Fiveable
Fiveable
You have 2 free guides left 😧
Unlock your guides
You have 2 free guides left 😧
Unlock your guides

General Biology I

28.1 Phylum Porifera

3 min readLast Updated on June 14, 2024

Sponges, the simplest animals, are filter-feeding aquatic creatures with unique body structures. They lack true tissues and organs, instead relying on specialized cells and a water current system for survival. Their simple yet effective design has allowed them to thrive for millions of years.

Sponges' bodies consist of outer and inner layers with a jelly-like middle. They feed by filtering water through tiny pores, trapping food particles with specialized cells. Sponges can reproduce both sexually and asexually, and their cells can transform into any type needed.

Phylum Porifera

Structure and function of sponges

Top images from around the web for Structure and function of sponges
Top images from around the web for Structure and function of sponges
  • Asymmetrical, sessile, aquatic invertebrates lack true tissues and organs (sponges)
  • Body structure consists of an outer layer (pinacoderm), inner layer (choanoderm) composed of choanocytes, and a gelatinous matrix between layers called the mesohyl
  • Water current system allows water to enter through small openings called ostia, flow through the sponge body, and exit through a large opening called the osculum
    • Water flow maintained by flagellated cells called choanocytes that create currents to bring in food and oxygen while removing waste
  • The spongocoel is the central cavity of the sponge where water collects before exiting through the osculum

Feeding and digestion in sponges

  • Filter feeders trap and consume food particles from the water that flows through their bodies
  • Choanocytes, flagellated cells lining the inner chambers, create water currents to bring in food and trap and phagocytize food particles
  • Amoebocytes, mobile cells within the mesohyl, transport and digest nutrients intracellularly and distribute them throughout the sponge body
  • No specialized digestive system as digestion occurs within individual cells (intracellular digestion)

Cell types and roles in sponges

  • Pinacocytes are flattened cells that cover the outer surface providing protection and support (skin cells)
  • Choanocytes (collar cells) are flagellated cells lining the inner chambers that create water currents for filter feeding and trap and phagocytize food particles
  • Amoebocytes (archaeocytes) are mobile cells within the mesohyl that perform various functions:
    • Transport and digest nutrients
    • Produce skeletal elements such as spicules or spongin fibers
    • Differentiate into other specialized cell types as needed
  • Porocytes are tubular cells that form the ostia and control water flow into the sponge
  • Sclerocytes secrete spicules, which are siliceous or calcareous skeletal elements that provide structural support (glass sponges)
  • Spongocytes secrete spongin fibers, which are flexible protein fibers that form the skeleton in some sponges (bath sponges)

Reproduction and development in sponges

  • Sponges can reproduce both sexually and asexually
  • Asexual reproduction occurs through:
    • Budding: small outgrowths develop and detach from the parent sponge
    • Fragmentation: pieces of the sponge break off and regenerate into new individuals
  • Sexual reproduction involves:
    • Production of gametes by specialized cells
    • External fertilization in the water column
    • Development of a free-swimming larva that eventually settles and metamorphoses into an adult sponge
  • Sponge cells exhibit totipotency, allowing them to differentiate into any cell type needed for regeneration or reproduction

Body plan and organization

  • Sponges have a simple body plan with no true tissues or organs
  • Three main types of body plans in sponges:
    • Asconoid: simplest form with a single central cavity (spongocoel)
    • Syconoid: more complex with folded inner walls and a central cavity
    • Leuconoid: most complex with a system of canals and chambers

Term 1 of 30

Amoebocytes
See definition

Amoebocytes are specialized cells found in sponges (Phylum Porifera) that play multiple roles in the organism's biology. These versatile cells are crucial for transporting nutrients, waste removal, and providing structural support within the sponge. Their ability to move through the mesohyl, the gelatinous matrix in which sponge cells reside, allows them to perform essential functions that contribute to the overall homeostasis of the sponge.

Key Terms to Review (30)

Term 1 of 30

Amoebocytes
See definition

Amoebocytes are specialized cells found in sponges (Phylum Porifera) that play multiple roles in the organism's biology. These versatile cells are crucial for transporting nutrients, waste removal, and providing structural support within the sponge. Their ability to move through the mesohyl, the gelatinous matrix in which sponge cells reside, allows them to perform essential functions that contribute to the overall homeostasis of the sponge.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

Term 1 of 30

Amoebocytes
See definition

Amoebocytes are specialized cells found in sponges (Phylum Porifera) that play multiple roles in the organism's biology. These versatile cells are crucial for transporting nutrients, waste removal, and providing structural support within the sponge. Their ability to move through the mesohyl, the gelatinous matrix in which sponge cells reside, allows them to perform essential functions that contribute to the overall homeostasis of the sponge.



© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Glossary
Glossary