What is a Sea urchin?
A: Sea urchins are spiny, globular echinoderms in the class Echinoidea.
How many species of sea urchin live on the seabed of
every ocean and inhabit?
A: About 950
They live at every depth zone from the intertidal
seashore down to how deep?
A: 5,000 meters (16,000 ft.)
The spherical, hard shells (tests) of sea urchins are
round and spiny, ranging in diameter from 3cm to what?
A: 10 cm (1 to 4 in).
Sea urchins move slowly, crawling with tube feet, and
they also propel themselves with what?
A: Their spines.
Although algae are the primary diet, sea urchins also
eat what?
A: Slow-moving animals.
In the food chain, what are the predators who eat sea
urchins?
A: The sea otter and the starfish, the
wolf eel, the triggerfish, and human
beings.
The fossil record of the Echinoids dates from when?
A: The Ordovician period, some 450 million years ago.
What are the closest echinoderm relatives of the sea
urchin?
A: The sea cucumbers (Holothuroidea); both are deuterostomes, a clade that
includes the chordates.
Species such as the slate pencil urchin are popular in
aquariums, where they are useful for what?
A: Controlling algae.
They have a rigid, usually spherical body bearing what?
A: Moveable spines.
The name urchin is an old word for what?
A: Hedgehog, which sea urchins resemble.
The spines are attached to ball-and-socket joints and
can what?
A: Point in any direction.
In most urchins, touch elicits a prompt reaction from
the spines, which converge toward what?
A: The touched point.
The internal organs are enclosed in a hard shell or
test composed of fused plates of what?
A: Calcium carbonate covered by a thin dermis and epidermis.
Sea urchins convert aqueous carbon dioxide using a
catalytic process involving nickel into what?
A: The calcium carbonate portion of the shell.
Sea urchins move by walking, using their many flexible
tube feet in a way similar to that of what?
A: Starfish.
The jaw apparatus consists of five strong arrow-shaped
plates known as what?
A: Pyramids.
In general, sea urchins are negatively attracted to
light, and seek to what?
A: Hide themselves in crevices or under objects.
Sea urchins are dioecious, having separate male and
female sexes, although no distinguishing features are what?
A: Visible externally.
In most cases, the female's eggs float freely in the
sea, but some species hold onto them with what?
A: Their spines, affording them a greater degree of protection.
The unfertilized egg meets with the free-floating sperm
released by males and develops into a free-swimming blastula embryo in how
long?
A: As few as 12 hours.
Initially a simple ball of cells, the blastula soon
transforms into a what?
A: A cone-shaped echinopluteus larva.
In some species, adults reach their maximum size in how
long?
A: In about five years.
The purple urchin becomes sexually mature in two years
and may live for how long?
A: Twenty years.
Adult sea urchins are usually well protected against
most predators by what?
A: Their strong and sharp spines, which can be venomous in some species.
The small urchin clingfish lives where?
A: Among the spines of urchins.