Pentaceros is an echinoderm, ie spiny skin organism, It is remarkably known for its five arms and regenerative capabilities, the presentation discusses various aspects of its nomenclature, taxonomy, biology including feeding, reproduction, development, ecological significance. It has direct similarities to the most primitive chordates the hemichordates during their development hence play an integral role in the evolution story as a connecting link.

1. PENTACEROS
Sea Pentagon or Starfish
By
Pranjal Gupta, BSc(H) Zoology, Ramjas College
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2.  Phylum-Echinodermata
Key features:
 Echinodermata means- “echinos – "hedgehog"
and derma – "skin”, i.e Spiny skinned organisms
 Have deutrostomic evolutionary line.
 Possess a true coelom called enterocoelom.
 Have mesodermal skeleton made of calareous
ossicles.
 Triploblastic and radially symmetrical. 2

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4.  Subphylum-Eleutherozoa
Key features:
 Mobile animals with the mouth directed towards
the substrate.
 Non pedicellate and free living.
 All living echinoderms except Crinodea( Sea
feathers) belong here.
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5.  Class-Asteriodea
Key features:
 Star shaped echinoderms hence called starfish.
 Have a central disc and fused arms(5 or more)
 Have tube feet operated by hydraulic system.
 Shows the property of autotomy.
 Pedicellariae present.
 Anus and madreporite aboral.
 Larval stages include Bippinaria and
Brachiolaria. 5

6.  Order-Phanerozonia
Key features:
 Body with marginal plates, with papulae(dermal
branchiae or skin gill) on aboral surface.
 Pedicellariae sessile, not crossed.
 Tube feet without suckers.
 Mostly burrowers in soft bottom.
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7.  Genus- Pentaceros
Key features:
 Large central disc, five arms short and tapering.
 Aboral surface concave with definite arranged
spines.
 Reticulate aboral skeleton, enclosing most of the
body.
 Upper marginal plates smaller than ventral one.
 Pedicellariae small and valvate type.
 Five ambulacral grooves with two double rows of
tube feet.
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8. GENERAL FEATURES OF STARFISH
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9. Pedicellariae
Madreporite
Stone canal
Ring canal
Radial canal
Arm
Cardiac stomach
Ambulacral ridge
Ampulla
Gonads
Pyloric duct
Pyloric ceca
Lateral canal
Dissection through aboral surface
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10. LOCOMOTION
Tube feet
Tube feet are the many small tubular projections found on the oral
surface of starfish.
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11.  Overview of tube feet:
1. Tube feet function in locomotion, feeding and
respiration.
2. The tube feet in a sea star are arranged in
grooves along the arms.
3. They operate through hydraulic pressure.
4. A sea star that is overturned simply turns one
arm over and attaches it to a solid surface, and
levers itself the right way up.
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12. T.S OF THE ARM OF PENTACEROS
Diagrammatical
representation
T.S through microscope
Tube feet consist of two parts: ampulla and podia. Ampulla contain both circular
muscles and longitudinal muscle, whereas the podia contain the latter only. Thus
the podia use suction to attach to the substratum.
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13.  HYDRAULIC SYSTEM:
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14. FEEDING MECHANISM
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15.  To grab hold of its prey, starfish first directs its
mouth towards it attaches itself to the prey via the
tube feet near the mouth then through its strong
arms gets hold of the prey completely. For a clam it
breaks open the bivalve shell through suction
mechanism.
 Once the clam is open, it ejects its cardiac stomach
placing it over the digestible parts of its prey. The
cardiac and the pyloric stomach then partially
digests what it can, producing a chowder-like slurry
that is then drawn back into the starfishes’ ten
digestive glands.
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16. Starfish’s mouth Starfish devouring a clam
Pyloric stomach visible
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17. AMBULACRAL OR WATER VASCULAR SYSTEM
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18. SEXUAL REPRODUCTION
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19. DEVELOPMENT OF PENTACEROS
Gastrulation
Bippinaria larva
Brachiolaria larvaJuvenile starfish
metamorphosis
Adult pentaceros
Early Bippinaria larva
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20. OTHER BIOLOGICAL SYSTEMS OF STARFISH
 Respiration occurs by dermal branchae or papulae.
 Excretion(NH3) by diffusion via gills or derminal branchia.
 Circulatory system open type and includes the haemal and
perihaemal system.
 Asexual reproduction- fission of the central discs or by
regeneration(autotomy).
 Nervous system with a nerve ring around the mouth and a
radial nerve in the ambulacral region of each arm.
 Tiedemann's bodies and polian vescicles are pouches on the
ring canal whose function may be osmoregulation or
hydraulic regulation within the water vascular system.
 Sensory organs-
1. Pedicellariae sensitive to touch.
2. Tube feet sensitive towards external factors and
orientation.
3. eyespots at the ends of the arms, each one made of 80–
200 simple ocelli covered with cuticle.
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21. DISTRIBUTION AND ECOLOGICAL ASPECTS OF PENTACEROS
 Distribution- It is found in U.K., U.S.A., India,
Panama and South America.
 Ecological status- Pentaceros is a threat to the
pearl industry since it generally devours on the
pearl producing oysters( Ostrea ).
 Sometimes it is also called the cushioned star.
 Usually found in calm shallow waters.
 It has been overharvested for souvenirs and the
aquarium trade.
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