MARCH 24 TH 2011 STARFISH DISSECTION PREP Starfish

MARCH 24 TH, 2011 STARFISH DISSECTION PREP

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. k 12. ut. us/science/whitaker/Animal_Kingdom/Sea. Star. 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