A statement of humility

1
I am a WORM!
-A statement of humility? -Doesnt hurt -A
statement of anatomical truth? -In part, yes.
Worms are bilaterally symmetric, elongated
animals without appendages, and usually with a
coelomic cavity -Essentially all complex animals
are based on this design, however modified
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Coelomate Animals
-Traditional view of animal evolution -Sister
group of the flatworms (acoelomates) is the
coelomate clade of animals with -Two
openings to gut -Body cavity (coelom) -They
have a tube within a tube body plan
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Function of Complete (mouth to anus) Gut
-Complete gut allows -Specialization of
different regions of the alimentary canal -Which
allows sequential processing of food, and
ultimately.. -Complete extracellular digestion
of food so basic compounds (amino acids,
sugars, fatty acids, etc.) are absorbed into a
circulatory system and distributed to each cell
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Function of Coelomic Cavity
-Coelomic cavity allows several possible
functions 1. Circulation Even without a
separate circulatory system, coelom can
facilitate circulation of -Digestive products
essential with complete gut, since digestive
products are absorbed across gut wall only in
hindgut -Excretory products in many animals
excretory system processes coelomic fluid.
Important in larger animals with small surface to
volume ratio -CO2 and O2 fluid serves to
transport gases between respiratory surfaces and
cells. Also important in larger animals with
small S/V ratios
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Function of Coelomic Cavity
-Coelomic cavity allows several possible
functions 2. Reproduction In many animals
(including us!), gametes are shed into in a
coelomic cavity, and in some animals the gametes
accumulate there before mating. Allows more
gametes to be exchanged at one time. Could even
be the original function of some coelomic cavities
An extreme example The Palolo worm, like many
other marine annelids, produces special body
segments, loaded with eggs or sperm, that
separate from the body and swim to the surface
for mating
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Function of Coelomic Cavity
-Coelomic cavity allows several possible
functions 3. Support and locomotion -Even in
absence of a hard skeleton, a sealed,
fluid-filled space can act to support an animal,
and provide something against which muscles can
act a hydrostatic skeleton -May have been the
initial stage in a change from locomotion by
cilia to locomotion by muscular
activity -Important for larger animals
movement is on same scale as size of body
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Types of Coelomic Cavities
-Acoelomates have no coelomic cavity. Mesoderm
fills in entire blastocoel space -In
Pseudocoelomates, mesoderm lines the inner part
of the body wall, and the blastocoel persists as
the pseudocoelom. Not lined completely with
mesoderm. -The true coelom is completely lined
with mesoderm (inside body wall and surrounding
gut, plus mesenteries). Coelomic cavity
originates in different ways.
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Types of Coelomic Cavities
-True coelom forms in one of two ways -In
protostomes other than pseudocoelomates, it forms
from splits in mesoderm (schizocoelous) -In
deuterostomes, it forms from outpocketings of the
archenteron (enterocoelous) In both cases,
mesodermal cells surround a new space, the coelom
and the mass of mesodermal cells with its
enclosed space grows to fill the entire
blastocoel.
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Traditional view of coelomate evolution
-Pseudocoelomates as one branch,
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Pseudocoelomates
-Several phyla of mostly small animals, some
miniaturized -Rotifers are one example small,
aquatic filter feeders. Males need not apply.
-Nematodes (roundworms) are the most diverse
pseudocoelomates -free-living forms important as
detritus eaters VERY abundant -Many parasitic
forms trichinosis, hookworm, river blindness,
elephantiasis
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Traditional view of coelomate evolution
-Pseudocoelomates as one branch, sister
to.. -Animals with a true coelom, which are
divided into
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Traditional view of coelomate evolution
-Pseudocoelomates as one branch, sister
to.. -Animals with a true coelom, which are
divided into -Protostomes, with a
schizocloelous coelom
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Protostome Coelomate Animals
-Some of the greatest phyla of invertebrate
animals -The MOLLUSCS, in which a dorsal shell
is secreted, and the coelomic cavity is reduced.
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Protostome Coelomate Animals
-Major Classes of molluscs include.. -Gastropoda
(snails and slugs) -Bivalves (clams, oysters,
mussels, scallops) -Chitons (chitons) -Cephalopo
ds (nautilus, squid, octopus)
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Protostome Coelomate Animals
-Some of the greatest phyla of invertebrate
animals -A few phyla of unsegmented coelomate
worms, like this fat inkeeper worm from
California mudflats
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Protostome Coelomate Animals
-Some of the greatest phyla of invertebrate
animals -The ANNELIDS segmented worms
-The segmentation allows independent movement of
each part of the body, permitting better
burrowing activity and finer control of body
movements. More later on segmentation.
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Protostome Coelomate Animals
Classes of Annelids -Polychaeta marine
segmented annelids. Some 45,000 species, both
mobile and sedentary. -Oligochaeta
Earthworms. One of natures engineers. -Hirudin
ea Leeches. Related to Oligochaetes, they suck
blood. Once used medicinally (still are!).
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Protostome Coelomate Animals
-Some of the greatest phyla of invertebrate
animals -The ARTHROPODS animals with a jointed
exoskeleton. The most successful phylum of
animals on earth.
-The arthropods are also segmented, and this
segmentation has partly led to the linkage of
arthropods and annelids in traditional
classifications
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Traditional view of coelomate evolution
-Pseudocoelomates as one branch, sister
to.. -Animals with a true coelom, which are
divided into -Protostomes, with a
schizocloelous coelom, and -Deuterostomes, with
an enterocoelous coelom
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Traditional view of coelomate evolution
-Pseudocoelomates as one branch, sister
to.. -Animals with a true coelom, which are
divided into -Protostomes, with a
schizocloelous coelom, and -Deuterostomes, with
an enterocoelous coelom -And the enigmatic
lophophorates
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Lophophorates
-Animals with a three-part coelom and a
characteristic set of tentacles near the mouth
a lophophore -Bear resemblances to both
deuterostomes and protostomes -The brachiopods
resemble clams and scallops, and at one time
filled the niches now occupied by bivalve
molluscs until one of the global extinction
events nearly wiped them out
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New view of coelomate evolution
-Data from nucleotide sequences, as well as from
anatomy and development, have produced a newer
view of animal relationships -Note different
placement of arthropods, the demise of the
pseudocoelomates, and the elevated placement of
flatworms
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Protostomes
Ecdysozoa
Lophotrochozoa
Eutrochozoa
-Another view of the new phylogeny, with fewer
taxa but with better-defined clades
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S
O
S
O
S
R
R
Comparison of characters between traditional and
alternative classification Cleavage patterns S
Spiral R Radial O Odd
25
Especially Nematodes
S
S
O
S
R
R
O
Comparison of characters between traditional and
alternative classification Cleavage patterns S
Spiral R Radial O Odd
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S
O
S
O
S
R
R
A
A
A?
Comparison of characters between traditional and
alternative classification A. Trochophore larva

27
Especially Nematodes
S
S
O
S
R
R
O
A
Comparison of characters between traditional and
alternative classification A. Trochophore larva

28
S
O
S
O
S
R
R
A
A
A?
B
B
Comparison of characters between traditional and
alternative classification A. Trochophore larva
B. Growth by molting
29
Especially Nematodes
S
S
O
S
R
R
O
B
A

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva
• Growth by molting

30
S
O
S
O
S
R
R
A
A
A?
B
B
C
C

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva
• Growth by molting
• True schizocoel

31
Especially Nematodes
S
S
O
S
R
R
O
C
B
A

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva
• Growth by molting
• True schizocoel

32
S
O
S
O
S
R
R
A
A
A?
B
B
C
C
D

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva D. Segmentation
• Growth by molting
• True schizocoel

33
Especially Nematodes
S
S
O
S
R
R
O
D
D
C
B
A

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva D. Segmentation
• Growth by molting
• True schizocoel

34
S
O
S
O
S
R
R
A
A
A?
B
B
C
C
D
E

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva D. Segmentation
• Growth by molting E. Complete gut
• True schizocoel

35
Especially Nematodes
S
S
O
S
R
R
O
D
D
C
B
A

• Comparison of characters between traditional and
  alternative classification
• A. Trochophore larva D. Segmentation
• Growth by molting E. Complete gut?
• True schizocoel Lacking only in flatworms