Photosynthesis

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Outline

• The coelom
• Molluscs
• Bivalves
• Cephalopods
• Gastropods
• Annelids
• Arthropods
• Crustaceans
• Uniramians
• Chelicerates
• Echinoderms

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Advantages of Coelom

• Protostomes vs. deuterostomes
• Differentiated according to three major events in
  embryological development
• 1 Cleavage
• Spiral cleavage in protostomes
• Radial cleavage in deuterostomes

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Protostomes Compared to Deuterostomes
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Advantages of Coelom

• 2 Fate of blastopore
• Mouth appears near blastopore in protostomes
• Anus appears near blastopore in deuterstomes
• 3 Coelom Formation
• Schizocoelom forms in protostomes
• Enterocoelom forms in deuterstomes

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Mollusks

• Mollusks (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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Body Plan of Mollusks
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Mollusks

• Mollusks (cont.)
• 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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Bivalves

• Clams, oysters, mussels, and scallops
• Shell of two hinged parts, closed by powerful
  muscles
• No head, no radula
• Circulatory system open
• Sexes are separate
• Ciliated gills hang down within mantle cavity on
  either side of visceral mass
• Beating of cilia causes water to enter cavity
• Filter Feeders capture tiny food particles
  suspended in water

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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

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Cephalopod Diversity
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Gastropods, cont.

• 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

• Phylum Annelida are
• Segmented partitions (septa) divide the
  well-developed, 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

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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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Earthworm, Lumbricus terrestris
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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 dessication

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Leeches

• Usually found in fresh water
• Same body plan as other annelids
• No setae
• Two additional suckers
• Some parasitic
• Keep blood flowing and prevent clotting by means
  of hirudin, a powerful anticoagulant

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Medicinal Leeches, Hirudo medicinalis
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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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Arthropod Skeleton and Eye
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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

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Crustacean Diversity
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Male crayfish, Cambarus
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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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Insect Diversity
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Two Types of Insect Mouthparts
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Female Grasshopper, Romalea
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Centipede and Millipede
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Chelicerates

• Include terrestrial spiders, scorpions, ticks,
  mites, horseshoe crabs and sea spiders
• All appendages attached to cephalothorax none on
  head
• First pair (chelicerae) are feeding organs
• Second pair (pedipalps) function in feeding or
  sensory

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Chelicerate Diversity
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Echinoderms

• Sea stars, sea urchins, sea cucumbers, and sea
  lilies
• Radial symmetry as adults (not as larvae)
• Internal calcium-rich plates with spines
• Central nerve ring with branches
• Water vascular system for locomotion

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Echinoderms
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Review

• The coelom
• Mollusks
• Bivalves
• Cephalopods
• Gastropods
• Annelids
• Arthropods
• Crustaceans
• Uniramians
• Chelicerates
• Echinoderms

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