Sponges are aquatic animals with simple structures. Like the name suggests, they have sponge-like bodies. Learn more about these organisms from this article.

Characteristics Of Sponges

You might be familiar with sponge, the soft porous material that is of great use. But, how many of you know that there is a group of marine animals with the same name and almost similar built? Yes, sponges are a group of animals which belong to the phylum Porifera, the name which literally means "pore bearer". As the name suggests, they are multicellular organisms with porous bodies. These pores allow water to circulate through them. It is this water canal system that allows sponges to survive and thus, it forms the lifeline for these organisms. They are simple organisms without any complex systems such as nervous, digestive or circulatory systems. Instead, they rely on the water canal system for all their life processes like obtaining food, oxygen supply, removal of wastes etc. There are many more interesting characteristics to learn about sponges. Read the following section for further details about sponges. 
 
General Characteristics Of Sponges

 

Morphological Characteristics

  • Sponges are simple animals with uncomplicated structures. They have a porous structure which is similar to the normal sponge we use. They derived their name from their porous body.
  • They have many openings called ostia, through which water enters their bodies. The single, large osculum allows water to flow out of the body.
  • Sponges occur in a wide range of colors. Also, they differ in size from species to species. The barrel sponge, a tropical species, can grow enormous enough to fit an adult man inside it.
  • Dried skeletons of sponges (spicules) are used in kitchens and bathrooms for cleaning and exfoliation purposes.
Anatomical Characteristics
  • Sponges are multicellular organisms with a certain level of cell differentiation.
  • They do not have tissues or organs to carry out specialized physiological functions like respiration, digestion etc.
  • Sponges have internal skeletal structures made of spongin (modified type of collagen) and/or or spicules. These skeletal structures are made of calcium carbonate or silica.
  • Sponges have a jelly like substance called mesohyl which is sandwiched between two layers of cells.
  • Sponges consist of flagellated cells called choanocyets. It is the wave like movements of the flagella of these cells that drives water through the body of the sponges.
Physiological Characteristics
  • Sponges depend on their body’s water canal system for their entire physiology. Water entering the body through the ostia brings food and oxygen, which are utilized by the organism. The waste materials are excreted through the canal and are eliminated by the water flowing out of the body.
  • Sponges feed on microscopic organisms like bacteria, protozoa and other small organisms in water.
  • Some species of sponges allow photosynthesizing microorganisms inside their body. Photosynthesis carried out by these organisms produces food and gives out oxygen during the process and hence, this symbiotic relationship benefits sponges with more oxygen and food than they actually consume.
  • Some species of sponges, which live in food-scarce environment, show changes in food habits. They feed on small crustaceans like scuds, water fleas etc.
  • Sponges have remarkable regenerative capacity. They can regenerate from any small fragments that break off from the main organism for any reason.
  • Adult sponges are sessile i.e., they remains attached to a substratum and are not capable of any movement. However, some species, especially the freshwater forms, are capable of amoeba like movements.
  • Unlike other animals, sponges do not have a complex immune system. However, some species are capable of rejecting the grafts from other species while they accept other grafts from the same species. This rejection occurs due to the presence of ‘grey cells’ which are found in some marine species. 
  • Sponges usually live for a few years. However, some tropical species can survive for more than 200 years.
  • Though sponges lack neurons and nervous system, they show certain coordinated activities. The main contraction of the body, which results in expelling water and excess sediments found blocking the water canal, is carried out in a coordinated manner. 
Reproductive Characteristics
  • Most sponges are hermaphroditic which means that they have both sexes in one organism. However, they cannot produce two types of gametes in a single spawn. Some of them produce male gametes while others produce female gametes.
  • Most of the sponges reproduce sexually. They release sperm cells (male gametes) to the water canal which are then transported out of the body by water pumped out through the osculum. Some species release their ova (female gametes) into water whereas some retain them within their body. The fertilized eggs form larvae which are capable of swimming. These larvae then settle on a favorable substratum and start growing there.
  • Some species of sponges reproduce by budding. This kind of asexual reproduction takes place when the situations are not favorable or when the temperature drops significantly. The gemmules (buds) formed by budding are capable of surviving in unfavorable conditions. When the conditions become favorable, these gemmules either form a new sponge or recolonize the skeletons of the parent sponges. 
Sponges are one of the most primitive forms of life. They are simple organisms with uncomplicated systems. However, skeleton of these aquatic animals are used for a variety of purposes. The characters listed above are generic to the animals; it may show variations according to the species.  





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