Porifera Circulatory System

Instructor: Taormina Lepore

Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology.

Explore the water-based circulatory system of phylum Porifera. Poriferans are aquatic animals, also known as sponges. Sponges don't have a true circulatory system, but accomplish the goals of nutrient and gas exchange through simple water flow.

Introduction to the Poriferan Body Plan

When you think of the word 'sponge', you may not immediately think of animals. But the phylum Porifera (the 'pore bearers'), also known as sponges, is a group of porous animals that live worldwide in our Earth's oceans and in a few freshwater environments.

Sponges have a simple body plan. Unlike many animals, they do not have a nervous system, muscular system, or even a true circulatory system.

Sponge body plan.
sponge body plan

There are a few types of sponge body plans and each one has a hollow body cavity, or spongocoel (SPUN-geo-seel), through which water and particulates circulate. Sponges push water into their body cavity using special flagellated collar cells, or choanocytes, which wave back and forth and move water in through many small pores, called porocytes. Think of the pores you see in a kitchen sponge; the concept is pretty similar. The porocytes dot the outer surface, or pinacoderm (also epidermis), of the sponge.

Sponges have a top opening, known as an osculum, through which the water then passes.

The sponge's body is made up of thin epithelial tissue that is great for absorbing things from the surrounding environment. It's the same basic kind of tissue that we have in our lungs for absorbing tiny molecules like oxygen. Connecting these epithelial cells is a web of loose connective tissue, or mesohyl, as well as tiny shards of glass-like silicon dioxide, or calcium carbonate, known as spicules. Flexible amoebocyte cells also partake in nutrient and oxygen absorption directly from the environment.

Poriferan body plans allow direct gas and nutrient exchange through their aqueous, watery surroundings. It is almost as if each individual poriferan cell carries out the functions of nutrient absorption, oxygen intake, and carbon dioxide expelling separately, like each cell were part of a colony of the larger animal.

But without a heart, veins, arteries, or blood to pump through them, how can we describe a cohesive poriferan circulatory system?

The simple answer has to do with where sponges live: in the water. Water is the basis for the circulation of nutrients and food particles throughout the poriferan body cavity.

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