Topic #10: Dimorphism in Hydrozoa

• Dimorphism is exhibited by Obelia
• Dimorphism

  • exhibited two forms which are Gastrozoid and Gonozoid
• Obelia is Colonial while Hydra is Solitary
• Hydrotheca

  • modified Perisarc that encloses Gastrozoid polyp and is exoskeleton-like for protection
• Blastostyle

  • contains small immature medusa called medusa buds
• Medusa Bud

  • when mature, it passes through the opening of Gonozoid and becomes free-swimming
• Gonophore

  • where the buds exit
• Perisarc

  • nonliving skeleton covering made of chitin
• Coenosarc

  • living skeleton covering continuous to gastrovascular cavity
• Fertilized eggs develop into planula larva in Cnidaria
• Planula Larva

  • ciliated and swims for 3 days to find a place and settle
• Planula Larva

  • becomes the young hydrozoid colony when settled
• Anuli

  • makes the colony flexible as it follows the water current
• Gastrozoid

  • feeding polyp that looks like a miniature Hydra
• Gastrozoid

  • enclosed by an exoskeleton called Hydroteca
• Gonozoid

  • reproductive polyps that look like cups
• Gonozoid

  • has medusa buds attached to blastostyle which exists through the Gonophore to grow
• Phylum: Cnidaria

  Class: Hydrozoa

  Order: Leptothecata

  Family: Campanulariidae

  Scientific Name: Obelia