some that grow as soft staple lumps on the ocean floor can reach a size of one meter high and two meters across. The bonds between sponge cells are very loose. Individual cells can dislodge themselves and crawl around the surface of a sponge. Sometimes two sponges next to each other merge and form a single organism. If a sponge is broken apart into individual cells, in many cases these cells will reorganize themselves into a sponge. If you break apart two sponges in this way they will reorganize themselves into a single sponge.

Commercial Uses of Sponges

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Sponges that are sold commercial having the living organism removed so that only the spicules and spongin remain. Of the thousands of species of sponge only a dozen or so have been harvested for commercial uses. Even outside of Greece sponges have traditionally been collected by divers of Greek descent.

Commercially-used sponges include the yellow sponge, sheep-wool sponge, velvet sponges, grass sponges, glove sponge, reef sponge, wire sponge and hardhead sponges from the Caribbean and Florida, and turkey cap sponge, turkey toilet sponge, zimocca sponge, honeycomb sponge and elephant-ear sponge from the Mediterranean.

Natural sponges have largely been replaced by synthetic sponges for commercial uses. Natural sponges are still used in things like surgery because they are softer and more absorbent than synthetic varieties. Deep water sponges have uses in fiber optics.

Sponges from tropical reefs contain analgesic and anticancer compounds. Possible cancer fighting agents have been found in compounds found sponges first studied in Fiji. A compound from a Caribbean sponge, discodermia, is in clinical trials for a treatment for pancreatic and other cancers. Another sponge-derived compound, Contignasterol, is being studied as an asthma treatment.

The study of virus-killing chemicals in a Caribbean sponge in the 1950s led to the discovery of the AIDS-fighting drug AZT as well as Acyclovir, used to treat herpes infections. These have been called the first marine drugs. Sponges have also yielded cytarabine, a treatment for a kind of leukemia.

Sea Squirts

Sea squirt are saclike creatures that spend most of their life span attached to rocks, coral reefs and wharf piles, Officially known as tunicates, they are members of the phylum Chordata. Although they are very simple life forms but they are believed to be the ancestors to the world's most sophisticated life forms: vertebrates. The evidence is a primitive proto-backbone found in the sea squirt larvae.

Sea squirts in a Korean market
Sea squirts have no tentacles. Instead they have two openings which are connected by a U-shaped tube. The entire structure is covered by jelly. Under water it is dilated and beautiful. When exposed by low tide they become blobs of jelly. When touched they shoot streams of water, hence their name.

Sea squirts are filter feeders. They draw water through one opening, pass it through a bag of jelly with slits and then expel it out the other opening. Food particles stick to the wall and are pushed with silica to a primitive gut. In some species the bag of jelly is pink or gold. In other species it is transparent. Some sea squirts look like World War II sea mines. Those found on reefs can be extraordinarily colorful.

Sea squirts begin life as tadpole-like, two-millimeter-long larvae. After a few hours or a couple of days, the larvae goes through a strange metamorphosis. First it glues three toes on its head to a hard surface. Then it tail and nervous system dissolve and it larval organs break down and are replaced by adult organs, and an entirely different animal emerges.

Yondelis is an anti-cancer agent derived from Didemin B, which in turn is derived from Caribbean sea squirts. It works as an inhibitory drug in the chemotherapy treatment of sarcomas and bone tumors and is being tested on patients with breast cancer. Scientists are experimenting with plasmalogen, another substance derived from sea squirts, as a tool in combating Alzheimer’s disease.

Flatworms and Other Marine Worms

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Flatworms are regarded as the simplest and most basic creature found in the sea. There are 3,000 species of them. Most but not all live the sea. Many are found in reefs, clinging under rocks and hidden in crevasses. Some of those found in coral reefs are quite colorful. Some flatworms cause serious illnesses in humans. Tapeworms and flukes are parasitic flatworms.

Like jellyfish, flatworms have a single opening to their gut which is used to take in food and excrete waste but unlike jellyfish they have a solid body. Flatworms have no gills and breath directly through their skin. Their undersides are covered by cilia, which beat and allow them to move slowly over surfaces. They have a network of nerve fibers but nothing that would qualify as a brain and they don’t have a circulatory system.

Despite their simplicity, flatworms have amazing powers. Some have been taught to negotiate their way through a maze. Not only that if they are killed and their flesh is feed to another flatworm they too can negotiate the maze.

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Christmas tree worms
Turbellarians are a kind of flatworm. They come in a number of different shapes. Although most are grey, black or translucent. Some found in coral reefs are brightly colored. Most are free-living rather than parasitic. The can vary in size from less than a centimeter to over 50 centimeters. Many large one are also very flat. They have primitive sense organs; move around by creeping or rippling their bodies; and feed on invertebrates.

Bristleworms are centipede-like creatures. Some six-inch-long creatures have poison-tip spines that stick up from their bodies and produce an excruciating sting. Marine bristle worms and tube worms are members of the annelida phylum along with earthworms and leeches. They have long long flexible tubelike bodies divided into compartments. Some sea worms build their tubular homes with mucus, it, using it as cement.

Image Source: National Oceanic and Atmospheric Administration (NOAA); Wikimedia Commons

Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

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