Choanocytes vs. Pinacocytes

What's the Difference?

Choanocytes and pinacocytes are two types of cells found in sponges, which are multicellular organisms belonging to the phylum Porifera. Choanocytes are specialized cells that line the inner surface of the sponge's body and have a distinctive collar-like structure surrounding a flagellum. They are responsible for generating water currents and capturing food particles through their collar, which acts as a filter. On the other hand, pinacocytes are flat, epithelial-like cells that cover the outer surface of the sponge. They form a protective layer and are involved in various functions such as gas exchange, secretion, and structural support. While choanocytes are primarily involved in feeding, pinacocytes play a more general role in maintaining the sponge's overall structure and functioning.


Cell TypeFlagellated cellsFlattened cells
FunctionGenerate water currents and filter food particlesForm the outer layer of the sponge body
StructureHave a collar of microvilli surrounding a flagellumFlat and thin cells forming a protective layer
LocationLine the inner chambers of the spongeCover the outer surface of the sponge
Role in ReproductionInvolved in the production of gametesNot directly involved in reproduction

Further Detail


Sponges, also known as Porifera, are fascinating organisms that belong to the animal kingdom. They are multicellular but lack true tissues and organs. Instead, sponges are composed of specialized cells that perform specific functions. Two important cell types found in sponges are choanocytes and pinacocytes. While both these cell types contribute to the overall functioning of sponges, they possess distinct attributes that set them apart. In this article, we will explore and compare the characteristics of choanocytes and pinacocytes, shedding light on their roles and significance within the sponge body.


Choanocytes, also known as collar cells, are one of the most distinctive cell types found in sponges. These cells are named after their unique structure, which includes a collar-like ring of microvilli surrounding a flagellum. Choanocytes are primarily responsible for generating water currents and capturing food particles in sponges. They play a crucial role in filter feeding, allowing sponges to obtain nutrients from the surrounding water.

Choanocytes possess several notable attributes. Firstly, their flagella beat rhythmically, creating water currents that draw in water through the sponge's pores. As water flows through the collar of the choanocyte, the microvilli trap small food particles, such as bacteria and plankton. These particles are then engulfed by the choanocyte through phagocytosis, providing the sponge with a source of nutrition.

Furthermore, choanocytes are highly specialized for their function. They have a large surface area due to the presence of numerous microvilli, which increases their efficiency in capturing food particles. Additionally, choanocytes possess a contractile collar that helps regulate the size of the collar opening, allowing them to adjust the flow of water and prevent the entry of larger particles that could potentially clog the sponge's internal system.

Another important attribute of choanocytes is their ability to differentiate into other cell types. In certain sponge species, choanocytes can transform into archaeocytes, which are totipotent cells capable of differentiating into various cell types required for sponge growth, repair, and regeneration. This attribute highlights the versatility and plasticity of choanocytes, making them essential for the overall development and maintenance of sponges.


Pinacocytes, also known as pinacoderm cells, are another crucial cell type found in sponges. These cells form the outermost layer of the sponge body, covering the surface and lining the internal canals and chambers. Pinacocytes are flat, epithelial-like cells that play multiple roles in sponges, including protection, gas exchange, and structural support.

Pinacocytes possess distinct attributes that enable them to fulfill their functions effectively. Firstly, they form a continuous layer that acts as a protective barrier, preventing the entry of foreign particles and pathogens into the sponge's internal environment. This protective function is particularly important as sponges are sessile organisms that rely on maintaining a clean and suitable habitat for their survival.

In addition to protection, pinacocytes are involved in gas exchange. These cells are thin and flat, allowing for efficient diffusion of gases across their surface. Oxygen can easily enter the sponge through the pinacocytes, while carbon dioxide and other waste gases can be expelled. This exchange of gases is vital for the metabolic processes occurring within the sponge's cells.

Furthermore, pinacocytes contribute to the structural integrity of sponges. They are connected to each other by specialized junctions, forming a tight epithelial layer that provides support and stability to the sponge body. This structural role is particularly important in maintaining the overall shape and form of the sponge, preventing collapse or deformation.

Pinacocytes also participate in the regeneration and repair processes of sponges. When a sponge is damaged, pinacocytes can migrate and cover the injured area, forming a temporary protective layer. This migration and reformation of pinacocytes contribute to the sponge's ability to heal and regenerate, ensuring its long-term survival and resilience.


While choanocytes and pinacocytes have distinct attributes, they also share some similarities. Both cell types are found in all sponge species and are essential for the survival and functioning of sponges. They are involved in maintaining the internal environment, obtaining nutrients, and contributing to the overall structure of the sponge body.

However, there are notable differences between choanocytes and pinacocytes. Choanocytes are primarily responsible for filter feeding and capturing food particles, while pinacocytes are involved in protection, gas exchange, and structural support. Choanocytes possess a unique collar structure with a flagellum, while pinacocytes are flat and form a continuous layer on the sponge's surface.

Choanocytes have a higher degree of specialization for their function, with numerous microvilli and a contractile collar. They also have the ability to differentiate into other cell types, contributing to sponge growth and regeneration. On the other hand, pinacocytes are more versatile in their roles, participating in multiple functions such as protection, gas exchange, and structural support.

Despite their differences, choanocytes and pinacocytes work together in a coordinated manner to ensure the survival and functioning of sponges. Choanocytes generate water currents that bring in food particles, which are then captured by the collar structure. Pinacocytes protect the sponge from external threats, facilitate gas exchange, and provide structural support. These two cell types complement each other, forming a cohesive system within the sponge body.


Choanocytes and pinacocytes are two essential cell types found in sponges, each possessing distinct attributes that contribute to the overall functioning and survival of these fascinating organisms. Choanocytes are responsible for filter feeding, capturing food particles, and have the ability to differentiate into other cell types. Pinacocytes, on the other hand, play roles in protection, gas exchange, structural support, and regeneration. While they have different functions, choanocytes and pinacocytes work together to ensure the efficient functioning and maintenance of sponges. Understanding the attributes of these cell types provides valuable insights into the biology and ecology of sponges, shedding light on the remarkable adaptations that have allowed these organisms to thrive in diverse aquatic environments.

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