How To Study Living Animals


3. THE SQUID—A TYPE OF MOLLUSCA

To show the Effect of a Much Reduced or Rudimentary Skeleton

Materials herunterladen.

Small squids, and a few large specimens for comparison and dissection.

Definitions.

Cephalopoda,

the name of the class to which the squid belongs herunterladen.

Caudal fin,

a horizontal structure at the posterior end of the squid.

Chromatophores,

irregular cells in the mantle which give color to the squid microsoft office kostenlos downloaden vollversion deutsch chip.

Exhalent siphon,

a funnel or tube opening on the ventral side just below the base of the arms or tentacles.

Pen,

a remnant of an exoskeleton imbedded in the mantle along the dorsal side.

Ink sac,

a sac containing a dark, sticky liquid which may be thrown out through the funnel into the water. The opening is near the inner opening of the funnel.

Observations.

1. What is the shape of the squid? To what is this shape adapted?

2. Identify the head and the well-developed eyes.

3. How many arms or tentacles are there? How are they arranged with reference to the mouth? What do you find on the distal ends of the arms? How do the arms vary as to size? What does the position and arrangement of the arms suggest as to their function?

4. Identify the exhalent siphon. Where may water enter the mantle cavity? Recalling the action of the siphons in the clam, suggest a method by which a squid is propelled through the water. In what direction must it swim?

5. Split the mantle along the ventral surface and spread apart. Identify the long plume-like gills, the ink sac, and the inner opening of the exhalent siphon. How many gills do you find?

Suggested drawings.

a. The squid side view.

b. The squid from the ventral side with the mantle split open, arrows to show direction of water.

Summary.

1. In what ways does a squid show relationship to the clam and the snail?

2. What has a squid gained through the reduction of its exoskeleton? What has it lost? What changes were necessary in its structure to offset the loss of an exoskeleton?