Squid Dissection NAME: 1

Transcription

1 NAME: 1 Squid Dissection Squid are members of the phylum Mollusca and of the class Cephalopoda. Cephalopoda is the most complex class in phylum Mollusca. Cephalopoda means "head foot" and this group has the most complex brain of any invertebrate. In this lab you will have the opportunity to dissect a squid and learn why it is such a successful invertebrate! All squid have a soft body with a covering called the mantle, which encloses all of the body organs such as the heart, stomach, and gills. Squid can be as small as a thumbnail or as large as a house. The giant squid can measure 60 feet in length and weigh three tons! Squid feed on small crustaceans, fish, marine worms, and even their own kind. They use their tentacles to quickly catch their prey, which is pulled in by the arms and down to the radula, or beak, which uses a tongue-like action to get food into the mouth so that it can be swallowed whole. Objectives: 1. Locate and identify major external and internal features and organs of a squid. 2. Understand and use basic dissection techniques and terms. 3. Critically examine the functions of several squid features and organs. Materials: squid* scissors probes forceps dissecting scopes (optional) dissecting pan (or lunch trays) paper towels diagram of squid External Anatomy: 1. Locate the funnel (also called the siphon or water jet). The funnel is found on the ventral side of the squid. Cephalopods shoot water out of the funnel to propel themselves through the water. 2. The tentacles and arms are attached to the head of the squid. Tentacles are longer than arms and are used to catch prey. Locate and compare the two. 3. Find the two large eyes on the head of the squid. Cephalopods have highly developed eyes for hunting. Remove the lenses from the eyes. 4. Locate the body, which is covered by the mantle, and fin. 5. Spread apart the tentacles and use a probe to feel inside the mouth. The beak (also called radula or jaws) can be felt inside the mouth. Open and close the beaks, noting how the ventral beak overlaps the dorsal beak. Before you pull out the beaks, imagine what they will look like on the inside. With tweezers, remove the beaks and place beaks together with dark pointed parts opposite one another. Manipulate them (open and close) as if the squid were eating.

2 NAME: 2 Label the external view of the squid.

3 NAME: 3 External Anatomy Questions 1. How many arms does your squid have? How many tentacles? 2. Based on the structure of the arms and the tentacles, describe how their purposes differ. What do the arms do and what do the tentacles do? 3. Draw arrows on the squid below to indicate the direction that water comes out of the funnel and the direction that the squid moves. 4. Name two external features that are adaptations for the squid s predatory life. How do these adaptations help the squid? Do you remember the general traits of molluscs we discussed in lecture? Name two traits that the squid shares with other mollusks. a. b. 6. a. What are chromatophores? b. Where are they found? c. What is the function? a. b. c. 7. Describe the shape and function of the beak. 8. What is the radula and where is it found?

4 NAME: 4 Squid Internal Anatomy Procedure: Place the squid ventral side up, pull the mantle up with the scissors where the water jet is, it should be loose and easy to pull up. Use scissors to cut from the water jet to the fins. Open the mantle to expose the structures inside. You may want to use dissecting pins to hold the mantle open so that you can observe the internal anatomy. Identify as many structures as possible. 1. Find the inksac, this is a small dark sac near the water jet. The inksac is located on the liver and empties out the funnel. The squid will squirt a cloud of ink to get away from predators. 2. To find the stomach, follow the esophagus through the beak toward the posterior. The long, silvery dark tube on the bottom of the liver (but appearing to be on top of the liver because of the squid's inverted position) is the ink sac. Be careful not to break it open. Locate the stomach and caecum. These lie together as one white, silky-looking tube, like a deflated bladder and a coiled sack. The bunched up organs that look like human intestines are digestive ducts for the squid. If you are curious about the liver, wait to cut it open until the end of the dissection. It contains a lot of brown, oily liquid which may obscure other organs. Try cutting open the stomach to see if your squid had a last meal. Many squid will have bits of partially digested crustaceans (pink and white pieces), or tiny fish scales and bones. 3. The anus empties into the water jet, use scissors to cut the water jet down the center so you can see the small opening of the anus. 4. Locate the gills. These are the long, feather-shaped organs that are attached to the sides of the mantle and extend along the anterior half of the mantle. 5. Identify the gill hearts, one on the posterior end of each gill (these are small, flat and white). Questions: Why are they white and our hearts are red or purple? The squid has a third heart (the systemic heart) that pumps blood to the rest of the body. 6. Find the hard point at the end (posterior region) of the fin and gently grip it with forceps pulling away from the squid. In this way you should be able to remove in one piece the pen. If you d like, you can gently pierce the inksac and write with the pen. The pen aids in structural support. 7. Find the gonads and determine the sex of the squid. Upon opening female specimens, the large, firm, white glands are seen first. Males do not have these. The glands lay on top of the other internal organs. These glands create the gelatinous matrix that envelops the eggs. In order to proceed further, carefully remove these glands. In females the eggs are jelly-like in a conical sac at the posterior end of the mantle. The male genital duct is a white, fluid-filled sac in the posterior end of the mantle. The sperm are stored in thin tubes in an elongated sac behind and along one gill.

5 NAME: 5 Label the internal anatomy.

6 NAME: 6 Internal Anatomy Questions 1. a. How many gills does the squid have? b. How many hearts does the squid have? 2. Where does the ink sac empty into and what is its function? 3. What is the function of the pen? What would happen if the squid didn t have a pen? 4. How do you think wastes exit the squid? 5. Was the squid you dissected male or female? How did you know?

7 NAME: 7