PHYLUM PORIFERA: SPONGES
PHYLUM PORIFERA: SPONGES Characteristics of Phylum Porifera: o Multicellular; body an aggregation of several types of cells differentiated for various functions, some of which are organized into incipient tissues with some integration o Body with pores (osita), canals, and chambers that form a unique system of water currents on which sponges depend for food and oxygen o Mostly marine; all aquatic o Radial symmetry or none o Outer surface of plat pinacocytes; most interior surfaces lined with flagellated collar cells (choanocytes) that create water currents; a gelatinous protein matrix called mesohyl contains amebocytes of various types and skeletal elements o Skeletal structure of fibrillar collagen (a protein) and calcareous or siliceous crystalline spicules, often combined with variously modified collagen (sponging) o No organs or true tissues; digestion intracellular; excretion and respiration by diffusion o Reactions to stimuli apparently local and independent in cellular sponges, but electrical signals in syncytial glass sponges; nervous system probably absent o All adults sessile and attached to substratum o Asexual reproduction by buds or gemmules and sexual reproduction by eggs and sperm; free-swimming flagellated larvae in most The Origins of Multi-cellularity: While sponges are multicellular, their organization is quite distant from other metazoans. A sponge body is an assembly of cells embedded in an extracellular matrix and supported by a skeleton of minute needlelike spicules and protein. Origin of Metazoa (Animals): Choanoflagelletes are solitary/colonial aquatic eukaryotes, with each cell carrying a flagellum surrounded by a collar of microvilli. Beating of the flagellum draws water into the collar, where microvilli collect tiny particles. Many choanoflagelletes are sessile and attached to hard surfaces. Choanoflagellete cells strongly resemble sponge feeding cells called choanocytes. Adult sponges have simple bodies; they are aggregations of several different cell types, including choanocytes, held together by an extracellular matrix. Most sponge bodies are not symmetrical, but some
appear radial. A sponge body has neither a mouth nor a digestive system. Phylum Porifera: Sponges: Sessile sponges draw food and water into its body instead. A sponge uses a flagellated ‘collar cell’, the choanocytes to move water. The beating of many tiny flagella, one per choanocyte, draws water past each cell, bringing in food and oxygen, as well as carrying away wastes. The sponge body is designed as an efficient aquatic filter for removing suspended particles from the surrounding water. Although their embryos are free swimming, adult sponges are always attached. The skeletal framework of a sponge can be fibrous and/or rigid. When present, the rigid skeleton consists of calcerous or siliceous support structures called spicules. The fibrous part of the skeleton comes from collagen protein fibrils in the intercellular matrix of all sponges. Collagen comes in several types of differing in chemical composition and form. One form of collagen is spongin. The presence of photosynthetic organisms inside the sponge led some to propose that spicules were able to transmit ight into the body. 3 classes of porifera: - Calcera - Hexactinellida - Demospongiae Calcera have spicules of crystalline CaCO3 with 1, 3 and 4 rays. Hexactinellida are glass sponges with 6-rayed siliceous spicules, where the 6 rays are arranged in 3 planes at right angles to each other. Demospongiae have a skeleton of siliceous spicules that develop around an axial filament, or sponging fibers, or both. A fourth clase, Homoscleromorpha, contains sponges that lack a skeleton/have siliceous spicules without an axial filament. Form and Function: Sponges feed primarily by collecting suspended particles from water pumped through internal canal systems. Water enters canals through a multitude of tiny incurrent pores in the outer layer of cells, a pinacoderm. Incurrent pores = dermal pores. Inside the body, water is directed past the choanocytes, where food particles are collected on the choanocytes collar. The collar comprises
many fingerlike projections, called microvilli. The use of the collar as a filter is one form of suspension feeding. The smallest particles, accounting for about 80% of the particulate organic carbon, are taken into choanocytes by phagocytosis. Choanocytes may acquire protein molecules by pinocytosis. Two other cell types, pinacytes and archaetocytes, play a role in sponge feeding. There are 3 main designs for a sponge body, differing in placement of the choanocytes. In the simplest as asconoid system, the choanocytes lie in a large chamber called the spongocoel. In the syncoid system, the choanocytes lie in canals. In the leuconoid system, the choanocytes occupy distinct chambers. Types of Canal Systems: Asconoids: Asconoid sponges draw water inside through dermal pores by the beating of large numbers of flagella on the choanocytes. These choanocytes line the internal cavity called the spongocoel. As the choanocytes filter the water and extract food particles from it, used water is expelled through a single layer osculum. This design has distinct limitations because choanocytes line the spongocoel and can collect food only from water directly adjacent to the spongocoel wall. Asconoids are small and tube-shaped, because if the spongocoel were large, most of the water and food in its central cavity would lie in ‘dead cavity’ inaccessible to choanocytes. Asocnoids occur only in class Calcera. Synconoids: Synconoid sponges have a tubular body and single osculum, but the body wall, which is really the spongocoel lining, is thicker and more complex than that of asconoids. The lining has been folded outward to make choanocyte-lined canals. Folding the body wall into canals increases the surface area of the wall and thus, increases the surface area covered by choanocytes. Most of the water in a canal is accessible to choanocytes. Water enters the syconoid body through dermal ostia that lead into incurrent canals. It then filters through tiny openings, or prosopyles, into the radial canals. Here food is ingestedby the choanocytes. The beating of the choanocytes’ flagella forces the used water through internal pores, or apopyles, into the spongocoel. Food capture does not occur in the syconoid spongocoel, so it is lined with epithelial-type cells rather than the flagellated celles present in asconoids. After the used water reaches the spongocoel, it exits the body through an osculum. During development, syconoid sponges pass through an asconoid stage, following which flagellated canals form by evagination of the body
wall. Syconoids occur in class Calera and in some members of class Hexactinellida. Leuconoids: Leuconoids have the most complex organization and permits an increase in sponge size. The surface area of the food-collecting regions with choanocytes is greatly increased; here the choanocytes line the walls of small chambers where they can filter all the water present. The sponge body has a lot of these tiny chambers. Clusters of flagellated chambers are filled from incurrent canals and discharge water into excurrent canals that eventually lead to an osculum. After food is removed, the used water is pooled to form an exit stream. The exit stream, containing the entire volume of water that entered the sponge over the myriad incurrent canals, leaves the sponge through an exit pore. Most species within class Calcera. Types of Cells in the Sponge Body: Sponge cells are loosely arranged in a gelatinous extracellular matrix called mesohyl, or mesenchyme. The mesohyl is the connective tissue of sponges; in it are found various fibrils, skeletal elements, and ameboid cells. Respiration and excretion occur by diffusion in each cell and, in freshwater sponges, excess water is expelled via contractile vacuoles in archaeocytes and choanocytes. Incurrent pores can close in response to heavy sediment in the water/other conditions that reduce efficiency of feeding. The most common response is closure of the oscula. Choanocytes, which line flagellated canals and chambers, are ovalshaped cells with one end embedded in mesohyl and the other exposed. The exposed end bears a flagellum surrounded by a collar. The collar comprises adjacent microvilli, connected to each other by delicate microfibrils, forming a fine filtering device for staining food particles from water. The beating flagellum pulls water through the sieve-like collar and forces water out through the open top of the collar. Particles too large to enter the collar become trapped in secreted mucus and slide down the collar to the base, where they are phagocytized by the cell body. Larger particles already have been excluded by the small size of the dermal pores and prosopyles. Food engulfed by the cells is passed to a neighbouring aracheocyte for digestion. Thus, digestion is entirely intracellular, so there is no extracellular gut cavity.
Archaeocytes are ameboid cells that move in the mesohyl. They phagocytize particles at the pinocoderm and receive particles for digestion from choanocytes. They can differentiate into any of the other types of more specialized cells in the sponge: - Sclerocytes secrete spicules - Spongocytes secrete the sponging fibers of the skeleton - Collencytes secrete fibrillar collagen - Lophocytes secrete large quantities of collagen Pinacocytes are thin, flat, epithelial-like cells that cover the exterior surface and some interior surfaces of a sponge. Some are T-shaped with their cell bodies extending into the mesohyl. A layer of pinacocytes is not part of the epithelium because a basal membrane is lacking in most sponges. Pinacocytes can ingest food particles by phagocytosis at the sponge surface. They are contractile and help to regulate surface area of a sponge. Some pinacocytes are modified as contractile myocytes which are usually arranged in circular bands around oscula/pores, where they help to regulate rate of water flow. Sexual reproduction: In sexual reproduction, most sponges are monoecious (have both male and female sex cells in one individual). Sperm sometimes arise from transformation of choanocytes. In Calcera and some Demospongiae, oocytes also develop from choanocytes; in other demosponges gametes are derived from archaeocytes. Most sponges are viviparous; after fertilization, the zygote is retained in and derived nourishment from its parent, and a ciliated larva is released. Sperm are released into the water by one individual and taken into the canal system of another. These choanocytes phagocytize the sperm; then the choanocytes transform into carrier cells, which carry the sperm through mesohyl to oocytes. Other sponges are oviparous, and both oocytes and sperm are expelled into the water. The free-swimming larva of most sponges is a solid-bodies parenchymula, although 6 other larval types exist, and some sponges exhibit direct development. The outwardly directed, flagellated cells of the parenchyma migrate to the interior after the larva settles and become choanocytes in the flagellated chambers.
Classification of Phylum Porifera: Class Calcarea: Have spicules of calcium carbonate that often form a fringe around the osculum (main water outlet); spicules needle-shaped or three or four rayed; all three types of canal systems (asconoid, syconoid, leuconoid) represented; all marine. Class Hexactinellida: Have 6-rayed, siliceous spicules extending at right angles from a central point; spicules often united to form network; body often cylindrical or funnel-shaped; flagellated chambers in simple syconoid or leuconoid arrangement habitat mostly deep water; all marine Class Demospongiae: Have siliceous spicules that are not 6-rayed, or sponging, or both; leuconoid-type canal systems; one family found in freshwater; all others marine. Class Calcera: Calera are calcareous sponges, so called because their spicules are composed of calcium carbonate. Spicules are straight (monaxons) or have 3-4 rays. They may be asconoid, leuconoid, or syconoid. Class Hexactinellida: Glass sponges form Class Hexactinellida. Nearly all are deep-sea forms that are collected by dredging. Most are radially symmetrical, with vase or funnel shaped bodies usually attached by stalks of root spicules to a substratum. Their distinguishing features include a skeleton of 6rayed siliceous spicules that are commonly bound together into a network forming a glass-like structure. Class Demospongiae: Spicules are siliceous, but are not 6-rayed. Spicules may be bound together by sponging, or may be absent. So-called bath sponges, Spongia and Hippospongia, belong to the group called horny sponges, which have spongin skeletons and lack siliceous spicules entirely.
appear radial. A sponge body has neither a mouth nor a digestive system. Phylum Porifera: Sponges: Sessile sponges draw food and water into its body instead. A sponge uses a flagellated ‘collar cell’, the choanocytes to move water. The beating of many tiny flagella, one per choanocyte, draws water past each cell, bringing in food and oxygen, as well as carrying away wastes. The sponge body is designed as an efficient aquatic filter for removing suspended particles from the surrounding water. Although their embryos are free swimming, adult sponges are always attached. The skeletal framework of a sponge can be fibrous and/or rigid. When present, the rigid skeleton consists of calcerous or siliceous support structures called spicules. The fibrous part of the skeleton comes from collagen protein fibrils in the intercellular matrix of all sponges. Collagen comes in several types of differing in chemical composition and form. One form of collagen is spongin. The presence of photosynthetic organisms inside the sponge led some to propose that spicules were able to transmit ight into the body. 3 classes of porifera: - Calcera - Hexactinellida - Demospongiae Calcera have spicules of crystalline CaCO3 with 1, 3 and 4 rays. Hexactinellida are glass sponges with 6-rayed siliceous spicules, where the 6 rays are arranged in 3 planes at right angles to each other. Demospongiae have a skeleton of siliceous spicules that develop around an axial filament, or sponging fibers, or both. A fourth clase, Homoscleromorpha, contains sponges that lack a skeleton/have siliceous spicules without an axial filament. Form and Function: Sponges feed primarily by collecting suspended particles from water pumped through internal canal systems. Water enters canals through a multitude of tiny incurrent pores in the outer layer of cells, a pinacoderm. Incurrent pores = dermal pores. Inside the body, water is directed past the choanocytes, where food particles are collected on the choanocytes collar. The collar comprises
many fingerlike projections, called microvilli. The use of the collar as a filter is one form of suspension feeding. The smallest particles, accounting for about 80% of the particulate organic carbon, are taken into choanocytes by phagocytosis. Choanocytes may acquire protein molecules by pinocytosis. Two other cell types, pinacytes and archaetocytes, play a role in sponge feeding. There are 3 main designs for a sponge body, differing in placement of the choanocytes. In the simplest as asconoid system, the choanocytes lie in a large chamber called the spongocoel. In the syncoid system, the choanocytes lie in canals. In the leuconoid system, the choanocytes occupy distinct chambers. Types of Canal Systems: Asconoids: Asconoid sponges draw water inside through dermal pores by the beating of large numbers of flagella on the choanocytes. These choanocytes line the internal cavity called the spongocoel. As the choanocytes filter the water and extract food particles from it, used water is expelled through a single layer osculum. This design has distinct limitations because choanocytes line the spongocoel and can collect food only from water directly adjacent to the spongocoel wall. Asconoids are small and tube-shaped, because if the spongocoel were large, most of the water and food in its central cavity would lie in ‘dead cavity’ inaccessible to choanocytes. Asocnoids occur only in class Calcera. Synconoids: Synconoid sponges have a tubular body and single osculum, but the body wall, which is really the spongocoel lining, is thicker and more complex than that of asconoids. The lining has been folded outward to make choanocyte-lined canals. Folding the body wall into canals increases the surface area of the wall and thus, increases the surface area covered by choanocytes. Most of the water in a canal is accessible to choanocytes. Water enters the syconoid body through dermal ostia that lead into incurrent canals. It then filters through tiny openings, or prosopyles, into the radial canals. Here food is ingestedby the choanocytes. The beating of the choanocytes’ flagella forces the used water through internal pores, or apopyles, into the spongocoel. Food capture does not occur in the syconoid spongocoel, so it is lined with epithelial-type cells rather than the flagellated celles present in asconoids. After the used water reaches the spongocoel, it exits the body through an osculum. During development, syconoid sponges pass through an asconoid stage, following which flagellated canals form by evagination of the body
wall. Syconoids occur in class Calera and in some members of class Hexactinellida. Leuconoids: Leuconoids have the most complex organization and permits an increase in sponge size. The surface area of the food-collecting regions with choanocytes is greatly increased; here the choanocytes line the walls of small chambers where they can filter all the water present. The sponge body has a lot of these tiny chambers. Clusters of flagellated chambers are filled from incurrent canals and discharge water into excurrent canals that eventually lead to an osculum. After food is removed, the used water is pooled to form an exit stream. The exit stream, containing the entire volume of water that entered the sponge over the myriad incurrent canals, leaves the sponge through an exit pore. Most species within class Calcera. Types of Cells in the Sponge Body: Sponge cells are loosely arranged in a gelatinous extracellular matrix called mesohyl, or mesenchyme. The mesohyl is the connective tissue of sponges; in it are found various fibrils, skeletal elements, and ameboid cells. Respiration and excretion occur by diffusion in each cell and, in freshwater sponges, excess water is expelled via contractile vacuoles in archaeocytes and choanocytes. Incurrent pores can close in response to heavy sediment in the water/other conditions that reduce efficiency of feeding. The most common response is closure of the oscula. Choanocytes, which line flagellated canals and chambers, are ovalshaped cells with one end embedded in mesohyl and the other exposed. The exposed end bears a flagellum surrounded by a collar. The collar comprises adjacent microvilli, connected to each other by delicate microfibrils, forming a fine filtering device for staining food particles from water. The beating flagellum pulls water through the sieve-like collar and forces water out through the open top of the collar. Particles too large to enter the collar become trapped in secreted mucus and slide down the collar to the base, where they are phagocytized by the cell body. Larger particles already have been excluded by the small size of the dermal pores and prosopyles. Food engulfed by the cells is passed to a neighbouring aracheocyte for digestion. Thus, digestion is entirely intracellular, so there is no extracellular gut cavity.
Archaeocytes are ameboid cells that move in the mesohyl. They phagocytize particles at the pinocoderm and receive particles for digestion from choanocytes. They can differentiate into any of the other types of more specialized cells in the sponge: - Sclerocytes secrete spicules - Spongocytes secrete the sponging fibers of the skeleton - Collencytes secrete fibrillar collagen - Lophocytes secrete large quantities of collagen Pinacocytes are thin, flat, epithelial-like cells that cover the exterior surface and some interior surfaces of a sponge. Some are T-shaped with their cell bodies extending into the mesohyl. A layer of pinacocytes is not part of the epithelium because a basal membrane is lacking in most sponges. Pinacocytes can ingest food particles by phagocytosis at the sponge surface. They are contractile and help to regulate surface area of a sponge. Some pinacocytes are modified as contractile myocytes which are usually arranged in circular bands around oscula/pores, where they help to regulate rate of water flow. Sexual reproduction: In sexual reproduction, most sponges are monoecious (have both male and female sex cells in one individual). Sperm sometimes arise from transformation of choanocytes. In Calcera and some Demospongiae, oocytes also develop from choanocytes; in other demosponges gametes are derived from archaeocytes. Most sponges are viviparous; after fertilization, the zygote is retained in and derived nourishment from its parent, and a ciliated larva is released. Sperm are released into the water by one individual and taken into the canal system of another. These choanocytes phagocytize the sperm; then the choanocytes transform into carrier cells, which carry the sperm through mesohyl to oocytes. Other sponges are oviparous, and both oocytes and sperm are expelled into the water. The free-swimming larva of most sponges is a solid-bodies parenchymula, although 6 other larval types exist, and some sponges exhibit direct development. The outwardly directed, flagellated cells of the parenchyma migrate to the interior after the larva settles and become choanocytes in the flagellated chambers.
Classification of Phylum Porifera: Class Calcarea: Have spicules of calcium carbonate that often form a fringe around the osculum (main water outlet); spicules needle-shaped or three or four rayed; all three types of canal systems (asconoid, syconoid, leuconoid) represented; all marine. Class Hexactinellida: Have 6-rayed, siliceous spicules extending at right angles from a central point; spicules often united to form network; body often cylindrical or funnel-shaped; flagellated chambers in simple syconoid or leuconoid arrangement habitat mostly deep water; all marine Class Demospongiae: Have siliceous spicules that are not 6-rayed, or sponging, or both; leuconoid-type canal systems; one family found in freshwater; all others marine. Class Calcera: Calera are calcareous sponges, so called because their spicules are composed of calcium carbonate. Spicules are straight (monaxons) or have 3-4 rays. They may be asconoid, leuconoid, or syconoid. Class Hexactinellida: Glass sponges form Class Hexactinellida. Nearly all are deep-sea forms that are collected by dredging. Most are radially symmetrical, with vase or funnel shaped bodies usually attached by stalks of root spicules to a substratum. Their distinguishing features include a skeleton of 6rayed siliceous spicules that are commonly bound together into a network forming a glass-like structure. Class Demospongiae: Spicules are siliceous, but are not 6-rayed. Spicules may be bound together by sponging, or may be absent. So-called bath sponges, Spongia and Hippospongia, belong to the group called horny sponges, which have spongin skeletons and lack siliceous spicules entirely.
