| The Squishy Cnidarians |
The Cnidaria (with a silent "C") are another of Earth's Phyla within the kingdom Animalia, alongside such
other Phyla as the Echinoderms, Mollusks, Arthropods and us Chordata. Their gelatinous bodies are
devoid of blood, brain tissue or respiratory organs and have only a single orifice leading to a single cavity,
but they have evolved one of nature's most sophisticated weapons, built entire undersea worlds from their
bodies, conquered every watery corner of the globe and even cheated death. First, let's talk about some of
the common types of Cnidaria, then we can get into the freaks!
other Phyla as the Echinoderms, Mollusks, Arthropods and us Chordata. Their gelatinous bodies are
devoid of blood, brain tissue or respiratory organs and have only a single orifice leading to a single cavity,
but they have evolved one of nature's most sophisticated weapons, built entire undersea worlds from their
bodies, conquered every watery corner of the globe and even cheated death. First, let's talk about some of
the common types of Cnidaria, then we can get into the freaks!
| Scyphozoa - the "classic" Jellyfish |
Jellyfish have always been tied with starfish as an almost symbolic inhabitant of the sea and Earth's most
famous animals without any brains. What most of us think of as a jellyfish is usually a Scyphozoan, like the
globsters above, which belong to the class "Medusozoa." A repetitive, involuntary contraction of the "bell"
(like a heartbeat) propels the animal blindly through the water, often trailing tentacles behind it to trap food
like a hungry, swimming cobweb. The thicker, ribbon-like appendages are the "oral tentacles" typically used
to grasp and hold prey, while the thinner, threadlike "fringe" tentacles are where many jellies pack row upon
row of tiny "cnidoblasts," a weapon completely unique to the cnidaria:
famous animals without any brains. What most of us think of as a jellyfish is usually a Scyphozoan, like the
globsters above, which belong to the class "Medusozoa." A repetitive, involuntary contraction of the "bell"
(like a heartbeat) propels the animal blindly through the water, often trailing tentacles behind it to trap food
like a hungry, swimming cobweb. The thicker, ribbon-like appendages are the "oral tentacles" typically used
to grasp and hold prey, while the thinner, threadlike "fringe" tentacles are where many jellies pack row upon
row of tiny "cnidoblasts," a weapon completely unique to the cnidaria:
| Cubozoa - the Box Jellies |
A slightly different group of Medusozoa, the Cubozoa are fundamentally similar to the Scyphozoa but
somewhat more sophisticated, with a sturdier "box" shaped bell capable of more rapid and directed
movement, a more advanced nervous system with more directional control, and in many species,
fully-functioning eyes. Not simple eye-spots or light sensors, but eyes with retinas, corneas and lenses,
clustered at the corners of the boxy body.
somewhat more sophisticated, with a sturdier "box" shaped bell capable of more rapid and directed
movement, a more advanced nervous system with more directional control, and in many species,
fully-functioning eyes. Not simple eye-spots or light sensors, but eyes with retinas, corneas and lenses,
clustered at the corners of the boxy body.
| The Hydrozoa |
Another member of the Medusozoa are the Hydrozoa or "Hydroids." Like the jellyfish, many species have
both an anchored "polyp" stage and swimming "medusan," but it is often the polyp that can be considered
the "adult," and may grow into a massive, plant-like colony of identical animals connected by a network of
gelatinous tubes; a plankton-eating jellyfish-tree.
both an anchored "polyp" stage and swimming "medusan," but it is often the polyp that can be considered
the "adult," and may grow into a massive, plant-like colony of identical animals connected by a network of
gelatinous tubes; a plankton-eating jellyfish-tree.
| The Anthozoa |
The "minimal" Anthozoan is what we call the sea anemone, an animal usually attached to a solid surface by a
thick stem. The mouth is pointed outwards and surrounded by stinging tentacles capable of lassoing
relatively large fish and crustaceans, though some venom-resistant animals may take up residence in its
tentacles as a beneficial partner (clownfish) or a tissue-feeding parasite (certain shrimp). Though they
appear sedentary, they can be capable of slug-like crawling, rolling, or even awkward swimming.
thick stem. The mouth is pointed outwards and surrounded by stinging tentacles capable of lassoing
relatively large fish and crustaceans, though some venom-resistant animals may take up residence in its
tentacles as a beneficial partner (clownfish) or a tissue-feeding parasite (certain shrimp). Though they
appear sedentary, they can be capable of slug-like crawling, rolling, or even awkward swimming.
| Now that you know your Cnidaria, continue to THE TOP TEN WEIRDEST |
I've talked about these before when I discussed how certain sea slugs can actually steal them for their
own use. Also called a cnidocyst or nematocyte, this intricate microscopic mechanism is a sort of hollow bulb
with an inverted tip. At the slightest brush of its hair-like trigger, the bulb floods with water to flip the
sharpened tip to an everted position, easily penetrating the skin of most other organisms. In the same
instant, a hollow cable is squirted into the wound to firmly anchor the sting while it injects debilitating venom.
own use. Also called a cnidocyst or nematocyte, this intricate microscopic mechanism is a sort of hollow bulb
with an inverted tip. At the slightest brush of its hair-like trigger, the bulb floods with water to flip the
sharpened tip to an everted position, easily penetrating the skin of most other organisms. In the same
instant, a hollow cable is squirted into the wound to firmly anchor the sting while it injects debilitating venom.
Many jellyfish have a life cycle consisting of both the swimming "medusa" form and a less famous but totally
cool "polyp" form, which lives anchored in place and continuously sprouts off new medusa. It is during the
swimming stage that Scyphozoans mate, producing larvae that settle into new polyps, or, in some species,
giving birth directly to new medusae.
cool "polyp" form, which lives anchored in place and continuously sprouts off new medusa. It is during the
swimming stage that Scyphozoans mate, producing larvae that settle into new polyps, or, in some species,
giving birth directly to new medusae.
Cubozoa include the infamous "sea wasps" and "Irukandji" jellyfish, notorious for some of the deadliest and
most agonizing stings in nature. Smarter, faster, less blind and more toxic, Cubozoa are pretty much just
Jellyfish 2.0.
most agonizing stings in nature. Smarter, faster, less blind and more toxic, Cubozoa are pretty much just
Jellyfish 2.0.
Much more complex are the Hydrozoans known as Siphonophores, which
work together more like organs in a body than whole animals in a colony.
Unable to survive independently, the polyps of a Siphonophore include
some members devoted entirely to feeding, some to reproduction and some
to locomotion. The deep-sea specimen on the left drags its feeding and
reproductive polyps behind a chain of bag-like swimming polyps.
work together more like organs in a body than whole animals in a colony.
Unable to survive independently, the polyps of a Siphonophore include
some members devoted entirely to feeding, some to reproduction and some
to locomotion. The deep-sea specimen on the left drags its feeding and
reproductive polyps behind a chain of bag-like swimming polyps.
Physalia physalis, the "Portuguese Man O' War," is probably the most
famous siphonophore, though commonly mistaken for a mere jellyfish. It
has no swimming polyps, but hangs in the water from a gas-filled float with a
raised sail, living at the mercy of the wind and current. Its tentacles pack an
uncommonly painful, sometimes life-threatening sting, and can reach
between 30 and 200 feet in length.
famous siphonophore, though commonly mistaken for a mere jellyfish. It
has no swimming polyps, but hangs in the water from a gas-filled float with a
raised sail, living at the mercy of the wind and current. Its tentacles pack an
uncommonly painful, sometimes life-threatening sting, and can reach
between 30 and 200 feet in length.
Siphonophores get particularly spectacular in the deep-sea abyss, where they may employ bioluminescence
to protect themselves or attract their prey. Some species can grow upwards of ninety feet in length, rivaling
their fellow gelatinous serpents, the colonial tunicates.
to protect themselves or attract their prey. Some species can grow upwards of ninety feet in length, rivaling
their fellow gelatinous serpents, the colonial tunicates.
Sisters to the Medusozoa, the class Anthozoa are animals famous for building an environment all their own,
the coral reef.
the coral reef.
Easily the most important of all Cnidaria are the corals, in particular the "hard" or "stony" corals whose rocky
skeletons create entire ecosystems - coral reefs - home to thousands of unique animal species. A single
coral polyp is similar to an anemone, but in most species, clones itself into dozens or hundreds of identical,
connected individuals who grow a calcerous "skeleton" around their bodies. Contracted into their skeleton,
the polyps are well protected and virtually unseen, but extend their tentacles or "bloom" regularly to collect
particles of food. Most corals reproduce by releasing large amounts of sperm and eggs into the surrounding
water, and in many cases an entire reef will spawn on the same night.
skeletons create entire ecosystems - coral reefs - home to thousands of unique animal species. A single
coral polyp is similar to an anemone, but in most species, clones itself into dozens or hundreds of identical,
connected individuals who grow a calcerous "skeleton" around their bodies. Contracted into their skeleton,
the polyps are well protected and virtually unseen, but extend their tentacles or "bloom" regularly to collect
particles of food. Most corals reproduce by releasing large amounts of sperm and eggs into the surrounding
water, and in many cases an entire reef will spawn on the same night.
Similar to the anemones are the genus Hydra, the most common Cnidaria found in fresh water environments.
Often microscopic or very nearly so, these little guys prey on tiny shrimp, protozoa or newly hatched fish, and
are given a greenish tint by algae living within their bodies.
Often microscopic or very nearly so, these little guys prey on tiny shrimp, protozoa or newly hatched fish, and
are given a greenish tint by algae living within their bodies.
"Solitary" corals are not unheard of; this mushroom coral (Fungiidae) consists of a single large polyp with a
biscuit-shaped skeleton that simply lies unanchored on the sea floor and can even creep from place to place.
Long thought to feed on only tiny plankton, certain mushroom corals were recently observed slurping entire
large jellyfish into their central mouths.
biscuit-shaped skeleton that simply lies unanchored on the sea floor and can even creep from place to place.
Long thought to feed on only tiny plankton, certain mushroom corals were recently observed slurping entire
large jellyfish into their central mouths.
The Alcyonacea or "soft" corals do not develop the sturdy skeletons of their cousins and cannot build coral
reefs, but may be covered in tiny, horny skeletal particles called sclerites. These bizarre "sea pens,"
inhabitants of the deep ocean, consist of feeding polyps attached to a single large root polyp, which can turn
to face the current or even "uproot" from the mud and move about.
reefs, but may be covered in tiny, horny skeletal particles called sclerites. These bizarre "sea pens,"
inhabitants of the deep ocean, consist of feeding polyps attached to a single large root polyp, which can turn
to face the current or even "uproot" from the mud and move about.
| written by Jonathan Wojcik |
