Download Echinoderms are invertebrates that have pentaradial

Echinoderms are invertebrates that have pentaradial symmetry, a spiny
skin, a water vascular system, and a simple nervous system.
LEARNING OBJECTIVE [ edit ]
Describe the characteristics of echinodermata
KEY POINTS [ edit ]
Echinoderms live exclusively in marine systems; they are widely divergent, with over 7,000
known species in the phylum.
Echinoderms have pentaradial symmetry and a calcareousendoskeleton that may possess
pigment cells that give them a wide range of colors, as well as cells that possess toxins.
Echinoderms have a water vascular system composed of a central ring of canals that extend along
each arm, through which water circulates for gaseous exchange and nutrition.
Echinoderms have a very simple nervous system, comprised of a nerve ring at the center and five
radial nerves extending outward along the arms; there is no structure resembling a brain.
There are two sexes in echinoderms, which each release their eggs and sperm into the water; here,
the sperm will fertilize the eggs.
Echinoderms can reproduce asexually by regeneration.
TERMS [ edit ]
water vascular system
a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food
and waste transportation, and respiration
podocyte
cells that filter the bodily fluids in echinoderms
madreporite
a lightcolored calcerous opening used to filter water into the water vascular system of
echinoderms
ampulla
the dilated end of a duct
pentaradial symmetry
a variant of radial symmetry that arranges roughly equal parts around a central axis at
orientations of 72° apart
Give us feedback on this content: FULL TEXT [ edit ]
Phylum Echinodermata
Echinodermata are so named owing to
their spiny skin (from the Greek "echinos"
meaning "spiny" and "dermos" meaning
"skin"). This phylum is a collection of
about 7,000 described living species.
Echinodermata are exclusively marine
organisms. Sea stars, sea cucumbers, sea
urchins, sand dollars, and brittle stars are
all examples of echinoderms . To date, no
Register for FREE to stop seeing ads
freshwater or terrestrial echinoderms are known.
Sea stars
Star stars are among the most familiar of marine invertebrates. They are members of the phylum
Echinodermata.
Morphology and Anatomy
Adult echinoderms exhibit pentaradial symmetry and have a calcareous endoskeleton made
of ossicles, although the early larval stages of all echinoderms have bilateral symmetry . The
endoskeleton is developed by epidermal cells and may possess pigment cells that give vivid
colors to these animals, as well as cells laden with toxins. Echinoderms possess a simple
digestive system which varies according to the animal's diet. Starfish are mostly carnivorous
and have a mouth, oesophagus, two­part pyloric stomach with a pyloric duct leading to the
intestine and rectum, with the anus located in the center of the aboral body surface. In many
species, the large cardiac stomach can be everted and digest food outside the body. Gonads
are present in each arm. In echinoderms such as sea stars, every arm bears two rows of tube
feet on the oral side which help in attachment to the substratum. These animals possess a
true coelom that is modified into a unique circulatory system called a water vascular system.
The more notably distinct trait, which most echinoderms have, is their remarkable powers of
regeneration of tissue, organs, limbs, and, in some cases, complete regeneration from a
single limb.
Sea cucumbers
Sea cucumbers are a member of the phylum Echinodermata which are found on the sea floor worldwide.
As with all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcified structures
that are usually reduced to isolated microscopic ossicles joined by connective tissue.
Water Vascular System
Echinoderms possess a unique ambulacral or water vascular system, consisting of a central
ring canal and radial canals that extend along each arm . Water circulates through these
structures and facilitates gaseous exchange as well as nutrition, predation, and locomotion.
The water vascular system also projects from holes in the skeleton in the form of tube feet.
These tube feet can expand or contract based on the volume of water (hydrostatic pressure)
present in the system of that arm. 1
11
10
9
8
7
2
3
4
5
6
The water vascular system of the sea star
1. Pyloric stomach 2. Intestine 3. Rectal gland 4. Stone canal 5. Madreporite 6. Pyloric duct 7. Pyloric
cecum 8. Cardiac stomach 9. Gonad 10. Ambulacral plates 11. Ampullae
The madreporite is a light­colored, calcerous opening used to filter water into the water
vascular system of echinoderms. Acting as a pressure­equalizing valve, it is visible as a small
red or yellow button­like structure (similar to a small wart) on the aboral surface of the
central disk of a sea star. Close up, it is visibly structured, resembling a "madrepore" colony.
From this, it derives its name. Water enters the madreporite on the aboral side of the
echinoderm. From there, it passes into the stone canal, which moves water into the ring
canal. The ring canal connects the radial canals (there are five in a pentaradial animal), and
the radial canals move water into the ampullae, which have tube feet through which the
water moves. By moving water through the unique water vascular system, the echinoderm
can move and force open mollusk shells during feeding.
Other Body Systems
The nervous system in these animals is a relatively simple structure with a nerve ring at the
center and five radial nerves extending outward along the arms. Structures analogous to a
brain or derived from fusion of ganglia are not present in these animals.
Podocytes, cells specialized for ultrafiltration of bodily fluids, are present near the center of
echinoderms. These podocytes are connected by an internal system of canals to the
madreporite.
Echinoderms are sexually dimorphic and release their eggs and sperm cells into
water; fertilization is external. In some species, the larvae divide asexually and multiply
before they reach sexual maturity. Echinoderms may also reproduce asexually, as well as
regenerate body parts lost in trauma.