Examine your petri dishes of regenerating planarians. The goal
here is to cut the planarians various ways and then speculate on the
distribution of neoblasts that would explain your results. What other
factors ( such as species or genetics) could be important. The class
should analyze results together and come up with a hypothesis as to
the gradient that exists for regeneration. Last year’s class had 70%
success rate for survival for one week after surgery. Did your
section do better or worst?
General introduction
Don't you ever laugh as a hearse goes by,
For you may be the next to die.
They wrap you up in a big white sheet,
And cover you up from your head down to your feet.
They put you in a big black box,
And cover you up with dirt and rocks.
All goes well for about a week,
And then your coffin begins to leak.
The worms crawl in, the worms crawl out,
The worms play pinochle on your snout.
They eat your eyes, they eat your nose,
They eat the jelly between your toes.
A big green worm with rolling eyes,
Crawls in your stomach and out your eyes.
Your stomach turns a slimy green,
And pus pours out like whipping cream.
You spread it out on a slice of bread,
And that's what you eat when you are dead.
To watch animals feed you will need to place food in containers.
There is a danger of fouling the containers. Please be careful
and add only the amounts specified in the instructions to your
containers. If a container looks foul to you, call the lab
instructors attention to it so she can add new water. If she
instructs you to do so, make sure you know whether you are to
add spring or salt water to your bowl.
A rule of thumb is that Clitellates (earthworms and relatives) are
terrestrial or fresh water forms, Polychaetes are salt water forms and
so are Sipunculids and Echiurans. We have plenty of the
microscopic fresh water forms, so these can be dumped when you
are done. It will ensure that the rest of the population does not suffer
from contamination.
Background:
Annelida consists of the segmented worms in the major classes Polychaeta
(bristleworms), and Oligochaeta (earthworms and relatives), with a total of about
12,000 known species in marine, freshwater, and terrestrial environments.
Most annelids have chitinous bristles, or chaetae, secreted by epidermal cells,
that project from the body. The body wall consists of a collagenous cuticle
secreted by the monolayered epidermis. The coelom is large, segmentally
compartmented, lined and well developed in polychaetes and oligochaetes but
reduced in leeches.
The circulatory system of most annelids is a set of tubular vessels, some of
which are contractile and serve as hearts. The circulatory system is absent or
greatly reduced in leeches. The system includes a dorsal longitudinal vessel
above the gut in which blood moves anteriorly, a ventral longitudinal vessel
below the gut, in which blood moves posteriorly, and paired segmental vessels
that connect the dorsal and ventral vessels. The digestive, circulatory, and
nervous systems are continuous and pass through the segments.
Respiration is accomplished in a variety of ways. In some, the general body
surface is sufficient but gills are present in most polychaetes, many leeches, and
a few oligochaetes. Excretory organs are metanephridia or protonephridia and
typically one pair is present in each segment. These osmoregulatory organs are
best developed in freshwater and terrestrial species. The sexes are separate in
polychaetes but oligochaetes and leeches are hermaphroditic. In the ancestral
condition paired clusters of germ cells were present in each segment and
released developing gametes into the coelom.
____________________________________________________________
Polychaetes
Most segmented worms found in marine environments represent a
major evolutionary branch of annelids--Class Polychaeta. The name
means "many bristles." The bristles, or setae, project from side flaps
called "parapodia." Parapods have a variety of shapes -- adaptations
for different habitats and life-styles. Species living in rocky
environments have leg-like parapods used in walking. In burrowing
species, parapodia function as digging paddles. In some worms the
parapodia are short and combine with peristaltic contractions to move
the worm through the mud. In others, the parapodia contract following
their power stroke, streamlining the worm for passage through the
mud.
Sedentary Polychaetes
Sedentary polychaetes are usually adapted to living permanently in
tubes or burrows; some attach themselves to rocks or piers. Many
sedentary polychaetes, like the lugworm, Arenicola, live in burrows in
sand or mud. The majority, however, are tube builders. Tubes of
different species vary greatly in their composition and structure. They
may be composed of sand, shell, or other particles held together with
mucus, or made entirely of organic substances secreted by the worm
that harden on contact with water.
Sedentary polychaetes have greatly modified head regions for
specialized feeding habits. Many are adapted for feeding on organic
matter deposited on the ocean floor.. The parapodia are reduced in
the sedentary polychaetes, and the setae of many tube-dwelling
forms are hooked to help the worm hold itself to the wall of its tube.
We have living representatives of the tube dwelling polychaetes.
The Potamilla are commonly known as "fanworms" or "feather
duster" worms due to a colorful appearance of a maroon or redcolored tentacular branchial crown. They are indirect depositfeeders. They have no proboscis. While feeding they spread out their
branchial crowns to trap suspended particles and to sweep with their
long mobile palps picking up deposited material (filter-feeding). Only
suitable sized particles are ingested while others are rejected at the
mouth. The more primitive members making temporary mucus tubes
and creep around actively.. The large ones never leave their tubes
and are associated with shallow water but smaller ones are able to
move around. and are common in deep seas.
1. Obtain a feather duster worm and place in a dish of sea water
(Salt water only please). Allow it to acclimatize to its new
environment. Study its feeding device under the stereoscope.
A. Include a movie or several photographs of its filter feeding in
your notebook. Use live phytoplankton available for feeding.
Worm in tube
The particles that land on the grooves can be
sorted with respect to size.
2. There may be other sedentary worms available for you to
observe. Obtain photographs. and compare the morphology of
at least one other specimen to the feather duster worms. Pay
particular attention to the head, which will tell you how these
animals feed. For example, some sedentary worms have long
tentacles with groves on them. These act as the “feathers” of a
feather duster worm. The food particles are moved along by
cilia in these grooves toward the mouth.
This week, another example of a sedentary worm we have in the
laboratory is Spirorbis
Spirorbis
In this genus and in the family Spirorbidae all species live in
permanent calcareous tubes cemented to algae, shells, or rocks.
These have cemented themselves to the walls and filter in the large
60-gallon tank.
Obtain a few specimens of this microscopic worm and place them in
a small Petri dish so they can acclimatize to their new conditions. Be
prepared to watch them for a few minutes so you can see them unfurl
their tentacular crown.
Obtain a video if possible of Spirobis “feeding” or at least trying
to investigate its surroundings for possible food items by
extending its tentacles from its tube.
3. Errant Polychaetes
Errant polychaetes include actively crawling or swimming forms,
which may, however, also spend time in burrows or crevices, or
under rocks on the seashore.. Many are predators on small
invertebrates; some are scavengers.. Most errant polychaetes have
well-developed head regions, which bear eyes, sensory tentacles,
and a specialized organ, the nuchal organ, thought to detect
chemicals. The anterior end of the gut often forms a protrusible
structure, the proboscis, sometimes equipped with strong chitinous
jaws and used in feeding. The setae of some polychaetes, e.g., the
tropical fireworm, are composed of calcium carbonate rather than
chitin and are hollow. These brittle setae are easily broken off and
contain a toxin that produces a painful reaction in humans. In the
scaleworms, a series of overlapping scales form a covering over the
animal's upper surface. In the sea mouse these scales are
completely covered by long, slender, feltlike setae projecting from the
parapodia.
We only have one representative of an errant polychaete and that is
the bristleworm. Many errant polychaetes are ferocious predators and
most aquarists remove them as soon as they are spotted. We do the
same, but have saved for your observation some of our disposed
specimens.
Please wear gloves when handling these specimens. They are
called fire worms for a reason. Please observe the jaws in these
specimens. Take a picture of those jaws and then obtain a
video of blood flow in your specimens that documents closed
circulation. You may also video closed circulation in
Lubriculus, a fresh water form, instead. This however will
involve more work as these thin worms must first be transferred
to capillary tubes.
_______________________________________________________
Clitellata
Clitellata, the sister taxon of Polychaeta, includes earthworms and
their allies. The head is reduced and its sensory functions
minimized.. Obvious in most is a girdle-like band of secretory
epidermis, the clitellum, near the anterior end of the worm, a collar
that forms a reproductive cocoon during part of their life cycle.
Oligochaetes are members of the Clitellata that lack the parapodia
characteristic of polychaetes although setae may be present. Also
lacking are head appendages These worms are hermaphroditic and
have gonads and reproductive equipment restricted to a few
specialized genital segments. Development is direct, without a larva.
In the laboratory, you will find several living representatives of
Clitellata annelids. You will use the earthworm as the model
organism. Earthworms are also know as night crawlers, belong
to the Oligochaeta, a clade of clitellate annelids that have
become very common in the United states. Please compare the
other living representatives to the living earthworm with regard
to overall anatomy, feeding and locomotion.
You may be surprised to find that the common species used in
biology classrooms is not a native. Lumbricus terrestris was probably
brought to the US in the 18th century. Their burrowing activities are
thought to be beneficial by most gardeners. Unfortunately in forests,
they redistribute nutrients, making them unavailable to other native
detritus feeders and young plants, and in the process, are destroying
the diversity of our forests. So although the burrowing activities of
many polychaetes are beneficial and stabilize habitats such as mud
flats, those of the night crawler for the most part are deleterious to our
forest ecosystems.
4. External Anatomy and locomotion of the common night
crawler
Obtain an earthworm, Lumbricus terrestris. Place it in a large
dish to study its external anatomy and locomotion.
Orientation
Examine the external features of the worm. The anterior end
is usually larger than the posterior and is round in cross section
whereas the posterior tends to be flattened dorsoventrally
A dorsal view of the anterior end of Lumbricus. The segments are
numbered.
Clitellum
A band of thickened secretory epithelium, the clitellum (clitell =
saddle), girdles the body near the anterior end. The clitellum
secretes a mucous cocoon, into which gametes and albumen are
released and where fertilization occurs,
Segments
The body is segmented and each segment is separated from its
neighbors by a distinct circumferential groove. The anteriormost true
segment is the peristomium (peri = around, stome = mouth). Anterior
to the peristomium is a small lobe, the prostomium (pro = before)
that, for embryological reasons , is not considered to be a segment.
The peristomium encircles the large, ventral mouth and is an almost
complete ring around the body. The segments are numbered anterior
to posterior beginning with the peristomium.
Count the preclitellar segments in your specimen.
____________ How many segments contribute to the clitellum?
_____________ Compare your counts with those made by other
students. Does the number of segments in each region appear
to be constant or variable? ____________
The segments posterior to the peristomium are complete rings,
without notches, and extend uniformly for the entire length of the
worm. The posterior most division of the body is the pygidium, which
encircles the anus at the posterior tip of the worm. Like the
prostomium, the pygidium is not considered to be a true segment.
Chaetae or Setae
The eight small chaetae or setae on each segment (except the first)
are usually visible with adequate magnification (25X). Chaetae or
setae are small chitinous bristles emerging from pores in the
integument on the ventral half of the worm. The setae are arranged
in four pairs, two on each side The chaetae are used as anchors
when burrowing to hold parts of the worm against the so that
elongation of the animal results in controlled, usually forward, motion.
A ventral view of Lumbricus. The worm has been rolled slightly to
reveal part of the right side.
The chaetae or setae are equipped with protractor and retractor
muscles and are retractile. In your specimen they may be withdrawn
in some, or even all, of the segments. Careful examination, however,
should reveal some segments with extended setae. Setae are amber
or brown, slightly curved, and short.
Rinse your worm gently with tap water and hold it in your hand on
the stage of the dissecting microscope. Focus on the lateral body
wall and watch the chaetae. You may see the animal retract or
protract some of its chaetae while you watch. Place it on a clean
dish, and watch it move. Does it seem to have difficulty moving
on the smooth glass surface. Place some stones and dirt in the
dish and now watch it move. a. Explain why it was difficult for
the earthworm with a muscle that essentially act to distort a
hydroskeleton to move on the glass dish but not the dish that
contains dirt and stones.. b. When the earthworm moves in dirt
(or wet sand) do any segments move as a unit? c. Does the
wave of contraction and relaxation move from front to back or
back to front?
5. Lumbriculus variegates is a detritus feeder like the earthworm
and a perfect example of severe miniaturization of form.
As always make sure you record your observations in your
journal.
a. Obtain a few mudworms. Place them is a small Petri or
observation dish. Note how this Oligochaete moves. Also take
one or two and put them on a wet paper towel. Note the
difference in “swimming” locomotion versus locomotion in
an environment were they can contact a surface.
b. You may be able at the highest power of your stereoscope
to focus and watch them feed. Use the fish food provided.
Add a few tiny tiny crushed pieces of one flake, or one
flake to the bowl. As always record your observation.
Notice how transparent at high power these worms are.
These worms are often used for experiments that look at the effects
of drugs on cardiovascular function.
Place your worm in a plastic pipette and let it move to the tip.
Then place the tip of a capillary tube close to the tip of the
pipette and gently squeeze. The worm should move into the
capillary tube, which you can place then in a small observation
dish. Observe the internal anatomy of the worm. Can you
trace blood flow from dorsal to ventral? Time dorsal vessel
contraction rate.
c. Take a video or photographs of blood flow, showing the
changes in vessel diameter. Any evidence for how these
animals respire? If you did not document close circulation in
the fire worms do so with these specimens. In other words,
show side vessels connecting to dorsal and ventral veins and
arteries.
Then add a bit of alcohol (70 % ETHANOL ONLY-Alcohol is very
toxic to invertebrates so start with 1ml or less in a dish 6 inches
in diameter. ) to bowl or simply place your bowl on an ice block.
d. What is the effect on heart rate? Describe the effect, noting
whether you used ice or alcohol in your notebook.
If we had more time in this lab, we could test a host of other
drugs and even determine a dose response curve. Do not place
any worms exposed to alcohol or cold back in the colony dish.
Place them in a separate dish until we can determine if they will
recover and not die and foul the colony dish..
6. Various small annelids. Examine several small species of
annelids to document the effects of size on segmentation and the
types of organs found in these species. These are Clitellates, and
surprisingly most belong to Oligochaeta or the same clade as the
much larger nightcrawler. .
Below are some photographs of some of the forms available.
Dero, back end, high power Yes that is the hind end, not the head, so
what is that claw like structure?
Aeolosoma-often multiplies by fission, can get very long worms with
several generations developing behind the parent generation.
So, are your cultures reproducing asexually?
Stylaria, Note large setae and prominent feeding structure at anterior.
So if that is what they use to feed, how do they feed?
Pick two forms, identify from the pictures which two forms you
picked. a1 and a2 Photograph your two forms including their
names in a corner of the photographs. b1 and b2. Compare
them to Lubriculus in overall morphology and anatomy (number
of segments, visibility of segments and clitellum, presence or
absence of circulatory vessels, etc.). Make sure you take some
of the green stuff in the culture with you, so you can watch them
feed as well.
Below are some urls that may help you in identifying anatomy
particular to a species, but do not simply download the photos or
videos as your own. We will know!!!
www.microscopyu.com then go to galleries then pond life
http://www.micrographia.com/specbiol/helmint/annelhom/olig01
00.htm#oligolink
The first few unidentified pics are probably aeolosoma.
http://www.microbelibrary.org/index.php/library/resources/3190aeolosoma-hemprichi-ingestion-of-soil-particles-and-digestion-ofmicrobial-films
What general trends do you see? Record your observations in
your journal.
c. Produce a movie of locomotion in one of these species. How
does the locomotion of your choice vary from that shown by
Lubriculus and the earthworm.
To examine these more closely, you may need to watch them
under a depression slide or under slight compression on a
regular slide. Only use low power, 10x or 20x so the slide can
still hold enough water for these to move.
7. Hirudinea : Leeches are Clitellates, but not Oligochaetes. They
belong to another group of Clitellates, known as the Hirudinea. We
only have 4 specimens, so when you are done pass your specimens
on.
Leeches are annelids modified for an ectoparasitic life style. The
body has a terminal posterior sucker and a dorsal subterminal anus.
An anterior sucker is present in all but one species (Acanthobdella
peledina).
As always make sure you record your observations in your
journal.
Obtain a living leech and place it in some fresh water. Allow the
leech to remain undisturbed for about 5 minutes in a well lighted
room. Pass your hand over the container so that a shadow falls
on the leech. a. Observe and record the leeches' actions.
b. Allow the leech to remain undisturbed for at least 5 minutes.
Use a plastic ruler or tongue depressor to stir up the water
surface. Observe and record the leech’s actions. What parts of
the leech are receptive to water movement? Why would leeches
have organs that are sensitive to water vibrations?
c. Watch it move and compare its movement with that of an
earthworm. Do you feel the leech relies on its hydrostatic
skeleton as much as an earthworm? Do you see types of
movement, you would not expect in animal such as an
earthworm without the “compact” body of a leech.
d. Finally examine the leech’s external anatomy. Does it have
more or less segments than an earthwork. Can it be divided into
the same three areas? Does it have chaetae?
e. Add a small snail or some fish food to your dish. Place it on
the side of the dish furthest from the leech. How does the leech
react? Watch your leech fed. If they are hungry enough they will
feed on the fish food even if they prefer snails. If your specimen
is cooperative, you will develop a respect for just how flexible a
body a leech can possess.
Other annelids???
8. Spoon worms.
Echiurans were included in the Annelida until recently. Your
textbook is very conservative and still includes them as class of
Annelida. Even by those that consider them a separate
phylum, they are still considered close relatives of the annelids.
The body of an echiuran lacks annelid-type segmentation, but
the distinctive free-swimming trochophore larval stages of
echiurans and polychaetes are very similar. Your teaching
instructor will set up the dish of spoon worms under the
microscope. a. Every one should take time to watch these
animals move and attempt to bury themselves again. b, If you
are lucky they may feed for you. Try fish food first, but mud,
blood worms or beefheart may also work. Watching that spoon
unfold is a sight you will not forget. Please remember to
record your observations in your journal. Spoon and
peanut worms are animals you many never again encounter in
your lives.
9. Peanut worms
Sipuncula -- These animals, which are commonly called
"peanut worms" because some have the general shape of
shelled peanuts, are not particularly well studied. Only about
320 species have been formally described, all marine and
mostly from shallow waters. While some (like the specimen of
Sipunculus shown below) burrow into sand and mud, others
(like this unidentified species from French Polynesia) live in
crevices in rocks, or in empty shells. Still others bore into rock.
For instance, sipunculans have no trace of important annelid
characters such as segmentation and chaetae (bristles). The
characters they do share with annelids (e.g. worm shape,
introvert, trochophore larva) are not restricted to annelids and
sipunculans, but are much more general. These animals are
now placed in a separate phylum, but were once considered
aberrant annelids. Now some believe they may even be more
closely related to mollusks. a. Obtain a peanut worm and
watch it move and feed. If possible take photographs or video
its introvert. Try fishfood ,bits of crushed mudworm!
Please remember to record your observations in your
journal.
Spoonworm.
At the end of lab, you should have videos of closed circulation in mudworms
or fireworms (easier). Some notes on circulation in mudworms in different
environments. You should also have notes and pictures documenting the
effect of size on structure in annelids.
This is really the first chance you will have to work with filterfeeders, please
spend some time just watching how they feed (documented by video).
You should also be able to compare spoonworms and peanut worm to the
typical annelid. Use earthworm or if you wish fireworm as your model.
There is a table in your book you can use as a model, but don’t simply copy it.
Also confine your observations to those you can see.
Peanut