Which phylum do sponges belong to

Simple vase-like sponges have a single large top opening, called the osculum through which water leaves the sponge. Most compound sponges have many oscula all over the body of the sponge. The oscula are surrounded by cells and are bigger than the ostia. Epithelial cells around the osculum can contract enough to close the opening, but the process is slow up to several minutes. The inner surface of the sponge is lined with cells called collar cells , also known as choanocytes Fig. The collar is made of fine tubes surrounding a long whiplike thread called a flagellum.

As flagella plural of flagellum in the collar cells move back and forth, they create a current of water that moves into the ostia and out the osculum.

Several gallons of water can circulate through a fist-sized sponge in a single day, bringing in tiny food particles such as suspended bacteria, bits of plant and animal matter, and tiny drifting planktonic organisms. As the water circulates, the fine tubes of the collar cells filter out the food particles and take them into the cells for digestion.

For this reason sponges are described as filter feeders. Between the outer surface of epithelial cells and the inner surface of collar cells is a jellylike material. In this jelly are the structures that support the sponge. There are also free-moving cells called amoebocytes Fig. During feeding, some of the particles taken in by the collar cells are passed on to amoebocytes, which carry them to other cells of the sponge. Several kinds of amoebocytes serve special functions, like producing the sponge skeleton, digesting and transferring nutrients, or reproducing themselves.

The skeletal elements of the sponge are produced by the amoebocytes. The amoebocytes produce spongin , the soft fiber that forms natural bath sponges.

These sponges feel soft and springy to the touch because they have soft skeletons made of flexible fibrous spongin. Other sponges have a stiff skeleton that feels prickly because it is made of hard, sliver-like spicules , which are also built by the amoebocytes. Some sponges have both spicules and spongin and feel both prickly and flexible. Many species of sponges can be identified by the shape and composition of their spicules Fig. Siliceous sponges have spicules made of silicon.

Calcareous sponges have spicules made of calcium. Spicules also have many shapes and sizes. While some sponges have no spicules, others have so many that they look and feel like lacy skeletons of glass Fig. All cells in a sponge are in contact with or near to seawater.

Because each cell exchanges oxygen and carbon dioxide and discharges waste products into the seawater, a sponge has no respiratory, circulatory, or excretory system. Sponges can reproduce either asexually or sexually. Asexually reproduction without eggs and sperm often occurs by budding , similar to growing a new branch on a tree. Cells on the side or base of the parent begin to bulge out and form a new organism.

The buds may remain attached to the parent, or they may detach and settle down nearby to form a separate organism. Sponges also reproduce sexually when specialized gametocyte cells produce sperm and eggs. Sponges undergo synchronous spawning and eject sperm and egg cells into the water. 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. 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.

The structure of a choanocyte is critical to its function, which is to generate a water current through the sponge and to trap and ingest food particles by phagocytosis. Note that there is a similarity in appearance between the sponge choanocyte and choanoflagellates Protista.

This similarity suggests that sponges and choanoflagellates are closely related and probably share a recent, common ancestry.

The cell body is embedded in mesohyl. The cumulative effect of the flagella from all choanocytes aids the movement of water through the sponge: drawing water into the sponge through the numerous ostia, into the spaces lined by choanocytes, and eventually out through the osculum or osculi. Meanwhile, food particles, including waterborne bacteria and algae, are trapped by the sieve-like collar of the choanocytes, slide down into the body of the cell, are ingested by phagocytosis, and become encased in a food vacuole.

Finally, choanocytes will differentiate into sperm for sexual reproduction; they will become dislodged from the mesohyl, leaving the sponge with expelled water through the osculum. The second crucial cells in sponges are called amoebocytes or archaeocytes , named for the fact that they move throughout the mesohyl in an amoeba-like fashion. Amoebocytes have a variety of functions: delivering nutrients from choanocytes to other cells within the sponge; giving rise to eggs for sexual reproduction which remain in the mesohyl ; delivering phagocytized sperm from choanocytes to eggs; and differentiating into more-specific cell types.

Some of these more-specific cell types include collencytes and lophocytes, which produce the collagen-like protein to maintain the mesohyl; sclerocytes, which produce spicules in some sponges; and spongocytes, which produce the protein spongin in the majority of sponges. These cells produce collagen to maintain the consistency of the mesohyl. Sponges are sessile, feed by phagocytosis, and reproduce sexually and asexually; all major functions are regulated by water flow diffusion.

Sponges, despite being simple organisms, regulate their different physiological processes through a variety of mechanisms. These mechanisms regulate metabolism, reproduction, and locomotion. Sponges lack complex digestive, respiratory, circulatory, reproductive, and nervous systems.

Their food is trapped when water passes through the ostia and out through the osculum. Bacteria smaller than 0. Particles that are larger than the ostia may be phagocytized by pinacocytes. In some sponges, amoebocytes transport food from cells that have ingested food particles to those that do not. For this type of digestion, in which food particles are digested within individual cells, the sponge draws water through diffusion. The limit of this type of digestion is that food particles must be smaller than individual cells.

All other major body functions in the sponge gas exchange, circulation, excretion are performed by diffusion between the cells that line the openings within the sponge and the water that is passing through those openings. All cell types within the sponge obtain oxygen from water through diffusion.

Likewise, carbon dioxide is released into seawater by diffusion. In addition, nitrogenous waste produced as a by-product of protein metabolism is excreted via diffusion by individual cells into the water as it passes through the sponge.