Page 309 - (DK) Ocean - The Definitive Visual Guide

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Reproduction

Most echinoderms have separate males and females,
which reproduce by releasing sperm and eggs,
respectively, into the water. Individuals often gather
to spawn at the same time, thereby increasing their
chance of success. This synchronized spawning is
initiated by factors such as daylight length and water
temperature. Each echinoderm group has its own FLOATING AIDS
type of larva with its own way of swimming, floating, Long, paired arms help
and feeding. Some starfish, for example, keep their sea-urchin larvae, such as RELEASING SPERM AND EGGS
this one from a sea potato
fertilized eggs and developing larvae in a pouch under or heart urchin, to float in By rearing up to spawn, sea cucumbers
their mouth, and nourishment comes in the form the plankton. Brittlestars ensure that their eggs drift away to mix
of yolk. In some brittlestars, the larvae are brooded have similar larvae. with sperm released by another individual.
in sacs inside the body, and the young are released
after metamorphosis. In most species, however, the Feeding
fertilized eggs drift in the plankton and develop into
free-floating larvae. The larvae eventually transform Echinoderms range from peaceful grazers and filter feeders
into their adult form and settle on the sea bed. to voracious predators. Carnivorous species of starfish extend
their stomach over their prey and digest it externally. In
contrast, most sea urchins are grazers, scraping rock
surfaces using teeth that resemble the chuck of an
electric drill. Combined with muscles and skeletal
plates, they form a complex, powerful feeding
apparatus called Aristotle’s lantern. Sea cucumbers
have an important role as sea-bed cleaners,
vacuuming up organic debris and mud.

FILTER FEEDING BY TUBE FEET
Feather stars raise their arms
to trap plankton using fingerlike
tube feet. The food is trapped
in mucus and passed down the
arms into the mouth.

Defense HUMAN IMPACT
If they can be broken open, sea urchins make a good meal for fish, FIGHTING OVER
sea birds, and sea otters. So, along with many other echinoderms, OYSTERS
they protect themselves from predators with their long, sharp
spines. These spines are mounted on ball-and-socket joints and can In European waters, the common
move in all directions, which turns them into fearsome weapons. starfish has a voracious appetite
If an echinoderm is attacked, spines may break off and embed for oysters and mussels. So,
themselves in the predator, creating a wound. Some spines are fishermen dredging the shellfish
also venomous, such as those belonging to the crown-of-thorns beds used to cut up the starfish
starfish. Fire urchins and flower urchins also have enlarged and throw the pieces overboard.
Unfortunately for the fishermen,
and venomous, pincerlike pedicellariae (see below), which this tactic proved ineffective,
are strong enough to sting humans. because starfish can not only
The cumbersome-looking sea cucumbers have no spines or regenerate their limbs, but if
protective plates, but they are far from defenseless. If attacked, a lost limb retains part of the
many eviscerate their gut (and sometimes other internal organs) central body disk, it is able to
as a decoy and regrow them later. Similarly, brittlestars can break completely regenerate the body.
free from attack by discarding an REGENERATING LIMBS
arm. Some tropical sea cucumbers This common starfish is
eject sticky white threads, called regrowing its two lost arms.
Sometimes, regrowth
Cuverian tubules, which are
produces one or more
strong enough to entangle and extra limbs.
restrain an attacking crab.
PEDICELLARIAE
Slow-moving urchins and starfish can become OCEAN LIFE
overgrown by planktonic larvae looking for a
place to settle. They defend themselves by
using spines modified into tiny pincers, called
pedicellariae, to catch and crush the larvae.