Phylum Sipuncula Key feature introvert

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Marine Biology Lecture 5

April 12, 2006 (part)

  1. Phylum Sipuncula

    1. Key feature

      1. introvert

        1. tentacles at end for deposit feeding (mucus covered)

        2. turns completely inside-out, except for tentacles at the end.

        3. nuchal organs: chemosensory

        4. Control of introvert and tentacles

          • hydrostatic pressure of coelom (via body musculature) everts the introvert; it is withdrawn by retractor muscles

          • hydrostatic pressure of compensatory sacs everts the tentacles themselves.

      2. Gas exchange over body surface (main part and introvert), tentacles.

      3. Reproduction: gametes spawned into the ocean

  2. Phylum Mollusca, the "soft-bodied" animals

    1. Body organization (hypothetical ancestral mollusc, HAM):

      1. Shell

      2. Mantle

        1. covers body organs, and in some molluscs, serves as only body covering

        2. secretes shell

        3. Associated sensory organs (tentacles, eyespots)

      3. visceral mass

      4. mantle cavity

        1. ctenidia (paired in HAM)

      5. head and sensory structures at head

      6. radula

      7. foot and epipodial tentacles

    2. Reproduction

      1. Quite variable depending upon class, even species.

    3. Class Polyplacophora: body organization (compare to HAM)

      1. Shell: Eight shell plates (“valves”) rather than a single shell

      2. Mantle: thickened, forms "girdle" around plates which serves as protection

      3. Mantle cavity: expanded along sides, multiple ctenidia

      4. Head reduced

    4. Class Polyplacophora: local species
      1. Cryptochiton stelleri: giant gumboot chiton.

        1. Appearance

          • Largest chiton in the world (to 1/3 meter)

          • Rough red mantle completely fused over shell plates

        2. Location

          • Primarily the low intertidal (maybe up to the low middle intertidal)

            • At low tide, it can carry out gas exchange in air as long as the ctenidia are kept moist.

          • Found in somewhat shaded areas.

        3. Other interesting details of life history
          • Feeds on red algae and kelp

          • Limited movement: Marked Cryptochiton found within 20 m after 2 years!

          • Grow slowly. Live 20 years or more.

          • Commensals live within mantle cavity (a.k.a. "pallial groove" along edges of foot, containing the ctenidia) and obtain food brought in by respiratory currents

      2. Katharina tunicata: black Katy chiton

        1. Appearance

          • Smooth black mantle often pulled far over the shell plates

            • Able to adjust its mantle position; sometimes completely closed up.

          • Plates also black

          • Foot is orange
        2. Location

          • Middle intertidal (mostly lower-middle, but venturing to upper-middle)
          • Found in areas of moderate to high wave action

          • Often in areas of sun exposure, although associated with algae

        3. Interesting details of life-history
          • Feed on brown and red algae, benthic diatoms

            • Can greatly reduce the amount of kelp in a region (more on this later)
          • Ability to pull its mantle over its shell is a defense against other organisms getting a foothold.

      3. Tonicella lineata

        1. Appearance

          • Distinct lines on valves

          • Pink coloration

        2. Location

          • Lower middle to low intertidal

          • Protected in crevices, within algae

          • Often associated with the sea urchin Strongylocentrotus purpuratus

        3. Interesting details of life-history
          • Feeds on crustose coralline algae, from which it gets its pink color

          • Sometimes exhibit homing behavior

      4. Mopalia spp.

        1. Appearance

        2. Location
          • Tolerates wide range of physical conditions

          • Found from the upper middle intertidal downward (different species in somewhat different locations)

        3. Interesting details of life-history

          • Algae eaters
        4. Those which are alternately submerged and uncovered show homing behavior, but those permanently in tidepools do not.

        5. Ranges of about 50 cm radius (small!)

Study questions will be combined with those for next outline

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