Echinodermata...spiny skin because most members of the group have defensive
spines on the outside of their body. They are found only in the sea and as
adults are either attached or can crawl around on the bottom. The 5 different
groups include 1 sea lilies (attached)2. starfish, 3. brittle stars, 4. sea
urchins, 5. sea cucumbers.
animals relatively high on the evolutionary scale, it is remarkable that a head
has never been developed.. Their weird symmetry is called pentamerism, a form
of radial symmetry with the body arranged around the mouth.
point symmetry is displayed by most of the modern day echinoderms possibly
making a stronger skeletal framework, but their larva have bilateral
symmetry.(so did their primitive ancestors).
skeleton is made up of many crystals of calcite (calcium carbonate). It
supports the body wall or test and the reinforced structure may be soft, sea
cucumbers or hard, sea urchins but is not a shell because it is covered by
living tissue (sand dollar).
drifting larva also has a skeleton which serve to support their delicate
swimming processes and another feature is their water vascular system
tentacles, tube feet are arranged in a double row along the upper side of each
arm bounding a food groove and along the branched arms (pinnules). The tube
feet can be extended by hydraulic pressure from within the animal and much of
the water vascular system is internal.
supplied with fluid from a radial water canal which runs down the center of
each arm just below the food groove and which sends a branch into each pinnule.
The radial water canal of each arm connects with that of its fellows via a
circular canal running along the gullet of the animal.
is generated inside the system by the contractions of some of the tube feet and
also by special muscles in the canal itself which generate local pressure
increases to distend the neighboring tube feet.
activities of the tube feet relate to gas exchange and food gathering. The feet
are equipped with mucus glands and when a small fragment of drifting food
collides with one, the fragment sticks to the foot which flicks it to the food
groove and passes to the central mouth. The double rows ensure efficient
*Some echinoderms also
use the tube feet for locomotion (stars, urchins and cucumbers).
feet occur in all sea urchins and many sea cucumbers. Sea stars inhabiting hard
substrates also have these feet and use them for locomotion and catching prey.
in the water vascular system is essentially sea water mixed with cellular and
driving the tube feet, the fluid is responsible for transporting food and
wastes, transporting CO2 and O2 and contains many cells,
coelomocytes which play a role in excretion, wound healing, and repair and
No excretory organs have been identified
nervous system is strange, as there is no head or aggregation of nerve organs,
the only real sense organs are the rudimentary eyes of starfish, chemosensory
receptors of sea urchins, and balance organs(stratocysts) in sea cucumbers, and
simple receptor cells widely spread over the surface of the animal responsive
to touch and chemicals in solution. There is a nerve cord running down each arm
close to the radial canal and control the tube feet and body wall muscles. Echinoderms are
sensitive to gravity and respond when turned upside down.
common European star feeds on mussels and oysters while the crown of thorn is
well known for its selection of certain reef building coral. Some burrowing
stars ingest their prey whole while invert their stomachs into the prey and
digest it within the bivalve. ..Explain how it pulls open prey.
of Crinoidea (feather stars)
echinoderms have long, branched arms and a regular arrangement of small side
appendages that are known as pinnules. For mobility, sea lilies are sessile and
are limited to bending movements of the stalk and flexion and extension of the
arms. The stalkless comatulids can move freely, being able to swim and crawl.
In terms of
habitats, crinoids prefer the tropics in coral reefs, in marine environments.
Some species live in cooler temperate waters among rocky reef and seaweed.
These creatures tend to be inconspicuous during the day and fully display
themselves at night to feed.
In the food
chain, crinoids feed by trapping small planktonic organisms using modified tube
feet. This food is passed down the crinoid's arms in mucus strings along a
ciliated food groove that leads to the mouth
urchins browse on algae on the surface and irregular urchins, sand dollars are
more specialized and live partially buried in the sand using modified spines
and tube feet to collect particles of detritus for food.
*Sea cucumbers use
their specialized tube feet around the mouth and sweep the surface of the mud
separate with a few being hermaphrodite, passing through a male stage before
becoming functional females
higher animals possessing a single hollow, dorsal nerve cord and body cavity
(vertebrates, ) However a number of lowly chordates display the phylums
characteristics and are aquatic. The two sub-phlya are Urochordata (sea
squirts) and Cephalochordata( lancelets).
squirts are bottom dwellers growing attached to rocks or other organisms, and
are encased in a thick protective tunic composed of a kind of cellulose or
tunic (thus Lamarck's name, tunicate). The tubular heart pulses first in 1
direction and then in an opposite direction, changing every few minutes.
top is the inhalant siphon and on the side the exhalant siphon. There is no
head. Water is pumped through the body, the gill collecting respiratory
material and acts like a filter for food particles.
are liberated from the anus near the external siphon. They may be solitary or
colonial. Larva have an important role in selecting a settlement point and
distributes the species. It is also the larva which displays the chordate
they are important as fouling organisms as well as evolutionary and zoological
interest. They are the 1st animals in which alternation of generations was
interesting, but unproven theory, (no fossils), is that vertebrates arose from
tunicate tadpoles swimming up rivers where they could exploit the rich organic
detritus coming down the river after the freshwater and land plants had become
an environment the development of a backbone to aid in swimming would confer a
great advantage. A mutation which produced NEOTENY (attaining sexual maturity
in the larval stage) would eliminate the sessile adult.
classes occur...Ascidiacea are sessile, living singly or in complex colonial
aggregations attached to submerged rocks, wharfs, ships etc. Some resemble
black, velvety bananas, others are rounded and pink called sea peaches, others
look like scarlet thumbs while others have the appearance of gnarled potatoes.
•One species, Botryllus,
grows as a glistening black or purple mat studded with rosettes of yellow and
pink openings like the petals of a flower.
second class is Thaliacea comprising pelagic, usually glass clear animals, more
or less barrel shaped. The third class the Larvacea are minute animals with
have an elongated fish like blade form and the notocord extended into the head.
There is no well developed brain, eyes or other sense organs. The adults live
in shallow water inshore and are commonly burrowers.