zoology

• Coelentertates


  Aquatic organisms, found mostly in the marine habitat
• Phyla of Coelentertates


  • Cnidaria
  • Ctenophora

  
• Phylum Cnidaria comprises 10,000 species scattered all over the world
• Cnidarians are colourful because of symbiotic algae which grow on them and are found in the coral reef
• This module covers topics in the Sub phylum Cnidarian, the most dominant sub phyla
• Cnidarians


  • Radially symmetric
  • Indirect development with larval stage known as Planula larvae and ciliated, motile, gastrula larva
• Cnidarians


  • Diploblastic - Epiderm & hypoderm
  • Tissues (First True metazons- Eumetazoans)

  
• Cnidarians


  • Incomplete digestive tract - coelenteron
  • Nervous system: simple nerve net, neurons and decentralized
• Cnidarians


  • They have stinging apparatus known as Cnidocysts. Many Cnidarians are effective predators
  • Cnidocysts consists of organelles called Cnidae. The most important Cnidae is the nematocyst- a tiny capsule with coiled thread covered by an operculum
  • The nematocyste is used for attack, defense and predation

  
• Cnidarians have a characteristic alternating life forms of sessile polyp (or hydroid form) and free swimming medusa (or jelly fish form)

  
• Polyps


  • Adapted to a sedentary life style, often attached to a substratum
  • Tubular in structure
  • Radial symmetry
  • Oral end called the hypostome or manubrium in hydrozoans
  • Tentacles surround mouth
  • May reproduce asexually by budding or pedal laceration
  • In class Hydrozoa, there are two types of polyps- Feeding polyps (Hydranths) and reproductive polyps (Gonangia)
• Medusa


  • Usually free swimming and have bell or umbrella shaped bodies
  • Often exhibit tentamerous symmetry because their body parts are arranged in fours
  • Move by jet propulsion
  • Found in all cnidaria except Class Anthozoa
  • Structure is made up of Exumbrella: convex upper (aboral) surface and Subumbrella: concave lower (oral) surface with a mouth at the center

  
• Classes of Phylum Cnidaria

  • Hydrozoa
  • Scyphozoa
  • Cubozoa
  • Anthozoa

  
• Class Hydrozoa


  • Most varied and derived of the cnidarian groups
  • Includes freshwater species (Hydra spp.)
  • Colonial species common (e.g Obelis sp.)
  • Most have typical dimorphic life cycle
  • Exists mostly as polyps and medusoid forms at different stages of their life cycle
  • Some are entirely polyp (Hydra) some are mostly medusoid (e.g Gonionemus)

  
• Typical Hydrozoans


  • Hydra - Lacks medusa stage, Asexual - budding, Sexual - gametes
• Atypical Hydrozoans


  • Gonionemus - reduced polyp form
• Colonial Hydrozoans


  • Obelia - Colony of specialized hydranths
  • Portuguese Man-O-War (Physalia physalis)
  • Fire Corals - NOT TRUE CORAL, Hydrozoan colony, TRUE CORAL - Anthozoan colony, Cnidocytes cause severe pain

  
• Class Scyphozoa


  • Typically thought of as jellyfish
  • Most have typical dimorphic life cycle - Polyp stage is atypical, Majority of life cycle spent in medusa form

  
• Typical Scyphozoans


  • Aurelia aurita (Moon jelly)
• Other Scyphozoans


  • Sea thimble jellyfish (Linuche unguiculata) - Tiny jellyfish (< 1 inch) that swarm in the spring, Adults and larvae ("sea lice") may cause a severe skin reaction in humans
  • Jellyfish (Mastigias sp., family Rhizostomeae) from Jellyfish Lake in Palau, western Pacific - Have lost their ability to sting and depend on zooxanthellae (alage) for nutrition

  
• Largest Cnidarian


  • Lion's Mane Jelly (Cyanea capillata) - Bell - 6 ft, Tentacles - 120 ft
• Class Cubozoa (Box jellies)


  • Typically solitary
  • Prominent medusa
  • Polyp is reduced or absent
• Cubozoans


  • Chironex sp.
  • Carybdeid, found in Darwin, Australia
  • Carybdea sivickisi, found in South pacific
  • Chironex fleckeri - Size of human head with tentacles (4) up to 9 ft long, 18-24 ft of tentacles can deliver enough poison to kill in <5 min.
• Class Anthozoa


  • Anemones & Corals
  • Lack medusa form
  • Form colonies (especially coral)
• Anthozoans


  • Giant anemone or purple-tipped anemone (Condylactis gigantea) often harbors cleaning shrimp among its tentacles, Common in Bermuda and the Caribbean
  • Anemone with Anemone Fish

  
• Anthozoans can move to avoid predators even though they are typically sessile
• Sub Classes of Class Anthozoa

  • Hexacorallia
  • Octacorallia
• Hexacorallia


  • 6-fold symmetry
  • Precipitate Ca3(CO3)2 from sea water to produce skeletal structures that become coral reefs
  • Contain zooxanthella
• Octacorallia


  • 8-fold symmetry
  • Form complex tube-like skeletal structures
  • Lack zooxanthella
• Reefs are shallow tropical waters rich in diversity of coelenterates, sponges and other aquatic fauna
• Reefs are typically colourful and rich in algae (symbiotic dinoflagellates)
• Reefs precipitate CaCO3 to form "exoskeleton" for the soft creatures inhabiting it
• Poriferans


  Commonly referred to as sponges
• Sponges are pore-bearing animals
• Sponges


  • Simplest multicellular animals
  • Their body is an assemblage of cells in an extracellular matrix, supported by skeletons known as spicules
  • Most live in marine environments (Seas and Oceans)
  • A few live in brackish (e.g. lagoon) and fresh water

  
• Sponges are primitive, and sedentary animals which lack a mouth, digestive canal or any other normal organ
• Suspension or filter feeders

  Remove plankton (food) from the water
• Marine sponges are larger & more colorful than freshwater sponges
• Sponges


  • Two types of openings: Ostium (tiny in-current pore from where water and food enters) and Osculum (large ex-current opening from where water and waste materials leaves)
• Types of sponge cells

  • Pinacocytes (cells of the pinacoderm)
  • Choanocytes (cells with collar and flagella)
  • Porocytes (cells attached to the collar of the choanocytes)
  • Amoebocytes/Archaeocytes (cells that can transform into any other cell type required)