Why are sponges sessile

They range in diameter from about a centimeter 0. Many species live in colonies that may be quite large. Adult sponges are sessile. This means they are unable to move from place to place. Root-like projections anchor them to solid surfaces such as rocks and reefs. Sponges have an internal skeleton that gives them support and protection.

An internal skeleton is called an endoskeleton. A sponge endoskeleton consists of short, sharp rods called spicules see Figure below. Spicules are made of silica, calcium carbonate, or spongin , a tough protein. They grow from specialized cells in the body of the sponge. Sponge Anatomy. A sponge lacks tissues and organs, but it has several types of specialized cells. Sponges are filter feeders. They pump water into their body through their pores. The water flows through a large central cavity called the spongocoel see Figure above.

As the water flows by, specialized collar cells which are also known as choanocytes filter out food particles such as bacteria. Collar cells have tiny hairs that trap the particles. They also have a flagellum that whips the water and keeps it moving. Once the food is trapped, the collar cells digest it see Figure below. Cells called amebocytes also help digest the food. They distribute the nutrients to the rest of the body as well.

Finally, the water flows back out of the body through an opening called the osculum. This helps them to move their young into new territories and to better evolve. When adult sponges sexually reproduce they produce free-swimming larvae every time.

No doubt in that process. Although the sponges are sessile as a whole being attached to the substratum, but the cells in the body of the sponges are not sessile. They digest the whole prey animal by capturing with their spicules, and later their body cells start to envelop and slowly migrate around the helpless prey and digestion starts to take place all extracellularly.

This is achieved due to the amoeboid movement of the body cells, showcasing the cell mobility only. Sponges are sessile because they remain attached to their hard substratum by means of their holdfast located at their basal body part which has complex tangles of root-like outgrowths that help them anchor firmly to the substratum.

Holdfast is also termed as Adhesive disc of the sponges. It is composed of a large number of root-like filamentous, stolon-like structures covered with delicate perisac, which extend from the basal region of the sponge and serve as holdfast for adhesion.

Sponges fall under the Phylum Porifera of the Animal Kingdom. And according to their Phylum, it has been characterized that sponges can be either solitary or colonial, but all are sessile in nature in their adult forms.

Sponges have been defined as sessile metazoans multi-celled immobile animals , that can remold their bodies and reshape it whenever required. They can remold their bodies because of their most types of cells that can move within their bodies, with a few types of the cells having the capability to transform from one type to another. The adult sponges or more broadly said that sponges are sessile and they cannot move around at all.

They have a cellular level of body organization and lack the presence of well-developed locomotory organs. If gametes sex cells; either sperm or egg from the same species meet, they form a larval sponge. After a period of planktonic drifting, the larva settles to a suitable location on the bottom and grows into an adult sponge. The drifting larval stage means that sponges can colonize new locations, even though as adults they remain attached in a sessile lifestyle. Freshwater sponges can live in areas that are subject to cyclical wet and dry periods.

They have a special strategy to help them deal with these harsh conditions. A gemmule is a small, encysted bud that can tolerate being dried out for a long period of time. When the gemmule is exposed to water, it can resume development as a sponge. Organisms that can undergo a phase where they are dormant to survive harsh conditions are said to be in cryptobiosis from the root words crypto meaning hidden and bio meaning life , because they do not appear to be living.

In reality, these organisms are in a state of suspended animation. See more information about cryptobiosis at Weird Science: Cryptobiosis. Large sponges have many small chambers where other organisms can live symbiotically Fig.

Although the sponges rarely benefit from this arrangement, they do not seem to suffer harm, and their symbionts , the organisms that live in them, do gain benefits. This type of symbiosis is called commensalism. For example, certain species of shrimp live in the chambers of sponges and feed on the particles that are flowing through the chambers. This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password.

Main menu About this Site Table of Contents. Home Biological Invertebrates Phylum Porifera. Phylum Porifera. MS-LS Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.

MS-LS Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms. MS-LS Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.

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.