Chapter 8 Lower Invertebrates

1. Chapter 8 Lower Invertebrates

2. Sponges • Phylum Porifera • Basic characteristics: • simple • asymmetric • sessile: permanently attached to a solid surface • have many shapes, sizes and colors

3. Sponge Structure and Function • Body is built around a system of water canals • ostia: tiny holes or pores through which water enters the sponge’s body • spongocoel: spacious cavity in the sponge into which water flows • osculum: large opening through which water exits from the spongocoel

5. Sponge Structure and Function • Lacking tissues, sponges have specialized cells • collar cells (choanocytes) use their flagella to provide force for moving water through the sponge’s body • pinacocytes in a layer provide an outer covering for the sponge

6. Anatomy of Sponge F A G D B • Key • A) Osculum • Pore • Amoebocyte • D) Spicule • E) Choanocyte • F) Flagella • G) Microfilaments E C D E

7. Sponge Structure and Function • Structural materials • spicules: skeletal elements that give support to a sponge’s body, produced by specialized cells and composed of calcium carbonate, silica or spongin • spongin: a protein that forms flexible fibers

8. Sponge Structure and Function • Sponge size and body form • size is limited by water circulation • asconoid: simplest form; tubular and always small, found in clusters • syconoid: sponges that exhibit the first stages of body-wall folding

9. Sponge Structure and Function • leuconoid: sponges with the highest degree of folding, which have many chambers lined with collar cells

10. Sponge Types Purple vase sponge Red barrel sponge

11. Sponge Structure and Function • Nutrition and digestion • sponges are suspension feeders – feed on material suspended in seawater • sponges are also referred to as filter feeders – they filter food from the water • collar cells trap ~ 80% of food which consists of small particles (0.1 to 1.0 micrometers in size) • sponges are one of the few animals that can capture such small sized particles

12. Sponge Structure and Function • Reproduction in sponges • asexual reproduction • budding: a group of cells on the outer surface of the sponge develops and grows into a tiny new sponge, which drops off and establishes itself • fragmentation: production of a new sponge from pieces that are broken off by physical processes, e.g., waves, storms, predators • sexual reproduction • most sponges are hermaphrodites • eggs usually develop from archaeocytes and sperm from modified collar cells • larval stage is called a planktonic amphiblastula

13. Fertilization Sperm cell engulfed by a collar cell Sperm cell (modified collar cell) Egg cell Embryo Planktonic amphiblastula larva Bud New sponge New sponge Larva settles and attaches to bottom or other surface Sexual reproduction Asexual reproduction Stepped Art Fig. 8-3, p. 195

14. Ecological Roles of Sponges • Competition • compete aggressively with corals and bryozoans for attachment space • Predator-prey relationships • few species eat sponges • spicules are like needles • some produce chemical deterrents

15. a few species of bony fish and molluscs and sea turtles (especially the hawksbill) will eat sponges

16. Ecological Roles of Sponges • Symbiotic relationships • sponges are mutualistic or commensalistic hosts to many organisms • e.g. symbiotic cyanobacteria • many organisms (shrimp, fish) live within the canals or spongocoel, for protection and to take advantage of water flow

17. Ecological Roles of Sponges • Sponges and nutrient cycling • boring sponges (family Clionidae) recycle calcium as they burrow into coral and mollusc shells Red boring sponge

18. Cnidarians: Animals with Stinging Cells • Phylum Cnidaria • Include jellyfish, hydroids, corals and sea anemones • Named for their cnidocytes—stinging cells • Cnidocytes are used to capture prey and protect the animal

19. Organization of the Cnidarian Body • Radial symmetry: many planes can be drawn through the central axis that will divide the animal into equivalent halves

20. Organization of the Cnidarian Body • Often exhibit 2 body plans within their life cycles: • polyp: benthic form characterized by a cylindrical body with an opening at 1 end, i.e., the mouth which is surrounded by tentacles • medusa: a free-floating stage (jellyfish) • Many cnidarians have both body plans, corals and sea anemones exist as polyps

22. Stinging Cells • Cnida: stinging organelle within a cnidocyte, which may function in locomotion, prey capture, or defense • nematocysts: spearing type cnida, which are discharged when the cnidocill—a bristle-like trigger—contacts another object

23. Stinging Cells • Stinging cells also triggered by certain chemical substances released by prey • Dangerous species • Portuguese man-of-war (painful stings) • box jellyfish (can kill within 3-20 minutes)

24. Box jelly fish sting Portuguese man of war sting Box jelly fish sting

25. Types of Cnidarians • Hydrozoans (class Hydrozoa) • mostly colonial • colonial forms contain 2 types of polyp: • gastrozooid = feeding polyp—functions in food capture • gonangium = reproductive polyp—specialized for reproduction

26. Types of Cnidarians • hydrozoans known as hydrocorals secrete a calcareous skeleton, e.g., fire coral • some produce floating colonies • e.g. Portuguese man-of-war

27. Types of Cnidarians • Jellyfish and box jellyfish • scyphozoans—true jellyfish (class Scyphozoa) • considered members of the plankton • medusa is predominant life stage

28. Types of Cnidarians • -box jellyfish (class Cubozoa) • box-shaped bells • relatively strong swimmers • Tropical • voracious predators, primarily of fish

29. Types of Cnidarians • Anthozoans (class Anthozoa) • include sea anemones, corals and gorgonians

30. Anthozoans (class Anthozoa) • sea anemones • benthic, all adults are sessile • polyps with a gastrovascular cavity divided into compartments radiating from the central one • though sessile, many can change locations

31. Types of Cnidarians • Anthozoans (class Anthozoa) • coral animals • polyps that secrete a hard or soft skeleton • scleractinian corals = hard, stony corals • form reefs along with coralline red algae and calcified green algae

34. Types of Cnidarians • Anthozoans (class Anthozoa) • soft corals • polyps that form plant-like colonies

37. Nutrition and Digestion • Gastrovascular cavity: central cavity where cnidarians digest their prey • functions in digestion and transport • waste products forced back out mouth • Many hydrozoans and anthozoans are suspension feeders • Jellyfish and box jellyfish are carnivorous, eat fish and larger invertebrates • Sea anemones generally feed on invertebrates, some large species feed on fish, shallow water species have symbiotic algae

39. Reproduction • Scyphozoans • in adult jellyfish and box jellyfish, sexes generally separate • medusae (sexual stage) release gametes into the water column for fertilization • planula larvae settle, grow into polyps, and reproduce medusa-like buds asexually • immature buds are released into the water column to grow into mature medusae

40. Young medusa Adult medusa Gastrovascular cavity Bell Gonad Tentacles Radial canal Mouth Oral arms Egg Young polyp Planula Asexual reproduction Sexual reproduction Stepped Art Fig. 8-16, p. 205

41. Reproduction • Anthozoans • asexual reproduction IS COMMON • pedal laceration: leaving parts of the pedal disk (base) behind to grow into new animals • fission: the anemone splits in two and each half grows into a new individual • budding produces large colonies of identical hard corals asexually • sexual reproduction • corals usually have male and female forms, gametes are released into water column • larval stage is a planula larva

42. Ecological Relationships of Cnidarians • Predator-prey relationships • cnidarians are predators • stinging cells discourage predation • sea turtles, some fish and molluscs prey on hydrozoans and jellyfish • Habitat formation • coral polyps form complex 3-dimensional structures inhabited by thousands of other organisms • coral reefs provide a solid surface for attachment, places for pelagic animals to rest and hide and buffer waves and storms

43. Ecological Relationships of Cnidarians • Symbiotic relationships • Portuguese man-of-war and man-of-war fish • reef-forming corals and zooxanthellae • Algae provide food and oxygen to coral through photosynthesis • Coral provides nutrients and carbon dioxide to algae through respiration • sea anemones... • and clownfish • and the hermit crab

46. Ctenophores • Phylum Ctenophora • Planktonic, nearly transparent • Ctenophore structure • named for 8 rows of comb plates (ctenes) which the animal uses for locomotion • ctenes are composed of large cilia • exhibit radial symmetry • lack stinging cells • bioluminescent

47. Ctenophores • Digestion and nutrition • carnivorous, feeding on other plankton, larval fish and fish eggs • may use branched tentacles in a net pattern, adhesive cells, jellyfish stingers to capture prey

48. Ctenophores • Ecological Role • can effect zooplankton abundance directly and fish populations by preying on fish larvae and eggs

49. The Evolution Of Bilateral Symmetry • Bilateral symmetry • body parts arranged such that only one plane through the mid-line of the central axis divides animal into similar right and left halves • allowed for streamline body shape increasing mobility • favored concentration of sense organs at one end of animal (cephalization)