Chapter 26 The Protostome Coelomates

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Chapter 26The Protostome Coelomates
http//www.zetnet.co.uk/pm/photos/snail.j
pg
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The Coelom

• -Fluid filled cavity in the mesoderm
• Organ systems can bend,twist and fold back on
  themselves because they are surrounded by
  lubricating coelomic fluid
  
• -Phyla based on features in embryonic
  development
  
• Spiral Cleavage mollusks,arthropods,annelids
• Radial Cleavage echinoderms,chordates

-Blastopore appears in blastula
Spiral-mouth develops near blastophoreprotosom
es Radial-anus forms near blastophore and mout
h develops elsewheredeuterosomes
Radial Spiral
http//pharyngula.org/index/weblog/comments/spi
ral_cleavage/
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EMBRYONIC DEVELOPMENT
-In protostomes,the coelom forms by splitting.
Process is schizocoelous -Deuterostomes form an
cavity in the embryonic gut, an enterocoelous
process.
www.laredo.edu/science/rviswanath/
Asking20about20Life20present/ch23_lecture.ppt


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PHYLUM MOLLUSCA MOLLUSKS
-Soft bodies that can be covered in a calcium
shell or the shell has been reduced and
internalized through the course of evolution
(Squids) -Characteristics Head-foot sensory
and motor organs Visceral Mass digestion,exc
retion, reproductive organs Mantletissue that
hangs over and around visceral mass and secretes
the shell Mantle cavity space that holds gill
s. Digestive,excretory and reproductive systems
discharge into it, which is washed out by water
Radula tooth-bearing strap of chitinous mate
rial almost like a tounge, used for scraping
algae and material, in some species, for combat
(In all classes except bivalves)
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Hypothetical primitive mollusk


www.bio.miami.edu/ dana/160/160S04_14.html
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Supply Systems
-Circulatory system consists of
-a muscular pumping organ -heart (With 3 chamb
ers) -Vessels to carry blood to and from heart
-Except for celphalopds, all mollusks have open
circulatory system -Use a hemocoel or blood cav
ity -Oxygen enters mollusks bodies through gill
s. Has large amount of surface area for gases to
diffuse. Goes in by diffusion,and down a
concentration gradient, across a moist membrane.
-Food in digestive tract is taken up by cells li
ning the digestive gland, passed into blood and
undigested materials are compressed,sent to anus
and washed out by water currents
-Nitrogenous wastes from metabolic activities are
removed though either one of the 2 nephridia
structures
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Four Minor Classes of Mollusks
Aplacophora- wormlike marine animals,have
radulamollusks -250 species, Solenogasters

http//www.whoi.edu/science/B/aplacophora/
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Minor classes (II)
Polyplacophora- flat body, dorsal shell formed
from 8 plates
-600 species, Chitons

http//www.sfu.ca/fankbone/v/lab07
.html
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Minor Classes (III)
Monoplacophora-single dorsal shell, 5 pairs of
gills, 6 pairs of nephridia, 8 pairs of retractor
muscles
-8 living species
http//manandmollusc.net/advanced_introduction/mol
l101monoplacophora.html http//www.fish.washingto
n.edu/naturemapping/mollusks/mono/6mono_int.html
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Minor Classes (IV)
Scaphopoda -long tubular shells, specialized
tentacles bring food particles like diatoms to
the mouth in the shell, live on the seashore350
species
Click this picture for a summary on mollusks
http//www.weichtiere.at/scaphopoda/haupt.html
http//members.shaw.ca/bcshell
s/mollusca.html
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Class Bivalvia
-7,500 species including clams,oysters,scallops,m
ussels -Two parts or valves in which the shell is
divided -Adductor muscles are used to close the
shell in times of danger -Also called Pelecypoda,
hatchet foot because it can quickly dig into
mud or sand. Some secrete protein to adhere to
rocks -Adhesive is being studied using DNA sequen
cing for dentistry and medicine
-Complex Nervous system and sense organs
-Can have 100 eyes on the fringe of its mantle
-Fertilization is internal or external,depending
on species
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Pacific Pink Scallop
Argopecten irradians (Notice the blue eyes)
http//www.island.us/divewhidbey/images/under74l.j
pg http//www.casdn.neu.edu/geology/department/
trips/NT9.html
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Class Gastropoda
-37,500 living species largest group of
mollusks, including snails,whelks, periwinkles,
abalones, and slugs -Single or no shell -Found i
n both salt and freshwater -Some members can dige
st cellulose and structural carbs.
-Include omnivores, herbivores, carnivores,
scavengers and parasites -Torsion causes the shel
l to twist 180º to the body. -Makes the shell, m
antle cavity, and visceral mass over the head of
the gastropod -Slugs evolved from losing their sh
ells -6 pairs of ganglia connected to nervous sy
stem -External and internal reproduction
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Gastropoda contd
-Gastropods with internal fertilization can be
hermaphrodites Could have resulted from the dif
ficulty of finding mates because they moved too
slow Sequential Hermaphrodites-males when young
, and females when older and larger
http//www.startpoint.gr/rain3.htm
http//www.consult-eco.ndirect.co.uk/lrc/inverts.h
tm
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Ganglionated Nervous Syetem of Gastropoda
Curtis, Helena and Barnes, N. Sue. Biology. New
York Worth Publishers, 1989.
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Class Cephalopoda
-600 living species -Large head, eyes, central mo
uth, 10 arms in the squid and 8 in the octopus,
90 in the Nautilus -Absence of shell makes the ma
ntle move more freely, easier to move, ex. Jet
propulsion of water -Well developed brains. Rapid
response due to bundle of large nerve fibers on
muscles of mantle -Internal fertilization male u
ses arm to transfer spermatophores to mantle of
felmale
Both http//www.cyberdive.org/gallery.html
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Evolutionary Link?
Annelids, or segmented worms and mollusks are
thought to have descended from a common
unsegmented coelomate ancestor
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PHYLUM ANNELIDA SEGMENTED WORMS
-9,000 species of marine, freshwater and
terrestrial worms -Metameresdivision of body int
o segments -Bodies have segmented coelom, tubular
gut, and closed circulatory system that
transports oxygen and food -Paired nephridia whic
h occur in each segment except head
-Centralized nervous systemsensory, touch,
taste, light-sensitive and moisture detecting
cells
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Class Oligochaeta Earthworms
-Unique movement from coelom divided by septa
between segments and each is divided left and
right -Digestive tract is one straight tube. Phar
ynx acts as a suction pump in mouth to draw in
leaves, dirt and decaying matter
Click picture for digestion animation
http//www.hhmi.princeton.edu/sw/2001/phughs/hughe
s/BioWeb/downloads/digestion_files/swbat_9.jpg
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Earthworms Contd
-Circulatory system is made up of longitudinal
vessels, one dorsal and many ventral
-Smaller vessels collect blood from the tissues
and feeds it to the dorsal vessel to be pumped
forward -Irregular contractions in vessels preven
t backflow -Respiration takes place through simpl
e diffusion. Gases of atmosphere dissolve in the
worms body. -In Excretion, the nephridia removes
nitrogenous wastes. Needed water, molecules and
ions are reabsorbed as waste products leave.
-Nervous system use mechanoreceptors for senseof
touch. Also have light-sensitive and moisture
sensitive cells
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-Each segment has clusters of nerves (ganglia)
-Reproduction Earthworms are hermaphrodites
-Two connect by mucous secretions (clitellum) to
exchange sperm -After they separate, the clitellu
m creates a cocoon where the eggs are fertilized

http//soils.usda.gov/sqi/soil_quality/soil_biolog
y/earthworms.html
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Class Polychaeta
-Almost all marine animals -Have tentacles, anten
nae, specialized mouthparts -Each segment has par
apodia to move, also function in gas exchange
because of large number of blood vessels
-Division of labor between segmentstagmosis
-Predators or sedentary feeders
-Separate sexes, external fertilization, free
swimming larvae
http//www.calacademy.org/research/izg/SFBay2K/gly
cindeworm.htm
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Class Hirudinea
-Leeches flat, tapered bodies with a sucker at
each end
-Hermaphrodites
-Obtain blood by either cutting a slit on the
host, or opening the skin through enzymes
-Secretes hirudin (and other substances) in
hosts blood to stop formation of blood clots
-Synthetic hirudin will be used for treating
heart attack victims and people with
atherosclerosis -Another substance is used for in
hibiting the spread of malignant cells from lung
cancers
http//news.nationalgeographic.com/kids/2003/10/ma
ggotsandleeches.html
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MINOR PROTOSTOME PHYLA
-Four of them are bottom dwelling marine worms
Phylum Sipuncula- 300 species peanut worms,
1-60cm in length, long proboscis can be retracted
into stout, bulblike body
Phylum Echiura- 100 species spoon worms, long
proboscis can be contracted to look like a spoon
http//www.nhm.org/guana/bvi-invt/bvi-surv/images/
othr-i01/sipunc.htm http//www.unice.fr/LEML/cour
sJDV/tp/tp4-1.htm
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Phylum Priapulida- 15 species burrowing worms,
0.5mm-20cm long, retractile proboscis with spines
to capture prey
Phylum Pogonophora- 100 species beard worms,no m
outh or digestive tract, has crown of tentacles
for taking in nutrients or has chemiosynthetic
bacteria for symbiosis with worms
http//shop.uwphoto.no/detail.asp?PRODUCT_IDesv04
0cd12 http//dsc.discovery.com/convergence/bluepl
anet/photo/photo_zoom2.html
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Remaining Three Phyla
-Characterized by unjointed appendages with
claws, have external cuticle that is molted
periodically

Pentastomids- 70 species, parasites of the
vertebrate respiratory system, separate sexes,
internal fertilization

Tardigrada- 350 species water bears, common in
freshwater and film of moisture on mosses
http//www.dorka.de/Gesundheit/Parasiten/paras.php
?datpentastomiden.htm http//zooexcurs.narod.ru/
izba/LivingBaikal/tardigrada.htm
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Onychophora- Like annelids soft bodies, segmen
t nephridia, muscular body walls, ciliated
reproductive tracts Like arthropods jaws, prote
ctive cuticle, large brains, circulatory and
respiratory systems -Antennae and eyes -Some lay
eggs, most give birth to live young
-Modern species are terrestrial, but fossils show
that they were marine animals

http//bioweb.uwlax.edu/zoolab/Table_of_Contents/L
ab-6a/Phylum_Onychophora_2/phylum_onychophora_2.ht
m
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THE LOPHOPHORATES
-Are protostomes, but could be seen as primitive
deuterostomes -Partitioned into several major co
mpartments -All aqautic include lamp shells, pho
ronid worms, bryozoans -All have a lohphophore l
ocated on anterior end, has tentacles that
captures small organisms and organic debris
PHYLA Brachiophora-250 living species,two valves
of the shell and dorsal and ventral, look like
Greek or Roman oil burning lamps
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Phoronida- 18 species worms that are 4-25 cm
long, live in tubes or ocean bottoms in shallow
water, most species are hermaphrodites, one
species can reproduce asexually
Bryozoans- 4,000 living species colonial
animals, found on film of salt or freshwater,
resemble colonies of moss, hermaphrodites, but
freshwater bryozoans can reproduce asexually.
Life cyclelarvae jumps from one grain of sand
to another and reproduce continues until a
suitable location for a colony is found.
http//virtual.yosemite.cc.ca.us/randerson/Marine
20Invertebrates/phoronid.htm