Coelomate Invertebrates

1. Coelomate Invertebrates Chapter 34

2. Introduction Coelomates have a body design that: 1. Repositions the body’s fluid 2. Allows complex tissues/organs to develop 3. Allows for a larger body size Coeloms evolved multiple times during animal evolution

3. Phylum Mollusca Mollusks are second in diversity only to arthropods -Exhibit a wide variety of sizes and body forms -Live in many different environments -Include snails, slugs, clams, octopuses and others

4. Phylum Mollusca

5. Phylum Mollusca (Cont.)

6. Phylum Mollusca Mollusks evolved in the oceans and most groups have remained there They are an important source of human food They are economically significant in other ways -Pearls are produced in oysters -Mother-of-pearl is produced in the shells of abalone Mollusks can also be pests -Zebra mussel (Dreissena polymorpha)

7. Mollusk Body Plan Mollusks are bilaterally symmetrical -Characterized by a reduced coelom surrounding the heart and excretory organs The digestive, excretory and reproductive organs are concentrated in a visceral mass Mollusks may have a differentiated head at the anterior end of the body

8. Mollusk Body Plan Mantle = A thick epidermis that covers the dorsal side of the body -Forms a cavity which houses the respiratory organs (ctenidia, or gills) and the openings of excretory, reproductive & digestive organs The muscular foot of a mollusk is adapted for locomotion, attachment, food capture -Or a combination of the above

9. Mollusk Body Plan

10. Mollusk Body Plan (Cont.)

11. Mollusk Body Plan Most mollusks produce an external calcium carbonate-rich shell -Used for protection -Some species have internalized or reduced shells Most mollusks have a rasping tongue-like organ called the radula -Used for feeding

12. Mollusk Body Plan

13. Mollusk Body Plan Nephridia = Special excretory structures that remove nitrogenous wastes -Consist of cilia-lined openings called nephrostomes Except for cephalopods, all mollusks have an open circulatory system Cephalopods have a closed circulatory system

14. Mollusk Reproduction Most mollusks have distinct male and female individuals Most engage in external fertilization In marine mollusks, embryos develop through spiral cleavage -Trochophores: Free-swimming larval stage -Second free-swimming larval stage -Only in bivalves and snails

15. Mollusk Reproduction

16. Classes of Mollusks There are eight recognized classes -Four are representatives of the phylum 1. Polyplacophora 2. Gastropoda 3. Bivalvia 4. Cephalopoda

17. Classes of Mollusks Class Polyplacophora (Chitons) -Marine mollusks that have oval bodies with eight overlapping dorsal calcareous plates -Body is not segmented under the plates -Most chitons are grazing herbivores

18. Classes of Mollusks Class Gastropoda (Snails and slugs) -A primarily marine group -Heads typically have pairs of tentacles with eyes at the ends -During embryological development, gastropods undergo 1. Torsion – Mantle cavity and anus are moved from the posterior to the front 2. Coiling – Spiral winding of the shell

19. Classes of Mollusks

20. Classes of Mollusks Class Bivalvia (Bivalves) -Includes clams, scallops, mussels, oysters and others -Have two lateral (right and left) shells (valves) hinged together dorsally -Most are sessile filter-feeders -Water circulation is mediated by siphons and rhythmic beating of cilia on gills

21. Classes of Mollusks

22. Classes of Mollusks Class Cephalopoda -Active marine predators -Foot has evolved into a series of arms equipped with suction cups -Squids have 10; octopuses, 8; and nautiluses, 80 to 90 -Have highly developed nervous systems -Exhibit complex patterns of behavior and a high level of intelligence

23. Classes of Mollusks

24. Classes of Mollusks Class Cephalopoda -Many have an ink sac and are capable of expelling ink to confuse predators -Octopuses and squids can change color using pouches of pigment called chromatophores

25. Phylum Annelida Annelid worms exhibit segmentation (building of body from repeated units) -Allows for specialization

26. Phylum Annelida An annelidconsists of a series of ring-like elements running the length of the body -Divided internally by septa The anterior (front) segments contain specialized sensory organs A ventral nerve cord connects the ganglia in each segment with each other and the brain

27. Phylum Annelida

28. Phylum Annelida Annelidsmoveusing their hydrostatic skeleton -Each segment contains chitin bristles (chaetae) that help anchor the worms Most have a closed circulatory system They exchange O2 and CO2 through their body surfaces Excretory system consists of a pair of ciliated, funnel-shaped nephridia per segment

29. Phylum Annelida Annelidshave traditionally been classified into three classes: 1. Class Polychaeta 2. Class Oligochaeta 3. Class Hirudinea Hirudinea is now considered a sub-class of Oligochaeta

30. Phylum Annelida Class Polychaeta (Polychaetes) -Mostly marine worms, such as tubeworms -Unusual forms and iridescent colors -Have a differentiated head -Have paired parapodia on most segments -Used in swimming, burrowing, crawling -Sexes are usually separate -Typically lack permanent gonads

31. Phylum Annelida

32. Phylum Annelida Class Oligochaeta (Earthworms and leeches) -Mostly terrestrial Earthworms -Consist of 100-175 segments, with a mouth on the first and an anus on the last -Lack eyes, parapodia and head -Have fewer setae than polychaetes

33. Phylum Annelida Earthworms are hermaphroditic -Clitellum secretes mucus that holds the worms together during copulation -Also secretes a mucus cocoon, in which the fertilized egg develops

34. Phylum Annelida Leeches -Occur mostly in freshwater -Usually flattened dorsoventrally -Cross-fertilization is obligatory -Have no chaetae (except for one species) -Medicinal leech, Hirudo medicinalis -Secretes anticoagulant

35. The Lophophorates Include two phyla of mostly marine animals: Bryozoa and Brachiopoda Both convergently evolved a lophophore -A circular or U-shaped ridge around the mouth with 1-2 rows of ciliated tentacles -Functions in gas exchange and feeding Most members undergo radial cleavage

36. Phylum Bryozoa Bryozoans are small and live in colonies -Their anus opens near their mouth -Asexual reproduction occurs frequently by budding

37. Phylum Bryozoa

38. Phylum Bryozoa (Cont.)

39. Phylum Brachiopoda Brachiopods have two calcified shells -Valves are dorsal and ventral (not lateral as in bivalves) -Solitary lophophorates -Each individual secretes a chitinous tube and lives out its life within it -Develop as protostomes (unlike brachiopods)

41. Phylum Arthropoda Arthropods are the most successful animals -2/3rd of all species are insects -For each human, 200 million insects are alive at any one time Are divided into four major classes: -Arachnids, myriapods, crustaceans and insects

42. Arthropod Morphology All arthropodshave jointed appendages -Modifications: antennae, mouthparts,legs Arthropods also have an exoskeleton made of secreted chitin and protein -Functions: protection & muscle attachment -Its thickness limits arthropod body size Arthropod bodies are segmented -Some segments are specialized into functional groups, or tagmata

43. Arthropod Morphology

44. Arthropod Morphology Arthropods have an open circulatory system Compound eyes are found in many arthropods -Composed of independent visual units called ommatidia Other arthropods have simple eyes, or ocelli -Have single lenses -Distinguish light from darkness

45. Arthropod Morphology

46. Arthropod Morphology Nervous system consists of a double chainofsegmented ganglia on ventral surface -Brain seems to be an inhibitor, rather than as a stimulator, as it is in vertebrates Respiratory system consists of tracheae and tracheoles -Connected to the exterior by spiracles

47. Arthropod Morphology

48. Arthropod Morphology Arthropods have a unique excretory system consisting of Malpighian tubules -Eliminates nitrogenous wastes as concentrated uric acid or guanine Arthropods periodically undergo molting -Shedding the outer cuticular layer

49. Arthropod Morphology

50. Class Arachnida Arachnids are largely terrestrial organisms -Spiders, ticks, mites, scorpions, and others The most anterior appendages, chelicerae, often function as fangs or pincers