Download Chapter 32 The Ecdysoans: The Molting Animals

Chapter 33 The
Ecdysoans: The
Molting Animals
Biology 102
Tri-County Technical
College
Pendleton, SC
Distinguishing Features
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Exoskeleton—firm, nonliving covering
which cannot grow as animal inside it
does
– molted (shed) and new, larger one made
Cannot use cilia for locomotion so new
forms evolved
 Hard exoskeleton impede passage of
oxygen into animal so new respiration
mechanisms evolved
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Features, cont.
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Exoskeleton may be thin and flexible
Thin, flexible exoskeleton called a cuticle
Provides some protection, but does NOT
support the body
Such animals rely on a hydrostatic skeleton
“Incompressible internal fluids that transfer
forces from one part of body to another when
acted upon by surrounding muscles”
Nematode Characteristics
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Commonly called roundworms ( one of must
abundant and universally distributed)
Have thick, multilayered cuticle secreted by
underlying epidermis
Exchange O2 and nutrients through cuticle
and intestine (one cell layer thick)
Move materials through gut by contracting
pharynx (highly muscular organ at worm’s
anterior end)
Predators, parasites, and free-living
Nematode Visual
Arthropod Characteristics
Regional segmentation, jointed
appendages, and exoskeleton (chitin
and protein)
 Possess hemocoel
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– Circulating fluid called hemolymph (no
distinction made between blood and
interstitial fluid surround body cells)
– Hemolymph exits vessels and percolates
through body tissues into large cavity
called the HEMOCOEL
Arthropod Visual
Pros and Cons of Exoskeleton
Advantages include protection and
points of attachment for muscles to
move appendages
 Relatively impermeable to water
 Disadvantage is the old exoskeleton
must be shed (molted) for an arthropod
to grow
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Phylum Arachnida
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Scorpions, spiders, ticks, and mites
 Cephalothorax with 6 pairs of appendages
– Chelicarae (either of first pair of appendages used
for grasping and crushing), Pedipalps (sensing or
feeling) and 4 pairs of walking legs

Gas exchange by book lungs (stacked
plates in internal chamber)
 Ability to make silk
Phylum Crustacea
Crabs, lobsters, shrimps, barnacles, &
others
 Two pair antenna, 3 or more pairs of
mouthparts (including mandibles),
walking legs of thorax, appendages
present on abdomen
 Gas exchange across thin areas of
cuticle or by gills
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Crustacea, cont.
Open circulatory system with
hemolymph
 Salt balance regulated by pair of
specialized antennal or maxillary glands
 Most are dioecious
 Some males have specialized pair of
appendages to transfer sperm to female
(intromittent organ)
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Crustacea Visual
Phylum Uniramia/SP Insecta
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Insecta has greater species divesity than all
other forms of life combined
Flight is key to insect success
1 or 2 pair of wings emerge from dorsal side
of thorax in most species
Wings are extension of cuticle (not modified
appendages)
Complete digestive system with specialized
regions
Insecta, cont.
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Excretory organs (Malphighian tubules) are
outpockets of the gut
Gas exchange by tracheal system with
openings via spiracles
Dorsal brain with pair of ventral nerve cords
Most undergo some type of metamorphosis
Are dioecious and reproduce sexually
Insecta Visual
Comparing the cavities…
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Coelom: fluid-filled body cavity completely
lined by mesodermally derived tissues; inner
and outer layers of tissue surrounding cavity
connect dorsally & ventrally to form
mesenteries which suspend internal organs
 Hemocoel: Open-circulatory system in which
fluid called hemolymph propelled by heart(s)
through short arteries into spaces called
sinuses surrounding tissues and organs
Comparing, cont.
Term “blood” best reserved for fluid in closed
circulatory system
 Body sinuses collectively called the
hemocoel which is NOT part of coelom
 In most arthropods, coelom that forms during
embryo stage becomes greatly reduced
 Hemocoel becomes main body cavity in
adults
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Metamorphosis
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Incomplete: type of development
during which young resemble adults but
are smaller and have different body
proportions
– grasshoppers
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Complete: type of development
characterized by larval stages (maggot,
grub, or caterpillar) which are VERY
different in appearance from adults