Porifera
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Questions and Answers

What is the main reason why gametes are produced and released at the same time?

  • Because of internal fertilization
  • Under the control of environmental signals (correct)
  • Due to the low population levels
  • To increase the chances of reproduction

    • What is a common reproductive adaptation in animals that live in areas with low population levels or are benthic?

  • Synchronous reproduction
  • External fertilization
  • Internal fertilization
  • Hermaphroditism (correct)

    • What is a characteristic of the reproductive tract in animals that undergo internal fertilization?

  • No modifications occur
  • A wide range of modifications occur (correct)
  • Only external fertilization occurs
  • A large number of gametes are produced

    • Why do freshwater animals commonly exhibit direct development?

    <p>Because of the hazards of current and turbidity</p> Signup and view all the answers

    What is the lowest level of organization among the metazoa?

    <p>Cellular level</p> Signup and view all the answers

    When were the porifera separated and given their own name?

    <p>1836</p> Signup and view all the answers

    What is a characteristic of poriferans?

    <p>They are asymmetrical or radially symmetrical</p> Signup and view all the answers

    When were the porifera placed in a separate branch of metazoans?

    <p>1875</p> Signup and view all the answers

    What is the characteristic feature of monaxons/streptasters?

    <p>They are short and spiny.</p> Signup and view all the answers

    What happens to tetraxons when they lose rays?

    <p>They become indistinguishable from monaxons.</p> Signup and view all the answers

    What is the characteristic of calthrops?

    <p>They have four rays of equal length.</p> Signup and view all the answers

    What is the characteristic of anatriaenes?

    <p>They have cladi in the same direction as the rhabdome.</p> Signup and view all the answers

    What is the characteristic of triaxon/hexactinal spicules?

    <p>They have 3 axes crossing at right angles, producing 6 rays.</p> Signup and view all the answers

    What is the characteristic of oxyasters?

    <p>They have pointed rays.</p> Signup and view all the answers

    What is the primary function of the pore diaphragm in sponges?

    <p>To regulate water flow by covering the pore</p> Signup and view all the answers

    What happens to polyaxons when they lose rays?

    <p>They form spheres.</p> Signup and view all the answers

    What type of cells are responsible for moving water through the sponge and obtaining food?

    <p>Choanocytes</p> Signup and view all the answers

    What is the function of myocytes in a sponge?

    <p>To regulate the opening of osculum</p> Signup and view all the answers

    What is the term for the layer of cells that forms the outermost layer of the sponge?

    <p>Pinacoderm</p> Signup and view all the answers

    What is the characteristic of sterrasters?

    <p>They have reduced rays to small projections from the surface.</p> Signup and view all the answers

    What is the main reason for the bright coloration of sponges?

    <p>Solar radiation protection and warning coloration</p> Signup and view all the answers

    What is the main component of spicules in sponges?

    <p>Organic material with inorganic substances</p> Signup and view all the answers

    What is the function of gland cells in sponges?

    <p>To secrete slime</p> Signup and view all the answers

    What is the characteristic shape of some sponges?

    <p>Vase-like or globular</p> Signup and view all the answers

    What is the name of the cells that line the internal cavities of the sponge?

    <p>Endopinacocytes</p> Signup and view all the answers

    What type of cells can differentiate into other types of cells?

    <p>Archeocytes</p> Signup and view all the answers

    What is the term for the contractile cells that form the outermost layer of the sponge?

    <p>Pinacocytes</p> Signup and view all the answers

    What is the main function of scleroblasts?

    <p>To secrete skeletal components</p> Signup and view all the answers

    What is the name of the canal through which water enters the sponge?

    <p>Incurrent canal</p> Signup and view all the answers

    What is the term for small spicules?

    <p>Microscleres</p> Signup and view all the answers

    What is the main component of the skeleton of some sponges?

    <p>Spongin fibers</p> Signup and view all the answers

    What is the term for the layer of cells between the pinacoderm and the spongocoel?

    <p>Mesohyl</p> Signup and view all the answers

    What is the primary function of choanocytes in sponges?

    <p>To propel water through the canal system</p> Signup and view all the answers

    In which direction are the choanocytes' flagella directed in sponges?

    <p>Toward the apopyles</p> Signup and view all the answers

    What is the result of the radial canals fusing at the distal ends in syconoids?

    <p>The formation of a mesenchymal cortex</p> Signup and view all the answers

    What is the path of water through the leuconoid sponges?

    <p>Through the dermal pores, into the subdermal spaces, and out through the excurrent canals</p> Signup and view all the answers

    What is the characteristic of the internal design of most leuconoids?

    <p>Hollow and irregular</p> Signup and view all the answers

    What is the result of the further out folding of the radial canals in leuconoids?

    <p>The formation of several smaller rounded chambers</p> Signup and view all the answers

    What is the characteristic of the canal system in leuconoids?

    <p>More efficient and complex</p> Signup and view all the answers

    What is the characteristic of the flagella in sponges?

    <p>They are not coordinated or synchronized in a particular direction</p> Signup and view all the answers

    Study Notes

    Life Cycle with Larval Stage

    • Leads to reproductive adaptations:
      • Synchrony: gametes are produced and released at the same time, controlled by environmental signals
      • Proximity: gametes are released near each other
        • Hermaphroditism: common in low population levels or benthic adults
        • Internal fertilization: leads to modifications of the reproductive tract, lower number of gametes produced than external fertilization

    Direct Development

    • Common in freshwater animals due to hazards of current and turbidity

    Phylum Porifera

    Introduction

    • Poriferans or sponges are the lowest among metazoa, with a cellular level of organization
    • They form only tissues and never organs
    • Ideal study of animals should start with the simplest, i.e., the porifera

    History

    • Debate about whether sponges are animals until the detection of water currents and contractile movements of the oscula in 1765
    • Grouped with anthozoans (corals and sea anemones) until 1825, when morphology and physiology were adequately understood
    • Separated and given the name Porifera in 1836, and placed in a separate branch of metazoans, the parazoa, in 1875

    Definition

    • Asymmetrical or radially symmetrical animals with a cellular grade of construction and no organs
    • Sessile animals with a body permeated with pores, canals, and chambers through which water currents pass

    General Morphology and Physiology

    • Most sponges are brightly colored, with coloration suggested to protect from solar radiation and as warning coloration
    • Shape: most are irregularly shaped with branching, encrusting, and massive growth forms, but a few have definite shapes like vase-like cylinders, globes, or peculiar branching patterns
    • Symmetry: irregularly shaped sponges are asymmetrical, while vase-like or globular forms are radial
    • Size: range from 1-2 mm in height to forms that may reach several meters in diameter

    Histology

    • Sponges are dipoblastic animals, with pinacoderm and mesohyl differing from the usual epidermis and mesenchyme of other metazoans
    • Pinacoderm:
      • Pinacocytes: flattened, polygonal, uninucleate cells that are contractile and form the outermost layer
      • Endopinacocytes: pinacocytes that line internal cavities like the walls of incurrent canals and the spongocoel
      • Porocytes: tubular cells extending from the pinacoderm to the spongocoel, pierced by a central canal that acts as the incurrent pore
    • Mesohyl:
      • Collencytes: with slender branching pseudopodia that may unite to form a network, secreting dispersed collagen fibers
      • Chromocytes: with pigment bodies
      • Thesocytes: with food reserves/vacuoles
      • Scleroblasts: secreting the skeletal components of the sponge, depending on the skeletal component
      • Archeocytes: with blunt pseudopodia, large nuclei, and a conspicuous nucleolus, undifferentiated and totipotent
      • Gland cells: attached to the surface of the sponge and secreting slime
      • Desmacytes/fiber cells: long, slender cells found in layers
      • Myocytes: fusiform, contractile cells usually arranged in a circular fashion to form a sphincter around the osculum or other opening

    Choanoderm

    • Choanocytes/collar cells: round or oval cells whose base rests on the mesohyl, with a flagellum and a transparent, contractile collar, responsible for moving water through the sponge and obtaining food

    Skeleton

    • Sponge skeleton may be spicules, spongin fibers, or basal encasements
    • Spicules/sclerites: minute to microscopic bodies with a crystalline appearance, consisting of simple spines or spines radiating from a point
      • Chemical composition: possessing an axis of organic material around which are deposited inorganic substances
      • Size: divided into two general sizes: microscleres and megascleres
      • Types: monaxons, tetraxons, triaxons, polyaxons, and spheres

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