Transcript Lecture 14, Ecdysozoa - Cal State LA

Phylum Nematoda
~25,000
species
Nematode muscles run the long way down body (longitudinal),
but no circular muscles go around the middle
- can’t squeeze itself to get fatter
or thinner on one end, the way
an earthworm can
Covered in a cuticle, tough outer covering
shed in a series of 4 molts during growth
- helps worms survive in hostile environments
C. elegans is a model organism for developmental biology
Phylum Nematoda
Ecological importance of nematodes:
- very abundant and important decomposers
- 200 per ml of coastal mud
- 90,000 per rotting apple
- 9 billion per acre of soil
Medical importance:
- parasitic forms cause diseases:
river blindness
elephantiasis
trichinosis
~25,000
species
Phylum Arthropoda
over 1,000,000
species!
Segmented bodies organized into specialized regions:
head, thorax, abdomen
Each body segment has paired, jointed appendages
Cuticle forms a well-developed exoskeleton covering outside;
-molting (ecdysis) is required for growth
Coelom is very reduced; not needed because muscles attach to
the exoskeleton
- main body cavity is a hemocoel
(open circulatory system, like molluscs)
Keys to Arthropod Success #1: Exoskeleton
Arthropods are encased in a hard external covering made of
proteins + chitin, coated with waxy fats
- gives protection from predators
- major pre-adaptation for life on land: they don’t dry out
(analogous to the cuticle of plants)
In crustaceans (crabs, lobster), cuticle is hardened by
calcium carbonate (like mollusc shells, coral skeletons)
Coelom is unnecessary as a hydrostatic skeleton
(and wouldn’t even work, since the body is so rigid)
 replaced w/ open circulatory system + hemocoel
Arthropod muscles anchor to inside of the exoskeleton...
Molting
Living inside a cuticle is like being trapped in a suit of armor:
how would you grow bigger?
Molting is a process of shedding the cuticle, allowing growth
- process is controlled by hormone ecdysone
(hence the group name, Ecdysozoa)
Cuticle is weakened by enzymes, then animal crawls out
all soft & naked
- animal sucks in air/water to inflate itself
- then secretes a new cuticle, which quickly hardens
- this leaves space inside the new cuticle for growth
Keys to Arthropod Success #2:
Jointed appendages
Appendages have muscles connected to the exoskeleton
Have multiple joints and branches, giving incredible flexibility
Appendages are adapted for different functions -antennae, mouthparts, claws, legs, flippers for swimming,
even gills for breathing, are all modified appendages
2-branch
limb of a
crab
1-branch limb of an insect
Keys to Arthropod Success #3:
Specialized body regions
Annelid worms are segmented, but don’t usually have clumps
of segments specialized into different body regions
Arthropods have body regions made of segments grouped
together and specialized for a function
- head, thorax and abdomen are regions specialized for
performing different tasks
- appendages on different segments do different things
- antennae on head for sensory perception
- claws on thorax for grabbing food, fighting
- legs on abdomen for walking + swimming
Body regions of an insect
Head
Thorax
Abdomen
Phylum Arthropoda
SUB-PHYLA:
Trilobitomorpha:
Trilobites (extinct, 350 mil yr ago)
Myriapoda:
Centipedes
Cheliceriformes:
Spiders, scorpions
Crustacea:
Crustaceans
Hexapoda:
Insects
Phylum Arthropoda
SUB-PHYLA:
Trilobitomorpha:
Trilobites (extinct)
Myriapoda:
Centipedes + millipedes
- many identical segments
- body is not separated
into thorax + abdomen
the way it is in insects
12,000
species
Phylum Arthropoda
SUB-PHYLA:
Trilobitomorpha: Trilobites (extinct, 350 mil yr ago)
Myriapoda:
Centipedes
Cheliceriformes: Spiders, scorpions
65,000 species
- 2-part body: cephalothorax & abdomen
- 1st pair of appendages = tiny feeding claws
(can’t really see them on spiders)
- instead of legs, appendages on abdomen are modified as
spinnerets that spin silk proteins into webs
SubPhylum Cheliceriformes
SubClass Merostomata
Horseshoe crabs
cephalo- abdomen
thorax
- once very common
- over-harvested, now rare
SubPhylum Cheliceriformes
SubClass Merostomata
Horseshoe crabs
cephalo- abdomen
thorax
SubClass ArachnidaScorpions, spiders, ticks
SubClass Arachnida
65,000 species
spider silk is 5x stronger than steel
yet more flexible than rubber
scorpion
spiders spin liquid proteins into
solid strands that may be sticky
for catching prey, or just strong
spider
orb weaver spider + web
many chelicerates are parasites,
including harmless mites and
blood-sucking ticks
mites
tick
Phylum Arthropoda
SUB-PHYLA:
Trilobitomorpha:
Trilobites (extinct)
Myriapoda:
Centipedes
Cheliceriformes:
Spiders, scorpions
Crustacea:
Crustaceans – crabs, lobster, shrimp
75,000 species
- body = 5-segmented head + thorax + abdomen
- one of the most successful groups of marine animals,
with 2 different groups that also colonized dry land
SubPhylum Crustacea
Body = 5-segmented head + thorax + abdomen
A pair of limbs is found on every segment, but modified:
- head: antennae & pincers for eating
- thorax: claws and walking legs
- abdomen: swimming legs
Some legs are flattened + used as “gills” for respiration
- like how parapodia of annelids can act as gills!
Shrimp: body of 19 segments: head, 5 segments
thorax, 8 segments
abdomen, 6 segments + tail
Thorax segments
Abdomen
swimming legs
walking legs
Crustacean Head
Each of the 5 head segments
has its own unique appendages
1
2
3
4
5
Class Maxillopoda: Barnacles
26,000 species
start life as a swimming larva, which glues its head onto a rock
at metamorphosis
adult secretes a hard shell, uses modified legs for filter-feeding
swimming larva
(looks like a crustacean)
adult cemented to rock
(doesn’t look crustacean-y)
Class Malacostraca
25,000 spp.
Decapods (“10-legs)
Isopods
- 14,000 species:
crabs, shrimp, lobster
- 10,000 species
- mostly marine but includes
terrestrial “pill bugs”
- 5 pairs of walking legs,
1st pair modified as claws
- carapace = protective shield
over head + thorax
carapace
Lobsters
Crabs
Carapace
Abdomen
powerful tail used
to scoot backwards
- abdomen is folded under thorax
- 5th walking leg flattened for swimming
Crustaceans on Land
Pill bugs (isopods) are
the most successful
crustaceans on land
Land hermit crabs must still
return to the ocean to spawn
no swimming larvae =
no need for water
Phylum Arthropoda
SUB-PHYLA:
Trilobitomorpha:
Trilobites (extinct)
Myriapoda:
Centipedes
Cheliceriformes:
Spiders, scorpions
Crustacea:
Crustaceans
Hexapoda:
Insects
~1,000,000 species so far…
SubPhylum Hexapoda: Insects
- Head with one pair of antennae, chewing mouthparts
- 3 segment on thorax = 6 legs (2 per segment)
- Wings often present, made of dorsal cuticle
-
Head
Thorax
Abdomen
compound eye
with many facets
spiracles
Insects decouple gas exchange and circulation
- air moves in through spiracles, little holes in the cuticle
- piped directly to each cell of the body through a system of
tubes (like air ducts) for efficient delivery of oxygen
- overcomes inefficient open circulatory system...
The Power of Flight
Wings contribute to the ecological dominance of insects by
providing a very efficient means of dispersal
- locate mates, new patches of food
-
ladybug preparing to fly
Most groups have 2 pairs of wings
- in beetles, first pair is modified
as a covering to protect back
pair, actually used for flying
Butterfly migration
Monarch butterfly migrates 2000 miles
each fall from the northeast to forests
in Mexico for the winter
- it congregates by the thousands in trees there;
is endangered by clear-cutting of forests
Monarch caterpillar
Batesian mimicry
Monarch caterpillar eats
milkweed plant, stores
toxic chemicals which
make adult butterfly taste
bad to predators
 Viceroy butterfly mimics the
Monarch, but tastes fine !
Coevolution of herbivorous insects and plants:
generating earth’s biodiversity
Most species on earth, by the numbers, are herbivorous insects
- half of all insect species are beetles that eat angiosperms
Studies suggest that when a population of angiosperms divided
into 2 different species, the beetles feeding on them also
divided into 2 new beetle species
- you have to be specialized to handle the toxic chemicals
most plants produce to defend themselves
Specialization allows many related species to co-occur in the
same habitat without competing 
Biodiversity: Insect Orders
The Apterygota
Protura
Collembola Springtails
The Exopterygota
Ephemeroptera Mayflies
The Endopterygota
Odonata Dragonflies
Coleoptera Beetles
Plecoptera Stoneflies
Thysanura Silverfish
Grylloblatodea Ice Bugs
Diplura Bristle-tails
Orthoptera Crickets + Grasshoppers
Neuroptera Lacewings
Strepsiptera Stylops
Mecoptera Scorpionflies
Phasmida Stick-Insects
Siphonaptera Fleas
Dermaptera Earwigs
Diptera True Flies
Embioptera Web Spinners
Lepidoptera Butterflies + Moths
Dictyoptera Cockroaches + Mantids
Trichoptera Caddis Flies
Isoptera Termites
Zoraptera
Psocoptera Bark and Book Lice
Mallophaga Biting Lice
Siphunculata Sucking Lice
Anoplura Biting + Sucking Lice
Hemiptera True Bugs
Homoptera Cicadas + Hoppers
Thysanoptera Thrips
Hymenoptera Ants, Bees + Wasps
Who is related to whom?
Mollusc
Annelid
Arthropod
share obvious segmentation
Who is related to whom?
Mollusc
Annelid
share trochophore larval stage
Arthropod
DNA sequences re-wrote the book
Lophotrochozoa
Molluscs
Based on
analysis of
DNA, gene
order…
Annelids
ancestor with
trochophore
larva
Ecdysozoa
Arthropods Nematodes
ancestor
with a
cuticle
…Protostomes
are now divided
into 2 major
sub-groups