Phylum Porifera - Sponges/Sea Sponges

Summary

Sponges are simple aquatic invertebrates that come in a variety of shapes and sizes, with most being marine and sessile, meaning they stay in one place for life. These filter feeders draw in water through small pores, trapping food and oxygen while expelling waste and carbon dioxide. Sponges lack true organs and are supported by a skeleton made of either spongin (protein fibers) or spicules (silica or calcium carbonate). There are four main classes of sponges based on their structure: Demospongiae, Calcarea, Hexactinellida, and Homoscleromorpha. Despite their simplicity, sponges are crucial to marine ecosystems.

Takeaways

• 🌊 Sponges are simple multicellular aquatic invertebrates, mostly marine, with some in freshwater and brackish waters.
• 🪨 Most sponges are sessile, anchoring themselves to a surface like rocks, corals, or shells, though a few can move very slowly.
• 🎨 Sponges vary in size from a few millimeters to 2 meters and can have diverse shapes such as tubes, cups, fans, or encrusting forms.
• 🍽️ Sponges are primarily filter feeders, using water currents to capture plankton, detritus, and bacteria; some species are carnivorous.
• 💨 Water enters sponges through tiny pores called ostia and exits through larger openings called oscula, facilitating feeding and respiration.
• 🌀 The inner canals and chambers of sponges are lined with specialized cells called choanocytes, which trap food and generate water currents with their flagella.
• 🏗️ There are three main sponge body structures: asconoid (small, tube-shaped), syconoid (larger with radial canals), and leuconoid (complex, colonial masses).
• 🧬 Sponge skeletons are made of spongin (flexible protein fibers), spicules (hard silica or calcium carbonate), or a combination of both for support and protection.
• 📂 Sponges are classified into four main classes based on morphology and skeleton type: Demospongiae, Calcarea, Hexactinellida, and Homoscleromorpha.
• 🔬 Class Demospongiae is the largest and most diverse, Calcarea have calcium carbonate spicules, Hexactinellida are glass sponges with silica skeletons, and Homoscleromorpha are small sponges with silica spicules.

Q & A

What are sponges and which phylum do they belong to?

Sponges are simple, multicellular aquatic invertebrates that belong to the phylum Porifera.

Are all sponges marine organisms?

No, while most sponges are marine, some are found in freshwater, and a few live in brackish water.

What does it mean when sponges are described as sessile?

Being sessile means that adult sponges are firmly attached to a substrate such as rocks, corals, or shells and remain in that spot for most of their lives.

How do sponges feed and what do they consume?

Most sponges are filter feeders; they consume suspended plankton, detritus, and bacteria. A few species are carnivorous.

What is the function of choanocytes in sponges?

Choanocytes, or collar cells, line the internal canals and chambers of sponges. They trap food particles with their sticky collars and generate water currents using their flagella, aiding in feeding and gas exchange.

Describe the three main types of sponge canal systems.

The three types are: 1) Asconoid: small, tube-shaped with water flowing directly into the spongocoel and out through a single osculum. 2) Syconoid: larger tubular bodies with incurrent canals, flagellated radial canals, spongocoel, and single osculum. 3) Leuconoid: most complex, form large colonial masses with multiple chambers lined with choanocytes and multiple oscula.

What structural components make up the sponge skeleton?

Sponges have a skeleton made of spongin (soft, flexible protein fibers), spicules (hard needle-like structures of silica or calcium carbonate), or a combination of both. Some sponges lack both and have only a soft body.

How are sponges classified into different classes?

Sponges are classified based on body structure, morphology, skeletal composition, and type of spicules into four main classes: Demospongiae, Calcarea, Hexactinellida, and Homoscleromorpha.

What distinguishes Class Demospongiae from other sponge classes?

Class Demospongiae is the largest and most diverse class, comprising about 90% of all sponge species. Their skeletons can include silica spicules, spongin fibers, or both.

What is unique about Class Hexactinellida (glass sponges)?

Glass sponges have a sturdy, lattice-like internal skeleton made of fused silica spicules, giving them a glassy appearance.

Can sponges move at all despite being sessile?

Yes, some sponges can move very slowly, creeping a few millimeters per day by contracting and shortening their cells.

What role do ostia and oscula play in sponge physiology?

Ostia are tiny pores through which water enters the sponge, bringing in food and oxygen. Oscula are larger openings through which water exits, carrying away waste and carbon dioxide.