Why do sponges produce gemmules

Sponge larvae are able to swim; however, adults are non-motile and spend their life attached to a substratum through a holdfast. The majority of sponges are marine, living in seas and oceans. There is, however, one family of fresh water sponges Family Spongillidae.

The great majority of the marine species can be found in ocean habitats ranging from tidal zones to depths exceeding 8, m 5. Sponges are classified within four classes: calcareous sponges Calcarea , glass sponges Hexactinellida , demosponges Demospongiae , and the recently-recognized, encrusting sponges Homoscleromorpha. The presence and composition of spicules and spongin are the differentiating characteristics between the classes of sponges.

Calcareous sponges, which have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively shallow marine waters where production of calcium carbonate is easiest.

They contain no spongin. Hemoscleromorpha sponges tend to be massive or encrusting in form and have a very simple structure with very little variation in spicule form all spicules tend to be very small.

Hexactinellid sponges have sturdy lattice-like internal skeletons made up of fused spicules of silica; they tend to be more-or-less cup-shaped. Sponge Spicule : Sponges are classified based on the presence and types of spicules they contain. Types of sponges : a Clathrina clathrus belongs to class Calcarea, b Staurocalyptu s spp. Unlike Protozoans, the Poriferans are multicellular. However, unlike higher metazoans, the cells that make up a sponge are not organized into tissues.

Therefore, sponges lack true tissues and organs; in addition, they have no body symmetry. Sponges do, however, have specialized cells that perform specific functions. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where nutrients are deposited, and leaves through a hole called the osculum. Primarily, their body consists of a thin sheet of cells over a frame skeleton. As their name suggests, Poriferans are characterized by the presence of minute pores called ostia on their body.

Since water is vital to sponges for excretion, feeding, and gas exchange, their body structure facilitates the movement of water through the sponge.

Structures such as canals, chambers, and cavities enable water to move through the sponge to nearly all body cells. Sponges are also known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding. They then either form completely new sponges or recolonize the skeletons of their parents. Most of the approximately 5,—10, known species of sponges are filter-feeders, feeding on bacteria and other food particles in the water.

However, a few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans. Other species host photosynthesizing micro-organisms as endosymbionts; these alliances often produce more food and oxygen than they consume.

Instead of true tissues or organs, sponges have specialized cells that are in charge of important bodily functions and processes. The morphology of the simplest sponges takes the shape of a cylinder with a large central cavity, the spongocoel, occupying the inside of the cylinder. Water can enter into the spongocoel from numerous pores in the body wall.

Water entering the spongocoel is extruded via a large, common opening called the osculum. However, sponges exhibit a range of diversity in body forms, including variations in the size of the spongocoel, the number of osculi, and where the cells that filter food from the water are located. The specialized cell types in sponges b each perform a distinct function. While sponges excluding the Hexactinellids do not exhibit tissue-layer organization, they do have different cell types that perform distinct functions.

Pinacocytes, which are epithelial-like cells, form the outermost layer of sponges, enclosing a jelly-like substance called mesohyl. Mesohyl is an extracellular matrix consisting of a collagen -like gel with suspended cells that perform various functions. The gel-like consistency of mesohyl acts as an endoskeleton, maintaining the tubular morphology of sponges. In addition to the osculum, sponges have multiple pores called ostia on their bodies that allow water to enter the sponge.

In some sponges, ostia are formed by porocytes: single, tube-shaped cells that act as valves to regulate the flow of water into the spongocoel. In other sponges, ostia are formed by folds in the body wall of the sponge.

Whereas pinacocytes line the outside of the sponge, choanocytes tend to line certain inner portions of the sponge body that surround the mesohyl. At this stage, the cells are able to reduce osmotic concentration but do not until favorable conditions return. Early in the germination process, the polyols are converted to glycogen, reducing the osmotic pressure and releasing the inhibition of cell division and metabolic rate. Both cell division and metabolic rate increase eventually leading to germination of the gemmules and production of a new sponge.

Abstract Sponges can be found in fresh or saltwater habitats. Publication types Review. Gemmules are resistant to drying up, they are resistant to desiccation due to weather, temperature, etc.

They are resistant to freezing, even in winters during the low temperatures. They are also resistant to anoxia, which means that they can survive even in extreme shortages of oxygen.

They can survive and lie around for long period of times, which means that they do not degrade, spoil, or rot. Gemmules resemble the endospore of bacteria. They are constituted of amoebocytes. They are surrounded by a thin layer of spicules for support and to deter the predators. These gemmules are super degrading resistant and can survive extreme environmental conditions that could even kill fully grown sponges.

The gemmules only resume growing after the environment has become less hostile. Do you know that these internal buds show resistance towards freezing and dehydration?

Yes, it is true. In fact, gemmules can even live in the absence of oxygen. The exterior gemmule layer is surrounded by endospore, further surrounded by spicule, which also protects.