The document summarizes key anatomical features of echinoderms, specifically sea stars. It describes the water vascular system including the ring canal, radial canals, tube feet, and associated structures like Polian vesicles and Tiedemann bodies. It also discusses the digestive, excretory, nervous, and sensory systems of sea stars. Key functions of the water vascular system include feeding, gas exchange, and transport of molecules. Sea stars have a central disk with arms extending from it, and feed on various invertebrates and detritus using their tube feet and digestive organs.

1. ECHINODERMATA
(Part-II)
By
SYED SHAKEEL SHAH
Department of Zoology
University of Narowal

2. Tiedemann Bodies: associated with ring canal and produces phagocytic cells
called coelomocytes.
Polian Vesicles: associated with ring canal and function in storing the fluid.
Radial canal: Five radial canals originate from ring canal and leads to arms of
star-shape echinoderms. Many lateral branches originated from each radial
canal and ends up to the feet-tube.
Tube feet: Emerge through the openings of skeletal ossicles.
•Internally, there is a bulb like, muscular structure called Ampula, which
when contract forces the water to enter into tube feet and causes it to
extend. Valves prevent back flow of water.
•There is a suction cup at the distal end of tube feet, which create
vacuum on contact with solid substrates. Thus helps in locomotion.

3. Other functions: Primary function of water-vascular
system is feeding (not water circulation).
•Exchange of respiratory gases and nitrogenous
wastes
Hemal System: strands of tissues that encircle along
ring canal and radial canals. Its function is not well-
known, but it is thought that it may act to transport
large molecules, hormones, coelomocytes (cells that
engulf and transport wastes)

4. FIGURE
Water-Vascular System of a Sea Star. The ring canal gives rise to radial canals
that lead into each arm. It opens to the outside or to the body cavity through
a stone canal that ends at a madreporite on the aboral surface. Polian vesicles
and Tiedemann bodies are often associated with the ring canal.

5. FIGURE
Body Wall and Internal Anatomy of a Sea Star. A cross section
through one arm of a sea star shows the structures of the water
vascular system and the tube feet extending through the
ambulacral groove.

6. FIGURE
Digestive Structures in
a Sea Star. A mouth
leads to a large oral
(cardiac) stomach and
an aboral (pyloric)
stomach. Pyloric cecae
extend into each arm.
(a) Aboral view. (b)
Lateral view through
central disk and one
arm.

7. FIGURE
Development of a Sea Star.
Later embryonic stages are
ciliated and swim and feed
in the plankton. In a few
species, embryos develop
from yolk stored in the egg
during gamete formation.
Following blastula and
gastrula stages, larvae
develop. (a) Early bipinnaria
larva (0.5 mm).
(b) Late bipinnaria larva (1
mm). (c) Brachiolaria larva (1
mm).
(d) Juvenile sea star (1 to 2
mm).

8. FIGURE
Class Ophiuroidea. (a) This brittle star (Ophiopholis aculeata) uses its long,
snakelike arms for crawling along its substrate and curling around objects in
its environment. (b) Basket stars have five highly branched arms. They wave
the arms in the water and with the mucus-covered tube feet capture
planktonic organisms.

9. Class Asteroidea
“Sea Stars”
• Marine, brightly colored, live on hard or sandy/muddy substrate.
• Asterias orange sea star.
Central disk: give rise to five arms.
• Oral opening (mouth) – middle of one side of central disk and covered with
movable spine.
Dermal Branchiae: Body wall folded b/w ossicles & function in gas exchange.
Pedicellariae: Pincher-like structure at aboral surface & clean debris from body &
protect it. Movable through spines or fixed.
Ambulacral groove: On the whole length of oral surface of each arm, series of
ossicles form this structure.
• Covered the radial canal & rows of paired tube-feet on either side of ambulacral
groove.
Tube-feet: Helps in movement in stepping motion. They are co-ordinated by
nervous system.

10. Maintenance Functions
Feeding:
• Feed snail, crustaceans, polychaetes (Annelid), corals (coelentrata), detritus
etc.
Mouth → esophagus → stomach (fill most of the coelom) → Intestine
→ Rectal cecae (uncertain function) → Anus
Stomach
↙ ↘
↓ ↓
Larger Smaller
↓ ↓
Receive ingested food give rise to duct that connect
to secretory & absorptive structures
called Pyloric Cecae.
Oral/cardiac stomach Aboral/pyloric stomach

11. • Two pyloric cecae extend to each arm.
• Some ingest whole prey & digest in stomach (extracellular).
•Undigested food expelled through mouth.
• Many feed on bivalves, by wrapping itself around it.
• Tube-feet attached to shell of bivalve & body wall muscles open it by force.
• When 0.1 mm valve opened, it penetrate its oral (cardiac) stomach into it &
release enzymes and partially digest it.
• Then, completely open the valve & take food into mouth & digest completely.
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EXCRETION
• Gases, nutrients, metabolic wastes transported into coelom by diffusion.
• Excretion of wastes (NH3 mostly) and gases occur by diffusion across body wall
& tube-feet.

12. NERVOUS SYSTEM
• It consists of nerve ring, radial nerves & nerve net.
• Nerve ring: around mouth & ring canal.
• Radial nerves: in each arm & co-ordinate the function of tube-feet.
• Nerve net: associated with body wall.
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SENSORY STRUCTURES
• Distributed over body & tube-feet.
• Respond to light, chemicals & mechanical stimuli.
• Photoreceptors at tips of arms.