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Knobby Black Cucumber
Sea cucumbers are generally scavengers, feeding on debris in the
benthic layer. (There are only a few exceptions to this, most notably a
few pelagic cucumbers and the species Rynkatropa pawsoni, which has a
commensal relationship with deep-sea angler fish.) The diet of most
cucumbers consists of plankton and decaying organic matter found in the
sea. One way they might get a supply of food is to position themselves
in a current where they can catch food that flow by with their
tentacles when they open. Another way is to sift through the bottom
sediments using their tentacles. They can be found in great numbers
beneath fish farms.
Some species in the family Holothuriidae (coral-reef sea cucumbers)
within the order Aspidochirotida can defend themselves by expelling
sticky tubules that entangle potential predators. Cuvierian tubules are
enlargements of the respiratory tree that float freely in the coelom.
When startled, a sea cucumber that possesses these tubules can expel
some of them through a tear in the wall of the cloaca; this process is
called eversion. The sea cucumber does not expel all of the tubules at
one time. Replacement tubules grow back in one-and-a-half to five weeks
, depending on the species.
They can be found in great numbers on the deep sea floor, where they
often make up the majority of the animal biomass. The body of deep
water holothurians is made of a tough gelatinous tissue with unique
properties that makes the animals able to control their own buoyancy,
making it possible for them to both living on the ocean floor or
floating over it to move to new locations with a minimum of energy.
Also in more shallow waters they can form dense populations. The
strawberry sea cucumber (Squamocnus brevidentis) of New Zealand, lives
on rocky walls around the southern coast of the South Island where the
number are something reaching densities of 1,000 animals in a square
metre. For this reason, one such area in Fiordland is simply called the
strawberry fields.
Sea cucumbers extract oxygen from water in a pair of 'lungs' or
respiratory 'trees' that branch off the cloaca just inside the anus, so
that they 'breathe' by drawing water in through the anus and then
expelling it. A variety of fishes, most commonly pearl fishes, have
evolved a commensalistic symbiotic relationship (commensalism) with sea
cucumbers in which the pearl fish will live in sea cucumber's cloaca
using it for protection from predation, a source of food (the nutrients
passing in and out of the anus from the water), and to develop into
their adult stage of life. Many polychaete worms and crabs have also
specialized to use the cloacal respiratory trees for protection by
living inside the sea cucumber.
Sea cucumbers reproduce by releasing sperm and ova into the ocean
water. Depending on conditions, one organism can produce thousands of
gametes.
The largest American species is Holothuria floridana, which abounds just below low-water mark on the Florida reefs.
The most common way to separate the sublasses is by looking at their
oral tentacles. Subclass Dendrochirotacea has 8-30 oral tentacles,
subclass Aspidochirotacea has 10-30 leaflike or shieldlike oral
tentacles, while subclass Apodacea may have up to 25 simple or pinnate
oral tentacles and is also characterized by reduced or absent tube
feet, as in the order Apodida.
Information from Wikepedia - http://en.wikipedia.org/wiki/Sea_cucumber
This species of sea cucumber is dark green in colour with ridges of spikes tipped with red |
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Knobby Black Cucumber (Stichopus chlorontus) easily seen at low tide
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