Phylum Annelida & Circulatory Systems
9.1
Lab #9 - Biological Sciences 102 – Animal Biology
Animals in the phylum Annelida include a variety of earthworms, leeches, and marine
polychaetes. Annelids can be freshwater, marine or terrestrial. Some are adapted to parasitic
living. They are typically elongate, wormlike animals that are circular in cross section and
have muscular body walls. The most distinguishing characteristic that sets them apart from
other wormlike creatures is their segmentation. They are often referred to collectively as the
"segmented worms." This repetition of body parts, also called metamerism (me-ta'me-ri'sum;
Gr. meta, between, + meros, part), not only is external but also is seen internally in the serial
repetition of body organs. Development of segmentation is of significance in the general
evolutionary trend toward specialization, for along with segmentation comes the opportunity for
segments to become specialized for certain functions. Such specialization is not as noticeable
in annelids as in arthropods, but the introduction of metamerism coincided with the rapid
evolution of advanced organization seen in arthropods and chordates, the only other phyla
emphasizing segmentation.
Division of the coelomic cavity into fluid-filled compartments also has increased the usefulness
of hydrostatic pressure in the locomotion of annelids. By shifting coelomic fluid from one
compartment to another through perforations in the dividing septa, differential turgor can be
effected, permitting a preciseness of body movement not possible in pseudocoelomates. The
coordination between their well-developed neuromuscular system and more efficient
hydrostatic skeleton makes annelids proficient in swimming, creeping, and burrowing.
Annelids have a complete mouth-to-anus digestive tract with muscular walls, so that digestive
tract movements are independent of body movements. There is a well-developed closed
circulatory system with pumping vessels, a high degree of cephalization, and an excretory
system of nephridia. Some annelids have respiratory organs.
The annelids are true coelomates which form their coelom by a separation or splitting o
mesoderm after it is laid down between the primitive gut and the body wall. Animals which
form a coelom in this manner are called schizocoelomates. The schizocoelomates are usually
protostomes.
The schizocoelomate group includes the phyla Annelida, Mollusca and
Arthropoda, among others.
Body
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Plan Features Retained by Annelids (seen in previously studied phyla):
bilateral symmetry
eucoelomic
high degree of cephalization =
well developed head with sensory
organs
triploblastic structure (endoderm,
mesoderm and ectoderm)
all organ systems are present
complete digestive system
excretory system
Body Plan Features Characteristics of Members of the Phylum Annelida
1. segmentation (metamerism) both internal and external
2. highly developed true coelomic cavity = eucoelomate
3. more complex closed circulatory system
4. fleshy parapodia in some members is likely an example of evolutionary convergence to
appendages and specialized gills seen in arthropods
5. well developed nephridia in most segments for excretion
6. some have respiratory organs (eg. feathery gills in some polychaetes)
Phylum Annelida & Circulatory Systems
9.2
Lab #9 - Biological Sciences 102 – Animal Biology
Phylum Annelida
Classification
Class Polychaeta (pol'e-ke'ta) (Gr. polys, many, +
chaiti?, long hair). Segmented inside and out; parapodia with many setae; distinct head with eyes, palps,
and tentacles; no clitellum; separate sexes, trochophore larva usually present; mostly marine.
Examples: Nereis, Chaetopterus.
Class Clitellata, Subclass Oligochaeta
(ol'i-go-ke'ta) (Gr. oligos, few, + chaiti'!,
long hair). Body segmented inside and
out; number of segments variable;
clitellum present; few setae; no
parapodia, head poorly developed;
coelom spacious and usually divided by
intersegmental
septa;
direct
development; chiefly terrestrial and
freshwater.
Examples: Lumbricus, Tubifex.
Class Clitellata, Subclass Hirudinae (hir'u-din'
ea) (1. hirudo, leech, + ea, characterized by).
Segments 33 or 34 in number, with many
annuli; clitellum present; anterior and posterior
suckers; setae absent (except Acanthobdella);
parapodia absent; coelom closely packed with
connective tissue and muscle; terrestrial,
freshwater, and marine. Examples: Hirudo,
Placobdella.
ADAPTATIONS OF AND USES FOR LEECHES
The medicinal leech is amphibious, needing both land and water, and resides exclusively in
fresh water. A typical habitat for H. medicinalis would be a small pond with a muddy bottom
edged with reeds and in which frogs are at least seasonally abundant.
The medicinal leech has a cylindrical, dorsoventrally flattened body divided into thirty-three or
thirty-four segments. The dorsal side is dark brown to black, bearing six longitudinal, reddish
or brown stripes, and the ventral surface is speckled. All members bear a posterior and
anterior disk-shaped sucker. The anterior sucker surrounds the oral opening where the teeth
for incison are located. In addition, the medicinal leech has five pairs of eyes located on its
front end. H. medicinalis has several pairs of testes and one pair of ovaries as well as a
thickening of the body ring, known as a clitellum, which is visible during the breeding season.
H. medicinalis breeds once during an annual season that spans June through August. It also
remains fertile over a period of years,unlike most other leech species. The act of copulation
takes place on land, where one leech attaches ventrally to one another by means of a mucus
secretion. All leeches are hermaphroditic and fertilization is internal. Sperm is injected into the
vagina by an extendable copulatory organ. A cocoon is formed around the clitellum and slips
Phylum Annelida & Circulatory Systems
9.3
Lab #9 - Biological Sciences 102 – Animal Biology
off the anterior section of the leech. The whole egg sac is laid in damp soil usually just above
the shoreline. After about 14 days, the eggs hatch as fully formed miniature adults.
Motility is achieved both in land and water. Hirudo medicinalis moves in water by contraction
of the longitudinal muscles of the body in a wave-like motion which propels it forward in the
water. Movement on land is accomplished by means of "looping", a movement similar to that of
inch worms. They attach themselves to the substrate alternately by their anterior and posterior
suckers.
Hirudo medicinalis is parasitic and the adults feed on the blood of mammals. It attaches to the
host by means of its two suckers and bites through the skin of its victim. Simultaneously, the
leech injects an anaesthetic so that its presence is not detected, and an anticoagulant in order
for the incision to remain open during the meal. It has three jaws, which work back and forth
during the feeding process, which ususally lasts about 20 to 40 minutes and leaves a tripartite
star-shaped scar on the host. After a full meal of 10ml to 15 ml of blood, the medicinal leech
may increase 8 to 11 times its initial body size. Leeches only feed about once every six months,
this is about how long the blood meal takes to be fully digested. Certain bacteria keep the blood
from decaying during the long digestion period. H. medicinalis may even go longer than six
months without food by digesting its own tissues.
The medicinal leech, as its name suggests, has historically been used for medicinal purposes,
mainly to remove "bad blood" from the diseased. Around 1850 this practice fell into disrepute,
but H. medicinalis is again becoming of value in medicinal practices. Today this species is used
to relieve pressure and restore circulation in tissue grafts where blood accumulation is likely
such as severed fingers and ears. The anticoagulant of leeches is also a fertile ground of
research for surgeries in which an incision must be kept open. In addition, leech saliva is
found to contain powerful antibiotics and anaesthetics which no doubt will prove useful in
future medicinal practice.
The anticoagulant produced by Hirudo is a potent inhibitor of thrombin – part of the
clotting cascade in vertebrates.
From the British Journal of Plastic Surgery – 2004
Hirudo Medicinalis and the Plastic Surgeon.
Whitaker IS, Izadi D, Oliver DW, Monteath G, Butler PE.
“Medicinal leech therapy is an ancient craft that dates back to ancient Egypt and the
beginnings of civilisation. The popularity of Hirudo Medicinalis has varied throughout history,
reaching such a peak in Europe in the early 19th century that supplies were exhausted.
During the latter half of the 19th century, their use fell out of favour, as they did not fit in with
the emerging concepts of modern medicine. Leeches have enjoyed a renaissance in the world of
reconstructive microsurgery during recent years, and their first reported use in alleviating
venous engorgement following flap surgery was reported in this journal [M Derganc, F Zdravic,
Venous congestion of flaps treated by application of leeches, Br J Plast Surg 13 (1960) 187].
Contemporary plastic and reconstructive surgeons in units throughout the United Kingdom
and Ireland continue to use leeches to aid salvage of failing flaps. We carried out a survey of all
62 plastic surgery units in the United Kingdom and the Republic of Ireland to assess the
current extent of use, and to investigate current practice. We have shown that the majority of
plastic surgery units in the UK and Ireland use leeches post-operatively and that the average
number of patients requiring leech therapy was 10 cases per unit per year. Almost all units use
antibiotic prophylaxis, but the type of antibiotic and combination used is variable. We outline
current practice and suggest a protocol for the use of leeches. Whilst the use of leeches is
widespread, the plastic surgery community has progressed little in defining indications for their
use or in achieving an accepted protocol for their application in units throughout the UK and
Ireland”.
Phylum Annelida & Circulatory Systems
9.4
Lab #9 - Biological Sciences 102 – Animal Biology
¾ Circulatory Systems
Open circulatory system = a circulatory system, characteristic of some invertebrates,
(eg, some molluscs and arthropods), in which blood flows through an interconnected system of
open sinuses rather than blood vessels. The tissues and cells are directly bathed by the blood
for gaseous exchange and nutrient uptake. The circulatory fluid is called the hemolymph or
endolymph.
Closed circulatory system = a circulatory system in which blood flows through blood vessels
at all times. Blood flows from arteries to capillaries and through veins, but the tissues
surrounding the vessels are not directly bathed by blood. Some invertebrates and all
vertebrates have closed circulatory systems
Heart = a pumping organ or series of modified arteries (eg. dorsal hearts) that have an innate
ability to contract due to their unstable resting membrane potentials. This organ beats on its
own with a regular rhythm without direct stimulation by the nervous system. However, the
nervous system may modulate the rhythmic contractions of this organ.
Arteries = thicker walls, smaller cross section, often pleated appearance.
Arteries carry blood away from the heart.
Veins = thinner walls, often collapse and look flattened in dissected specimens.
Veins carry blood to the heart.
Arterioles = considerably smaller than arteries and thus provide the greatest resistance to
blood flow. In animals that have a closed circulatory system, arterioles carry blood from
arteries to capillaries.
Capillaries = vessels made of a single layer of endothelial cells surrounded by a basement
membrane. These are the only vessels whose walls are thin enough to allow for exchange of
gases, nutrients, and waste products. These substances move down their concentration
gradients (oxygen is higher in the blood than the tissues so it moves from the blood to the
tissues; carbon dioxide levels are higher in the tissues and so it moves into the blood
Veins = relatively thin walls, smaller muscle layer relative to arteries, more distensible than
arteries.
Veins carry blood to the heart.
Venous Valves = in some animals, one way flap valves that prevent the backflow of blood
caused by the force of gravity. These valves are needed as the venous blood pressure is
considerably lower than the arterial blood pressure. Blood is forced through the valves by
skeletal muscle action. Veins run between skeletal muscle fibers and as the fibers contract,
blood is forced through the veins in vertebrates and some invertebrates.
¾ DRAW THE DIAGRAM ON THE BOARD OF EARTHWORM CIRCULATION BELOW:
Phylum Annelida & Circulatory Systems
9.5
Lab #9 - Biological Sciences 102 – Animal Biology
LAB PROCEDURE
LAB SCORE:
NAME:
Refer to the chapter on annelids in the Hickman text for illustrations, diagrams
and additional information about segmented worms.
Observation of Living Specimens
Class Clitellata
Subclass Oligochaeta (terrestrial and freshwater segmented worms)
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Observe the specimens and/or diagrams of the earthworm, Lumbricus terrestris.
Record the descriptive information requested at the end of the lab for this species.
Class Clitellata
Subclass Hirudinea (leeches)
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Observe the specimens and/or diagrams of the mixed leeches in the genus Hirudo.
Record the descriptive information requested at the end of the lab for this species.
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Observe the end of lab class demonstration by your instructor of the locomotion and
feeding activity of the medicinal leech, Hirudo medicinalis.
Class Polychaeta (marine segmented worms)
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Observe the specimens and/or diagrams of the various available polychaetes.
Record the descriptive information requested at the end of the lab for these species.
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The polychaete subclasses Errantia and Sedenteria are somewhat artificial groupings
and in this lab are solely used to categorize species based on their degree of mobility
and feeding strategies rather than to indicate any degree of common evolutionary
descent. Errantia and Sedenteria are no longer valid subclasses.
¾ Microscopy Procedures
Class Polychaeta (marine segmented worms)
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Read and review the features of the clamworm Nereis in your lab manual.
Observe a microscope slide of a cross section of the polychaete Nereis and identify
the basic structures from your lab manual.
Observe a microscope slide of a Nereis parapodium and identify the basic structures
from your lab manual.
Class Clitellata
Subclass Oligochaeta (terrestrial and freshwater segmented worms)
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Read and review the features of the earthworm Lumbricus in your lab manual.
Observe a microscope slide of a cross section of the intestinal region of the
oligochaete Lumbricus and identify the basic structures from your lab manual.
Observe a microscope slide of a cross section of the nephridia/nephridiopore of
Lumbricus and identify the basic structures from your lab manual.
Phylum Annelida & Circulatory Systems
9.6
Lab #9 - Biological Sciences 102 – Animal Biology
¾ Earthworm Dissection Procedure (see the supplemental lab manual)
Class Clitellata
Subclass Oligochaeta (terrestrial and freshwater segmented worms)
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Review all of exercise 12B in the lab manual.
As per your instructor’s directions, obtain a live Lumbricus terrestris (earthworm)
Follow the directions for behavior observation, external structure identification
and internal structure dissection provide by both the lab manual and by your
instructor.
¾ Be sure to perform the behavioral observations BEFORE
euthanizing your earthworm.
¾ DRAW AND CLEARLY LABEL A DIAGRAM OF YOUR EARTHWORM
DISSECTION BELOW.
Phylum Annelida & Circulatory Systems
9.7
Lab #9 - Biological Sciences 102 – Animal Biology
Living Specimens Data
Class Clitellata
Subclass Oligochaeta (terrestrial and freshwater segmented worms)
Scientific name: Lumbricus terrestris
Common name:
Dimensions of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Class Clitellata
Subclass Hirudinea (leeches)
Scientific name: Hirudo medicinalis
Common name:
Dimensions of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Phylum Annelida & Circulatory Systems
9.8
Lab #9 - Biological Sciences 102 – Animal Biology
Note that the old, historically used Subclasses of Errantia and Sedenteria are no longer
valid taxonomic categories, we use them for simplification of study only.
Class Polychaeta
“Errantia” (errant, free-living segmented worms)
Scientific name:
Common name:
Color of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Class Polychaeta
“Errantia” (errant, free-living segmented worms)
Scientific name:
Common name:
Color of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Class Polychaeta
“Errantia” (errant, free-living segmented worms)
Scientific name:
Common name:
Color of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Phylum Annelida & Circulatory Systems
Lab #9 - Biological Sciences 102 – Animal Biology
Class Polychaeta
“Sedentaria” (sedentary, segmented tube worms)
Scientific name:
Common name:
Color of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Class Polychaeta
“Sedentaria” (sedentary, segmented tube worms)
Scientific name:
Common name:
Color of this specimen:
Notes & observations to help you remember and distinguish this group/species:
Class Polychaeta
“Sedentaria” (sedentary, segmented tube worms)
Scientific name:
Common name:
Color of this specimen:
Notes & observations to help you remember and distinguish this group/species:
9.9
Phylum Annelida & Circulatory Systems
9.10
Lab #9 - Biological Sciences 102 – Animal Biology
HOMEWORK – use the internet to help you answer these questions:
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What is a sabellid worm?
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Briefly describe and/or draw a flowchart diagram to show the lifecycle of a typical
leech.
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Briefly describe how the parchment tubeworm Chaetopterus feeds and what it
typically eats.
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What is the feeding strategy of the polychaete worm Nereis and what does it
typically eat?
Phylum Annelida & Circulatory Systems
Lab #9 - Biological Sciences 102 – Animal Biology
LABORATORY NOTES:
9.11
Phylum Annelida & Circulatory Systems
Lab #9 - Biological Sciences 102 – Animal Biology
LABORATORY NOTES:
Chaetopoda by Haeckel
9.12