| The Prickly Echinoderms |
Exclusively marine, the Phylum Echinodermata includes such animals as starfish, sea urchins and sea
cucumbers; famous to all, but appreciated by few. Brainless and eyeless, Echinoderms have a "skeleton" of
tile-like nodules held together by a thin skin, and move not with a network of muscle tissue, but by the
movement of water through a network of specialized vessels; a biological hydraulic system. They typically
begin their lives as planktonic larvae with bilateral symmetry (two-sided, like ourselves), until the left side
begins to grow what will become the adult body, completely absorbing the right. As with some of my past
articles, I'm going to review the major groups of these ancient creatures before presenting a count-down of
the most unusual! Let's start off with the one that even children can name...
cucumbers; famous to all, but appreciated by few. Brainless and eyeless, Echinoderms have a "skeleton" of
tile-like nodules held together by a thin skin, and move not with a network of muscle tissue, but by the
movement of water through a network of specialized vessels; a biological hydraulic system. They typically
begin their lives as planktonic larvae with bilateral symmetry (two-sided, like ourselves), until the left side
begins to grow what will become the adult body, completely absorbing the right. As with some of my past
articles, I'm going to review the major groups of these ancient creatures before presenting a count-down of
the most unusual! Let's start off with the one that even children can name...
| Asteroidea - the Sea Stars |
Perhaps one of the ocean's most iconic inhabitants, starfish or "sea stars" are characterized by at least five
flexible "arms" radiating from their center, each lined with hundreds of sucker-tipped "tube feet" used in
locomotion. With an incredibly simple nervous system encircling the mouth and running down each arm, any
large enough portion broken off from a starfish will regenerate into an entire new animal. While starfish may
feed upon carrion or vegetable matter, the majority of species are strictly carnivorous, feeding on slower or
sedentary animals such as corals, sponges, limpets and especially mussels. Such prey is commonly digested
externally, over the course of days, when the starfish extrudes its stomach inside-out to digest its helpless
victim alive. Though they lack sight, the body of a starfish may be dotted with light-sensitive cells, and high
concentrations may form "eyespots" on the tip of each arm.
flexible "arms" radiating from their center, each lined with hundreds of sucker-tipped "tube feet" used in
locomotion. With an incredibly simple nervous system encircling the mouth and running down each arm, any
large enough portion broken off from a starfish will regenerate into an entire new animal. While starfish may
feed upon carrion or vegetable matter, the majority of species are strictly carnivorous, feeding on slower or
sedentary animals such as corals, sponges, limpets and especially mussels. Such prey is commonly digested
externally, over the course of days, when the starfish extrudes its stomach inside-out to digest its helpless
victim alive. Though they lack sight, the body of a starfish may be dotted with light-sensitive cells, and high
concentrations may form "eyespots" on the tip of each arm.
| Ophiuroidea - the Brittle Stars |
Generally more mobile than the starfish, brittle stars or "serpent stars" are usually distinguishable by their
thin, spiny, extremely flexible arms attached to a central disk. Unlike Asteroidea, the circular mouth may be
ringed with jaws like a toothed sphincter. Their diet is as varied as that of the other stars, and some may prey
upon even speedy fish and crustacea. Other species may feed by trapping plankton, standing upon one or
more arms and reaching the rest into the current.
thin, spiny, extremely flexible arms attached to a central disk. Unlike Asteroidea, the circular mouth may be
ringed with jaws like a toothed sphincter. Their diet is as varied as that of the other stars, and some may prey
upon even speedy fish and crustacea. Other species may feed by trapping plankton, standing upon one or
more arms and reaching the rest into the current.
| Echinoidea - the Urchins and Sand Dollars |
Walking cacti of the sea, urchins are globular creatures usually coated in loosely attached spines of varying
size and shape, which may be employed as legs in addition to the tube-feet, protect the animal from
predators (in some cases with a venomous sting!), and are now known to be photosensitive, meaning that
the spines themselves collectively function as a simplistic, compound eye. Virtually all urchins were once
believed to be scavengers or herbivores, but certain deep-sea species are now known to prey upon their
fellow Echinoderms, the crinoids.
size and shape, which may be employed as legs in addition to the tube-feet, protect the animal from
predators (in some cases with a venomous sting!), and are now known to be photosensitive, meaning that
the spines themselves collectively function as a simplistic, compound eye. Virtually all urchins were once
believed to be scavengers or herbivores, but certain deep-sea species are now known to prey upon their
fellow Echinoderms, the crinoids.
Somewhat more obscure than the urchins are their discoid sisters the sand dollars, whose fuzz-like spines
and flattened bodies allow for easy movement through sand or mud. Remarkably, the larvae of some species
respond to predator attack by spontaneously cloning themselves, splitting in half to increase the odds of
survival.
and flattened bodies allow for easy movement through sand or mud. Remarkably, the larvae of some species
respond to predator attack by spontaneously cloning themselves, splitting in half to increase the odds of
survival.
| Holothuroidea - the Sea Cucumbers |
Lying on what other Echinoderms would consider their side, the sea cucumbers take on a more elongated,
worm-like appearance, sifting through water and sediment for planktonic food with their oral tentacles.
Famously, many Holothurians defend themselves by self-evisceration, expelling a portion of their internal
organs and tissues to entangle, confuse or distract potential predators, and may also release a cloud of
lethal toxins. The collagen fibers of their body wall can be loosened and tightened as necessary, allowing the
cucumber to shift between a more solid or more liquid state.
worm-like appearance, sifting through water and sediment for planktonic food with their oral tentacles.
Famously, many Holothurians defend themselves by self-evisceration, expelling a portion of their internal
organs and tissues to entangle, confuse or distract potential predators, and may also release a cloud of
lethal toxins. The collagen fibers of their body wall can be loosened and tightened as necessary, allowing the
cucumber to shift between a more solid or more liquid state.
| Pelmatazoa - the Crinoids or "sea lilies" |
In ancient times, crinoids were among the most widespread and diverse life in the ocean, with a multitude of
bizarre shapes and lifestyles. Today, these haunting creatures have been reduced to only two types; the
stalked "sea lilies" and unstalked "feather stars," both more common in the lightless abyssal zone. Both
types are "suspension feeders," meaning that they spread their appendages in the water to trap bits of
drifting food. Though many ancient species were permanently rooted in place, the stalked crinoids are
capable of crawling to new locales.
bizarre shapes and lifestyles. Today, these haunting creatures have been reduced to only two types; the
stalked "sea lilies" and unstalked "feather stars," both more common in the lightless abyssal zone. Both
types are "suspension feeders," meaning that they spread their appendages in the water to trap bits of
drifting food. Though many ancient species were permanently rooted in place, the stalked crinoids are
capable of crawling to new locales.
"Feather stars" begin life similar to their stalked relatives, but eventually break free from the stalk body and
live a more active life, even swimming rather elegantly.
live a more active life, even swimming rather elegantly.
| Now that you're acquainted with the basic forms of echinodermata, continue to THE TOP TEN WEIRDEST |