Cliona

Cliona is a genus of sponges under the Phylum Porifera. The Cliona common name that is widely and commonly known is boring sponges. This is because of their unique ability to bore holes through the calcareous rocks, shells of molluscs and limestones. They are also found inside oysters where they bore through the calcareous shell surface and this leads to great losses for the pearl industry. Of the genus of Cliona sponge, one of the most abundant species or the well-known sponges that are generally found or are characteristic of the genus is Cliona celata.

Cliona Classification

As mentioned above, the Cliona are a genus of sponges that come under the Phylum of Porifera. Under Porifera, the Cliona sponge is categorized under the Demospongiae class. Further classification classifies these boring sponges (Cliona common name) in the order of Clionaida. The Cliona or the boring sponges belong to the family of Clionaidae. Under the family, the genus of sponges Cliona is categorised.

Forms of Cliona

Cliona appear generally in two distinct forms. These two forms are large and conspicuous i.e. easily visible. These two forms of the cliona sponge are (i) Boring form and (ii) Massive form. 

(i) Boring Form: This is the characteristic stage which is the main reason for the cliona common name of boring sponges. This stage signifies the developing or the growing stage of Cliona. It is recognisable as rounded protuberance, known as papillae sticking out of the calcareous and limestone surfaces. Hence, these are the forms that are usually found in oyster and mussel beds. The organisms of the species Cliona celata are generally yellow in colour and show yellow papillae sticking out of the limestone or their typical boring surfaces. These forms of Cliona celata look like yellow lemon lobes.

(ii) Massive form: This is the stage when the Cliona has outgrown the limestone, calcareous or shell surface and there is nothing much to bore i.e. it has outgrown its habitat. Out of all the Cliona sponge species mostly only the Cliona celata species is found to have these massive forms. The typical characteristics of this massive form, which is also known as ‘Raphyrus’, is that they are wall-shaped and have flattened papillae. The massive form has raised rounded ridges which are as wide as 40 cm across. Large oscules with raised rims are present on the top of the ridges. There are thick plate-like structures standing on the edge of the massive forms. Large specimens can grow up to 100 cm wide and 50 cm high. The Cliona celata are usually bright to deep yellow colour in the massive form stage and there is the darkening of the colour when taken out of water. Sometimes they are observed with red colouring around the ocular surface openings. The surface, which is quite smooth at this stage, is usually covered by tuberculate inhalant papillae. In this stage, the sponge is inflexible and has a firm consistency.

Cliona Reproduction

The Cliona celata can reproduce sexually and asexually. The Cliona sponge can either reproduce by simple mitotic cell division or release the sperm in the water in the hopes that they encounter a female egg. In other methods, the larvae of Cliona can attach themselves to molluscs, in which over time the host will die. After the death of the host, they began to grow and colonise.

Cliona Characteristics

Apart from the different forms of the Cliona, there are distinctive external and internal qualities that the boring sponges (Cliona common name) have. For example, they have evenly distributed inhalant sieve-like openings. As given above, they have a tough outer layer which is also compact. The outer surface is usually smooth and mosaic-like. The internal structure of the Cliona does not show any skeletal structure. Thus, it can be said the internal features are confusing without any remarkable differentiation. Although not much differential, the internal structure is composed of sharp pointy spicules which are of two types: megascleres and microscleres which can be viewed under a microscope. There are also apertures present in the boring stage at the tips of the papillae. In the massive form, the oscules are the apertures.   

The Cliona sponge in these two types of forms is generally found in lagoons and reefs. As per their unique quality they form big colonies and excavate calcareous surfaces to which they are attached. They can be usually found in yellow, orange and green colour. 

Lastly, an interesting characteristic of Cliona sponge is that they usually shrink when taken out of the water and can become almost invisible. The oscules which are open inside the water, when taken out disappears. This is because of the papillae contract when taken out of the water.