Which member of the phylum Porifera is the oldest metazoan group still existing on our planet?

The correct answer is Sponges.

Key Points

• Sponges (phylum Porifera) are considered the oldest metazoan group still existing on Earth, dating back to the Precambrian era, approximately 600 million years ago.
• They are simple multicellular organisms that lack tissues, organs, and a nervous system but possess specialized cells for various functions like feeding and reproduction.
• Sponges rely on a water canal system to filter feed, making them highly efficient filter feeders in aquatic ecosystems.
• Their fossil records suggest that they played a significant role in the evolution of early marine ecosystems and are considered a cornerstone in the study of evolutionary biology.
• Sponges are exclusively aquatic, with the majority being marine, although some freshwater species also exist.

Additional Information

• Phylum Porifera:
  • Porifera, commonly known as sponges, derive their name from the Latin word "porus" (pore) and "ferre" (to bear), referring to their porous bodies.
  • They exhibit asymmetrical or radial symmetry and are sessile as adults.
  • Sponges have a skeleton made of spicules (calcareous or siliceous) or spongin fibers, providing structural support.
• Water Canal System:
  • Sponges use a specialized canal system comprising ostia (pores), spongocoel (central cavity), and osculum (excurrent opening) to circulate water for feeding, respiration, and excretion.
  • This system is driven by the beating of flagella in specialized cells called choanocytes.
• Reproductive Strategies:
  • Sponges reproduce both sexually (via gametes) and asexually (budding, fragmentation, or gemmules).
  • They are hermaphroditic, meaning an individual can produce both eggs and sperm, although cross-fertilization is common.
• Ecological Importance:
  • Sponges serve as habitat-forming species, providing shelter for various marine organisms.
  • They play a crucial role in nutrient cycling by filtering large volumes of water and capturing microscopic particles.
• Evolutionary Significance:
  • Sponges are considered basal metazoans, representing an evolutionary link between unicellular and multicellular life forms.
  • They offer insights into the origin and evolution of multicellular animals due to their simple body structure and cellular organization.