Question

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

• A. Anemones
• B. Sponges
• C. Sycon
• D. Hydra

Answer 1

Answer:

B. Sponges

Phylum Porifera: The Ancient Life Forms

Oldest Metazoan Group: Sponges

• Sponges, belonging to the phylum Porifera, represent the oldest metazoan group that still exists today.

• Fossil evidence suggests that sponges have been around for at least 580 million years, predating even the Cambrian explosion.

• This makes them one of the earliest examples of multicellular animal life (metazoans) on Earth.

Key Characteristics of Porifera

• Sessile: Adult sponges are generally immobile and attach themselves to a substrate.

• Porous Body: Their bodies are characterized by numerous pores called ostia, which allow water to enter.

• Water Vascular System: Water flows through canals and exits through a larger opening called the osculum. This system is used for feeding, respiration, and excretion.

• Cellular Organization: Sponges exhibit a relatively simple level of organization, with cells that are specialized but not arranged into true tissues or organs.

• Feeding: They are filter feeders, capturing tiny food particles from the water that passes through their bodies.

• Reproduction: Sponges can reproduce both sexually and asexually (budding).

Ecological Significance

• Sponges play an important role in marine ecosystems by filtering large volumes of water, which helps to clarify it.

• They also provide habitat and shelter for various small marine organisms.

Classification within Porifera

• The phylum Porifera is typically divided into three main classes based on the type of skeletal elements they possess:

  1. Calcarea: Spicules made of calcium carbonate.

  2. Hexactinellida (Glass Sponges): Spicules made of silica, often with six rays.

  3. Demospongiae: Spicules made of silica (not always six-rayed) and/or a proteinaceous spongin network. This is the largest class.