Transcript Slide 1

Deutrostomia
Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/
Deutrostomia
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Deutrostome means mouth second and encompasses a number of
animal groups including our own.
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The phylogenetic relationships between all of these animals are
continually changing as more is discovered about them and so
here is an account of the phylogeny taken from one source (the
tree of life) even though it is disputed in other places
PHYLUM: ECHINODERMATA
 Sea urchins, Sand dollars and Sea stars.
 6000 living species in 5 classes
 All examples are marine and there are no
parasitic forms.
PHYLUM: ECHINODERMATA
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General
characteristics
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Spiny-skinned animals
possessing calcareous
ossicles embedded in
the dermis and spines
protruding from the
surface: this creates
an internal skeleton.
PHYLUM:
ECHINODERMATA
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General characteristics
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They are radially symmetrical in the adult phase and are
characterized by having five rays, or multiples of five
(pentamerous). This penta-symmetry is most apparent in star fish
and least apparent in sea cucumbers. Echinoderms have not
always been radially symmetrical: fossil forms are bilaterally
symmetrical (with a left and right side and a front and back).
Echinoderm Larval stages (bipinnaria) are also bilaterally
symmetrical.
PHYLUM: ECHINODERMATA
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General characteristics
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Body walls are composed of three layers of cells. Most tissues are
ciliated. There is no head region, brain nor segmentation
PHYLUM: ECHINODERMATA
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General characteristics
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All have tube feet which extend by hydraulic pressure from the
animal's water vascular system, which are used variously for
locomotion, burrowing, exchange of gases (respiration) and
feeding
PHYLUM: ECHINODERMATA
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General
characteristics
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The digestive tract is
simple usually
complete (but may
lack an anus and
therefore be
incomplete).
PHYLUM: ECHINODERMATA
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General characteristics
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Respiration is achieved by minute gills (dermal papulae) which
protrude from the coelom, by tube feet and in the case of sea
cucumbers by a cloaca1 respiratory trees. A circulatory system
radiates from the central coelom, the coelom is lined with ciliated
peritoneum and is usually large and its fluid contains free
amoebocytes. Part of the larval coelom becomes a water vascular
system usually having many tube feet, serving for locomotion, food
handling, or respiration.
PHYLUM: ECHINODERMATA
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General
characteristics
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The nervous system
consists of a circum
oral ring and radial
nerves into each
arm.
PHYLUM: ECHINODERMATA
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General characteristics
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The sexes are separate (rare exceptions), and alike externally;
gonads are large with simple ducts; ova are abundant. The larva is
free-swimming, and is characterized by a conspicuous
metamorphosis to become adults. A few species are viviparous, a
few reproduce asexually by self-division, and many regenerate lost
parts readily. For example star fish are generally capable of
replacing one or more lost arms; sometimes, even a single arm
can regenerate into an entire animal.
PHYLUM: ECHINODERMATA
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Classes of living echinoderms
Asteroidea (sea stars and star fish)
Crinoidea (sea lilies and feather stars)
Holothuroidea (sea cucumbers)
Echinoidea (sea urchins and sand dollars)
Ophiuroidea (brittle stars)
PHYLUM: ECHINODERMATA
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Classes of living echinoderms:
Asteroidea (sea stars and star
fish)
General structure of a star fish:
External
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The Lower surface with the
mouth is called the oral surface.
The upper surface with the anus
is called the aboral surface. Both
the mouth and anus are centrally
situated.
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
Asteroidea (sea stars and star
fish)
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General structure of a star fish:
Oral Surface
Has five ambulacral grooves, one
in each ray from which extends two
or four rows of tube-feet. The ray
may be flexed slowly by a few
retractor muscles in the body wall.
Aboral Surface - Many spines of
various sizes, pedicellariae and
dermal papulae at the base of the
spines, a madreporite which is the
entrance to the water vascular
system and an anal opening.
PHYLUM:
ECHINODERMATA
Classes of living echinoderms:
Asteroidea (sea stars and star fish)
General structure of a star fish: Internal System
 An endoskeleton of calcareous plates or ossicles is bound together by
muscles and connective tissue with an epidermis.
 Around their base are many modified spines, the pedicellaria, which
resemble tiny jaws or scissor blades mounted on a stalk.
 When stimulated mechanically or chemically, the pedicellaria may be
opened by muscles.
 Their function is to keep the aboral surface clean, to aid in the capture
of small food particles and protect the dermal papulae which are thin
walled extensions of the coelom and facilitate gaseous exchange.
PHYLUM:
ECHINODERMATA
Classes of living echinoderms:
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Asteroidea (sea stars and star fish)
General structure of a star fish:
Water Vascular System
The water vascular system is a division of the
coelom
a system of hollow interconnected tubes filled
with water.
Water enters the system via the madreporite
on the aboral disc. The water vascular system terminates in a tube-feet
(Podia) in the grooves on the oral surface.
The sequence of canals in the water vascular system is as follows:
Madreporite (sieves the water)
Stone Canal (runs downwards)
Ring Canal (encircles the mouth)
5 Radial Canals (one per ray arm)
Numerous Transverse Canals (perpendicular to radial canal)
Ampullae: The head of the tube feet.
PHYLUM: ECHINODERMATA
Classes of living echinoderms: Asteroidea (sea stars and
star fish)
General structure of a star fish: Water Vascular System
 The water vascular system is a hydraulic pressure
system.
 The star fish moves by means of its tube feet.
 A tube feet elongates as the muscles surrounding the
ampullae contract forcing fluid in to the foot.
 On the bottom of the foot is a sucker which adheres to
the substratum
 Longitudinal muscles then contract, shortening the ray
arm and help pull the star fish forward.
 Tube feet are also used for capturing and handling food,
and for respiration and excretion.
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
Asteroidea (sea stars and star fish)
General Structure of a Starfish: Digestive System
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This is a short but complete system
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Mouth
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Short oesophagus
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Thin wall stomach - large Cardiac stomach
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- small aboral Pyloric stomach
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From the Pyloric a tube passes into each ray arm.
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In each ray arm it divides into two branches called hepatic cecae
from here many lateral pouches exist.
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Above the stomach is a slender intestine splits in to two branched
pouches, the rectal and intestinal cecae
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Anus
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
Asteroidea (sea stars and star fish)
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Food
Starfish eat almost any animal matter, and are also
carnivorous on oysters, mussels, barnacles, clams
etc.
Small food: passes directly to the mouth via the
pedicellaria or tube feet.
Bivalves: the starfish opens the shell halves slightly
using its ray arms and tube feet. The cardiac
stomach is everted between the gap in the shell
halves. Digestive enzymes are released and the prey
tissue is broken down into a fluid which is swept in to
the hepatic cecae by the action of cilia. Nutrients are
stored in the hepatic ceca.
PHYLUM: ECHINODERMATA
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Classes of living echinoderms: Asteroidea (sea stars and star fish)
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Respiration
Gaseous exchange between dermal papulae and tube feet.
Dermal papulae are outpockets of the coelom that pass through minute
openings in the skeleton.
They are covered with cilia on the
internal and external surfaces.
The external cilia keep a current
of oxygenated water passing over
the outside, and the internal cilia
circulate the coelomic fluid into the
papulae.
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PHYLUM:
ECHINODERMATA
Classes of living echinoderms:Asteroidea (sea stars and star fish)
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Excretion
Ammonia is the principal soluble nitrogenous waste
it diffuses through thin areas of the body surface, especially tube feet
and dermal papulae.
Particulate waste are picked up by the amoebocytes within the coelom;
these amoebocytes are subsequently eliminated through the walls of
the dermal papulae.
PHYLUM: ECHINODERMATA
Classes of living echinoderms: Asteroidea (sea
stars and star fish)
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Nervous System and Sense Organs
This consists of a nerve ring around the mouth
plus five large radial nerves that run parallel to
the radial canals of the water vascular system
Most echinoderms respond to touch, gravity,
light and chemical stimuli.
Sense organs are poorly developed.
At the end of each ray is a small tactile tentacle
and a light sensitive eyespot composed of 80 to
200 ocelli.
Most echinoderms are negatively phototaxic and
generally seek shade.
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
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Asteroidea (sea stars and star fish)
Reproduction and Regeneration
Sexes are separate.
A pair of branched gonads in the
perivisceral coelom - base of each arm
Female starfish release up to 2.5
million eggs at once
Males produce even more sperm.
External Fertilization and development
Echinoderm development: fertilized
cell  cleavage two-egg stage 
blastula  gastrula  bipinnaria
branchiolaria  undergoes
metamorphosis pentasymnetrical
starfish.
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
Holothuroidea (Sea
Cucumbers)
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They feed on detritus, which they
take into the mouth by large
modified tube feet surrounding it.
The remaining tube feet
resemble those of the starfish
and are used for locomotion.
Although there are five
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
Crinoidea (Sea Lilies)
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Occur as free living forms
(feather star) or sessile forms
(sea Lilies)
These animals are highly
calcified, and generally occur in
deep waters.
Collect food by ciliary currents
set up on their complex arms.
Tube feet are present only as
small papillae on the sides of
the ambulacral grooves.
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
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Ophiuroidea (Brittle Stars)
Possess five arms radiating from a
central disc
Tube feet lack suckers
movement brought about by muscles
which connect successive ambulacral
ossicles
They are detritus feeders, having a
capacious stomach but lack any
extension of the gut into the arms and
lack an anus
Collect food by ciliary currents set up on
their complex arms
Tube feet are present only as small
papillae on the sides of the ambulacral
grooves.
PHYLUM: ECHINODERMATA
Classes of living echinoderms:
Echinoidea (Sea Urchins)
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Have a rigid body wall or test composed of closely fitting calcareous
plates embedded in the dermis.
Oral surface large compared to the aboral surface.
The mouth is surrounded by powerful jaws which can scrape off
encrusting organisms from the rocks.
The spines borne on the test are long and movable and are
interspersed with pedicellaria.
The numerous tube feet are very extensible and project beyond the
spines`