Mader: Biology 8th Ed.

The Protostomes

Chapter 30

Mader: Biology 8th Ed.

Outline• Molluscs

– Bivalves• Cephalopods• Gastropods• Annelids• Arthropods

– Crustaceans– Uniramians– Chelicerates

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Advantages of Coelom

• Protostomes and deuterostomes are differentiated according to three major events in embryological development.– Cleavage

Spiral cleavage in protostomes.Radial cleavage in deuterostomes.

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Advantages of Coelom

– Fate of blastoporeMouth appears near blastopore in

protostomes.Anus appears near blastopore in

deuterstomes.– Coelom Formation

Schizocoelom forms in protostomes.Enterocoelom forms in deuterstomes.

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Molluscs• 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.

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Molluscs– 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.

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Body Plan of Molluscs

Mader: Biology 8th Ed.

Bivalves

• 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

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Bivalves

• Open circulatory system• Sexes are separate• Clams, oysters, mussels, and scallops

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Bivalve Diversity

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Cephalopods

• 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

• 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.

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Gastropod Diversity

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Annelids• Annelids (phylum Annelida) are segmented.

– Partitions (septa) divide the well-developed, fluid-filled coelom, which acts as hydrostatic skeleton.

Specialized digestive tractClosed circulatory systemVentral solid nerve cordMost are marineSetae (bristles) help in movement

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Polychaete Diversity

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Earthworms

• 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.

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Earthworms

Mader: Biology 8th Ed.

Earthworms

• 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

• 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.

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Earthworm Reproduction

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Leeches

• 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

• 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.

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Arthropods

– Variety of respiratory organs.– Occurrence of metamorphosis.

• Three major arthropod subphyla– Crustaceans

Crayfish– Uniramians

Centipedes– Chelicerates

Spiders

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Crustaceans

• 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

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Crustaceans

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Uniramians

• 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

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Female Grasshopper

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Centipede and Millipede

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Chelicerates

• 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.

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Chelicerate Diversity

Mader: Biology 8th Ed.

Review

• Molluscs– Bivalves

• Cephalopods• Gastropods• Annelids• Arthropods

– Crustaceans– Uniramians– Chelicerates

Mader: Biology 8th Ed.