DISSECTION DISCOVERY OF THE STARFISH
Kingdom: Animalia
Phylum: Echinodermata
Class: Asteroidea
Common name: Sea star
Other echinoderms:Brittle star, sand dollar, sea cucumber, sea urchin
Characteristics of the sea star:
Bodies covered with hundreds of small spines
Found in coastal waters along rocky seashores
Feed on bivalves and worms
Have five rays (arms) branching out from a central disk, therefore having radial symmetry
Able to regenerate its rays
Materials:
1)starfish
2)dissecting tray
3)hand lens
4)dissecting scissors
5)probe
6)forceps
Procedure:
1)Rinse the starfish.
2)Notice the dorsal and ventral sides.
3)Count the number of rays and notice the basic shape.
Part 1: Dorsal side
4)Use the probe to tap the hard, stoneline sieve plate on the dorsal side, near the center.
5)Touch the starfish’s skin and note the texture.
6)Use the hand lens to examine the skin and notice the many coarse spines that cover the entire dorsal surface. The hard, white structures are spines. Around the base of the spines are jawlike structures which capture small animals and keep the epidermis free of foreign objects. Use the hand lens to also locate the jawlike structures. Refer to Figure 1 below.
***INSERT PIC HERE - SEE MS. WIENER IF YOU DON’T HAVE ONE
7)Use the probe to touch the skin between the spines. The soft blotches between the spines are gills. They get oxygen.
8)Locate a small red or yellow buttonlike structure on the central disk. This structure contains many tiny pores through which water enters the water-vascular system. The water vascular system is a system of water-filled canals that function in movement and feeding.
9)Find the anus in the center of the central disk. The anus, which opens out from the intestine, is the opening through which solid wastes are eliminated from the body.
Part 2: Ventral side
10)Turn the starfish upside-down. Locate the mouth in the opening at the center. Notice the small spines that surround the mouth. Many types of starfish feed by pushing part of the stomach out through the mouth. The stomach secretes enzymes that digest prey.
11)Find the suckerlike tube feet lining the grooves in the center of each arm. These help the starfish grip.
12)Look for a small reddish spot at the tip of each arm. This is an eyespot. It is sensitive to light but does not see images.
Part 3: Internal anatomy
13)Use the dissecting scissors to cut off 1 cm. from the tip of 2 of the arms on the side of the starfish opposite the sieve plate by inserting a scissor point into the opening at the tip of the arm and cutting toward the center of the starfish on each side of the arm (not down the center). You should make a flap of skin that can lift up and cut off.
14)Locate the large, yellowish-brown digestive glands that fill each arm.
15)Use the forceps to remove the digestive glands from each arm onto the dissection tray.
16)Find the light colored clusters at the bottom of the body cavity toward the center of the starfish. These are reproductive organs.
17)The zipperlike, bony ridge running through the center of the arm is part of the internal skeleton. The small, clear bulbs on either side of the bony ridge are the internal parts of the tube feet.
Type and answer the next 21 questions for your grade!
Observation Questions (10 points)
1)What is the basic shape of the starfish?
2)How many arms does it have?
3)What is the feel of the starfish’s spines?
4)What do the tube feet look like?
5)How many rows of tube feet does your starfish have?
Conclusion Questions (21 points)
6)What is the function of a starfish’s spines?
7)What are the 3 functions of the tube feet?
8)How does a starfish take in food?
9)How does respiration occur in the starfish?
10)List 2 adaptations of the starfish that make it well adapted to life in marine waters.
11)When a starfish pries open the shell of a clam or oyster, the mollusk resists. Even if the shell open only slightly, the starfish will get its meal. How does this happen?
12)How can a starfish move equally well in any direction?
Definitions: Describe and/or define the following words as they relate to the starfish:
(18 points)
13)sieve plate
14)spines
15)jawlike structures
16)gills
17)water vascular system
18)eyespot
19)digestive glands
20)reproductive organs
21)tube feet