Download Name Marine Biology--Mr. Nelson PHYLUM ANNELIDA LAB

Name
Marine Biology--Mr. Nelson
PHYLUM ANNELIDA LAB--Looking at Sea Worms
Background:
The organisms in the Phylum Annelida (Latin annellus, "ring") are referred to as
segmented worms to distinguish them from the non-segmented flatworms and
roundworms. This phylum includes the common earthworm, leeches, and a large number
of freshwater and marine species that are unfamiliar to most people. The distinguishing
characteristic of this phylum is metamerism, the division of the body into similar
segments that are arranged linearly along the anterior-posterior axis.
The annelids are divided into three major classes:
1. Class Hirudinea (leeches)--Leeches represent a group of annelids
specialized for blood sucking. They may be found attached to marine fishes
and invertebrates. The mouth and the posterior end are modified as suckers.
They have no parapodia.
2. Class Oligochaeta (freshwater species and earthworms)-Conspicuous segmentation; lack a well-developed head; few setae
per segment; hermaphroditic. Usually found in fresh water or moist
soils.
3. Class Polychaeta (sea worms)--Practically all representatives of
the Phylum Annelida in the marine world are polychaetes. Each of
their body segments is provided with a pair of extensions known as
parapodia. Typical parapodia have stiff bristles, or setae.
Parapodia have many functions depending on the lifestyle of the
polychaete. They are flattened and are used as a further aid in
locomotion in crawling polychaetes but may be reduced in
burrowing species. All polychaetes feature a well-developed head
with several pair of eyes and sensory structures. Deposit and
suspension-feeding species are provided with various types of
tentacles and feeding structures used in the capture of food.
Carnivorous species often sport a retractable pharynx armed with
jaws.
The polychaete, Nereis, will be used to represent the third class. It resembles
others in this phylum with its distinct segmentation and similar structures found in each
of these segments. There are many species of this marine form, as well as a variety of
habitats and life styles. The Nereis is very active and a voracious predator. Other
polychaetes are less so or burrowers, each with adaptations to best fit its niche.
Objectives:
1. To identify the external and internal structures of annelids.
2. To recognize some of the major systems, functions, and associated structures.
Procedure:
External Anatomy
1. Get a preserved Nereis (sea worm) and a preserved earthworm to place on the dissection tray. Mr.
Nelson will come around to place a living Nereis on your tray.
2. Compare the Nereis to the earthworm. What external characteristic results in them both being
placed into the Phylum Annelida and not one of the other two phyla of worms (Phylum Nematoda-the roundworms, Phylum Platyhelminthes--the flatworms)?
3. Notice that the sea worm's body is divided into segments. Measure the length of your seaworm.
Estimate the number of segments on a sea worm and record the number below. Compare your number
with two other groups. Does it appear that as annelids grow in length, they add more segments or
does each segment get thicker?
Length:
# of segments:
4. Lay out both your sea worms on the dissecting tray with the ventral surface (mouth) down. Figure
20-2 shows the dorsal and ventral view of the anterior (or head region) and may be helpful in
orientation. With your fingers or the forceps, gently squeeze the anterior region of your living sea
worm. Two sharp hooks (jaws) should stick out from the mouth, showing that this is the worm's
anterior.
5. Now that you have used the location of the mouth to determine dorsal vs. ventral. Describe two
other characteristics on the Nereis, which help to distinguish the dorsal vs. ventral surfaces.
1.
2.
6. Besides the mouth, describe how one could recognize the anterior vs. posterior regions of a
Nereis?
7. Use the information below and your textbook, to correctly label the following parts which
have been left off Figure 20-2.
Label: Prostomium, mouth, cirri
figure 20-2 here page 105 chapter 20 lab
Notice that the proboscis is extended in the dorsal view. The Nereis is an active species and has a welldeveloped head as well as various sensory organs: eyes and cirri (also called tentacles), at the anterior
end. Your specimen will most likely have its proboscis retracted with only the mouth showing. The
head is composed of two segments: the prostomium covers the dorsal area over the mouth, and the
peristomium that contains the mouth.
8. Use the information below, to correctly label the following parts which have been left off figure 20-3.
Label: parapodium, setae, epidermis
figure 20-3 from page 105 chapter 20 lab
All of the segments will look very much the same, except toward the posterior or tail end. All
segments, with the exception of the last, have parapodia on them. Parapodia are paddle-like
appendages (one pair per segment) that also contain hair-like setae. The setae provide traction
and grip when the worm is moving over a surface. The skin of the worm is called its epidermis.
9. The parapodia aid the worm in locomotion. Observe your living Nereis by placing it in tray of salt
water. Use the theme of “Structure is Related to Function” to describe how do the parapodia seem to
aid in locomotion in the water?
10. Use the internet, textbook and/or this lab to suggest a function for the setae (It is not protection).
Earthworms have them too.
Respiratory System:
The parapodia also act as gills and absorb oxygen from the water and transfer it into the internal
structures. The parapodia are much larger in some species as well as reduced in others, with the
earthworm not having any parapodia, only setae.
Internal Anatomy
12. Now we will look at some internal structures of the Annelids. Due the buoyancy of water, the
Neries does not support have to have the same level of support as the terrestrial earthworm. Therefore,
we will dissect the earthworm because its internal organs/structures are more defined.
13. Take your preserved EARTHWORM specimen and stretch it out on your dissecting tray, dorsal side
up. Put a dissecting pin in the posterior end to anchor it. Insert another pin in the tippity-tip-tip of the
prostomium. This will stabilize your specimen while you expose its internal organs. Don't worry it
won't be too gruesome.
14. First we will practice. Take your scapula and start at the posterior end, cutting lightly anteriorly.
Remember the epidermis is very thin. Cut a section about 1.5 inches long and pin back the epidermis
with dissection pins. You will know if you go too deep, because wastes from the cut intestine will be
visible. Practice not cutting to deep as to damage internal structures.
15. Now for the real part. Practice is over. Beginning at the tippity-tip-tip of the anterior end, cut
through the skin with the scalpel. Make the cut just slightly to the right of the midline (center of worm,
lengthwise). Carefully cut the skin without cutting the underlying tissues. As you cut, pin the skin on
both sides to the tray. Cut and pin back only the first quarter of the worm.
Digestive System:
Its proboscis and jaws are located just within the mouth. Food enters the worm's mouth, then it is
digested in a food tube, the digestive tract. The mouth is connected to a wider part of the digestive
tract called the pharynx. The pharynx connects with a narrow esophagus, located in segments 6
through 14. Food moves from the esophagus into the crop. The crop, in segments 15 and 16,
temporarily stores the food. Then the food passes into the gizzard, where it is ground up with
sand that is ingested with it. Next, the food passes into the intestine, where it is further digested
and then important nutrients are absorbed into the blood. Finally, solid wastes are eliminated
through the anus, located in the last two segments. Note that the digestive tract is separated from
the skin by the fluid-filled space called the coelom. Figure 8-9 will help to orient you to the
digestive system.
add figure 8-9 page 185 of laboratory investigation 8
16. When you have located the crop and gizzard of the earthworm, invite Mr. Nelson over to your group
it tell you the function of the crop and gizzard. With a dull probe, gently touch the crop and gizzard to
compare their hardness. Based on the functions of the crop and gizzard, which is harder and why?
17. Put these Neries structures in order, starting at the anterior and moving posteriorly, when the
proboscis in not extended:
jaws, intestine, mouth, gizzard, anus, crop
18. As you studied in the Phylum Coelenterata, hydra, sea anemones, and jellyfish have a two-way
digestive systems, some animals (like you and I) have a one-way digestive system. Which type is found
in the Phylum Annelida?
19. Use your text or the internet. What does a Neries eat?
19. Review the function of the digestive system. What important digested substances get absorbed
from the intestine and carried to the rest of the worm's body by the blood?
Circulatory System:
Annelids feature a closed circulatory system, one where the blood is always enclosed in blood
vessels (open circulatory systems have no vessels; blood is just pumped through the body cavity).
The main structures of this system are the dorsal and ventral blood vessels connected by lateral
vessels along the intestine. In the anterior region, these lateral vessels are enlarged into 5 hearts
(see figure 8-9). These blood vessels carry important nutrients (oxygen and food), to the various
organs, and carry away liquid wastes.
place figure 20-4 page 106 Chapter 20 lab
20. Use the previous information, to correctly label the following parts, which have been left off
figure 20-4. Label: blood vessel, hearts.
21. Use the diagram above. Is the blood vessel you labeled the dorsal or ventral blood vessel?
22. In your dissected worm, your best chance will be to see the dorsal blood vessel. Given the way you
cut the earthworm, why is it difficult to see the ventral blood vessel?
22. Worms in the Phylum Annelida have a closed circulatory system. What does this mean?
23. Do we have an open or closed circulatory system?
Excretory System:
Along with the circulatory system, the nephridia take care of filtering liquid wastes from the body
fluid and eliminating them. Pair of nephridia are found in each segment. Each looks like a
curled up tube. You will need the dissecting scope if you want to locate these. Each nephridium
has an external opening called the nephridiopore, located on the ventral surface of the worm.
24. What structure in your body serves the same functions as the nephridia?
Nervous system:
The nervous system of this group is important for its increased complexity from lower phyla as
well as its similarity throughout the phylum. The paired ventral nerve cord (easily noticed when
lifting the intestine) gathers at the anterior end to become the cerebral ganglion. This system can
control the intricate movements of the muscles for movement and the hydrostatic pressure (water
movement) to maintain shape and structure within the worm's flexible body.
25. Keeping in mind terms like anterior, posterior, dorsal, and ventral, how does the location of the
nerve cord in the sea worm compare to the location of the nerve cord in your body?
Muscular System:
Muscles are found within the walls of the worm and are used in intricate ways to move around in
its surroundings. The proboscis is also controlled by a set of muscles to reach out and grasp its
prey. When relaxed the jaws and proboscis are retracted into the mouth.
25. How does the living sea worm use its muscles to move when out of the water? Do you see an
"accordion like" motion or a "whip like" motion?
26. The Phylum Platyhelminthes contains "flatworms". One example is a tapeworm. Tapeworms are
parasitic and live in the intestines of many different species of vertebrates (including marine
vertebrates). The head region of a tapeworm has evolved to attach to the inner wall of the intestine by
hooks and suckers. Unlike the Annelid worms you looked at in lab, tapeworms do not have a mouth or
gut. Describe how a tapeworm obtains food and by what process?