Spongilla

Spongilla is a freshwater sponge seen in slow-moving streams, lakes, and ponds. It stays attached to submerged objects like plants and rocks. When faced with tough conditions, it forms gemmules. These are special internal structures that help it survive cold, drought, or low oxygen, and later grow into a new sponge when the environment is better.

Spongilla has a thin outer cellular layer (pinacoderm: made of flattened pinacocyte cells) called the dermal layer. Its body is soft to the touch. The dermal layer contains spicules. Spicules are tiny, hard structures that give the sponge its shape and protection.

Classification of Spongilla

Spongilla is an animal that belongs to a group called Porifera. It is part of the class Demospongiae. These sponges have soft bodies supported by tiny parts called spongin fibres or spicules. Some have both. The detailed classification is:

Taxonomic Rank

Classification

Kingdom

Animalia

Phylum

Porifera

Class

Demospongiae

Order

Spongillida

Family

Spongillidae

Genus

Spongilla

The common species is Spongilla lacustris.

Physical Features and Structure

Spongilla varies in colour from light yellow to green. The green colour comes from symbiotic green algae called zoochlorellae living inside. These algae provide extra food through photosynthesis.

The sponge may be branched or unbranched. Its surface has many small pores called ostia. Water enters through these ostia and leaves through one or more larger openings called the oscula.

The skeleton is made of spongin fibres mixed with siliceous spicules. Spicules may be simple or shaped. Siliceous spicules (oxeas, microscleres) mixed with spongin fibres; shapes vary.

The sponge’s canal system is of the leuconoid type. This means it has a complex network of small branching canals and flagellated chambers. Water moves through these canals for feeding and breathing.

Water Flow and Feeding

Water enters the sponge through the ostia. It flows into incurrent canals and then into flagellated chambers lined by special cells called choanocytes. These choanocytes have flagella that create water currents and trap food particles like bacteria and small organic matter.

After passing through the chambers, water moves to the excurrent canals. It finally exits the sponge through the osculum.

Gases like oxygen move in and waste products move out by diffusion through the sponge’s body.

Habitat and Ecological Role

Spongilla grows in freshwater bodies such as ponds, lakes, and streams.
It firmly holds onto submerged logs, rocks, plants, or sticks.
This sponge filters out bacteria, protozoans, and small particles.
By filtering, Spongilla helps keep the water clean and safe.
Many small creatures rely on Spongilla for food and habitat.

Reproduction

Spongilla can reproduce both sexually and asexually.

Sexual Reproduction:

Spongilla has both eggs and sperm in the same sponge (hermaphroditic).
Sperm from one sponge enters another through ostia.
Fertilisation happens inside the sponge’s body.
Fertilised eggs develop into swimming larvae.
Larvae settle down and form new sponges.

Asexual Reproduction:

Spongilla reproduces by making buds or gemmules (the internal, resistant bodies that survive adverse conditions).
Gemmules are tough internal buds made of cells.
They can live through harsh weather like freezing or drying.
When the environment is good, gemmules grow into new sponges.

Examples of Spongilla Species

Besides Spongilla lacustris, several other species belong to this genus. Some examples include:

Spongilla alba
Spongilla arctica
Spongilla mucronata
Spongilla helvetica
Spongilla wagneri

These species vary slightly in form and habitat but share similar basic characteristics.

Importance of Spongilla

Spongilla filters out small dirt and bacteria from freshwater.
This keeps the water clean and supports life in the water.
Fish, plants, and insects all benefit from clean surroundings.
Tiny animals often live around or inside Spongilla for shelter.
Its presence shows good oxygen levels and relatively clean water.

Summary

Spongilla is a soft freshwater sponge living on submerged rocks and plants in ponds and streams. It helps keep water clean by filtering out bacteria and debris. To survive harsh conditions, it forms gemmules. This sponge can reproduce in multiple ways and supports various small creatures in its freshwater home.