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LAB 7 – INVERTEBRATES
Phylum Cnidaria
 among the simplest animals (only sponges are less complex)
 cnido = Greek for nettle (prickly plant)
 all cnidarians have cnidocytes – specialized stinging cells that assist them in capture of prey and
defence
 most are marine
 general body plan consists of two layers of cells surrounding a cavity
 they are radially symmetrical
 two life forms:
o polyp – a generally sessile form in which the oral surface (mouth) is upward and the
other end, aboral surface is attached to a substrate
o medusa – a free-swimming form in which the mouth is usually downward
 some cnidarians show only one form or both (= dimorphic life cycle)
 some have a life cycle that constantly changes between the two forms
 Hydra (class Hydrozoa) is a small freshwater polyp with no medusa stage (unlike other
hydrozoans)
o the hydra attaches its basal disc (foot) to a substrate and extends its tentacles and body
column
o if disturbed, the hydra may curl up into a ball
o the hydra may move in the following ways:
 gliding on its foot
 inching along with its tentacles and foot
 somersaulting
 floating on a bubble of gas secreted by the foot
o hydras are carnivores
o they capture prey with their tentacles and restrain them with toxic stings of their
nematocyst
o the food is transferred to the mouth, partially digest
in the gastrovascular cavity, and then absorbed by the
gastrodermal cells (in which intracellular digestion
occurs)
o undigested material exits the mouth
o acetic acid can cause the hydra to discharge its
nematocysts from their cnidocytes which contain
harpoon-like structures
o hypostome – the conical elevation with the mouth
opening at its tip. When hydra is not actively feeding,
cells stick together and cover the opening
o tentacles – food-catching arms that radiate from the
hypostome. Tentacles contain cnidocytes for
capturing prey and defence
o gastrovascular cavity – location where digestion
and absorption of food occurs. Some gas exchange
(respiration) also occurs in the cells lining this cavity
(gastrodermis) as well as across the epidermis
o body column – composed of mesoglea sandwiched
between two tissue layers of cells:
 epidermis – outer layer of epithelial cells
 gastrodermis – inner layer of epithelial
cells
o mesoglea – a thin gelatinous layer between the
epidermis and gastrodermis. Only seen as a thin dark line in hydras but may be larger in
other cnidarians. It acts as a hydrostatic skeleton
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basal disc – lower posterior end of the body that is used to attach to a substrate and
assists in locomotion
cell types in Hydra:
o epitheliomuscular cells – cells that act as epithelial cells by covering and lining both
surfaces and as muscle cells by having contractile fibres. One type of these cells has
longitudinal muscle fibres and is located in the epidermis. The other contains circular
muscle fibres and is located in the gastrodermis. These two types work antagonistically to
enable movement. In the gastrodermis, epitheliomuscular cells can also engulf partially
digested food particles from the gastrovascular cavity and complete digestion
intracellularly
o cnidocytes – also called cnidoblasts. They are cells in the epidermis most concentrated
in the tentacles and hypostome. These cells contain nematocyst capsules, which are
triggered by cnidocils, bristle-like projections on the outer surface of the cnidocyte. The
cnidocils are modified epidermal cilia. Nematocysts can be either stinging, entangling or
adhesive (this is a key way of identifying different cnidarians)
o neurons – nerve cells that extend along the base of the epidermis and the gastrodermis.
These neurons form a nerve net in each tissue layer. Neurons in the mesoglea connect
the two nerve nets together
 sensory cells – a type of neuron located in the epidermis that is sensitive to
external stimuli and chemicals in the water. Impulses from sensory cells are
relayed to neurons of the nerve net that synapse with epitheliomuscular cells.
This results in coordinated muscular movement
o gland cells – cells located in the epidermis of the basal disc that secrete a sticky
substance used in anchoring the basal disc to the substrate. There are also gland cells in
the gastrodermis that secrete digestive enzymes
o interstitial cells – cells located between the epitheliomuscular cells of the epidermis
(difficult to locate) that are like stem cells and can differentiate into other cell types such
as neurons and cnidocytes
reproduction of Hydra:
o Hydra can reproduce both sexually or asexually
o in sexual reproduction, gametes (sperm and egg) unite to produce a zygote
o gametes are produced in gonad, which appear like a small lump in the epidermis of the
body column
o sperm is produced in testes in the upper half of the body near the tentacles and one egg is
produced in each ovary in the lower half of the body, near the foot
o the ovaries are slightly larger than the testes
o some are hermaphroditic. Most hydra, however, are individual sexes
o sexual reproduction usually occur in the fall
o sperm swims to egg by entering the ovary through a hole in the epidermis
o the zygote produces a hard covering and drops to the sediments and will remain dormant
until spring when a polyp emerges
o asexual reproduction is accomplished by budding, which occurs when a new individual
grows as a bud off of a parent hydra. This new organism is an identical copy to its parent.
Eventually, the bud detaches when it has grown enough to capture its own food and live
independently
o budding usually takes 2 to 4 day to complete
Gonionemus (class hydrozoa) is a small, shallow, temperate, marine medusa
it is about 2.5 cm in diameter
some species of this genus cling to seagrasses rather than swimming
some species of this genus are poisonous to human because they have a powerful toxin in their
nematocysts
unlike other hydrozoans, Gonionemus spends most of its life in the medusa stage, which resembles
an upside down polyp, with its mouth and tentacles facing downwards
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most of the body is expanded to form a dome-like structure with a thick mesoglea which acts as a
buoy and a hydrostatic skeleton
 bell – the dome-shaped structure made of
epidermis, gastrodermis, and mesoglea
 tentacles – arms hanging from the edge of the
bell, which are used for capturing prey and
attaching to objects. There are about 80+
tentacles on some species
 tentacular bulbs – dark swellings located at the
base of each tentacle that contain interstitial
cells, which will develop into cnidocytes to
replace discharged ones on the tentacles
 adhesive pads – located near the tips of the
tentacles and are used for attaching to seagrasses
or macroalgae
 cnidocytes – stinging cells that occur in spiral
swellings (batteries) along the length of the
tentacles. Each cnidocyte contains a nematocyst
that explosively projects a tube capable of
penetrating the tissue of its prey and injecting a
paralysing poison
 velum – a shelf under the edge of the bell.
Epitheliomuscular cells in the velum and bells contract to eject a jet of water downward, pushing
the animal upwards. Down movements are passive. Scyphozoan medusae lack a velum
 manubrium – a tube that hangs in the space inside the bell terminating with the mouth and
leading to the stomach. It is homologous to the hypostome in the Hydra.
 stomach – site of extracellular digestion
 mouth – site of ingestion at the end of the manubrium. The edge of the mouth is ringed by fleshy
projections called oral lobes. These structures assist with ingestion. Indigestible food is eliminated
through the mouth, as well
 radial canals – four canals radiating out of the manubrium that are extensions of the stomach
 ring canals – connecting with the ends of the radial canals and running around the edge of the
bell. Along with the stomach, the canals form a gastrovascular system to partially digest and
circulate food throughout the body. Food particles can be engulfed by gastrodermal cells and
digestion is then completed intracellularly
 statocysts – small swellings between the bases of the tentacles that contain a stone suspended on a
flexible stalk. The pressure of the stone against the cells lining the cavity of the statocyst provides
the basis for orientation with respect to gravity. Statocysts are thus sensory structures that perceive
the direction of gravity
 gonads – site of gamete production. There are four gonads that hang in the bell
 a fertilized egg quickly develops into a planula – a ciliated larva. The free-swimming larva soon
attaches to a substrate and becomes a polyp. The polyp reproduce asexually by budding and then
each polyp produces medusa buds that grow into adult medusae
Phylum Annelida
 annelida means “little rings”
 this phylum contains earthworms, tubeworms, and leeches
 phylum is collectively called segmented worms because the body of most annelids are made up
of many essentially similar segments
 externally, segmentation is seen by their external ringed appearance, and internally it is seen by
septa within the body cavity
 the most known annelid is the common earthworm, Lumbricus terrestris
 earthworms live in moist, organically rich soil
 they are detritivores
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when digging, earthworms swallow the soil and break it up. The soil that passes thorough the
digestive tract (castings) forms a cement that is partially utilized to line their burrows
burrows allow air and water to easily penetrate the soil, and exposes less reach soil
external anatomy of earthworms:
o the surface of the earthworm is covered in a thin cuticle that is secreted by the epidermis.
The cuticle protects the worm from desiccation
o glandular cells of the epidermis produce mucus to form an additional protective layer and
aid in locomotion and respiration
o earthworms are bilaterally symmetrical, therefore we use the words anterior,
posterior, dorsal, and ventral to describe the worm instead of oral and aboral
o earthworms’ bodies are cylindrical. The anterior end is slightly more cylindrical and
thicker
o the ventral surface is a lighter colour and flatter than the dorsal surface
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one each segment, there are 4 setae or bristles that are contained in epidermal pits and
function to anchor part of the earthworm to the substrate while resting. They are on the
ventral surface
o the earthworm is made up of about 100 segments
o segment 1: - the anterior-most end, which contains the mouth, which appears as a
ventral slit. The prostomium is a fleshy lobe that precedes the mouth and the
peristomium is a lobe that surrounds the mouth
o segments 9 and 10: - contain pores on the ventral side the lead to seminal receptacle
that store sperm
o segment 14: - contains two pore on the ventral side, the female genital pores, that
release eggs
o segment 15: - contains two pores on the ventral surface, male genital pores, that release
sperm. Sperm travels down two seminal grooves to the clitellum
 earthworms are hermaphroditic
o segment 26: - genital setae are located within swollen tissue on the ventral side and help
hold the ventral surfaces of two worms together during copulation
o segments 32 o 37 (approximately): - a thicken band of epidermis called the clitellum
that secretes a cocoon in which the egg and sperm are deposited
o last segment: - location of the anus
 unlike cnidarians, annelids have a complete digestive tract
earthworm locomotion:
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earthworms move by controlling antagonistic muscle groups (circular muscles and
longitudinal muscles) and by their hydrostatic skeleton
o the circular muscles contract squeezing fluid up their coelom, which elongates the
anterior
o the longitudinal muscles then contract to shorten the body and pull up the posterior end
o setae are used to anchor certain segments during locomotion
earthworm circulation:
o earthworms have a ventral and a dorsal blood vessel
o one-way valves are present in the dorsal blood vessel
internal anatomy of earthworms:
o internal organs (viscera) fill a fluid-filled cavity, the coelom, which is enclosed within the
body wall (epidermis and two muscle layers)
o the coelom acts as a hydrostatic skeleton
o each segment, except the anterior most, contains a portion of the digestive, excretory,
nervous and circulatory systems
o the anterior segments contain the special reproductive, digestive, circulatory and nervous
organs
o digestive tract – runs down the middle of the body from mouth to anus
o pharynx – the first digestive organ after the mouth that is a light-coloured swollen
structure and is a muscular organ that pulls soil and detritus into the digestive tract.
Anchored to the pharynx and the body wall are radial muscles that dilate the pharynx to
assist with ingestion of detritus
o oesophagus – a thin-walled tube where soil and detritus passes that lies under the aortic
arches (tubular heart) and is partially covered by a large white mass (the reproductive
organs)
o crop – just posterior of the reproductive organs, it is a widening in the oesophagus and is
a storage pouch
o gizzard – follows the crop and grinds food
o intestine – long straight tube that extends posteriorly from the gizzard to the anus. The
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intestine is the site of absorption of food and water into the blood. Indigestible food is
expelled at the anus
the interior of the earthworm is not cylindrical, rather a large dorsal fold projects into the
lumen of the intestine. This structure is the typhlosole, and its main function is to
increase the area of absorption
the seminal vesicles are composed of three lobes and partially cover the oesophagus.
They store sperm
testes are contain within the seminal vesicles and are the site of sperm production.
Mature sperm pass by fine ducts (vas deferens) from the seminal vesicles to the male
genital pores
eggs are produced in eggs and are carried to female genital pores by the oviduct
seminal receptacles – store sperm colleted during copulation
during copulation, worms lie with their ventral sides touching are facing opposite
directions. They grip each other using setae and the clitellum produces mucus and sticky
secretions to help hold them together. With the aid of muscular contraction, sperm travel
from seminal grooves to seminal receptacles. The animals separate after sperm is
exchanged
after copulation, the clitellum of each earthworm secretes a cocoon made out of chitinous
material and the anterior end produces a mucus tube
the earthworm backs up out of the cocoon and the eggs are fertilized as the pass over the
seminal receptacles. The cocoon is then slipped off and left near the surface of the earth.
The mucus tube disintegrates and the cocoon hardens and shrinks
earthworms have a closed circulatory system and the blood is carried in blood vessel
the dorsal blood vessel passes over the dorsal surface of the crop, gizzard and intestine. It
is the largest blood vessel in the body and contains coagulated blood
five pairs of aortic arches encircle the oesophagus (first arch is just below the pharynx in
segment 7 and the fifth is between the second and third lobes of the seminal vesicles at
segment 11)
the ventral blood vessel lies below the digestive tract. The two blood vessels are
connected by the aortic arches which are the main pumping organs
in each segment, the ventral blood vessel forms capillary beds that supply blood to the
organs and body wall. This blood is then picked up by the dorsal branches that return the
blood to the dorsal vessel
oxygen and carbon dioxide are exchanged in capillaries in the epidermis
annelids have a more centralized nervous system
they have a pair of ganglia (cluster of neurons) that acts as a brain. These are called the
cerebral or suprapharyngeal ganglia. These ganglia are dorsally located just anterior to
the pharynx at segment 3. They are the main centre for the coordination of sensory and
motor function
a second pair of ganglia (subpharyngeal ganglia) lies below the pharynx in segment 4.
These ganglia control most motor functions and reflexes (they are necessary for
movement)
without suprapharyngeal ganglia, the worm could still move but not in coordination with
environmental stimuli
the ventral nerve cord is ventral to the ventral blood vessel and just dorsal of the body
wall. It runs the length of the earthworm with a swelling, a ganglion, in each segment
from each segmental ganglion, three pairs of segmental nerve branch into each
segment. The segmented ganglia of the nerve cord coordinate the muscular contractions
of the body wall
sensory receptor cells exist within the epidermis. They receive sensory information such
as light, chemicals and pressure from the external environment and transmit them to the
suprapharyngeal ganglia
the earthworm’s excretory system is composed of paired organs, nephridia, repeated in
almost every segment. Each nephridium picks up chemical from coelomic fluid and from
blood capillaries and excrete these waste through a pore, the nephridiopore in the body
wall
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Vermicomposting
 earthworms take raw organic material from the soil, rework them and combine them with minerals
of the earth to make nutrient-laden worm castings
 vermicomposting – the process done by humans in using earthworms and microorganisms to
convert organic waste into black, earthy smelling, nutrient-rich humus for growing healthy plants
 vermicomposting system:
o container/box – shallow, only about 30 cm deep (worms are surface feeders) box that
has a top to retain moisture and keep out light. It has drainage holes to control moisture
and ventilation holes to provide adequate air circulation
o bedding – moist shred newspaper and computer paper, decomposed leaves, and peat
moss
o redworms (Eisenia foetida) – also called red wigglers, manure worms, fish worms, or
fecal worms. They process a large amount of organic material naturally in manure,
compost, or decaying leaves. They can process up at least half their body weight per day
in organic material. They also reproduce quickly in confinement
o food waste – redworms will eat just about anything including coffee grind, banana peels,
fruits and vegetable waster, plate scrapings, egg shells, spoiled food, etc. Putrefaction is
the process of breaking down proteins
o controlled environment – controlled temperature, moisture, acidity, and ventilation.
Redworms tolerate about 0oC to 32oC. Optimal temperature is 13-25oC. There skin must
be moist for exchange of air to take place so water is added to the bedding whenever
necessary. Air is allowed to circulate for respiration
o maintenance – preparing the bedding, regularly digging and burying the food waste,
harvesting the worms at the end of the cycle and making use of the castings after about 3
months. Add fresh bedding when needed
Microcosm Experiment
 tests the efficiency of Daphnia magna in grazing different kinds of algae (one which is taken from
the microcosm tanks)
 Daphnia are small crustaceans that graze on algae and bacteria (not filamentous ones – they clog
the Daphnia’s filtration system)
 hypothesis: Daphnia will suffer from greater mortalities when placed in a vessel with only
filamentous algae
 D. magna is from phylum Anthropoda. It is common plankton in lakes in North America. It is
herbivorous and feed on microalgae, bacteria and detritus
 D. magna are efficient filter feeders. Because they are so efficient, they are commonly used to
clear out lakes of algal blooms
 lake managers frequently reduce fish populations (planktivores) to increase Daphnia population –
biomanipulation
 we set up 4 beakers:
o control – no Daphnia, yes Chlamydomonas (unicellular algae)
o 10 Daphnia, Chlamydomonas
o control – no Daphnia, spoonful of algal mat from microcosm tank wall
o 10 Daphnia, spoonful of algal mat from microcosm tank wall
 hypothesis: beaker B will have clearest water
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LAB 8 – INVERTEBRATES II
Phylum Mollusca
 second most diverse phylum (after arthropods)
 includes snails, slugs, shellfish (clams, mussels, oysters), octopus, squid
 lack segmentation
 all have an open circulatory system, except cephalopods
 we will examine a terrestrial gastropod, the brown garden snail, Cantareus aspersus
 this species is native to Europe, but is now world-wide, mainly in temperate regions
 the brown garden snail is herbivorous
o it is considered a pest, since it is capable of causing large economic losses in agriculture
 it is used as a subject for research in neurobiology and behaviour
 external anatomy of terrestrial gastropods (e.g. Cantareus):
o has a very strong foot
 can be very difficult to lift
 slide forwards or backwards to alleviate suction
 spray water to moisten snail  increase in activity
o shell – composed of calcium carbonate and proteins secrete from the mantle
 most gastropods exhibit dextral or right-handed coiling on the shell (starting
from the apex). This coiling is due to differences in growth rates on each side of
the shell
 many gastropods can withdraw their visceral mass and foot into the shell for
protection. The operculum on the dorsal surface of the foot acts as a lid for this
purpose
o foot – a muscular organ whose main function is locomotion. It contains specialized
glands that produce and secrete mucus along which the snail grips and slides
 gastropods frequently leave chemicals in their mucus trails to alert other
members of their species where food is
 this mucus can also be used to reduce water loss, to allow strong adhesion to a
substrate, and to form egg cases after fertilization
o tentacles – terrestrial gastropods have two pairs on their head and are primarily used for
olfaction (smell/taste). Chemoreceptors are located with the tentacles’ epidermis
 inferior tentacles – shorter tentacles used primarily to detect chemicals on the
ground
 superior tentacles – longer tentacles used to detect airborne chemicals. The
eyes are usually located on these tentacles (they contain photoreceptors, but no
lenses)
 locomotion in terrestrial gastropods:
o most gastropods move by using rhythmic wave of muscular contractions in their foot
 contractions that extend across the width of the foot are said to be monotaxic
 contractions that alternate between the left and right sides are said to be ditaxic
 contractions can move with or opposed to the direction of locomotion (either
anterior or posterior)
 direct waves – the lifting of the posterior edge of the foot and forward
placement, followed by a forward wave of contractions
 retrograde waves – the lifting of the anterior edge of the foot followed by the
stretching and attachment of it in a more forward location and a backward wave
of contraction
o mucus aids in movement
o taxis – directed movement towards (positive taxis) or away from (negative taxis) a
particular stimulus
 phototaxis –directed movement relative to light
 geotaxis – directed movement relative to gravity
 terrestrial gastropods typical exhibit negative geotaxis (they prefer to
move up inclines/slopes
 chemotaxis – directed movement relative to a chemical source
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unlike bivalves, gastropods are not filter feeders and actively search for
food
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respiration:
o aquatic molluscs use gills
o terrestrial molluscs exchange gases through their mantle
o these surfaces must remain moist for gas exchange to occur
 terrestrial gastropods have evolved different adaptations to reduce desiccation
o pulmonates (subgroup Pulmonata) have highly a vascularized mantle cavity, which acts
as a primitive lung (evolved independently of vertebrate lung)
 gases are allowed to pass into and out of a small opening in the lung, called a
pnemostome
 reproduction:
o most gastropods, including Cantareus, are hermaphroditic
o sexually mature snails release pheromones (chemical attractants) to attract others of their
species
o open meeting, two snails will undergo a ritualized courtship involving the touching of
tentacles and feet
o during copulation, individuals will reciprocally exchange sperm packet which then are
stored until the recipient is ready to fertilize its eggs
o snails have increased fertilization rates by their sperm
 species, such as Cantareus, have evolved a method to improve their chances of
paternity
 prior to copulation, sperm donor releases a “love dart” from the genital pore,
shooting it into the body of the sperm recipient
 love dart is covered in a special mucus that improves the survival of the dartshooter’s sperm so that at the time of fertilization, there is more of its sperm left
to fertilize the eggs
Phylum Arthropoda
 most complex and diverse invertebrate phylum
 arthropods exhibit:
o bilateral symmetry
o segmentation
o cephalisation – sense and control of organs focused at the anterior end
o exoskeleton
o jointed appendages
 crustaceans are a group within Arthropoda that are highly adapted to aquatic life (very few are
able to live on land)
o e.g. shrimp, lobster, Daphnia, crayfish
 small crustaceans that compose part of the zooplankton in lakes and oceans are commonly food
for fish and baleen whales
 wood louse is an example of a terrestrial crustacean
 crayfish (Cambarus sp.) are common inhabitants of freshwater lakes and streams throughout the
world
 crayfish are considered a Cajun delicacy
 crayfish are active at night, seeking refuge under rocks and logs by day
 they are largely opportunistic feeders and their diet varies from algal and plant material to
tadpoles, benthic (bottom-dwelling) invertebrates, and fish eggs
 crayfish are relatively short-lived (living only about 2-3 years)
 closest relatives are lobster and shrimp
 external anatomy:
o arthropods are bilaterally symmetrical (like annelids, unlike cnidarians)
o the body of the crayfish is covered by a hard cuticle composed of chitin
 chitin is secreted by underlying epidermal cells and is made by the deposition of
calcium carbonate
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this covering act as a protective outer layer (exoskeleton) to which muscles are
attached
 the exoskeleton is inextensible, so is molted/shed regularly to allow the animal
to grow in size
divisions in exoskeleton show that the body is organized into definite regions:
 the head and thorax are covered by a fused dorsal shield (the carapace) with a
groove (cervical groove) dividing the two regions
 collectively, the head and thorax are called the cephalothorax
 compound eyes are located on the hard and are separated by an anterior
pointed projection of the dorsal shield, the rostrum
 arthropods are the only animals with compound eyes (containing more
than one lens)
 arthropods posses gill located in a cavity (the gill chamber) formed by the
downward flap of the carapace and the transparent chitinous wall of the thorax
 the last region of the body is the abdomen, which comprises almost half of the
animal’s body length. The abdomen begins at the posterior end of the carapace
the body of all arthropods are regularly divided into segments
junction of adjacent segments is covered by thin flexible chitin permitting movement at
the joints
arthropods have much less segments than annelids
 chordates have even fewer segments
crayfish exhibit structurally specialized appendages for carrying out specific functions
such as tasting, feeding, feeling, walking, and copulating
 during development a pair of appendages form on each segment
 each appendage, regardless of function, forms from similar embryonic
beginnings
each appendage is made of:
 basal stalk – attaches the appendage to the ventral surface of the body
 two distal branches – e.g. swimmerets. The distal branches characterize
crustaceans as biramous arthropods
 crayfishes’ appendages no longer have two obvious distal branches
 different organs, such as the crayfish’s appendages are said to be
homologous, because they come from similar embryonic origins and
have structural relationships
o some of these structures may differ in appearance
 when there are similar structures in different segments of an organism,
even having a different function, it is called serial homology
the head contains five pairs of appendages:
 1 pair of antennules – short, branched filaments for touch and taste and
equilibrium. The openings to the balancing organs, statocysts, are located in the
bases of the antennules
 1 pair of antennae – long slender filaments with a short fan-like branch for
touch and taste. An excretory pore, the nephridiopore, from the green glands is
located at their base, on the ventral surface of the crayfish
 1 pair of mandibles – jaws used for crushing and chewing food. The mouth is
located between the mandibles
 2 pairs of maxillae – both pairs handle food and deliver it to the mandible. The
posterior (second) pair has a paddle-shaped gill bailer that covers the opening of
the gill chamber and keeps water from flowing forward over the gills
the thorax contains eight pairs of appendages:
 all appendages except the 1st maxilliped have gills in their bases
 3 pairs of maxillipeds – function in touch, taste, and food handling. They are
attached just posterior to the maxilla
 5 pairs of walking legs – the 1st pair (the chelipeds) have large pincers that are
used for defence and capturing/crushing prey. The 2 nd and 3rd pair have small
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pincers and are used mainly for locomotion. On females, the 3 rd pair houses the
genital pore that releases eggs. The 4th and 5th pair carry a sperm receptacle
where sperm is stored. On male, the 5th pair has a genital pore where sperm is
released
the abdomen contains six pairs of appendages:
 1st-5th pairs are swimmerets
 1st pair – in males, swimmerets act as a tube for sperm transfer. In females, the
swimmerets are vestigial and serve no function
 2nd pair – in males, swimmerets are hardened to aid sperm transfer. In females,
the swimmerets hold fertilized eggs for incubation. In both sexes, these
appendages aid in respiration by circulating water
 3rd, 4th, and 5th pairs – these swimmerets are biramous. They are used for water
circulation in both sexes. In females, they aid in carrying the eggs
 6th pair – called the uropods. The uropods are flat, broad and fan-shaped. On
this last abdominal segment, the posterior projection is the telson. The telson
and uropods form the tail fan that can be used for backwards swimming
Table 1 - Summary of Crayfish Appendages
BODY
REGION
HEAD
THORAX
BODY
SEGMENT
1
2
3
4
antennule (with statocyst in base)
antenna (with nephridiopore at base)
mandible (jaw)
1st maxilla
touch, taste, and equilibrium
touch and taste
crushing and chewing food
food handling
food handling and draws water over
gills
touch, taste, and handling of food
touch, taste, and handling of food
touch, taste, and handling of food
defence, food capture and handling
walking and grasping
2nd maxilla
6
7
8
9
10
1st maxilliped
2nd maxilliped*
3rd maxilliped*
1st walking leg* (cheliped)
2nd walking leg*
3rd walking leg* (with female genital
pore at base)
4th walking leg*
5th walking leg* (with male genital
pore at base)
gills attached to their bases
1st swimmeret – male
1st swimmeret – female
11
13
*
14

FUNCTION
5
12
ABDOMEN
APPENDAGE
15
2nd swimmeret – male
2nd swimmeret – female
16
3rd swimmeret
17
4th swimmeret
18
5th swimmeret
walking and grasping
walking
walking
respiration
transfer sperm to female – male
no function – female
water circulation – both sexes
transfer sperm to female – male
carry eggs – female
water circulation – both sexes
carry eggs – female
water circulation – both sexes
carry eggs – female
water circulation – both sexes
carry eggs – female
backwards swimming
19
uropod
internal anatomy:
o respiratory system:
 in crayfish, respiration occurs through the gills
 some gills extend from the bases of the walking legs and other are attached to the
inner wall of the gill chamber
11 of 26

o
o
o
respiration can occur on land as long as water can stay trapped in the gill
chamber
 the gills’ structure provide an enormous surface area specialized for the diffusion of
gases
 as water enters under the carapace and is moved over the gills by the beating of the
gill bailer and movement of leg, gas exchange occurs. The oxygen depleted water is
then expelled fro the anterior end of the gill chamber
circulatory system:
 heart – in its natural location, it appears to be a triangular, whitish structure with a
pair of small holes. It is actually diamond-shaped and has three pairs of holes. The
heart is located directly beneath the thoracic groove of the carapace, just anterior to
the abdominal segments.
 crayfish and arthropods have an open circulatory system
 the heart lies in a dorsally located space (the pericardial sinus) into which blood
collects
 blood enters the heart via holes (ostia) and is pumped out through seven main
arteries to the rest of the body
 there are no veins in an open circulatory system
 valves in the ostia and arteries prevent backflow
 smaller open-ended blood vessels branch off the seven main arteries and allow blood
to flow freely into and through other sinuses that form the body cavity of arthropods
(called hemocoel). Blood travels through these sinuses to gills and gas exchange
occurs. The oxygenated blood travels back to the pericardial sinus and is pumped by
the heart to the rest of the body via arteries
 oxygen is carried in blood by the protein hemocyanin, which gives the blood a
transparent colour (as opposed to haemoglobin which gives blood a red colour)
reproductive system:
 in males, a pair of small testes lay ventral and slightly anterior to the heart/ They
look like a strand of tissue
 coiled seminal ducts carry the sperm from the testes to the genital pores at the base
of the 5th pair of walking legs. The 1s pair of swimmerets are used to convey the
sperm to the seminal receptacle of the female
 fertilization is external
 in females, a pair of pinkish ovaries lay in a similar position to the testes in males
 there size varies from small to large containing orange eggs depending on the time of
year
 ovaries appear more granular than testes
 a pair of oviducts lead from the ovaries to the genital pores on the bases of the 3 rd
pair of walking legs from where eggs are released. The seminal receptacle is located
on the ventral surface between the 4th and 5th pair of walking legs and is the site of
sperm
 mating occurs in the fall, but females do not release an egg until spring
 fertilized eggs attach to the female’s swimmerets for about six weeks until hatching
and then several more weeks until the juvenile crayfish metamorphose and are large
enough to survive independently
digestive system:
 paired digestive glands are located on both sides of the heart. They are soft, creamcoloured, and fill up most of the thorax
 the digestive glands connect to the posterior end of the stomach. Food from
the stomach are washed into microscopic tubules of the glands where
further enzymatic digestion and absorption occurs
 the stomach is a large structure located anterior of the digestive glands and just
posterior to the compound eyes. On both sides of the stomach, muscles are present
attached to the underside of the carapace, and are known as mandibular muscles.
12 of 26
o
o
o
o
These muscles attach the stomach to the mandibles of the mouth. The stomach is
divided by a dark horizontal band into two chambers:
 cardiac stomach – the larger of the two chambers and locate anteriorly. It
is line with a cuticle and chitinous teeth (the gastric mill). Food is
pulverized, strained and sorted by the gastric mill, which is operated by a
set of strong muscles. Initial enzymatic digestion of food begins here
 pyloric stomach – posterior to the cardiac stomach and receives the food
from that chamber. Indigestible food is separated out and sent to the
intestine. The digestible material is forced into tubules leading to the
digestive glands
 intestine – a straight muscular organ that conducts waste food material to the anus
for expulsion
 mouth – starting point of the digestive system. It is surrounded by specialized
appendages for catching and shredding food. Food passes from the mouth to the
stomach by a short passageway, the oesophagus
nervous system:
 the CNS of arthropods consists of a ventral chain of ganglia (clusters of nerve cells)
known as the ventral nerve cord (VNC) and a large group of anterior ganglia, the
brain
 the brain’s ganglia are larger than ganglia of the ventral nerve cord
 this is because the brain controls sense organs and crayfish behaviour
 the brain is located just posterior of the eyes
 to nerves run posteriorly around the oesophagus rejoining to form the ventral nerve
cord
 in almost every segment, the ganglia of the VNC branch off laterally to nerves to
other parts of the body (these nerves are microscopic)
 statocysts consists of a fluid-filled chamber lined with setae and sand grains
(statoliths). The movement of the sand grains against the innervated setae allows the
crayfish to detect its position giving it a sense of balance and equilibrium
 the statocysts are located inside the base of the antennules
excretory system:
 green glands – lie just below the eyes. They are circular and green (only in live
crayfish). These organs remove unwanted substances from the blood and excrete
fluid wastes of excretory pores (nephridiopores) located on small conical elevations
at the base of the antennae
musculatory system:
 the largest muscles are in the abdomen
 flexor and extensor muscles make up an antagonistic muscle pair to allow
movement
 rapid movement is accomplished by extending the abdomen and uropods and telson
and suddenly flexing them under the body, thus propelling the animal backward
 the walking legs are used for slower movement
 the abdominal extensor muscles are pairs, long and dorsally located. When
contracted they straighten the abdominal region
 the abdominal flexor muscles flank the intestine and it overlying blood vessel along
the midline. When contracted, they flex or curl the abdominal region
Microcosm Experiment:
 the hypothesis from lab 7 was confirmed



13 of 26
LAB 9 – FISHES
The Bony Fishes (Osteichthyes)
 fish species are divided into three major groups:
1. Agnatha – jawless fishes
2. Chondrichyes – cartilaginous fishes
3. Osteichthyes – bony fishes
 examples of bony fishes include the yellow perch and the guppy
Reproduction in Vertebrates
 reproduction amongst vertebrate species is highly variable
 most species have separate sexes (gonochoric)
 some species are hermaphroditic or posses only one sex (female)
 before copulation the male displays a courtship, and the female chooses a suitable mate
 some vertebrate species are monogamous, some polygamous, and often polygynous
 some species of fish and amphibians have external fertilization where eggs are released into
water or onto a substrate by the female and are then fertilized by the male
 depending on the species, some may protect the eggs, while others will leave them to fend for
themselves
o an inverse relationship exists between the amount of parental care given and the number
of eggs produced by the female (fecundity)
 vertebrates that release unfertilized eggs and have subsequent fertilization and development
outside the female’s body are called oviparous
o nourishment for the developing embryo comes from a yolk sac within the egg
o examples of oviparous species include most bony fishes, amphibians, reptiles, and all
birds
o not all oviparous species have external fertilization
 some fishes and amphibians, as well as all reptiles, birds and mammals have internal fertilization
o the female receives the male’s sperm inside her reproductive tract, and the eggs are
fertilized there
o some animals then lay their eggs (oviparous)
 the shell forms around the egg after fertilization while the egg is still inside the
female’s reproductive tract
 the egg and hatchling usually receive subsequent parental care
 many sharks and some reptiles and bony fish are ovoviviparous. This is because eggs are
internally fertilized and develop within the female’s reproductive tract. The egg is still nutrionally
dependent on the yolk and not the mother. The eggs are unshelled and are only covered by a thin
membrane surrounding the embryo and yolk. The egg is fully hatched at the same time of birth
 most mammals and some amphibians and fishes (mainly sharks) are viviparous, which means at
an early stage in development, the embryo hatches within the mother’s womb (amphibians and
fishes) or else develops a placenta connecting it to the mother (in mammals). The embryo is reliant
on the mother for nourishment. Fully developed young are released at birth
 certain fishes, including the guppy are called livebearers because they give birth to developed
offspring rather than eggs
o livebearers are wither ovoviviparous or viviparous
o guppies, swordtails, platys, and mollies are ovoviviparous livebearers
The Guppy (Poecilia reticulata)
 guppies are the most popular fishes for home aquariums
 via selective breeding, guppies have been produced with very bright colours and abnormally large
fins
 guppies are native to rivers and streams of South America and some of the Caribbean Islands
 they are omnivorous and opportunistic feeders – they aren’t picky about what they eat
 their diet in the wild usually consists of algae, insect larvae, other invertebrates, fruits from
hanging trees, and eggs and larvae from other fish species (including their own)
 males are usually 3.5 cm in size and females are usually 5 cm in size
 guppies are at constant risk of predation
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


they reach sexual maturity at 2-3 months
sexual dimorphism in guppies:
o sexual dimorphism – distinct physical differences between sexes
o guppies exhibit sexual dimorphism as opposed to the yellow perch
o females are usually larger than males
o males possess a modified anal fin (gonopodium), which is used in reproduction
 fin rays on the anal fin form a tube that is used to transfer sperm to the female
o wild male guppies are very colourful with iridescent blue, orange and reds on their
bodies and fins
o wild females appear quite drab in appearance
o at sexual maturity, females possess a dark patch (gravid spot) just anterior to their anal
fin
sexual behaviour in male guppies:
o like other animals, male guppies compete for the opportunity to mate with females
o such competition can involve physical combat or visual and auditory display
o females usual select males with the most elaborate mating displays
o loud mating displays can often attract unwanted predators
o guppies, who live in Neotropical streams, have evolved a mating display according to
natural selection, that is a balance between elaborateness and crypsis
o some male guppies go all out and risk being preyed upon
o other males attempt sneaky copulation by which they sneak up beside the female a
quickly insert their gonopodium into the female’s reproductive tract
o although females avoid sneaky copulation, it is sometime successful in fertilizing her
eggs
o sigmoid display – male orientates himself in front of or to the side of the female. He then
curves his body into an S shape and begins to quivers. He may move up and down several
millimetres in a water column, and may erect his dorsal and caudal fins. He may also
around to her side and attempt to mate. Sigmoid displays are used by males during
courtship (he wants to mate with the female’s cooperation). Sigmoid display is usually
cut short because the female moves or another male gets in the way
o sneak attempt – male makes no sigmoid display. Rather he sneaks in quickly and
attempts to mate without the female’s cooperation
o copulation – following sigmoid display or sneak attempt, the male inserts the
gonopodium into the female to transfer sperm to her reproductive tract. If the female is
receptive, the two fishes may spin around together while connected. If she is not
receptive she will dart away. Following a successful copulation, the male moves away
and jerks his body. The reason for this is not clear, but may be a display to other females
and males, or is an action to refill the gonopodium with sperm, or it is a way to remove
external parasites acquired during copulation
o interference – male positions himself between a female and another male who is
displaying to the female. This is non-aggressive behaviour
o Experimental Design:
 tanks will be filled with one female guppy and varying numbers of male guppies
 the females have been separated from the males and will only be added to the
tank when observations are ready to be taken
 in each group:
 one person records the observations and keeps time
 one person is assigned to each male guppy
 only the female’s general behaviour should be recorded at the bottom of the data
sheet
 it is important to not touch the fish or tap the tanks
 procedure:
 Group 1 will assign a number to each male according to their
decreasing size
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
Group 1 will sketch the colour patterns and fin shapes (dorsal and
caudal) for each male
 Group 1 will rank the males according to size and colour
 record observations for 5 minutes n the data sheet
 tally the numbers for all males, and record the general behaviour of the
female
 proceed to the next tank, reassign roles, and repeat data collection on
the new data sheet
 each group will record observations for all three tank sex ratios
The Yellow Perch (Perca flavescens)
 external anatomy:
o the body is divided into three parts: head, trunk, and tail
o the body has a streamlined shape
o the head is continuous with the trunk without any narrowing for a neck or projecting
appendages
 this allows for a smooth movement of water over the body
o the gill openings mark the border between head and trunk
o the anal and urogenital openings mark the border between the trunk and tail
o the mouth opening is formed by a strong set of bones forming the upper (maxilla)
and lower (mandible) jaws
o the maxilla and the mandible are connected in such a way that the mouth can de
distended and opened widely to take in large pieces of food
o tiny teeth exist on the jaws but are used mainly in the yellow perch for ensuring that
food doesn’t escape the mouth, rather than for biting or crushing
o the perch’s mouth is terminal, which indicates that the fish usually feeds by
overtaking prey
 if the mouth were inferior (ventral) then it is a bottom feeder
 if the mouth were superior (dorsal) then it is a surface feeder
o the body’s surface is covered in hard scales that are arranged to assist in streamlining
 all the scales point backwards
 each scale is overlapped by those more anterior and dorsal to it
o the basal (anterior) edge of the scale is normally buried in a special socket in the skin
 this part of the scale possesses annual growth rings (annuli) that can be
used to age the fish (similar to trees’ annual rings)
o the projecting (posterior) edge of the scale possesses small, comb-like teeth, called
ctenii
 this feature give the scale the name: ctenoid scale
o the whole scaly layer is cover by epithelium
o near the mouth are two pairs of external nares (nostrils)
 the external nares open into the olfactory pits in which lie the organs of
smell
 the external nares are not connected to the respiratory system as in humans
 water enter each nasal sac through the anterior nasal opening and leaves
through the posterior opening
o posterior to the eyes are the opercula (gill covers)
 they act as protection for the respiratory structures underneath and act as an
important component in the pumping system which force water over the
gills
 under the an operculum lies four gill arches, each bearing two rows of gill
filaments
o fins are membranous extensions of the epidermis and are supported by fin rays
 unpaired fins – used for stabilization, prevention from rolling over and for
forward propulsion
 anterior dorsal fin – begins at the anterior most point of the trunk
on the dorsal side
16 of 26
o it is supported by spiny rays
posterior dorsal fin – lies directly behind the anterior dorsal fin
o it is supported by soft rays
 anal fin – posterior to the anal and urogenital openings on the
ventral side
o it is supported by both spiny and soft rays
 caudal fin – located at the posterior end of tail and is used for
forward propulsion
o it is supported by soft rays only
 paired fins – used in braking, turning, and prevention of rolling
 pectoral fins – located high on the sides of the trunk and just
behind the opercula; these fins are homologous to the forelimbs of
tetrapods
o in less evolutionarily advanced fish species (e.g. salmon,
trout) the pectoral fins are located more ventral
 pelvic fins – located on the sides of the trunk just posterior to the
pectoral fins; these fins are close together on the anterior ventral
surface of the trunk
o these fins are homologous to the hind limbs of tetrapods
o in less evolutionarily advanced fish species, these fins are
located more posteriorally
o the lateral line runs down either side of the perch’s body
 it is a row of scales each perforated by small holes that are connected to a
small water-filled canal along each side of the fish
 within the canal are sensory organs called neuromasts
 neuromasts consist of clusters of ciliated sensory receptors called
hair cells
 the cilia of the hair cells are embedded in a gelatinous capsule
called the capula
 the capula extends into the lateral line and bends with water
disturbance
 synapsing with hair cells are sensory neurons that send sensory
information to the brain
 because of the asymmetrical distribution of the cilia, the fish can
differentiate between water moving from head to tail or water
moving from tail to head
 the lateral line system can also allow the fish to detect disturbances
from predators and other organisms
 the lateral line system also helps in schooling and can detect the
movement of the rest of the school
internal anatomy:
o the vertebral column is a chain of small bones, the vertebrae, forming a strong yet
flexible support for the body. From the dorsal surface of each vertebra arises a spike
of bone, the neural spine
o attaching to the lateral surface of the vertebra is the ribs. There are two sets of ribs
on each side of the fish
 ventral ribs – large ribs that form a protective cage around the body cavity
 dorsal ribs – small and delicate ribs. They are attached to the ventral ribs
and then eventually branch off. This ribs are unique to bony fish and to no
other vertebrate
o the muscles of the body are arranged into vertical segments called
myomeres/myotomes. The myomeres are shaped like a sideways W
o the muscle fibres of the myomeres are firmly attaches to sheets of connective tissue
running between the myomeres, called myocommota. The myocommota are


17 of 26
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
attached to the vertebral column and to the ribs, this giving the muscles a strong
framework
because of an absence of ribs and a coelom in the tail, muscles are supported by
haemal spines projecting from the mid-ventral surface of the vertebral column
liver – large orange-brown mass of tissue at the anterior end of the body cavity. It
stores glycogen and produces bile
bile is released by the gallbladder into the intestine and aids in lipid digestion
the gallbladder is located under the right lobe of the liver
the stomach lies underneath the liver and connects at a right angle to the intestine
at the junction between the stomach and the intestine are three short, finger-like
projections, the pyloric caeca. The pyloric caeca secrete enzymes that aid in
digestion and help the intestine to absorbs nutrients
the intestine is long and coiled and connects the stomach to the anus where waste is
expelled
mesentery – thin connective tissue that holds together all the internal organs
the spleen is a reddish organ that is found under the intestine. It is not part of the
digestive system but part of the circulatory system. The spleen stores blood and
assists in the destruction of red blood cells (which gives it its red colour)
the coelom is lined by a thin shiny layer of connective tissue (the peritoneum)
 this same tissue forms the mesentery with the coelom and the pericardial
sac around the heart
the air bladder (swim bladder) is located dorsal to the digestive tract along the
vertebral column. It is a large sac with whitish walls. When the fish is living, it is
filled with air and is used by the fish to adjust buoyancy
gas are added and subtracted from the air bladder by the gas gland in the wall of the
air bladder
near the air bladder is a long reddish-brown strip of tissue along the vertebral
column. This is the kidney
the kidney filters out metabolic waste and other substances from the blood and
excretes them in urine
urine is carried by ducts from the kidneys to the urinary bladder, which expels the
urine into the external environment through a urinary pore located in the urinary
papilla in males. In females, the urinary bladder is incorporated into the oviduct to
form a urogenital sinus which expels the excretory waste through a urogenital pore
in male perches, a pair of greyish-white testes are located between the air bladder
and the intestine and are full of sperm
inside each testis lies a duct, the vas deferens
the two vasa deferentia join in the posterior midline to form a genital sinus which
opens to the exterior through a genital pore between the urinary pore and the anus
in female perches, the ovaries fuse during embryonic development to form one large
structure
the ovaries are orangish-pink and are filled with thousands of eggs (ova). Mature ova
are discharged into a central ovarian cavity where the are passed down the oviduct to
the external environment through the urogenital pore located posterior to the anus
yellow perches undergo external fertilization
yellow perches are oviparous
embryonic development occurs inside the egg capsule outside the female’s body
yellow perches spawn in the spring
the yellow perch has a two-chambered heart, the chambers being the atrium
(auricles) and the ventricle
the atrium receives blood from the sinus venosus
the ventricle pumps blood out via the bulbus (conus) arteriosus
the sinus venosus receives blood returning from the body in the right and left
common cardinal veins, which brings the blood to the atrium and then to the
ventricle
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o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
the atrioventricular valve between the atrium and the ventricle prevents backflow
when the ventricle contracts to pump the blood to the bulbus arteriosus
the ventricle has a thick muscular wall and is pyramidal in shape. It is the main
pumping mechanism for the circulatory system
blood from the bulbus arteriosus flows to the ventral aorta
the ventral aorta has branches of in the eight afferent branchial (gill) arteries. The
ventral aorta extends the length of the gill arch and send capillary branches into the
gill filaments where they join branches to the efferent branchial arteries
as blood pass through the gills, carbon dioxide and wastes are lost to water and
oxygen is picked up
the branchial arteries carry the oxygenated blood to the dorsal aorta and the carotid
arteries
the dorsal aorta extends from its origin along the length of the trunk and continues as
the caudal artery through the haemal arches in the tail
branches from the dorsal aorta and caudal artery supply oxygenated blood to the
internal organs and the body muscles
internal carotids supply oxygen to the brain
the arteries are joined by capillary networks in body tissues to the common cardinal
veins (at this point, the blood is deoxygenated)
blood circulation is essentially a single cycle (heart  gills  body  heart)
in the yellow perch, the brain and spinal cord are protected in the skull and
vertebral column respectively
in Agnathans and Chondrichtyans these structures are cartilaginous
fish detect sound with the lateral line and the inner ear
 within the inner ear of bony fishes are calcareous structures, otoliths, that
are enclosed in fluid-filled sacs (saccules)
 otoliths vibrate from sound waves transmitted through water
 the otoliths’ movement stimulates sensory cells that send signals to the
brain
 the brain can interpret these impulses as sound
 in some fish species, the air bladder is connected to the inner ear to amplify
the vibrations (these species usually are sensitive to high frequency sounds)
 fishes that tend to be preyed upon by dolphins tend to be sensitive to
ultrasonic sounds used by dolphins in echolocation
the inner ear contains semicircular canals, which aid in balance and orientation to
gravity
 these are three are fluid-filled canals arranged in different planes: posterior
vertical canal, anterior vertical canal, and horizontal canal
the otoliths, like the scales, exhibit daily growth rings and can be used to age the fish
the brain of vertebrates is simply an enlargement of the anterior spinal cord
the brain is formed by the folding of embryonic tissue during development, just like
the spinal cord
 both the brain and spinal cord have hollow regions, unlike the CNS in
invertebrates
the brain in vertebrates is divided into three regions:
 forebrain – involved in olfaction
 midbrain – involved in vision
 hindbrain – involved in hearing
meninges – gelatinous pigmented membrane around the brain
part of the brain:
 optic lobes – paired structures that are the largest in the brain and assist in
visual perception. Emerging ventrally and anteriorly are the optic nerves
which attach to the eyes
 telencephalon – located anterior to the optic lobes, this part of the brain is
homologous to the cerebrum in mammals
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



olfactory lobes – located ventrally to the telencephalon and assist in
olfaction. The olfactory tracts contain nerves that travel from the olfactory
lobes to the nares
auricular (acoustic) lobes – located just posterior to the optic lobes and
assist in hearing. Acoustic nerves connect the auriclar lobes to the inner ear
cerebellum – unlike in mammals, the cerebellum in fishes is not divided
into hemispheres but is singular
medulla – located ventral to the cerebellum, the medulla is the anterior
portion of the spinal cord that connects to the brain
20 of 26
LAB 10 – ANIMAL ANATOMY AND PHYSIOLOGY
Skeletal Anatomy of Vertebrates
 tetrapods are descendants of fishes
 tetrapods are four-limbed vertebrates that include, amphibians, reptiles, birds, and mammals
o tetrapods are vertebrate that have been able to inhabit land
o early amphibians had various adaptations which enabled them to spend short periods of
time on land
o later vertebrates evolved independency from aquatic environments
o some tetrapods have returned to the sea
 the skeleton of all tetrapods follows a basic patterns, and individual species have adapted it to best
suit its environment and lifestyle
 the tetrapod skeleton is divided into two major divisions:
o axial skeleton – consists of the skull, vertebral column, and the rib cage
o appendicular skeleton – consists of the pectoral and pelvic girdles and their associated
limbs
The Axial Skeleton
 the skull (or cranium) is the most complicated part of the skeleton
 its main function is to protect the brain and sensory organs
 it is made of numerous plates, which at birth are allowed to grow as the brain grows. When the
brain has completed its growth, the plates fuse together
 cranium space has grown throughout time to adapt to the enlargement of brains amongst species
 the skull contains sensory capsules that can facilitate the sensory organs
 at the front of the skull is a complex of nasal bones that make up the nasal capsule which contains
the olfactory organs
 the eyes are protected by a large ring of bones that completely encircle the orbit. This space is
large enough to allow the muscles that move the eye in its orbit
 behind the orbit are the otic capsules that provide protection for the middle and inner ear
 the back of the skull connects to the neck muscles that are strong enough to support the head
 there are also articular surfaces (occipital condyles) that permits the skull to pivot smoothly along
the first vertebra of the vertebral column
 the fist two vertebrae are specially designed to allow this pivoting and are called the atlas and
axis, respectively
 in lower vertebrates (amphibians and some reptiles) the oral and nasal cavities are not separated.
In this case, the floor of the skull acts as the roof of the mouth
 in higher tetrapods (crocodiles, birds, mammals) the secondary palate has evolved, which divides
the nasal passage from the oral cavity
 jaws first evolved in cartilaginous fishes to aid in food capture
 jaws and teeth vary across tetrapods
 maxilla – the upper jaw formed by the bottom of the skull
 mandible – the lower jaw hinged below the skull and attached by masseter muscles
 temporal fenestra/fossa – holes in the temporal region of the skull that provide more surface area
for muscle attachment from the jaw
o in some mammals, these muscles fully encircle the cranium to a bony crest on the top of
skull to improve attachment
 teeth are attached to the upper an lower jaws
o diversity of teeth is greatest amongst mammals
o dentition diversity is caused by different diets
 the vertebral column (backbone or spine) attach to the posterior of the skull and travels down the
length of the animal
 the segmented vertebral column is a stack of individual vertebrae which move with each othe
 each vertebra has adapted a form for a specific function
 the three main functions of the vertebral column are:
o to provide a flexible, protective covering for the spinal cord
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on the dorsal surface is a space, the neural arch through which the nerve cord
can pass
o to support the weight of the body’s thoracic and abdominal cavities
 fishes have straight spines because the water supports their weight
 flexion of the spine is lateral
 dorso-ventrally curved spines allows for the trunk to be lifted up and for a
different type of locomotion than the side-to-side locomotion of early tetrapods
 each vertebra has a thick rounded centrum that aids in weight bearing
 cartilaginous intervertebral discs exist between centra to prevent damage
between centra during movement
o to provide surfaces or muscle attachment
 the vertebrae are differentiated into 5 categorires:
o cervical vertebrae – neck
o thoracic vertebrae – thoracic regions
o lumbar vertebrae – abdominal region
o sacral vertebrae – pelvic region
o caudal vertebrae – tail
 the thoracic vertebrae have two transverse processes to which the ribs attach
 the ribs are flattened, curved bones that encircle and protect the heart and lungs
 the ribs are connected at the mid-line by the sternum
 in fish, the ribs act as an attachments for the myomeres
 ribs have been lost evolutionarily in frogs
 ribs became important as the thoracic pump evolved for respiration in later tetrapods
The Appendicular Skeleton
 paired appendages become increasingly important in locomotion
 in fishes, the pectoral and pelvic girdles give rise to the pectoral and pelvic fins
 in tetrapods, the pectoral girdle gives rise to forelimbs and the pelvic girdle gives rise to hind
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the pectoral girdle is found at the anterior end of thoracic cavity
this girdle is not directly attached to the vertebral column but is attached by muscles and ligaments
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for this reason the scapula is broad and flat, providing maximal surface area for muscle
attachment
the pectoral girdle is supported ventrally by the clavicle which is connect to the sternum
the bones of the pectoral girdle provide a rounded cavity which allows for a ball and socket joint
to form between the pectoral girdle and the humerus (upper bone of the forelimb)
the lower forelimb is made up of the radius and ulna
the ulna articulates with humerus by a hinge joint
the pelvic girdle is firmly fused to the vertebral column
o this provides greater strength in propulsion in locomotion
there is a ball and socket joint that forms between the pelvic girdle and the head of the upper hind
limb bone, the femur
the lower hind limb is made up of the tibia and the fibula
Museum Modules
 Module A – The Appendicular Skeleton and Locomotor Adaptations
o in this module the bones associated with the pectoral and pelvic appendages will be
examined
o we will also examine how the appendages have changed to suit different types of
locomtion
o several types of mammalian locomotion include:
 running (cursorial)
 jumping (saltatorial)
 digging (fossorial)
 swimming
 climbing (arboreal)
 flying (aerial)
o of the running mammals there are three variations on this locomotion type characterized
by how which bones they use to support their weight:
 plantigrade – animal walks on full foot (heel is stays on ground)(e.g. humans)
 digitgrade – animal walks on toes
 unguligrade – animal walks on hoof
 Module B – Mammalian Tooth Structure and Diversification
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LAB 11 – MAMMALS
The Rat
 the Norwegian or brown rat (Rattus norvegicus) will be dissected in this lab
 the ribs of the rat are attached at the mid-ventral line to the sternum
 at the posterior end of the sternum is a cartilaginous flap called the xiphoid cartilage
 the diaphragm separates the thoracic cavity from the abdominal cavity
The Respiratory System
 the diaphragm is naturally in a dome shape
o muscle fibres are attached radially from its edge so that upon contraction, they flatten the
central part of the dome
 repeated contraction and relaxation of the diaphragm allows mammals to inhale and exhale
 intercoastal muscles exist between the ribs and assist in ventilation
o the volume of the thoracic cavity is increased when the intercoastal muscles contract to
raise the rib cage and the diaphragm contracts and flattens
o the volume is decreased when the intercoastal muscles and diaphragm relax
 the thoracic cavity is lined by pleural membrane
 lying on the heart is a brown mass, the thymus gland, that is the site for lymphocyte maturation
into T-cells
 the trachea, windpipe, is a tube with rings of cartilage around its walls (for strength)
 dorsal to the heart, the trachea splits into two bronchi that go to each lung
 within the lungs, the bronchi further split in many branchioles
 at the end of each bronicholes are microscopic clusters of air chambers, alveoli
 the alveoli are surrounded by capillaries in which gas exchange occurs
The Digestive System
 rodents, which includes rats, are gnawers
 they have huge incisor teeth and small molars (used for grinding the food nipped of by the
incisors)
 mechanical digestion begins in the mouth, and chemical digestion begins by enzymes present in
saliva
 the opening of the trachea is called th glottis, which is protected by a flap, the epiglottis
o the epiglottis prevents food from entering the respiratory tract
 the oesophagus runs parallel to the trachea and pierces the diaphragm as it leads into the stomach
 abdominal viscera (organs) are suspended by mesentry which is a sheet of tissue continuous with
the peritoneum
 the stomach is covered by lobes of the liver
 the stomach is a storage chamber ad well as a site for mechanical and chemical digestion
 glands within the stomach secretes gastric juices (that include HCl and enzymes that are involved
in the preliminary digestion of proteins)
 these enzymes (zygomens) are inactive until activated by hydrochloric acid
 located near the stomach is the spleen, which is not connected to the digestive system, but is rather
and accessory organ to the circulatory system
 the stomach connects to the small intestine through the pyloric sphincter (a muscular valve that
controls the flow of food)
 the first few centimetres of the small intestine is the duodenum which is connected to the liver
and pancreas via ducts
 the pancreas acts as an endocrine gland by producing insulin and other hormones, and as a
digestive gland by secreting enzymes and sodium bicarbonate for digestion
o these secretions are conducted to the duodenum via ducts
 the liver secretes bile that contains bile salts, bile pigments and cholesterol
o bile salts break down fats
 bile is usually stored in the gallbladder
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o the rat lacks a gallbladder
the section o the small intestine following the duodenum is the jejunum
the remaining portion of the intestine is the ileum
the small intestine functions in nutrient absorption and chemical digestion
within the small intestine are finger-like projections, villi, that increase the surface area of the
intestine to maximize absorption
the ileum is connected to the colon of the large intestine by the ileocolic valve
in the colon, water is absorbed and fecal material forms from undigested food
near the end of the ileum in the large intestine is a large sac, the caecum
the caecum is large in herbivorous animals
o in humans, it is reduced as the appendix
the large intestine has a ascending, transverse, and descending portions that continue to the
rectume that terminates in the anus
peristalsis – slow rhythmic contraction and relaxation of involuntarily controlled smooth muscles
o these muscles are both longitudinal and circular
o peristalsis is responsible for the mixing and movement of food along the digestive tract
Table 2 - Summary of Functions of Digestive Organs of Mammals
Digestive Organ
mouth
pharynx + oesophagus
stomach
Action
mechanical and chemical digestion
transport of nutrients
mechanical and chemical
digestion, some absorption of
small molecules (alcohol, water)
small intestine
chemical digestion, absorption of
nutrients, water
large intestine
water absorption, feces formation
Chemical Action on Nutrients
starches → disaccharides
none
proteins → peptides
lipids → fatty acids
starches → disaccharides
disaccharides → monosaccharides
proteins → peptides
peptides → amino acids
none
Urogenital System
 includes both reproductive organs and excretory/urinary organs
 in males, the penis and urethra are the only two organs that function in both system
o all other structures are independent to one system
 in a female rat, there are three external openings:
o anus – closest to tail
o vaginal opening – in the middle
o urethral opening – opens at the tip of the clitoris
 urinary bladder – small, muscular sac used to store urine
 urethra – tube leading from the bladder to the urinary opening
 ureters – tubes that conduct urine to the bladder from the kidneys
 kidneys – a pair of organs that are the main organs of the urinary system. They receive blood from
the heart and filter out wastes and excess nutrients. The kidneys form urine
 the kidneys are surrounded by adipose tissue (fat)
 renal cortex – outer layer of the kidney
 renal medulla – inner region of the kidney
 adrenal glands – located on the anterior surface of the kidneys, they are not part of the urinary
system, but rather the endocrine system
 in the female, dorsal to the bladder is the vagina, which divides into two large uteri, the sites of
offspring development
o primates have only one uterus
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the oviducts (fallopian tubes) extended from the anterior surface of the uteri and coil around the
ovaries
o the oviducts end in a funnel that is close to the ovary
ripened eggs (ova) are released from the ovaries and fall into the oviducts’ funnels
o peristalsis and cilia move the ova down the tubes
o fertilization occurs in the oviducts
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