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Coelom and Invertebrates: Molluscs, Annelids, Arthropods, and Echinoderms

Explore the advantages of coelom and learn about the body plans and characteristics of molluscs, annelids, arthropods, and echinoderms. Discover the diversity and features of bivalves, cephalopods, gastropods, and more.

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Coelom and Invertebrates: Molluscs, Annelids, Arthropods, and Echinoderms

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  1. More Invertebrates

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

  3. 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

  4. Protostomes Compared to Deuterostomes

  5. 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

  6. 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

  7. Body Plan of Mollusks

  8. 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

  9. 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

  10. Bivalve Diversity

  11. 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

  12. Cephalopod Diversity

  13. 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

  14. Gastropod Diversity

  15. 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

  16. Polychaete Diversity

  17. 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

  18. Earthworm, Lumbricus terrestris

  19. 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

  20. 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

  21. 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

  22. Medicinal Leeches, Hirudo medicinalis

  23. 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

  24. Arthropod Skeleton and Eye

  25. Arthropods • Variety of respiratory organs • Occurrence of metamorphosis • Three major arthropod subphyla • Crustaceans • Crayfish • Uniramians • Centipedes • Chelicerates • Spiders

  26. 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

  27. Crustacean Diversity

  28. Male crayfish, Cambarus

  29. 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

  30. Insect Diversity

  31. Two Types of Insect Mouthparts

  32. Female Grasshopper, Romalea

  33. Centipede and Millipede

  34. 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

  35. Chelicerate Diversity

  36. 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

  37. Echinoderms

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

  39. More Invertebrates

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