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Bio202 Lab 10: Nematoda, Mollusca, and Annelida

Bio202 Lab 10: Nematoda, Mollusca, and Annelida. Chapters 37 & 38. Phylum Nematoda. Nematodes, commonly called roundworms Ubiquitous--found everywhere, span all habitable environments bilaterally symmetrical Cylindrical Unsegmented (unlike most tapeworms). Phylum Nematoda.

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Bio202 Lab 10: Nematoda, Mollusca, and Annelida

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  1. Bio202 Lab 10: Nematoda, Mollusca, and Annelida Chapters 37 & 38

  2. Phylum Nematoda • Nematodes, commonly called roundworms • Ubiquitous--found everywhere, span all habitable environments • bilaterally symmetrical • Cylindrical • Unsegmented (unlike most tapeworms)

  3. Phylum Nematoda • Pseudocoelomate – body cavity between mesoderm and endoderm • Contrast with Acoelomate, Coelomate (Fig 38.1) • advanced animal characteristics • complete digestive tract and other internal body cavities • Most species of nematodes are free living, though the most infamous species cause disease.

  4. Phylum Mollusca • Mollusks are far more diverse than most people realize. • Snails, Clams, Octopuses, Squid, Chitons • Occur in marine, freshwater, and terrestrial habitats. • Bilaterally symmetrical • Coelomate – body cavity bounded by mesoderm • Contrast with Acoelomate, Pseudocoelomate (Fig 38.1)

  5. Phylum Mollusca • Protostomes • Bilateral • Metazoan • Determinate, spiral cleavage

  6. Cleavage

  7. Spiral Cleavage In Mollusk Embryo

  8. Spiral Cleavage In Mollusk Embryo

  9. Phylum Mollusca • Protostomes • formation of a mouth and anus directly from a blastopore (opening in blastula) • formation of the coelom by splitting of the embryonic mesoderm

  10. Blastula and blastospores • Solid ball of cells (morula) develops fluid-filled center (blastocoel). • Blastospores are produced by budding of blastula

  11. Phylum Mollusca • Mollusks are far more diverse than most people realize. • Snails, Clams, Octopuses, Squid, Chitons • Bilaterally symmetrical • Protostome • Coelomate • Occur in marine, freshwater, and terrestrial habitats.

  12. Phylum Mollusca • Visceral mass – tissue forming center of body • muscular foot used in locomotion • many mollusks have a head • most mollusks form a shell, and are classified by shell type • Radula • organ used for scraping, drilling, or capturing prey. • Not found in Bivalves

  13. Phylum Mollusca • circulatory system • Heart • usually, an open system through which the blood circulates freely.

  14. Class Polyplacophora (chitons) • Shell • eight dorsal overlapping plates • Foot • ovaly flattened • extends from back to front (dorsoventral) • Mouth • scraping radula. • Chiton sp.

  15. Class Gastropoda (snails) • Gastropods are terrestrial as well as aquatic. • shell • single and often coiled, sometimes absent. • Mouth • has a radula.

  16. Class Bivalvia (clams, oysters) • Shell • in two dorsally hinged halves (valves). • Foot • flattened on the sides (laterally) • often used to burrow • Mouth • no radula. • Cilliated gills used for filter feeding • can filter particles as small as a virus; oyster harvesting is quickly shut down following a pollution alert. • Anodonta sp. • Pinctada sp.

  17. Class Cephalopoda (octopus, squid) • Shell • Usually absent • single and coiled if present (very rarely). • Foot • modified into tentacles • image-forming eyes • mouth usually with pinching beak. • Loligo sp.

  18. Phylum Annelida (Segmented Worms) • Segmented • segments are divided internally by septa • bilaterally symmetrical • Protostome • coelomates. • Cerebral ganglion (brain) is well developed • circulatory system is closed • digestive tract is complete.

  19. Class Polychaeta (marine worms) • Body is distinctly segmented (believed to be an adaptation to burrowing). • Segmentation allows fine control of annelids’ hydrostatic skeleton in concert with circular and longitudinal muscles to alternately expand and contract segments to aid burrowing.

  20. Class Polychaeta (marine worms) • paired appendages of each body segment are apparent in polychaetes. This arrangement of appendages indicates a common ancestry with arthropods (next chapter) • Leeches are the most modern and highly modified of the annelids, as is true for parasitic groups of other phyla. Why is that a common theme?

  21. Class Polychaeta (marine worms) • body is distinctly segmentedThe most anterior (toward the rear) segment (prostomium) has sense organs as a head. • Parapodia: paired, lateral appendages extending from the body segments • Setae: small, bristlelike appendages often occuring in pairs on lateral and ventral (frontal) surfaces • Nereis sp. • Aphrodita sp. • Chaetopterus sp.

  22. Class Oligochaeta (oligochaetes) • Segmentation • Distinct • No parapodia • Prostomium (38.12) • Fleshy, small lobe before mouth. • Setae • present but small • Lumbricus terrestris

  23. Class Hirudinea (leeches) • Body • Flattened • anterior (frontal) and posterior suckers • no head development. • Segmentation • greatly reduced • No setae • Hirudo medicinalis

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