Cnidaria

Simple, But Complicated: All About Aggregating Anemones

Anemones

They’re carnivores. And their harpoon-like tentacles are filled with powerful venom. If aggregating anemones grew bigger, divers would have reason to be very afraid. But thankfully, the anemones remain relatively small and their tiny harpoons (nematocysts) cannot penetrate our skin deep enough to deliver toxin to our bodies’ pain receptors. I learned these facts, and a few others, while researching this article. For instance, did you know that their tentacles can fire venomous miniature harpoons that repel predators and anemones unlike themselves? That a “demilitarized […]

Cnidarians Known as Hydroids: Animals Looking Like Plants

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Once again we dive into Cnidaria, a large phylum that contains approximately 10,000 species. Phylum members include many animals that attract attention because of their bright colors: sea anemones, corals, sea pens, gorgonians and jellyfish. These creatures can afford to flaunt their beauty because most of them have defensive polyps loaded with nematocysts (also called cnidocytes) that can fire venomous miniature harpoons. Lucky for us, most of these weapons are too tiny to penetrate our skin. Cnidarians currently belong to one of four classes: Anthozoa […]

Not Your Average Anemones: Examining Unusual Species

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We’ve discussed cnidarians in this column several times and will likely do so many more. There are about 10,000 species in this phylum and since most of them live in the ocean, divers encounter them all the time. Many are photogenic, which is why my files are full of their images. The two forms of cnidarians, polyps and medusae, are, according to The Shape of Life, “essentially mirrors of each other.” Polyps (i.e., anemones) are attached to a surface on one end by the pedal […]

Admiring California Hydrocoral

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Much prized by underwater photographers for its beautiful colors, California hydrocoral (Stylaster californicus) is one of the 350 species of hydroids in the Phylum Cnidaria. A close cousin of the fire corals found in tropical waters, it is not a true (stony) coral.  Cnidaria (the “C” is silent) is not a small, insignificant phylum. It contains approximately 10,000 species, at least 100 of which are dangerous to humans. The phylum name means “nettle” in Greek and its members include some of the most photogenic animals […]

California’s Undersea Flower Animals: The Stony Corals

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It’s a fact stranger than fiction: there are underwater creatures commonly found in the Pacific Ocean off the California coast that are biologically classified as “flower animals.” The class is Anthozoa, formed from two Greek words, anthos, meaning “flower” and zoa, meaning “animals,” and it contains the stony corals. Anthozoa is a class within the photogenic phylum Cnidaria (the “C” is silent), which means “nettle” in Greek. Besides corals, phylum members include sea anemones, sea pens, gorgonians, jellyfishes and hydroids. Cnidarians have two forms, polyps […]

Pretty But Poorly Understood Polyps: Sea Anemones

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Among the approximately 10,000 species that belong to the phylum Cnidaria (the ‚ “C” is silent), there are at least 100 that are dangerous to humans. The phylum name means “nettle” in Greek and its members include sea anemones, corals, sea pens, gorgonians, jellyfishes and hydroids. Most of them are carnivores and most have nematocysts, which are used for defense and catching food. Fortunately, sea anemones are not dangerous to humans; their tiny harpoons (nematocysts) cannot penetrate deep enough into our skin to deliver toxin […]

Gorgonian Corals: Admiring California’s Sea Fans

Gorgonian corals, known as sea fans and also called horny corals, belong to the Phylum Cnidaria (the “C” is silent), which means “nettle” in Greek and includes hydroids, anemones, jellyfish and corals. All cnidarians are carnivores and their tentacles contain tiny harpoons (nematocysts) that can be fired to repel predators and catch food.  There are two cnidarian forms, polyps and medusae. Polyps are attached to a surface on one end by the pedal disk, while the oral disk at the other end is unattached and […]

Aggregating Anemones: Gangsters of the Sea?

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Imagine what Hollywood would do with a film about anemones. Take aggregating anemones for example. They are relatively small, but these carnivores are well armed and can be surprisingly aggressive toward their neighbors, so you might imagine they’d be cast in a gangster movie — with lots of special effects like fiery explosions and crash scenes. Their tentacles can fire venomous miniature harpoons that repel potential predators including anemones unlike themselves. Mother Nature is perfect for the “good cop” role of peace negotiator. In real […]

Purple Hydrocoral

Much prized by underwater photographers for its beautiful color, purple hydrocoral (Stylaster californicus) is not a true coral but one of the 350 species of hydroids in the Phylum Cnidaria, which also includes anemones and jellyfish. It is a close cousin of the fire corals found in tropical waters. I’ve seen Stylaster californicus in four hues—purple, red, pink and blue. This hydrocoral has been found as deep as 368 feet and as shallow as 15. The colonies may reach 12 inches in height and their […]

A Hydroid That Stands Alone

For the most part, a person who knows a hydroid, knows a whole bunch of hydroids. While it is true that many hydroids will be found in one environment together, the main reason it’s hard to get to know just a single individual hydroid is because these animals tend to form colonies. Numerous individuals will be joined together into what appears to be one unit. Take for example the Ostrich-plume Hydroid (Aglaophenia latirostris). The graceful beauty of this species is popular with divers and underwater […]

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