Echinodermata Echinodermata

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unclear
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info
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and brought the supported by has to summarize for synthesis.
presentation to a evidence shown, but themselves.
logical & effective
closure
main points clear.
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questions the
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to link answer to
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presentation.
Echinodermata
Greek: spine skin
Defining Characteristics:
• water vascular system, a network of hydraulic
canals derived from 1 of 3 paris of coelomic
compartments that form during development;
function in locomotion, feeding, and gas exchange
• pentamerous (five pointed) radial symmetry in
living adults; larvae are bilateral
• calcareous ossicles derived from mesodermal
tissue forming an endoskeleton
• mutable connective tissue (stiffness and fluidity
can change rapidly through the nervous system
Echinodermata
Greek: spine skin
• remarkable and morphologically diverse animals
that include the sea lilies, sea stars, sea urchins,
sea biscuits, and sea cucumbers
• marine and mostly bottom dwellers
• ~6,500 extant species in 5 classes (Crinoidea,
Holothuroidea, Echinoidea, Opiuroidea,
Asteroidea)
• ~13,000 extinct species in 16 classes
• at least 85 species are known to be toxic or
venomous
Other systems and features:
• digestive system - usually complete with anus on
aboral surface
• hemal system - function not clear (nutrient
transport?), little or no role in gas exchange
• nervous system - a diffused net typically of three
rings centered on mouth with radiating branches
• excretion - tissue level; no specialized organs
• respiratory - different types of specialized gills;
tube feet
• reproduction - gonochoric with external
fertilization; planktotrophic larva (dipleurula)

Class Asteroidea (sea stars)
• star-shaped, free moving, pentamerous animals
• hollow arms project from a central disc
• range from 2 cm to ~1 m in diameter
• occur worldwide, largely in coastal waters
• ~ 1500 species
Asteroidea
Water-Vascular System
• consists of the hydraulic tube feet and internal coelomatic canals
• canals: circumoral ring canal, radial canals, lateral canals, stone canal
(opens aborally into a small chamber, madreporic ampulla, which joins the
madreporite)
• the WVS is lined by a myoepithelim and thus is ciliated and muscular
Class Asteroidea (sea stars)
• the mouth is located centrally on the underside of the disc (oral
surface)
• a large furrow (ambulacrum) extends radially from the mouth along
each arm
• each ambulacrum contains two or four rows of tube feet
• the upper (aboral) surface bears an anus (when present) and a large,
button-like madreporite (a sieve plae)
Asteroidea
Water-Vascular System
Ampulla
Ossicle
Tube foot
Sucker
• each lateral canal has a valve and terminates in an ampulla and a tube
foot (x40,000!)
• the ambulacral ossicles form the floor of the ambulacral groove
• longitudinal muscles of the ampulla contract => foot’s extension +
attachment => longitudinal muscles of the foot contract => pulling
force => detachment
• adhesion is largely chemical, but adhesion by suction may also occur

Asteroidea
Water-Vascular System
• each lateral canal has a valve and terminates in an ampulla and a tube
foot
• the ambulacral ossicles form the floor of the ambulacral groove
• longitudinal muscles of the ampulla contract => foot’s extension +
attachment => longitudinal muscles of the foot contract => pulling
force => detachment
• adhesion is largely chemical, but adhesion by suction may also occur
Asteroidea
Digestive system
• most of the space in the disc and arms is occupied by digestive system
• the mouth opens into a short esophagus that leads to a large stomach
• the stomach is divided by a horizontal constriction into a large, oral
cardiac stomach and a smaller aboral pyloric stomach
• pyloric stomach receives ducts from a pair of pyloric ceca in each arm
• pyloric seca are elongate, hollow, branched extensions of the stomach
Radial canal
Tube foot
Perivisceral
coelom
Pyloric cecum
Pyloric stomach
Anus
Mouth
Ring canal
Cardial stomach

Asteroidea
Nervous system
• the peripheral nervous system includes two intraepithelial nets,
the sensory ectoneural system in the epidermis and the motor
hyponeural system in the coelomic lining
• the CNS consists of ectoneural and hyponeural circumoral
nerve rings and radial nerves
• The motor component of the radial nerve innervates the
ampullae, tube feet, and body-wall muscles, while the sensory
part receives input from the sense cells and organs
• no ganglia, no glea
Asteroidea
Hemal system
• three interjoined radial sets of
vessels, each consisting of a hemal
ring around the gut and five
sometimes branched radial vessels
• the hyponeural hemal ring, the
gastric hemal ring, and the genital
hemal ring
• Two specialized vessels called
gastric hemal tufts cross the
perivisceral coelom and unite the
gastric hemal ring with the axial
hemal vessel and heart
• the three hemal rings are united
by the vertical axial hemal vessel
(axial gland) that lies in the wall of
the axial canal
Ectoneural
nerve net
Hyponeural
nerve net

3 Bilateral symmetry
Anteroposterior body organization
Medial nerve cord
Gut and CNS parallel
Complex life cycle with larva
Ciliated band in larva
b
1 Brachiolar complex (larva)
2 Rudiment ectoderm invaginates
3 Cilated band rearranged in larva
4 Radial symmetry
Loss of cephalization and brain?
Radial nerve cords
Gut and CNS orthogonal
Water vascular system with podia
Calcareous endoskeleton
Metazoa
Regeneration and clonal reproduction
Larvae
Adults
feather stars sea stars brittle stars sea urchins sea cucumbers
Morphology
(Crinoidea) (Asteroidea) (Ophiuroidea) (Echinoidea)
Genes : sites of expression
Asterozoa
Echinodermat
Eleutherozoa
ry history of body architecture and regulatory genes within the
hinodermata (b). Reconstructed changes in morphology (left)
mental roles and expression domains of regulatory genes
he expression domains and roles of several regulatory genes
ropods and chordates (a, 8) 8–11 , despite their phylogenetic
orphological disparity 2,5,6 . These similarities probably reflect
architectural features, such as bilateral symmetry and an
is (a, 3) between protostomes and deuterostomes. Morpholo-
istinguish phyla (such as a,1) and groups of related phyla( a, 2)
ome such cases, changes in the developmental roles of
, 5 and 7) have been identified that may have been involved
e derived structures 9,10,17 . The origin of echinoderms followed
rthropods and chordates, and involved substantive modifica-
?
Echinozo
Sexual reproduction and
development
7 Hox cluster domains along A/P axis
distal-less anterior CNS
engrailed ganglia along CNS
orthodenticle
8 Hox genes domains along A/P axis
5 orthodenticle ciliated band (larva)
6 engrailed rudiment invagination
7 distal-less brachiolar arms (larva)
distal-les subtrochal cells (larva
8 engrailed ectoderm
(skeletogenesis)
orthodenticle podia
distal-les podia
tions in basic body architecture (b, 2) 1–6 ; already present was a complex life cycle
involving a larva that fed using a ciliated band (a, 3) 1–6 . Data reported here and
taken from the literature 8–11,19 allow us to reconstruct changes in the expression
domains of three regulatory genes during the origin and radiation of echino-
derms. Several derived features of gene expression are shared by asterozoan
and echinozoan echinoderm species (b, 7), implying that they were present
before the divergence of these clades over 490 Myr ago 22 . The origin of these
features could be even earlier (arrow near base of cladogram), but expression
data are currently unavailable for crinoids, the most basal clade of extant
echinoderms. Other features of gene expression appear to be limited to a
single class (such as b, 4 and 6), suggesting later origins or subsequent losses
within other lineages. Phylogenetic relationships are from refs 2, 6, 7 and 14.
Egg Embryo Early larva Late larva Juvenile
bilaterally symmetrical
of echinoderm development. Echinoderm embryos and larvae
etrical 1,6,16 . In late larvae, discrete populations of ectodermal
cells on the left side of the body proliferate to form the
ent (green crescent). The first radially symmetrical structures
udiment (disc near late larva). During metamorphosis, many
left-right asymmetrical
radially symmetrical
Echinoderm embryos and larvae are bilaterally symmetrical. In
late larvae, discrete populations of cells on the left side of the
body proliferate to form the imaginal adult rudiment. During
metamorphosis, the rudiment gives rise to much of the radially
metamorphosis.
symmetrical juvenile (green).
Lowe and Wray, 1997 Nature
larval tissues (blue) are lost, and the rudiment gives rise to much of the juvenile
(green). Domains of regulatory gene expression fall into three distinct symmetry
classes: bilateral in embryos and early larvae; left–right asymmetric in late larvae,
during establishment of the imaginal rudiment; and radial during and after
Nature © Macmillan Publishers Ltd 1997
6 OCTOBER 1997 719
Sexual reproduction and
development
• Asteroids are typically gonochorists with
external fertilization and a complex life cycle
that includes a planktotrophic larva
• Up to 2,500,000 eggs
• Development includes radial cleavage,
regulative development, and enterocoelous
origin of the coelomic cavities
• The bilaterally symmetric, suspensionfeeding
larva (bipinnaria -> brachiolaria)
Class Crinoidea
crown
stalk
• The main part of the body is supported above the substrate
either by a long stalk or by a series of grasping claws (cirri)
• suspension feeders with mouth oriented upward
• feather starts and sea lilies (~700 species)
cirri

Class Echinoidea [“spine-like”]
• Lack arms; the ambulacra and oral surface expanded aborally to cover
most of the body
• ossicles are joint to form a rigid test (like a shell but internal)
• podia pores pass through the ambulacral plates
• adults generally possess an Aristotle’s lantern - a complex system of
ossicles and muscles used for grazing and chewing
• ~1000 species
Class Ophiuroidea [“snake-like”] (Brittle stars)
• Well-developed ossicles in the arms form a linear series of articulating
“vertebrae” joined together by connective tissue and muscles
• the oral surface bears 5 pair of invaginations (bursal slits), which may serve
for gas exchange and as brood chambers for embryos
• ~2100 species
Class Holothurioidea (sea cucumbers)
buccal podia
• The body is worm-shaped, elongated along the oral/aboral axis
• approximately one-third of species live in the deep sea, where they account
for up to 90% of benthic biomas
• the calcareous ossicles are reduced in size and embedded in the body wall
• highly branched, muscular respiratory structures extend from the cloaca
into the coelomatic cavity (respiratory tree)
• ~1200 species

NATURE | VOL 392 | 5 MARCH 1998
b
Ciliated band in larva
1 Brachiolar complex (larva)
Larvae
Adults
feather stars sea stars brittle stars sea urchins sea cucumbers
Morphology
(Crinoidea) (Asteroidea) (Ophiuroidea) (Echinoidea) (Holothuroidea)
Genes : sit
2 Rudiment ectoderm invaginates
3 Cilated band rearranged in larva
4 Radial symmetry
Loss of cephalization and brain?
Radial nerve cords
Gut and CNS orthogonal
Water vascular system with podia
Calcareous endoskeleton
Asterozoa
Echinodermata
Lowe and Wray, 1997 Nature
Eleutherozoa
?
Echinozoa
Eleuterozoa
Nature © Macmillan Publishers Ltd 1998
Echinozoa
Cryptosyringida
8 Hox genes do
5 orthodenticle
6 distal-less
7 distal-less
distal-less
8 engrailed
orthodenticle
distal-less