Porifera (Parazoans)

Porifera (Parazoans)

• 'Porifera' means "pore-bearing."
• Sponges are highly harvested for research.
• Sponges live in marine environments.

Structure

• Sponges have a cellular level of body organization and a simple body plan.
• They exhibit asymmetrical or radial symmetry.
• Sponges obtain food through filtration.
• The mesohyl is the middle layer, known as the "no germ layer."
  • It is composed of spongin and spicules.
    • Spongin is a collagen protein forming a network of fibers within the mesohyl.
    • Spicules are needle-like skeletal elements made of calcium carbonate or silica that stiffen the mesohyl. They are crucial for sponge identification and have three classes: Calcarea (calcium), Demospongiae (calcium and/or silica), and Hexactinellida (silica).
• The spongocoel is the large, central cavity where water enters.
• The osculum is where water exits, functioning as both mouth and anus.
• Porocytes are tube-like cells forming the pores (ostia) and controlling water entry into the spongocoel.
• Prosopyles facilitate the movement of water and food particles to the choanocytes.
• Ostium/Ostia are incurrent pores allowing water to enter the sponge.

Incurrent vs. Excurrent Pores

• Incurrent pores (ostia) are openings where water enters the sponge, facilitating filter-feeding and gas exchange.
• Excurrent pores (osculum) are large openings through which water is expelled, carrying nutrients and oxygen through smaller pores (ostia).

Difference Between Choanocytes vs. Amoebocytes

• Choanocytes are flagellated collar cells among sponges, derived from choanoflagellates (ancestors), with a whip-like flagellum, lining the body plan and facilitating filtering and water movement.
• Amoebocytes, derived from amoeba, facilitate digestion, food absorption, and have pseudopodia to engulf.

Classification of Sponges

• Classification is based on body type.
• Hydra is a counterpart (freshwater, no flagellated collar cell).
• Dissection and microscopic identification are essential for distinguishing sponge body plans and types.
  • Asconoid sponges have the smallest size and simplistic body plan. They are radially symmetrical with a central cavity (spongocoel).
  • Syconoid sponges are middle-sized. One of the bases in classifying, has thick body wall, thicker with more complex canal systems than asconoid sponges.
  • Leuconoid sponges are the largest with the most complex canal system, typically asymmetrical. It provides a large surface area for filtering water.

Reproduction in Poriferans

• Sponges are mostly capable of asexual reproduction.
  • Asexual Reproduction:
    • Budding occurs in asconoid and syconoid sponges.
    • Fragmentation.
    • Regeneration repairs damaged tissues.
  • Sexual Reproduction:
    • Monoecious sponges are hermaphroditic, having both male and female reproductive organs.
      • Sperm is identified from Choanocytes.
      • Eggs are identified from Amoebocytes.
    • Fertilization can be Internal (more advantageous) or External (disadvantageous due to pH levels, temperature, currents, and predators).
    • Cleavage is holoblastic, dividing the egg into distinct blastomeres.
• Sponges respire through diffusion.

CNIDARIA (Coelenterata)

• There are ~9,000 species.

Description and Compostion of Cnidaria

• Cnidarians include jellies (jellyfish; cnidocytes), hydras (freshwater), sea anemones, and corals (hard or soft).
  • They have a single opening for both mouth and anus.
• Cnidarians are soft-bodied invertebrates (except for hard corals) and are carnivorous.
• They possess stinging capsules called nematocysts.
• Cnidocytes contain nematocysts and are inverted cells.
• Majority have tentacles.
• Cnidarians are diploblastic, sessile, have a nerve net, gastrovascular cavity, simple muscles, and radial symmetry.

Body Forms

• Medusa/Medusae are umbrella-shaped with a mouth surrounded by tentacles.
• Polyp is tube-like, surrounded with tentacles.
  • It occurs in hydras, corals, and sea anemones, but some (corals and sea anemones) are medusa in their first stages of life.
• Mesoglea is gelatinous between endo and ecto, a hydrostatic skeleton.
• Zooxanthellae are tube dwellers, symbiotic protists that use photosynthesis.

Coral Bleaching

• Coral bleaching is built upon global warming.
  • Pollution.
  • High/Warmer Temperature.

Sensory Organs

• Statocysts sense gravity and determine its direction.
• Ocelli/Ocellus are light-sensing spots.
• Respiration is facilitated through simple diffusion.

Reproduction in Cnidaria

• Asexual reproduction occurs through budding, fragmentation, or regeneration.
• Sexual reproduction involves gametes (external fertilization).
  • Majority of cnidarians are hermaphrodites.

Three Classes Under Phylum Cnidaria

• Anthozoa: anthozoans, sea anemones, corals, sea pens; sessile
• Hydrozoa: hydrozoans; hydroids, siphonophores, and some medusae
• Scyphozoa: scyphozoans; true jellyfish; medusa
  • Cubozoa: cubozoans, old classification; box jellyfish

Ecology

• Corals are distributed worldwide.
• Criteria for cnidarians:
  • Temperature.
  • Water depth.