The document provides an overview of the class Asteroidea (starfish). It discusses their classification in the animal kingdom, general characteristics, skeleton, symmetry, mode of life in marine environments, and methods of reproduction, respiration, feeding, and evolution. Starfish generally have five arms radiating from a central disc, come in various colors, prey on mollusks, and can regenerate lost arms. Their skeleton is made of calcium carbonate ossicles and they have a water vascular system used for movement and respiration.
4. General characteristics of Astoidea
• Usually sedentary along shorelines
• Starfish or sea stars
• Come in a variety of colors
• Prey on bivalve mollusks such as
clams & oysters
• Have 5 arms that can be
regenerated
• Arms project from the central disk
• Mouth on oral surface (underside)
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5. EXAMPLE (STAR FISH )
• Starfish or sea stars are star-
shaped echinoderms belonging to
the class Asteroidea. Common usage
frequently finds these names being
also applied to ophiuroids, which are
correctly referred to as brittle stars or
"basket stars". About 1,500 species of
starfish occur on the seabed in all the
world's oceans, from the tropics to
frigid polar waters. They are found
from the intertidal zone down to
abyssal depths, 6,000 m (20,000 ft)
below the surface.
•
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6. TYPES OF STAR FISH
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• Most starfish have five arms that
radiate from a central disc, but the
number varies with the group.
• Luidia ciliaris has seven arms, members
of the Solasteridae have ten to fifteen
while the
Antarctic Labidiasternnulatus can have
up to fifty. It is not unusual in species
that typically have five arms for some
individuals to possess six or more
through abnormal development.
•
8. Water vascular system
• Water vascular system: hydraulic
system for locomotion, food &
waste transportation, & respiration.
• • Water vascular system: consists
of set of waterfilled canals
branching from ring canal ( encircles
gut). The canals lead to tube feet,
(sucker-like appendages).
Madreporite is entrance of this
system
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9. Skeleton (body wall) & grade of organization
• Skeleton- below dermis
• made of ossicles (CaCO3)
• lattice like connections
• Calcium carbonate
• with spines and tubercles
• Muscle layer- below dermis
• Peritoneum that lines coelom
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• Epidermis- outer surface; includes
• mucous cells
• epithelium
• Pedicellariae- jawlike appendages of the
epidermis
• can open and close
• used to clean body of debris or put
debris on body
• Dermis- includes
• nerve cells
• connective tissue
11. Mode of life & Environment
• Mode Of life • Environment
Marine water
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12. Reproduction
• Most species of starfish are gonochorous, there being
separate male and female individuals
• Some species are simultaneous hermaphrodites,
producing eggs and sperm at the same time and in a
few of these
• Each starfish arm contains two gonads that
release gametes through openings called gonoducts,
located on the central disc between the arms.
• Fertilization is generally external but in a few species,
internal fertilization takes place
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13. Reproduction summary
• dioecious; external fertilization
• usually 10 gonads; 2 in each arm
• have fissiparity- division of central disc
into two animals
• free living larvae
• bipinnaria- first larval form develops into
• brachiolaria - shows development of arms
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14. Respiration
• Starfish rely on osmosis, in order to gather oxygen from the surrounding water The
hole on the top of their bodies is called madreporite.
• Water is gathered through the madreporite and fills a cavity in the center of the
starfish's body called the coelom.
• The coelom is intersected by a number of body canals that run from the center of the
starfish to the tips of each arm.
• These canals fill with the water from the coelom.
• The tube feet that are connected to these canals also fill with water.
• Carbon dioxide then flows through the thin skin of the starfish's tube feet and body
into the surrounding water while oxygen travels through the skin membrane and into
the starfish's body.
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15. Feeding and its mechanism
• Tube feet attach to bivalve mollusk
shells & create suction to pull
valves apart slightly
• Starfish everts (turns inside out) its
stomach through its mouth &
inserts it into prey
• Stomach secretes enzymes to
partially digest bivalve then
stomach withdrawn & digestion
completed inside starfish
• Starfish are powerful hunters and
primarily feed on mollusks. Their
main sources of food are clams,
oysters sand dollars and mussels
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16. Evolutionary history
• Echinoderms first appeared in the fossil record in the
Cambrian
• The first known asterozoans were the Somasteroidea,
which exhibit characteristics of both groups
• Starfish are infrequently found as fossils, possibly
because their hard skeletal components separate as
the animal decays
• However, although starfish fossils are uncommon,
there are a few places where accumulations of
complete skeletal structures occur, fossilized in place
in Lagerstätten — so-called "starfish beds
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18. References
• Lawrence, J. M., ed. (2013). Starfish: Biology and Ecology of the
Asteroidea. Johns Hopkins University Press. .
• Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate
Zoology, 7th edition. Cengage Learning.
• Byrne, M.; O'Hara, T. D.; Lawrence, J. M. "Asterias amurensis". Starfish:
Biology and Ecology of the Asteroidea. pp. 177–179. in Lawrence (2013)
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