33

Concept 33.1: Sponges are basal animals that lack tissues

1. Sponge body structure: Sponges have a porous body with specialized cells called choanocytes (collar cells) that line the interior. Water flows through pores into a central cavity and out through an opening called the osculum.

2. Why sponges are basal: Sponges are considered basal animals because they lack true tissues and organs. Their simple body plan and cell-level organization place them at the base of the animal phylogenetic tree.

3. Label the sponge (not shown): Key structures typically include:

   • Ostia: small pores where water enters

   • Spongocoel: central cavity

   • Choanocytes: create water current and trap food

   • Osculum: large opening where water exits

4. Hermaphrodites: Most sponges produce both eggs and sperm, though typically not at the same time, to prevent self-fertilization.

Concept 33.2: Cnidarians are an ancient phylum of eumetazoans

5. Eumetazoans have: true tissues; cnidarians have a radial, diploblastic body plan.

6. Body plan diagrams (not shown): Examples:

   • Polyp: sea anemones, corals

   • Medusa: jellies (jellyfish), hydrozoans

7. Nematocysts: Specialized stinging organelles within cnidocytes; they discharge barbed threads to capture prey.

8. Cnidarian skeleton: Hydrostatic skeleton.

9. How it works: Fluid-filled gastrovascular cavity provides support; muscle contractions push against fluid, allowing movement.

10. Coral reef threats:

    • Ocean acidification

    • Climate change (coral bleaching)

    • Pollution and overfishing

Concept 33.3: Lophotrochozoans

11. Bilateria characteristics:

    • Bilateral symmetry

    • Triploblastic (three tissue layers)

12. Flatworm shape helps diffusion: Their flat, thin bodies increase surface area relative to volume, enabling gas exchange directly with the environment.

13. Flatworm groups:

    • Planarians: free-living; eat via pharynx; simple nervous system

    • Flukes: parasitic; complex life cycles with multiple hosts

    • Tapeworms: parasitic; absorb nutrients through skin

14. Planarian labeling: Typically includes:

    • Eyespots

    • Ganglia

    • Gastrovascular cavity

    • Pharynx

    • Mouth (mid-ventral side)

15. Digestive system: Two-way; same opening for ingestion and egestion.

16. Trematode intermediate host: Usually a snail.

    • Infection: Penetrate skin during water contact.

    • Schistosomiasis: ~200 million affected worldwide.

    • Symptoms: Abdominal pain, diarrhea, blood in urine/stool.

17. Tapeworms attach using: scolex with hooks and suckers.

    • Transmission: Eating undercooked infected meat.

18. No digestive system: They absorb pre-digested nutrients directly from host intestines via large surface area.

19. Mollusc structures:

    • Foot: locomotion

    • Radula: scraping food

    • Visceral mass: contains organs

    • Mantle: secretes shell, covers visceral mass

20. Mollusc classes:

    • Gastropoda: snails, slugs; single spiral shell

    • Bivalvia: clams, mussels; two shells, filter feeders

    • Cephalopoda: squid, octopuses; intelligent, tentacles

21. Mollusc extinction causes:

    • Habitat destruction

    • Pollution

    • Invasive species

22. a. Leeches: secrete anesthetic and anticoagulant; used in medicine to prevent clotting after surgery.
    b. Earthworms: aerate and fertilize soil through burrowing and digestion.

Concept 33.4: Ecdysozoans

23. Root words:

    • ecdyso– = shedding (molting)

    • –zoan = animal

24. Trichinosis: Acquired by eating undercooked pork infected with Trichinella larvae.

25. Trichinella adaptations: Alters host gene expression to build protective capsules around larvae.

26. Arthropods are successful because:

    • Exoskeleton

    • Segmentation

    • Jointed appendages

    • High species diversity (~10^18 estimated individuals)

27. Exoskeleton material: Chitin

    • Growth: Must molt (ecdysis) to grow

28. Open circulatory system: Hemolymph pumped into open cavities bathing organs directly.

29. Respiration:

    • Aquatic: Gills

    • Terrestrial: Tracheal tubes or book lungs

30. Arachnids:

    • 6 pairs of appendages

    • 4 pairs of walking legs

    • Examples: spiders, scorpions, ticks, mites

31. Spiders: Inject venom, liquefy prey tissue, and suck it up.

32. Book lungs surface area: Thin plates stacked to increase surface area for gas exchange.

33. Myriapods:

    Example	Legs/Segment	Diet
    Millipede	2	Detritivore
    Centipede	1	Carnivore

34. Lobster/crayfish appendages: Typically 19 pairs (5 pairs of walking legs + other specialized appendages).

35. Crustacean examples: Crabs, lobsters, shrimp, barnacles

36. a. Insect legs: 6 legs (3 pairs)
    b. Body regions: Head, thorax, abdomen

37. Metamorphosis types:

    • Incomplete: Egg → nymph → adult (e.g., grasshoppers)

    • Complete: Egg → larva → pupa → adult (e.g., butterflies)

38. Wings: Analogous (evolved independently in birds and insects)

39. Beetle success: Adaptive radiation, hardened wings, diverse diets, wide habitats

Concept 33.5: Echinoderms and Chordates

40. Clade: Deuterostomia of bilaterian animals

41. Echinodermata = “spiny skin”

42. Echinoderm groups:

    • Sea stars

    • Sea urchins

    • Sea cucumbers

43. Water vascular system: Network of hydraulic canals used for locomotion (tube feet), feeding, and gas exchange.

44. Bilateria membership: Larvae have bilateral symmetry, despite adult radial symmetry.

45. Relatedness: Echinoderms and chordates share deuterostome development (blastopore becomes anus, radial cleavage, etc.) but did not evolve from one another.

46. Key phylogenetic differences:

    • Porifera: No true tissues

    • Cnidarians: Radial symmetry, stinging cells

    • Echinoderms & chordates: Deuterostomes

    • Platyhelminthes: First triploblastic, no body cavity

    • Nematodes vs. annelids/molluscs: Roundworms are pseudocoelomates and molt

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