Phylum Arthropoda
• “Jointed foot”
• Contains at least 75% of the described, living species of animals
• Almost 90% of the arthropods are insects
• Marine, fresh water, terrestrial and airborne
• Size range < 1mm mites to 4 m spider crabs
Phylum Arthropoda
• Exoskeleton (chitin)
• moult
• Jointed appendages
• Body divided into 2 or 3 sections
• Straight gut
• Brain and ganglia
• Open circulatory system
• Dioecious
Phylum Arthropoda
Metameric segmentation Tagmatizaion
Phylum Arthropoda
Insects Crustaceans Spiders & Scorpions
Cirripeds Copepods Isopods Amphipods Decapods
Phylum ArthropodaClass Crustacea
• 52,000 described
species, 10 to 100
times more
undescribed
• Most are free-living
and marine
• Two pairs of antennae
• Biramous limbs
• Nauplius larva
Phylum ArthropodaClass Crustacea Subclass Cirripedia
• Barnacles
• Classified as
molluscs until 1830
• First fully studied
and classified by
Charles Darwin
• ~ 1200 species
• e.g. acorn barnacle
Balanus sp
Phylum ArthropodaClass Crustacea Subclass Cirripedia
• Barnacles are
shrimp standing
on their head
(cemented to
the substrate)
and feeding with
their feet (called
cirri)
Phylum ArthropodaClass Crustacea Subclass Cirripedia
• e.g. Goose neck barnacles
Pollicipes sp
• Barnacles do not
have a true heart
• Do not have gills,
instead oxygen
diffuses through their cirri
• Sensitive to touch and have
a single eye
Phylum ArthropodaClass Crustacea Subclass Cirripedia
• Most Barnacles
are filter feeders
and use the water
currents for their
feeding
advantage.
Phylum ArthropodaClass Crustacea Subclass Cirripedia
Phylum ArthropodaClass Crustacea Subclass Cirripedia
• Barnacles are sessile
free living but some are
parasitic
(Rhizocephalans).
• Decapod host
• Only the larval form
resembles that of barnacles
• the adults lack appendages and internal
organs except for gonads
Phylum ArthropodaClass Crustacea Subclass Copepodia
• 13,000 described
species and half are
parasitic
• they form the largest
animal biomass on earth
• Main contributor to
secondary productivity
and the carbon sink of
the world oceans
Phylum ArthropodaClass Crustacea Subclass Copepodia
• Very small (1-2 mm)
• Mostly marine / planktonic
• Thin transparent cuticle
• One compound eye (red)
• No heart
• Lack gills (oxygen diffuses
thru the cuticle)
• Abdomen has no
appendages
Phylum ArthropodaClass Crustacea Subclass Copepodia
• Tide pool copepods e.g.
Tigriopus sp
• Can survive
freezing, high
temperatures, desiccation
and extreme salinity
changes
Phylum ArthropodaClass Crustacea Subclass Copepodia
• Copepods have bristle-like
setae that act as
mechanorecptors.
• An array of such sensors
allows detection of patterns of
water flow around the body
caused by approaching prey
or predator, and the copepod
can distinguish between the
two.
Phylum ArthropodaClass Crustacea Subclass Copepodia
• Copepods are
dioecious
• Planktonic copepods
use pheromones
emitted by the
swimming
female, which leaves a
trail in the water that the
male can follow to
locate the female
Phylum ArthropodaClass Crustacea Subclass Copepodia
• During mating
• Male grips the female
with his antennae, The
male then transfers
sperm to the female.
Eggs are sometimes laid
directly into the water, but
many species enclose
them within a sac
attached to female's body
until they hatch.
Phylum ArthropodaClass Crustacea Subclass Copepodia
• Eggs hatch into a nauplius
larvae
• The nauplius moults 5 or 6
times, before emerging as
a "copepodid larva".
• After a further five
moults, the copepod finally
takes on the adult form.
• Egg to adult can take one
week or one year
depending on species
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Isopoda
• Mostly free-living marine
e.g. Idotea sp
• Crawl rather than swim
• Terrestrial – pill bug
• Some parasitic
(fish, shrimp and crab
hosts)
• Biphasic molt
• Carapace – cephalic
shield
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Isopoda - Elongated flat and somewhat
arched bodies
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Isopoda• Females are brooders
• After female moults males
deposit sperm into the brood
pouch
• Eggs pass from the oviduct
into the pouch and are
fertilized on the way
• Isopods hatch from the eggs
as manca (adult like but last
pair of walking legs are
missing). Become juveniles 3
moults later
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Isopoda
• No free-swimming
larval stage
Endemism
Dispersal limited to the
crawling ability of the
individual
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Isopoda
• Excirolana
vancouverensis
Consume 53% of body
mass in 1 minute
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• c-shaped bodies
flattened laterally
• Free living mostly
marine and freshwater
• Swim or hop
• Do not have a
carapace
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Females have a brood
pouch
• Hatch as miniature adults
• Development varies with
temperature
• For some, gender varies
with temperature (cold =
male, warm = female)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Amplexus – large males
grasp onto females with
their gnathopods and
carry them for several
days
• Females moult before
they shed their eggs and
are vulnerable to
predation
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Females secrete a
pheromone in her urine
which triggers the
guarding behaviour in
males plus they lose the
desire to eat them
• After her eggs are
fertilized her exoskeleton
hardens and the male is
encouraged to leave
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Amphipods are difficult to
identify, due to their small
size, and the fact that they
must be dissected. As a
result, ecological studies and
environmental surveys often
lump all amphipods together
• Around 7,000 species of
amphipods have so far been
described
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Most planktonic
species are
symbionts with
gelatinous animals
sometime during
their lifecycle.
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Few are parasitic
– The whale lice - these are
dorso-ventrally flattened, and
have large, strong claws, with
which they attach themselves
to baleen whales. They are the
only parasitic crustaceans
which cannot swim during any
part of their lifecycle
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Amphipoda
• Caprellids
– Skeleton Shrimp.
• their body shape and
colour help them blend
with their surroundings and the gentle back and
forth sway resembles substrate within the water
current.
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• 15,000 species, half of
these are crabs, ¼ are
shrimp and the other ¼
are anomurans
• Most are marine but
some are freshwater
and a few are
terrestrial
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Deca = ten, pod = foot
• Appendages
– 5 pairs on the thoracic
segment, 1st usually a claw
– Three pairs, maxillipeds
(mouth parts)
– Each abdomen segment
has a pair of pleopods
– Tail fan telson and uropod
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• anatomy
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Shrimp vs Prawn
Lamellar gill vs
branched
– Two pairs of claws vs
three
– Brood eggs before
hatching vs doesn’t
brood
Phylum ArthropodaClass Crustacea Subclass
Malacostraca
Shrimp Prawna
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Caridia
• Shrimps
– Adapted for swimming
– Bodies are laterally
compressed
– Slender legs and well
developed swimmerets
(pleopods)
– Rostrum
– Compound eyes
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Coonstripe or Dock Shrimp (Pandalus danae)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Humpback or King Shrimp (Pandalus hypsinotus)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Smooth or Ocean Pink Shrimp (Pandalus jordani)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Pink Shrimp - Spiny (Pandalus borealis)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Prawn or Spot Shrimp (Pandalus platyceros)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Sidestripe or Giant Shrimp (Pandalopsis dispar)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Caridia
• Heptacarpus sp.
• Intertidal shrimps
• Transparent or a
variety of colours
• Hide during the
day, feed and are
easily seen at night.
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Caridia
• Life cycle
– Spend 1st years as
males then switch to
females.
– Females brood their
eggs (50,000 – 1
million)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Caridia
• Life cycle
– Eggs hatch nauplii
larvae (yolk sac)
– metamorphosis into
zoeae (feed on algae)
– Metamorphisis into
myses (feed on algae
and zooplankton
– Metamorphosis into
young shrimp
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Caridia
• Amazing shrimps
– The pistol shrimp
– The mantis shrimp
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Differently tailed
• Have 5 pairs of
periopods but 1 pair is
internal and used to
keep their gills clean
• If you see a crab with
four legs then it is an
anomuran.
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Squat Lobsters
• The body is usually flattened
• the abdomen is typically folded
under itself
• the first periopods are greatly
elongated and armed with long
chelae (claws).
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Porcelain crab
– less than 15 mm (0.6 in) wide
– flattened bodies as an adaptation
for living in rock crevices
– readily lose limbs when attacked
– use their large claws for
maintaining territories
– They feed by using long setae
(feathery hair on the mouthparts
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Heart crab
– Related to the Alaskan king
crab
– the asymmetry of the crab's
abdomen, which is thought to
reflect the asymmetry of
hermit crabs, which must fit
into a spiral shell (pleopods
are smaller on one side)
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Hermit crabs
– Live in gastropod shells
usually.
– Spirally coiled soft
abdodmen
– Pleopod assymetry
– tip of abdomen is adapted
to clasp onto the columella
of the shell.
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Hermit crabs
– vacancy chains: when a
new, bigger shell becomes
available, hermit crabs
gather around it and form a
queue from largest to
smallest. When the largest
crab moves into the new
shell, the second biggest
crab moves into the newly
vacated shell and so on.
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Anomura
• Hermit crabs
• Symbiosis:
– with the sponge
– With anemones
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Brachyura
• True crabs
• Eg. Hemigrapsus sp
reduced abdomen is
entirely hidden under the
thorax
Telson not
functional, uropods are
absent
Phylum ArthropodaClass Crustacea Subclass Malacostraca
• Order Decapoda
• Infraorder Brachyura
• True crabs
• New research suggests
that crabs not only suffer
pain but that they retain a
memory of it.
Pycnogonid – sea spider
• Body not divided into
distinct regions
• Very slow moving
• Appendages at the
head which are used
to groom the opposite
sex’s legs and are
used by the males to
carry fertilized eggs
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