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

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