Different Types of Sponges

These organisms that do not have a definite form Their body is delicate and filled with a soft substance known as mesohyl resembling jellies. Being aquatic creatures, their body allows absorbing fluids, water, oxygen and food, with relative ease than other animals.

An interesting point to note about sponges is that they don't have a digestive, circulatory or nervous system. These organisms extract food out of water entering their body through pores. Since the sponges need some kind of substrates like rocks to remain stable in the sea, they are also termed as sessile - sedentary organisms. There are more than 7000 sponge species and possibly more would be discovered in the future. The major forms include encrusting-sheets, mounds, tubes and upright-sheets.

Sponges are known to feed on bacteria however, in some cases microbes live inside their body as endosymbionts - an organism living in symbiosis with its host, and inside its body. Some of thes have also turned carnivores where food is scarcely available.

Types of Sponges
This organism is primarily classified on the basis of characteristic structures, for example spicules, used by them to reinforce the mesohyl. Different types of sponges or classes formed in the process of reinforcing are explained below.

Calcarea or Calcareous Sponges
Classification of sponges is based on the reinforcing structures being used. Here, the structures in case of calcareous sponges are known as spicules. They form the skeleton of calcareous sponges and are made up of calcium carbonate. These are just about 10 cm in length, however, they encompass all the different types of body plans such as

• Asconoid (Indefinite shape)
• Syconoid (Tubular body)
• Leuconoid (Flagellated chambers)

Demosponges
These are made of spicules just like the calcareous sponges; in this type however, spicules are formed of fibers produced from a protein called 'spongin'. These are biggest of al and form 90% of the total number. Demosponges live in both warm and cold areas of the sea. They reproduce sexually as well as asexually. These organisms exhibit a huge variety in form and are much more diversified than any other class. Asexual reproduction takes place by means of gemmules and budding. Gemmules are internal buds capable of development in favorable conditions; they are otherwise dormant. According to Mr. Gordon Love, a scientist working in California University, demosponges came into existence as early as 635 million years ago i.e. in the Neoproterozoic era.

Glass Sponges
These are not very common as they can mostly be found at great depths in oceans. Their body is cup-shaped, and spicules made up of siliceous compounds. Glass sponges live for 15,000 years and they are the longest living creatures on earth. These are very much sensitive to external stimuli and thereby, capable of reacting quickly owing to electric impulse they generate.

There is another criterion to classifying glass sponges further i.e. their ability to build reefs. Sponges are therefore, classified as follows.

• Reef Building Sponges: These are made up of funnel-shaped Heterochone calyx or Finger Goblet Sponge, growing 1.5m in height. It is found in shades of yellow and white color. Other two species of reef-builders are Aphrocallistes vastus also known as Cloud Sponge and the Farrea occa. The unique characteristic of Cloud sponges is their mitten-like outgrowth. These are funnel-shaped and 2 m in height. Farrea occa is the biggest of these three and it has 15 m height.
• Non-reef Building Sponges: There are four species of non-reef builders - white in color with height about 50 cm. Staurocalyptus dowlingi, Acanthascus platei, Acanthascus cactus and Rabdocalyptus dawsoni are the different non-reef builders.

These sponge species create different forms of reefs thus, increasing the biological diversity in oceans. Reefs are beneficial in maintaining the population of fish and other marine creatures. These organisms lead a long life but are known to grow slowly. Efforts are being taken worldwide to save them. Experts suggest that regions inhabited by sponges need to be declared as marine protected areas (MPA). It is our collective responsibility to preserve this neglected, but important form of life.