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Fall 2012
Lecture 33. Arthropoda II Introduction to Arthropod subphyla
Students should be able to: distinguish among the 5 major
sub-groups of arthropods with respect to tagmata and appendages
explain the morphological and behavioral changes associated with
colonization of land in each of the major groups Explain why an
open circulatory system is not problematic for these fast-moving
organisms.
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A hard exoskeleton limits growth
Molting means that external growth occurs in stages, sometimes
called instars
Consequences of an exoskeleton support for walking on land sites
for muscle attachment protection against predators chitin reduces
water loss
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! Hired as a wildlife biologist in Australia, your first task is
to assist in dissecting a dead crocodile. You find small wormlike
animals in the nasal cavity. They have tiny claws, a hardened
exoskeleton, and one of them is molting. The head biologist says
oh, pentastomids, eh? When you go to your textbook, where do you
start looking?
! a) under Mollusca ! b. under Annelida ! c) under Ecdysozoan
phyla ! d) under Lophotrochozoan phyla ! e) under Protostomia
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Subphylum Trilobita extinct group of marine arthropods !
abundant and diverse 250-500 million years ago ! bottom dwellers,
probably scavengers
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Arthropod diversity: four major extant groups Chelicerata
arachnids, horseshoe crab Myriapoda centipedes, millipedes
Crustacea crabs, shrimp, lobsters, barnacles, etc. Hexapoda insects
and allies
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Subphylum Chelicerata (90,000 species)
spiders
scorpions
ticks
mites
horseshoe crabs
extinct, but probably first terrestrial arthropods
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Chelicerae
Pedipalps
First two pairs of appendages
QuanSticky Notespiders have multiple eyes with diff
function.Chelicerae: inject enzymepedipals: sensory, sperm
transfer
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two tagmata, 4 prs walking legs prosoma = cephalothorax
opisthosoma = abdomen
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horseshoe crabs mite
mite ticks
mite
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Some spiders filter-feed in air, others cast the net, or hunt
prey
silk glands http://www.youtube.com/watch?v=BUELYcGDCc4
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Subphylum Crustacea crabs, shrimp, lobsters, barnacles, isopods,
copepods, etc. (50,000 species)
In some a carapace covers the head and abdomen
Many have 3 tagmata
head thorax abdomen
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QuanSticky Notecarapace: extension of the head
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Aquatic crustacean life cycles include a feeding
nauplius larval stage with 3 prs of appendages
Zygote
various specialized later stages with molts between each.
for example, a later stage in the crab life cycle
QuanSticky Notelarvae have a lots of spikes to protect against
predators
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Barnacles are sessile and come in 2 types: acorn or
goose-neck
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Barnacles are almost all monoecious and mate reciprocally.
However, they are sessile animals with internal fertilization,
so!
QuanSticky Notebarnacles have very long penis compared to its
body size. Its reach its penis into other barnacles to mate
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Sow bug (rolly polly) a terrestrial isopod
if it is a crustacean on land, how does it respire?
QuanSticky Noteindependently evolve pseudo-trachea (indentation
of exoskeleton) to bring air in
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Subphylum Hexapoda ! Class Insecta and Class Entognatha
3 tagmata (head, thorax, abdomen) and 6 legs (hence subphylum
name)
They form the most species-rich group on earth, occupying almost
every habitat and lifestyle.
1 million +species
head thorax abdomen
QuanSticky NoteInsects are terrestrial crustaceans
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Hexapoda insects and allies
! three tagmata: head, thorax and abdomen ! one pair of antennae
(two pairs in other crustaceans) ! three pairs of legs (located on
the thorax) ! respiration by tracheae (system of air tubes
extending into body)
spiracle
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The first great insect radiation is associated with the
evolution of wings and took place in the Carboniferous about 345
million years ago. Insects had the air to themselves until
pterosaurs evolved (280 mya); birds did not evolve until 150
mya.
Comparative gene expression studies suggest that wings arose
from dorsal appendages at the base of the legs. In crustaceans the
dorsal appendages are used for respiration.
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The second great radiation follows the evolution of flowering
plants about 65 to 70 mya. You already know about the coevolution
between plants and their pollinators, but many herbivorous insects
depend on plants for food or habitat.
Australian green ants
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Think pair share
Insects are rapidly moving organismsflight
muscles require a good oxygen supply. How can arthropods survive
and thrive with an open circulatory system?
QuanSticky Notehave trachea --> separate oxygen carry
system
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Mouthparts are very diverse
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There are ectoparasites and endoparasites
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Bot fly life cycle ! Imagine having this larva in the skin over
your skull!
! The bot fly is 12 to 18 mm long, blue-black in colour and
lives for 8 or 9 days. The female bot fly captures an insect, often
a mosquito, and deposits its eggs on the abdomen. When the insect
bites a vertebrate host, the larva within the egg senses the change
of temperature, hatches and falls off the insect onto the new host.
It penetrates the skin via the puncture mark or through a hair
follicle. Once within the subcutaneous tissue, the larva respires
and excretes waste via a tube which passes to the skin and forms
the characteristic punctum. The larva grows for around 8 weeks,
then emerges and drops to the ground to pupate into an adult
fly.
! Digital Infestation with the Human Bot Fly ! R.D. Lawson and
M. Rizzo ,
Duke University Medical Center, Division of Orthopedic Surgery,
USA
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Placozoa, Mesozoa, Acoelomorpha, Nemertea
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Gnathostomulida, Micrognathozoa, Rotifera x 2, Acanthocephala,
Cycliophora, Gastrotricha
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Entoprocta, Phoronida, Brachiopoda,
Bryozoa,
Echiura, Sipunculida
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Priapulida, Kinorhyncha, Loricifera,
Tardigrada, Nematomorpha
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Chaetognatha,
Hemichordata
Xenoturbellida
