ZOOLOGY LABORATORY
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PHYLUM ARTHROPODA
(Greek Arthon = Joint; pus, podos = foot)
OVERVIEW
 Dominant group of invertebrates
 Wide ecological spectrum
 Well-distributed in different environments
 They are highly abundant
 Molting – necessary to allow for growth and
required for hormonal control
 Hemocoel – open system of sinuses
 A divers phylum of animals that have ¾ of all
known species
 Approximately 1.1M species of arthropods have
been recorded to date
 Sizes range from 4m to 0.1mm
 They are abundant and they have a wide
ecological distribution due to active lifestyle and
varied modes of feeding
 Species have various adaptations to live on
different habitats and in the bodies of many
living things
 Some of them are agents of disease and
compete with humans for food
 Others are beneficial for plant pollination and
serve as food within the ecosystem, and
produce various products with economic value
PHYLOGENETIC RELATIONSHIPS
 Mandibulate hypothesis – divides arthropods
into two clades
Source: BIO422 Lecture
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Mandibulata – myriapods, hexapods,
and crustaceans; they are related by
their presence of a mandible which gives
them an advantage over their modes of
nutrition
Chelicerata – other arthropods with
chelicerae but no mandibles
Mitochondrial genome data supports
mandibulate hypothesis
GENERAL FEATURES
 Jointed, specialized appendages
 They possess metamerism with modification
Reduced
Fused
Specialized
 Capable of shedding their exoskeleton
 They have a hemocoel and hemolymph
Hemocoel – derived fusion of embryonic
blastocoel; much reduced coelom
Hemolymph – an open circulatory system
unique in arthropods
 Some of them would have metamerized
striated muscle
Helps the organism adapt in the
environment
 They have a wide ecological distribution and
partake in different roles
Carnivore
Herbivore
Omnivore
 They thrive in many types of ecosystems be it
terrestrial or aquatic
 They serve provide both ecological and
economic benefits
Pollination
Food chain
They produce a variety of useful products
 Some are considered to be disease causing
and as pests
Versatile exoskeleton
• The main component is the cuticle which is
highly protective, jointed, and flexible so as
to provide mobility
• The exoskeleton consists of an inner thick
procuticle and outer thin epicuticle with both
having several layers called lamina
The epicuticle is composed of proteins
and lipids while any insects have waxes
on the outermost layer to reduce water
loos
The protein layers are stabilized and
hardened by a chemical linking called
sclerotization
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Many of them undergo metamorphic
changes that have different larval and
adult stages
Larvae and adults feed on different
organisms and occupy different habitats
to avoid intraspecific competition
CHELICERATA
 Class Merostomata
Tachypleus or limulus
 Arachnida
Nephilia or argiope
Heterometrus
Segmentation and appendages
• Provides locomotion
• Many segments may be fused or combined
into specialized groups called tagmata
• Differentiated and highly specialized for
division of labor
• Limb segments are hollow levers moved by
internal striated muscles
• These segmentations and appendages allow
for
Better sensing
Better food handling
Walking
swimming
Respiration and sensory organs
• They have an efficient tracheal system
Terrestrial arthropods have air tibes for
direct oxygen transport into tissues and it
allows high metabolic rates but may limit
body size
Aquatic arthropods have internal or
external gills on the other hand
• They have highly developed sensory organs
Eyes ay be simple light sensitive ocelli and
ay as well be a compound eye
Other sensory structures are for
- touch
- Sell
- Hearing
- Balancing
- Chemical reception
Behavior and metamorphosis
• They tend to have complex behavior
patterns
Arthropods
surpass
most
other
invertebrates in complex and organized
activities
Some of which are innate and some are
learned
• They use diverse resources through
metamorphosis
Source: BIO422 Lecture
General features
 Some are terrestrial and some are aquatic
 Antennae is absent
 Chelicerae – first pair of appendages is used
for feeding due to lack of a jaw or mandible
 Two-part body plan
Cephalothorax (prosoma) – fusion of the
head and thorax
Abdomen (opisthosoma)
CLASS MEROSTOMATA
Subclass Xiphosurida (xiphos+surida = sword tail)
• Horseshoe crabs (tachypleus sp.)
There are 5 species in the genera
They mostly live in shallow water
They have an unsegmented carapace
Cephalothorax (Prosoma) has:
- 1 pair of pedipalps
- 4 pairs of walking legs
- 1 pair chelicerae
Abdomen (Opisthosoma) has:
- 6 pairs of broad, thin, appendages
fused in the median line
Carapace has 2 rudimentary and 2
simple eyes
• Prosoma and opisthosoma
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Chelicera, gnathobase and chilaria are used
for feeding
Pedipalps are used for locomotion
Telson
Behavior
• They swim with their abdominal plates open
• The feed at night on worms and small
mollusks using chelicerae and walking legs
• They come to the shore at high tide to mate
• Females burrow into sand to lay eggs
• Males follow to add sperm before eggs are
covered in sand and warmed by the sin
• Young larvae hatch and return to sea at next
high tide
• Larvae are segmented and resemble
trilobites
Class Arachnida (arachne = spider; araneus =
spiderweb)
• Most of them are predaceous
• Two tagmata: cephalothorax and abdomen
is joined by the pedicel
• Abdomen:
Reproductive organs
Respiratory organs
- Book gills
- Trachea
• Cephalothorax:
Pair of chelicerae
Pair of pedipalps
4 pairs of walking legs
• They have around 80,00 species
• Most are free living with them being more
common in warm, dry regions
• Most are predaceous and have:
Claws
Fangs
Poison glands
Stingers
• Legs have 7 segments
• Epigynum conceals the female genital pore
• Lung slit and tracheal plate are the parts
responsible for the respiration of the organism
• They have no antenna or mandibles
• Pedipalps of males are modified for sperm
transfer
• Spinnerets
• They have no antenna or mandibles
• Sucking pharynx ingests fluids and soft tissues
from bodies of their prey
• Some spiders have spinning glands to make
silken webs for food capture
• The abdomen houses the reproductive and
respiratory organs
Order Araneae (spiders)
Source: BIO422 Lecture
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They have 8 simple eyes, but many of them
have poor vision
They have around 40,00 species
Spiders are predaceous and mostly ambush
and trap insects
Their cephalothorax is unsegmented (few are
segmented)
They suck liquefied tissues after injecting
venom and digestive juices
They have book lungs and trachea for their
respiratory organs
Malpighian
tubules
–
used
for
osmoregulation
Potassium solutes and wastes drain into
the intestines
This is considered as an excretory organ
for arachnids or spiders
Resorptive cells – captures potassium, water,
and uric acid
Coxal glands – primarily used for excreting
urine
Sensilla – mechanoreceptors which covers
the leg and can detect air currents, web
vibrations, and other stimuli
Liquid scleroprotein - secretion that hardens
as it is extruded
Silk – the web; used in forming egg sacs, nest
lining, nursery, and wrapping prey
Interaction with spiders
• Most people fear spiders
• Tarantulas are not dangerous
• Black widow spiders – dangerous; their
venom is neurotoxic
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ZOOLOGY LABORATORY
Brown recluse spider – their hemolytic venom
destroys tissue around the bite
Some Australian and south American spiders
are the most dangerous and aggressive
species with some of the most toxic venoms
which cause intense pain and neurotoxicity
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GENERAL NATURE OF A CRUSTACEAN
 Main distinguishing feature is having two pairs
of antennae
 The head also has a pair of mandibles and
two pairs of maxillae
 One pair of appendages on each of the
body segments (Some segments may lack
appendages)
 They are mostly marine freshwater and
terrestrial species
 They have around 16-20 segments
Ancestral forms had up to 60 segments
 Major body tagmata
Head
Thorax
Abdomen
Order Acari (Akari = tick; Akares = tiny)
• Mites and ticks
• They are the most medically and
economically important arachnid group
• Approximately 40,000 species have been
described
• They can be found worldwide in both
aquatic and terrestrial habitats and extend
to deserts, polar areas, and hot springs
• Many of them are parasitic during at least
one life stage
• Most mites are less than 1 mm long
• Ticks are approximately 3cm in size due to
distension from feeding on blood
• They exhibit a complete fusion of
cephalothorax and abdomen with no signs
of external segmentation
• Mouthparts are on the tip of the anterior
capitulum
• Chelicerae help pierce, tear, or grip food
• Pedipalps have a fused base called a
hypostome
• Rostrum or tectum extends dorsally over the
mouth
CRUSTACEANS
 Crustaceans are named for their hard
exoskeletons
 They have over 67,000 described living species
 These organisms also fill a variety of ecological
roles
 Crustacea make up over 80% of all named
animal species
 They are probably the most abundant animals in
the world are members of the copepod genus
Calanus such that they are called the insects of
the sea
Source: BIO422 Lecture
Crustacean form and fuction
• The secreted cuticle is made of Chitin,
protein, and calcareous material
• Harder and heavier plates have more
calcareous deposits
• The joints are soft and thin which allows the
organism some degree of flexibility
• The abdomen ends with telson that bears the
anus
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Molting – physiological process of making a
larger cuticle
Physiology
of
molting
affects
reproduction, behavior, and many
metabolic processes
Occurs often in young animals as they
grow and may slow down in adults
Environmental factors
- Temperature
- Day length
- Other stimuli that may trigger CNS to
begin ecdysis
Ecdysis – shedding of the old cuticle needed
to grow in size
The underlying epidermis of the organism
secretes the cuticle
Subphylum Crustacea
• They are mostly aquatic and terrestrial
organisms
• Crustaceans have gills
• Crustaceans also have an excess skeleton
made out of chitin which is subject for ecdysis
• Two pairs of antennae are present
• Two pairs of maxillae are on the head
• There is a pair of appendages on each body
segment of the organism
• Representative species
Class malacostraca
Penaeus monodon -tiger shrimp
Litopenaeus vannamei – white shrimp
Scylla serrata – mudcrab
Cambarus sp. or panulirus sp. – lobster
HEXAPODA
 Terrestrial and aquatic organisms
 Tagmata
Head
Trunk
Abdomen
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Six legs
Compound eyes are present
Two pairs of wings on most of the representative
species
Two classes
Entognatha – small group with the bases
of mouthparts enclosed within the head
capsule
Insecta – enormous class that have
ectognathous mouthparts, but bases of
mouthparts lie outside the head capsule
- Neoptera – can fold their wings into
the back of the abdomen
- Paleoptera – cannot fold their wings
into the back of the abdomen
Subphylum Hexapoda
Class Insecta
• General groups are based on wing presence
Pterygotes: winged insects
Apterygotes: wingless insects
Thysanurans: primitive wingless insects
• The number of known species is estimated at
1.1M
• There is an estimated number of 30M species
worldwide
• Their exoskeletons have sclerites which are
made out of scleroproteins
• These organisms have six uniramous legs
• They have three body segments
Head
Thorax
- Prothorax
- Mesothorax
Source: BIO422 Lecture
ZOOLOGY LABORATORY
- Metathorax
Abdomen
• Their appendages are attached to the head
and thorax
• Abdominal appendages may be greatly
reduced or be totally absent
• Insects can undergo metamorphosis
Ametabolous (Direct) – Not true for
insects; but true for some arthropods
Hemimetabolous (Incomplete) – middle
stages are composed of different forms
of nymphs with the latter ones having
developed an advantage compared to
the previous stages
Holometabolous (Complete) – they start
with an egg, develops into three instars of
larvae, develops into a pupa, and
eventually emerges as an adult
Insect wings
• Flies have thin and membranous wings
• Beetles have thick and thorny front wings
• Butterflies and moths have wings covered
with scales
Feeding strategies
• Most feed on plant tissues or juices and are
herbivorous or phytophagous
• Some are predaceous on other insects or
other animals while others are scavengers or
saprophagous
• Mouthparts are adapted depending on the
mode of nutrition of species
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Auditory reception – tympanal organs
Chemoreception – sensory pits
Visual reception – simple and compound
eyes
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Other senses – temperatures, humidity
gravity, and other physical properties
Diapause: Period of dormancy
• Diapause – an important adaptation to
survive adverse environmental conditions
• It can occur at any stage and may remain
dormant for some time
• It is internally controlled but may be as well
triggered by environmental cues such as day
length, rain, and temperature
• Hibernation – winter dormancy
• Estivation – summer dormancy
• It usually/always occur at the end of an
active growth stage so that the insect is then
ready for another molt
MYRIAPODA
 Mainly terrestrial found in decaying wood,
crevices, rocks, or arboreal
 Paired appendages
 Two antennae
 Compound eyes are absent
Sense organs
• Mechanoreception – sensilla and seta
Source: BIO422 Lecture
Subphylum Myriapoda
• “Many footed”
• Myriapods have two tagmata with paired
appendages along most segments
• Subphylum Myriapoda has four classes
Chilopoda (centipedes)
Diplopoda (millipedes)
Pauropoda (pauropods)
Symphyla (symphylans)
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These organisms make use of a trachea to
transport gases
Their execution is usually done by Malpighian
tubules
Class Chilopoda
• These organisms have flattened bodies
• They usually live at moist areas under logs
bark and stones
• They
usually
prey
on
earthworms,
cockroaches and other insects
• They have venom claws, and they chew with
mandibles
• These organisms have 15 pairs of long legs
• There are approximately 3000 species
worldwide
• Most of them are harmless but a few large
tropical centipedes are dangerous
Centipede body plan
• 177 segments
• Each segment, except the one behind the
head and last two, bears a pair of jointed
legs
• The last pair of legs is longer and is used for
sensory functioning
• Head
One pair of antennae
A pair of mandibles
One or two pairs of maxillae
• Eyes are on either side of the head and
consists of groups of ocelli
Centipede reproduction
• Sexes are separate with unpaired gonads
and paired ducts
• Some lay eggs and others are viviparous
• The young resemble adults and do not
undergo metamorphosis
Class Diplopoda
Source: BIO422 Lecture
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Millipedes are known to be less active than
centipedes
They prefer dark moist places under logs or
stones
What they do usually for defense is to roll into
a coil
Some species secret toxic or repellant fluids
from special repugnatorial glands on the side
of the body
They mostly eat decayed plant matter, but a
few eat living plant issue
The presence of much more legs gives them
a much more graceful movement
They don't have a venom claw or poison
fang
There are more than 10,000 species
worldwide
LABAN LANG!
ZOOLOGY LABORATORY
Source: BIO422 Lecture
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