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The Protostomes
Chapter 30
Mader: Biology 8th Ed.
Outline
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Molluscs
– Bivalves
Cephalopods
Gastropods
Annelids
Arthropods
– Crustaceans
– Uniramians
– Chelicerates
Mader: Biology 8th Ed.
Advantages of Coelom
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Protostomes and deuterostomes are
differentiated according to three major
events in embryological development.
– Cleavage
 Spiral cleavage in protostomes.
 Radial cleavage in deuterostomes.
Mader: Biology 8th Ed.
Advantages of Coelom
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Fate of blastopore
 Mouth appears near blastopore in
protostomes.
 Anus appears near blastopore in
deuterstomes.
Coelom Formation
 Schizocoelom forms in protostomes.
 Enterocoelom forms in deuterstomes.
Mader: Biology 8th Ed.
Molluscs
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Molluscs (phylum Mollusca)
– Have three-part body plan.
 Visceral Mass
 Contains internal organs.
 Mantle
 May secrete shell and/or contribute
to development of gills or lungs.
 Foot
 Muscle adapted for locomotion,
attachment, or food capture.
Mader: Biology 8th Ed.
Molluscs
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Nervous system consists of several
ganglia connected by nerve cords.
Coelom is reduced, and largely limited to
the region around the heart.
Heart pumps hemolymph through vessels
into hemocoel.
Mader: Biology 8th Ed.
Body Plan of Molluscs
Mader: Biology 8th Ed.
Bivalves
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Possess two-part shell that is hinged and
closed by powerful muscles.
Have no head, radula, and very little
cephalization.
Within mantle cavity, ciliated gills hang down
on either side of visceral mass.
– Beating of cilia causes water to enter
cavity.
 Filter Feeders
Mader: Biology 8th Ed.
Bivalves
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Open circulatory system
Sexes are separate
Clams, oysters, mussels, and scallops
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Bivalve Diversity
Mader: Biology 8th Ed.
Cephalopods
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Head Footed
– Force water out mantle cavity
Tentacles and arms capture prey by
adhesive secretions or suckers
Beak used to tear prey apart
Well-developed sense organs
Closed circulatory system
Spermatophore packets passed from males
to females
Mader: Biology 8th Ed.
Cephalopod Diversity
Mader: Biology 8th Ed.
Gastropods
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Have elongated, flattened foot.
Well-developed head region.
– Eyes and tentacles project from coiled
shell.
Gills are found in mantle cavity in aquatic
gastropods.
Mantle functions as lung in terrestrial
gastropods.
Mader: Biology 8th Ed.
Gastropod Diversity
Mader: Biology 8th Ed.
Annelids
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Annelids (phylum Annelida) are segmented.
– Partitions (septa) divide the welldeveloped, fluid-filled coelom, which acts
as hydrostatic skeleton.
 Specialized digestive tract
 Closed circulatory system
 Ventral solid nerve cord
 Most are marine
 Setae (bristles) help in movement
Mader: Biology 8th Ed.
Polychaete Diversity
Mader: Biology 8th Ed.
Earthworms
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Do not have well-developed head or
parapodia.
– Setae protrude in pairs directly from
surface of body.
– Food drawn into mouth by action of
muscular pharynx.
 Digestion and absorption occur in long
internal intestine.
 Typhlosole increases surface for
absorption.
Mader: Biology 8th Ed.
Earthworms
Mader: Biology 8th Ed.
Earthworms
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Segmentaion evidenced by:
– Body rings
– Coelom divided by septa
– Setae on most segments
– Gangli and lateral nerves in each segment
– Nephridia in most segments
– Branch blood vessels in each segment
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Earthworms
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Reproduction
– Hermaphroditic
– Two worms lie in parallel to each other
facing in opposite directions.
 Fused midbody segment (clitellum)
secretes mucus, protecting sperm from
drying out as they pass between worms.
Mader: Biology 8th Ed.
Earthworm Reproduction
Mader: Biology 8th Ed.
Leeches
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Usually found in fresh water.
Same body plan as other annelids.
– No setae
– Two additional suckers.
 Keep blood flowing and prevent clotting
by means of hirudin, a powerful
anticoagulant.
Mader: Biology 8th Ed.
Arthropods
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Arthropods (phylum Arthropoda) have freely
movable jointed appendages.
Very successful due to many characteristics.
– Rigid, jointed exoskeleton.
 Must molt as they grow.
– Segmented, but some segments are
fused into regions.
 Head, thorax, abdomen.
– Well-developed nervous system.
Mader: Biology 8th Ed.
Arthropods
Variety of respiratory organs.
– Occurrence of metamorphosis.
Three major arthropod subphyla
– Crustaceans
 Crayfish
– Uniramians
 Centipedes
– Chelicerates
 Spiders
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Crustaceans
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Decapods are the most familiar and
numerous of crustaceans.
– Shrimp, lobsters, crayfish, and crabs.
 Thorax bears five pairs of walking legs.
 Head and thorax fused into
cephalothorax.
 Covered by nonsegmented carapace.
 Abdominal segments equipped with
swimmerets.
 Respiratory system consists of gills.
Mader: Biology 8th Ed.
Crustaceans
Mader: Biology 8th Ed.
Crustaceans
Mader: Biology 8th Ed.
Uniramians
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Include insects, millipedes, and centipedes.
– Appendages attached to the thorax and
abdomen only have one branch.
– Head appendages include only one pair of
antennae, one pair of mandibles, and one
or two pairs of maxillae.
– Live on land and breathe by tracheae.
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Female Grasshopper
Mader: Biology 8th Ed.
Female Grasshopper
Mader: Biology 8th Ed.
Centipede and Millipede
Mader: Biology 8th Ed.
Chelicerates
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Include terrestrial spiders, scorpions, ticks,
mites, horseshoe crabs and sea spiders.
– First pair of appendages (chelicerae) are
feeding organs.
– Second pair of appendages (pedipalps)
function in feeding or sensory.
 All appendages attached to
cephalothorax.
– No appendages on heads.
Mader: Biology 8th Ed.
Chelicerate Diversity
Mader: Biology 8th Ed.
Review
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Molluscs
– Bivalves
Cephalopods
Gastropods
Annelids
Arthropods
– Crustaceans
– Uniramians
– Chelicerates
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.