Detailed Study Notes on Sponges and Cnidarians

Types of Sponges

  • Indicator of Sponge Types
    • Differentiated by canal systems.
    • A distinction noted by the number of rays in the spicule (e.g. spiffy wall).
    • Majority of sponges are marine; only one family is freshwater.
    • Sponges make up over 90% of all species in the world.

Class Calcarea (Calciferous Sponges)

  • Characteristics
    • Composed of spicules made from calcium carbonate.
    • Types of spicules:
      • Needle-shaped with two rays.
      • Triradiate spicules with three rays.
      • Quadriradiate spicules with four rays.
    • Canal systems can be of three types:
    • Esconoid.
    • Syconoid.
    • Leuconoid.
    • Naming deriving from calcium carbonate presence.

Class Hexactinellida (Glass Sponges)

  • Characteristics
    • Spicules composed of silica.
    • Can have four or six points.
    • Lack of esconoid canal system; can have
    • Syconoid or Leuconoid canal types.
    • Typically cylindrical or funnel-shaped.
    • Some members are among the oldest organisms on Earth, with ages up to 15,000 years.

Reproductive Systems in Sponges

  • Reproduction Modes
    • Can reproduce both sexually and asexually.
    • Asexual reproduction via fragmentation (biting or breaking).
    • Sexual reproduction
    • Most sponges are hermaphroditic.
    • Produce both egg and sperm gametes.
    • Sperm are released; eggs remain within the sponge.
  • Zygote Characteristics
    • Zygotes have flagella (
    • Capable of motility, which is uncommon for zygotes in other organisms).

Branch Points in Animal Classification

  • Branch Point 1: Tissue Types
    • Distinction between animals based on the presence/types of tissues.
  • Branch Point 2: Symmetry
    • Separation of animal phyla by symmetry types:
    • Cnidarians exhibit radial symmetry.
    • All other animals show bilateral symmetry.
    • Definitions:
    • Radial Symmetry: Circle-based symmetry; can be divided into equal parts by multiple lines.
    • Bilateral Symmetry: Symmetrical only by a single line.
  • Characteristics of Cnidarians
    • True tissues (diploblastic nature: endoderm and ectoderm, no mesoderm).
    • Gastrovascular cavity for digestion; nerve net instead of a centralized brain.
    • Mostly marine but some freshwater forms exist (e.g. freshwater jellyfish).

Form Types in Cnidarians

  • Polyp and Medusa Forms
    • Polyp: Stationary form; anchored to surfaces; appears as a tube.
    • Medusa: Freely swimming, upside-down polyp form (common jellyfish form).
    • Some species have both forms in their life cycle while others remain purely in polyp form.
  • Feeding Mechanism
    • Cnidarians can ingest larger food items compared to sponges.

Cnidocyte and Nematocysts in Cnidarians

  • Definitions
    • Nematocytes: Stinging cells unique to cnidarians, containing nematocysts (the stinging mechanism).
    • Trigger Mechanism: When the trigger on the nematocyte is touched, the nematocyst discharges and can sting prey or predators.
  • Functionality
    • Capture of prey.
    • Defense against predation.

Class Hydrozoa

  • Developmental Stages
    • Exhibits all stages within one organism: polyp stage, medusa stage, and zygote stage.
    • Diblastic nature (true diploblastic development).

Class Scyphozoa

  • Characteristics
    • Includes most large jellyfish.
    • Some may achieve bell diameters exceeding 2 meters and long tentacles reaching up to 60-70 meters.
    • Found primarily in open and deeper ocean waters.

Class Anthozoa (Flower Animals)

  • Characteristics
    • Includes polyps that resemble flowers, lacking a medusa stage.
    • Occupies various marine environments.

Class Cubozoa (Box Jellyfish)

  • Characteristics
    • Unique cube-shaped bell structure.
    • Possesses specialized eyes (though not true eyes) capable of detecting light and movement.
    • Notable for potent venom affecting humans.

Phylum Ctenophora

  • Characteristics
    • Commonly known as comb jellies.
    • Small in size, typically around 10 cm.
    • Lacks stinging cells; has a complete gut (mouth and anus).
    • Noted for their adaptation as the largest organisms using cilia for locomotion.

Branch Points in Worm Classification

  • View of Worm Phyla
    • Classification based on body cavities (acoelomate, pseudocoelomate, and coelomate).
  • Flatworms
    • Incomplete guts system (one opening for ingestion and waste).
  • Roundworms and Annelids
    • Possess complete guts (two openings).
  • Distinctions:
    • Flatworms and annelids as lophotrochozoans; roundworms as ecdysozoans.

Distinctions in Animal Development (Protostomes vs. Deuterostomes)

  • Differences between Protostome and Deuterostome Development
    • Cleavage:
    • Protostomes: Spiral and determinate.
    • Deuterostomes: Radial and indeterminate.
    • Coelom Formation:
    • Protostomes: Solid masses of mesoderm split to form coelom.
    • Deuterostomes: Coelom forms as outpocketings of the primitive gut.
    • Blastopore Fate:
    • Protostomes: Mouth develops from blastopore.
    • Deuterostomes: Anus develops from blastopore.

Types of Coelomates

  • True Coelom
    • Entirely surrounded by mesoderm.
  • Pseudocoelomate
    • Body cavity not entirely surrounded by mesoderm.
  • Acoelomate
    • Lacking any body cavity.

Summary of Key Cnidarian Features

  • Unique Traits
    • Cnidarians are radially symmetrical.
    • Possess true tissues and a gastrovascular cavity.
    • Exhibit both polyp and medusa forms in some classes.
    • Use nematocysts for predation and defense.

Concluding Remarks

  • Diversity of Life
    • Different animal groups evolve unique adaptations for survival and defense.
    • Understanding these branch points is crucial for classifying and differentiating animal phyla.