MARCH 24TH, 2011
Starfish Main Ideas
Starfish hunt bi-valves (clams, oysters, and mussels). These
organisms are very strong and have shells, so a starfish needs to
be able to tire them out. They therefore use water pressure and
not muscles to move, because muscles get tired first.
Once they have tired out their prey and opened the shell some,
they invert their first stomach into the prey and eat it inside out.
Dissolved food goes into the second stomach for more digestion,
and then into the intestine to be absorbed.
Because this is happening underwater and its messy, they need
lots of stomach acids and other digestive chemicals. Most of the
space in their bodies goes into making these.
Starfish have radial symmetry and can move, attack, or defend in
any direction… slowly. They have an ‘eye’ at the tip of each leg to
sense light. They have no brain center but lots of nerves that give
them a good sense of touch.
Dissection Write-Up
1)
2)
3)
4)
5)
6)
External anatomy
Internal anatomy
Diagram of external ventral side
Diagram of a cross section of a leg
Diagram of the top layer of internal anatomy (mainly digestive organs)
Diagram of the bottom layer of internal anatomy (reproductive organs and
leg structure)
7) Data table:
a) Group name
b) Radius of starfish
c) Mass of starfish
d) Mass of digestive organs
9) Scatterplot of radius(x) vs. starfish mass (y)
10) Scatterplot of starfish mass (x) vs. digestive mass (y)
All diagrams should include labels.
Starfish Diagram
EXTERNAL ANATOMY
Arms – locomotion, capturing prey
Central Disc – site of main organs
Sieve Plate (Madreporite) – filtered water intake
Tube Feet – Used for gripping, moving, hunting
Skin Gills (Dermal Branchiae) – diffusion of oxygen and carbon dioxide
Pedicellariae – miniature pincer stalks
Ambulacral Groove – centered in arm, it has up to 4 rows of hydraulic spines.
Ambulacral Spines – powered by water pressure, use: locomotion, capturing prey.
Mouth – ventral opening of digestive track
Anus – dorsal opening of the digestive track
Water Vascular System – used for locomotion
http://www.pgjr.alpine.k12.ut.us/science/whitaker/Animal_Kingdom/SeaStar/SeaStar.html
http://www.k-state.edu/organismic/echinoderms_and_protochordates.htm
Starfish Diagram 2
INTERNAL ANATOMY
Intestine – absorb digested food
Digestive Glands – create chemicals to digest food
Gonads – reproductive organs
Cardiac Stomach – can be inverted out through the mouth to eat food
Pyloric Stomach – second stomach connected to the cardiac stomach
Stone Canal – connects the sieve plate (madreporite) to the ring canal
Ampulla – water nodules which connect to suction feet
Ossicle – provides support and structure to arms
Radial Canal – water channels going lengthwise along each arm
Ring Canal – ring connecting all five water channels to the cardiac stomach
Suggested Incisions
1)
2)
3)
4)
5)
6)
Find mass with scale
Observe external features
Pin ventral side down
Cut off the tips of 2 legs
Cut dorsal skin up 2 legs
Carefully connect the incision between the 2 legs, and proceed around
the middle. Remove dorsal skin over middle.
7) Observe top layer of internal features
8) Remove digestive organs but not reproductive organs.
9) Observe bottom layer of interal features
10) Find digestive organ mass with scale