Sponges: Phylum Porifera Lecture Notes PDF

SPONGES : Phylum Porifera Prepared by JIEWARD C. CASUMPANG Faculty, Science Dept., MSU-GS Outline Today Next Meeting Sponges (Growth habits and forms) Sponge Physiology Ecologica...

SPONGES : Phylum Porifera Prepared by JIEWARD C. CASUMPANG Faculty, Science Dept., MSU-GS Outline Today Next Meeting Sponges (Growth habits and forms) Sponge Physiology Ecological Relationships Reproduction and Development Characteristics of Phylum Porifera Brief Survey of Sponges Form and Function Taxonomy of Phylum Porifera Types of Canal Systems Phylogeny and Adaptive Types of Cells Diversification Types of Skeletons Sponges Phylum Porifera From Latin words, porus = pore, fera = bearing Bear myriads of tiny pores and canals that constitute a filter-feeding system Water flow through the unique canal systems, brings in food and oxygen and carries away their body wastes. 2 simple layers of cells Outer pinacoderm Inner choanoderm Between layers lies mesohyl ECM home to up to ten different cell types and stiffened by a skeleton of minute spicules of calcium carbonate or silica and collagen Sponges Most sponges have no organs or true tissues, and even their cells show a certain degree of independence. Example, dissociated sponge cells can reform a new sponge body No nervous system or sense organs, but sponges do have simple contractile elements. Size: few millimeters to great loggerhead sponges (2 or more meters) Brightly colored (pigments in their dermal cells) Red, yellow, orange, green, purple Their color fades when removed from water Irregular in shape Sponges Forms: some stand erect, some are branched or lobed, others are low, encrusting Some bore holes into shells or rocks Some growth habits and forms of sponges Sponges Are an ancient group with abundant fossil record extending back to the Precambrian to early Cambrian period. Living poriferans were assigned to three classes: Calcarea – having calcareous spicules Demospongiae – having a skeleton of siliceous spicules or spongin or both Hexatinellida – six-rayed siliceous spicules Fourth class: subset of Demospongiae Homoscleromorpha – thin encrusting sponges that have simple spicules or lack spicules entirely. Sponges Cladogram depicting evolutionary relationships among the four classes of sponges with living representatives Ecological Relationships Most of the 5000 or more sponge species are marine, although some 150 species occupy fresh water. Few occupy brackish water Their embryos are free- swimming, adults are attached usually to rocks, shells, corals, or other submerged objects Ecological Relationships Some bottom-dwelling forms even grow on sand or mud. Their growth patterns often depend on shape of the substratum, direction and speed of water currents, and availability of space, so that the same species may differ markedly in appearance under different environmental conditions. Sponges in calm water may grow taller and straighter than those in rapidly moving waters. Ecological Relationships Many animals such as crabs, nudibranchs, mites, bryozoans, and fish, live as commensals or parasites in or on sponges. Larger sponges particularly tend to harbor a large variety of invertebrate commensals. Sponges also grow on many other living animals such as molluscs, barnacles, brachiopods, corals, and hydroids. One sponge has been described that preys shrimp Some crabs attach pieces of sponge to their carapace for camouflage and protection, since most predators seem to find sponges distasteful. Ecological Relationships One reason for the success of sponges as a group is that they have few enemies. Elaborate skeletal framework and often noxious odor Most potential predators find sampling a sponge about as pleasant as eating a mouthful of glass splinters embedded in evil-smelling gristle. Some reef fishes, graze on shallow-water sponges Sponges and the microorganisms that inhabit them, produce a variety of bioactive chemicals. One extract from a marine sponge appears effective against leishmaniasis (caused by apicomplexan parasite) Some sponge species is used for treating herpetic infections Ecological Relationships Many bacteria isolated from marine taxa also have antimicrobial or antiviral effects: Example, some inhibit Staphylococcus aureus infections and others are active against E. coli (some strains may cause food poisoning) These and other results have increased interest in sponge culturing as a source of valuable pharmaceuticals. Characteristics of Phylum Porifera Form and Function Sponges are sessile Their only body openings are pores, usually many tiny ones called ostia for incoming water, and one to a few large ones called oscula (sing. oculum) that serve as water outlets. These openings are connected by a system of canals, some are lined with peculiar flagellated collar cells called choanocytes whose flagella maintain a current of environmental water through the canals. The choanocyte lining forms the choanoderm. Form and Function Choanocytes not only keep the water moving but also trap and phagocytize food particles from the water. Collapse of the canals is prevented by the skeleton, may be composed of needle-like calcareous or siliceous spicules, a meshwork of organic spongin fibers, or a combination of the two. Types of Canal Systems Most sponges have one of three types of canal systems 1. Asconoid 2. Syconoid 3. Leuconoid 1. Asconoids – Flagellated Spongocoels Have the simplest organization Small and tube-shaped Water enters through microscopic dermal pores into a large cavity called spongocoel (lined with choanocytes) Choanocyte flagella pull water through the pores and expel it through a single large osculum 1. Asconoids – Flagellated Spongocoels Leucosolenia (Gr. Leukos, white, + solen, pipe) is an example Slender, tubular individuals grow in groups attached by a common stolon, or stem, to objects in shallow seawater 1. Asconoids – Flagellated Spongocoels Another example: Clathrina (L. clathri, latticework) Bright yellow, intertwined tubes All asconoids are in the class Calcarea  2. Syconoids – Flagellated Canals Look somewhat like larger editions of asconoids (from which they were derived). They have a tubular body and a single osculum, but instead of a simple choanocyte layer lining the spongocoel, as in asconoids, this layer in syconoids is folded back and forth to make canals. The choanocytes line certain folds are called radial canals  2. Syconoids – Flagellated Canals Water, entering the body through dermal pores, moves first to incurrent canals and then into radial canals via small lateral openings called prosopyles From the radial canals, filtered water moves through apopyles into the spongocoel, finally exiting by the osculum. Cross section through the body wall of the sponge Sycon, showing the canal system  2. Syconoids – Flagellated Canals The spongocoel in syconoids is lined with epithelial-type cells rather than with the choanocytes found in asconoids. Syconoids are in the Calcarea. Sycon (Gr. Sykon, a fig) is a commonly studied example of the syconoid type of sponge Cross section through the body wall of the sponge Sycon, showing the canal system  3. Leuconoids – Flagellated Chambers Leuconoid organization is the most complex of the sponge types and permits an increase in sponge size Most leuconoids form large masses with numerous oscula Clusters of flagellated chambers are filled from incurrent canals and discharge water into excurrent canals that eventually lead to the osculum  3. Leuconoids – Flagellated Chambers There is no spongocoel Most sponges are of the leuconoid type, which occurs in most Calcarea and in all other classes.  The three types of canal systems, demonstrate an increase in the complexity and efficiency of the water-pumping system, but they do not imply an evolutionary or developmental sequence. The leuconoid grade of construction has evolved independently many times in the sponges Possession of a leuconoid plan is of clear adaptive value It increases the proportion of flagellated surfaces compared with the volume, thus providing more collar cells to meet food demands.  Types of Cells Sponge cells make layers, as in the choanoderm and pinacoderm, or are loosely arranged in mesohyl The mesohyl is the connective tissue of the sponges; in it are found various ameboid cells, fibrils, and skeletal elements. Several types of cells occur in sponges. 1. Pinacocytes The nearest approach to a true tissue in sponges is arrangement of the pinacocyte cells of the external pinacoderm layer. These thin, flat, epithelial type cells cover the exterior surface and some interior surfaces, but only in one group do they rest on a basal lamina ECM. Some are T-shaped, with their cell bodies extending into the mesohyl. Pinacocytes are modified as contractile myocytes, which are usually arranged in circular bands around the oscula or pores, where they help to regulate the rate of water flow. Myocytes contain microfilaments similar to those found in muscle cells of other animals. 2. Porocytes Tubular cells that pierce the body wall of asconoid sponges, through which water flows are called porocytes.  3. Choanocytes Choanocytes, which line flagellated canals and chambers, are ovoid cells with one end embedded in mesohyl and the other exposed. The exposed end bears a flagellum surrounded by a collar Electron microscopy shows that the collar is composed of adjacent microvilli, connected to each other by delicate microfibrils so that the collar forms a fine filtering device for straining food particles from the water.  3. Choanocytes The beat of flagellum pulls water through the sievelike collar and forces it 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.  3. Choanocytes Larger particles have already been screened out by the small size of the dermal pores and prosopyles. Food engulfed by the cells is passed to a neighboring archaeocyte for digestion. 3. Choanocytes 4. Archaeocytes Are ameboid cells that move through the mesohyl and perform a number of functions They can phagocytize particles at the external epithelium and receive particles for digestion from choanocytes It can differentiate into any of the other types of more specialized cells in the sponge Other cells 5. Spongocytes secrete the spongin fibers of the skeleton 6. Collencytes secrete fibrillar collagen Types of skeletons Gives support to a sponge, preventing collapse of canals and chambers The major structural protein in the animal kingdom is collagen, and fibrils of collagen occur throughout the extracellular matrix of all sponges Various Demospongiae secrete a form of collagen called spongin Demospongiae also secrete silicious spicules, and calcareous sponges secrete spicules composed mostly of crystalline calcium carbonate that have one, three or four rays.  Types of skeletons Glass sponges (Hexactinellida) have siliceous spicules with six rays arranged in three planes at right angles to each other. There are many variations in the shape of spicules, and these structural variations are of taxonomic importance. Outline Today Next Meeting Sponges (Growth habits and forms) Sponge Physiology Ecological Relationships Reproduction and Development Characteristics of Phylum Porifera Brief Survey of Sponges Form and Function Taxonomy of Phylum Porifera Types of Canal Systems Phylogeny and Adaptive Types of Cells Diversification Types of Skeletons Sponge Physiology Sponges feed primarily on particles suspended in water pumped through their canal systems. They consume detritus particles, planktonic organisms, and bacteria in sizes ranging from 50 μm (average diameter of ostia) to 0.1 μm (width of spaces between the microvilli of the choanocyte collar) Pinacocytes may phagocytize particles at the surface, but most larger particles are consumed in the canals by archaeocytes that move close to the lining of the canals. Sponge Physiology The smallest particles, accounting for about 80% of the particulate organic carbon, are phagocytized by choanocytes. Digestion is entirely intracellular (occurs within cells), a chore performed by the archaeocytes. Sponges consume a significant portion of their nutrients in the form of organic matter dissolved in water circulating through the system Sponge Physiology Such material is apparently ingested by a process similar to phagocytosis. Sponges have no respiratory or excretory organs; these functions are performed by diffusion. Contractile vacuoles occur in the archaeocytes and choanocytes of freshwater sponges Sponge Physiology All of a sponge’s life activities depend on a current of water flowing through its body. A sponge pumps a remarkable amount of water. Some large sponges can filter 1500 liters of water a day. At least some sponges can crawl (move laterally over their supporting substratum) at speeds of up to 4 mm per day. This ability may give them an advantage over more sessile encrusting organisms in competition for space. Reproduction and Development All sponges can reproduce both sexually and asexually In sexual reproduction, most sponges are monoecious having both male and female sex cells in one individual Sperm arise from transformation of choanocytes. In Calcarea and at least some Demospongiae, oocytes also develop from choanocytes; in other demosponges, oocytes apparently develop from archaeocytes. Reproduction and Development Sperm are released into the water by one individual and taken into the canal system of another. There, choanocytes phagocytize them, transform into carrier cells, and then carry the sperm through the mesohyl to the oocytes. Other sponges are oviparous and expel both oocytes and sperm into the water. Ova are fertilized by motile sperm (without carrier cells) in the mesohyl. Reproduction and Development There, the zygotes develop into flagellated larvae, which break loose and are carried away by water currents. The free-swimming larva of most sponges is a solid-bodied parenchymula The outwardly directed, flagellated cells on the larval surface migrate to the interior after the larva settles and become choanocytes in the flagellated chambers. Reproduction and Development  Reproduction and Development The loose organization of sponges is ideally suited for regeneration of injured and lost parts, and for asexual reproduction. Sponges reproduce asexually by fragmentation and by forming external buds that detach or remain to form colonies. In addition to external buds, which all sponges can form, freshwater sponges and some marine sponges reproduce asexually by regularly forming internal buds called gemmules Reproduction and Development These dormant masses of encapsulated archaeocytes form during unfavorable conditions. They can survive periods of drought and freezing and more than three months without oxygen. Later, with the return of favorable conditions for growth, archaeocytes in the gemmules escape and develop into new sponges. Brief Survey of Sponges Class Calcarea (Calcispongiae) Calcarea are calcareous sponges, so called because their spicules are composed of calcium carbonate. Their spicules are straight monaxons or have three or four rays Class Calcarea (Calcispongiae) The sponges tend to be small—10 cm or less in height—and tubular or vase shaped. They may be asconoid, syconoid, or leuconoid in structure. Although many are drab, some are bright yellow, red, green, or lavender. Leucosolenia, Clathrina, and Sycon are common examples. Class Hexactinellida (Hyalospongiae) Hexactinellids are nearly all deep-sea forms. Most are radially symmetrical and range in length from 7 to 10 cm to more than 1 m. One distinguishing feature, reflected in the name Hexactinellida, is the skeleton of six-rayed siliceous spicules bound together in an exquisite glasslike latticework  Class Hexactinellida (Hyalospongiae) The tissue structure of hexactinellids differs so dramatically from that of other sponges that some scientists advocate placing them in a subphylum separate from other sponges. The body is syncytial—there are many nuclei inside a single very large plasma membrane. This single, continuous syncytial tissue is called a trabecular reticulum. A 1-m-diameter glass sponge makes the largest syncytium known within the animals.  Class Hexactinellida (Hyalospongiae) The trabecular reticulum is bilayered and can be sheetlike or tubular. Between the layers of the sheet, or inside the tubes, is a thin collagenous mesohyl in which cells, such as archeocytes or choanoblasts, occur Diagram of part of a flagellated chamber of hexactinellids. The primary and secondary reticula are branches of the trabecular reticulum, which is syncytial. Cell bodies of the choanoblasts and their processes are borne by the primary reticulum and are embedded in a thin, collagenous mesohyl. Processes of the choanoblasts end in collar bodies, whose collars extend up through the secondary reticulum. Flagellar action propels water (arrows) to be filtered through the mesh of collar microvilli Class Hexactinellida (Hyalospongiae) Choanoblasts and other cells are connected to each other, and to the trabecular reticulum, by cytoplasmic bridges. Choanoblasts are unusual cells that make two or more flagellated outgrowths called collar bodies. The flagellum on a collar body beats to drive water flow in the same way that it would on a choanocyte.  Class Hexactinellida (Hyalospongiae) An assemblage of collar bodies forms a flagellated chamber. Here, the trabecular reticulum branches to become two distinct bilayered sheets: a primary reticulum and a thin secondary reticulum that lacks mesohyl. The two sheets make a sandwich around the center of a collar body Class Hexactinellida (Hyalospongiae) Collar bodies extend through openings in both sheets, but the openings surround the collar bodies tightly. There is a space between the two sheets. To collect food, the incurrent water is directed to the primary reticulum, where pores enter the space between the primary and secondary reticular sheets. Class Hexactinellida (Hyalospongiae) Water entering this space must leave by moving through the mesh of microvilli on collar bodies; water cannot go anywhere else because it is blocked by the secondary reticulum. Food particles captured on microvilli are shared throughout the syncytium. Class Hexactinellida (Hyalospongiae) The lattice-like network of spicules in many glass sponges is of exquisite beauty, as seen, for example, in Euplectella (NL. from Gr. euplektos, well-plaited), a classic example of Hexactinellida Class Demospongiae Demospongiae comprise approximately 80% of all sponge species, including most larger sponges. Their skeletons may be composed of siliceous spicules, spongin fibers, or both Class Demospongiae All members of the class are leuconoid, and all are marine except one family, the freshwater Spongillidae. Freshwater sponges occur widely in well-oxygenated ponds and streams, where they encrust plant stems and old pieces of submerged wood. They resemble a bit of wrinkled scum, pitted with pores, and are brownish or greenish in color. Freshwater sponges die and disintegrate in late autumn, leaving gemmules to survive the winter. Class Demospongiae Marine Demospongiae vary in both color and shape. Some are encrusting; some are tall and fingerlike; and others are shaped like fans, vases, cushions, or balls Class Demospongiae Some sponges bore into and excavate molluscan shells and coral skeletons. Loggerhead sponges may grow several meters in diameter. So-called bath sponges belong to the group called horny sponges, which have only spongin skeletons. Class Demospongiae They can be cultured by cutting out pieces of the individual sponges, fastening them to a weight, and dropping them into the proper water conditions. It takes many years for a horny sponge to grow to market size. Most commercial “sponges” now on the market are synthetic, but the harvest and use of bath sponges persists. Class Homoscleromorpha Homoscleromorphs are marine sponges that occur in a range of colors, but live in cryptic habitats, so they are often overlooked. They are more common in nearshore habitats, but they do occur in deep water. Sponges in this class were formerly placed in Class Demospongiae, but were separated because they possess unique features such a basal lamina composed of ECM underlying the pinacoderm cell layer Class Homoscleromorpha Pinacoderm cells link to the ECM with adherens junctions but do not link to each other with desmosome junctions. Proteins called cadherins function as adhesives in desmosome junctions and are also used in making adherens junctions, but not all cells capable of making adherens junctions can make desmosomes. The pinacoderm layer fails to meet the definition of a true tissue epithelium and is instead called an incipient epithelium. Class Homoscleromorpha The class is divided into two clades, one whose members lack spicules entirely, and the other with spicules that do not form Representative genera are Plakina, Oscarella, and Corticium. Taxonomy of Phylum Porifera Class Calcarea (cal-cárē-ә) (L. calcis, lime, + Gr. spongos, sponge) (Calcispongiae) Have spicules of calcium carbonate that often form a fringe around the osculum; spicules needle-shaped or three- or four-rayed; all three types of canal systems (asconoid, syconoid, leuconoid) represented; all marine. Examples: Sycon, Leucosolenia, Clathrina. Class Hexactinellida (hex-ak-tin-el′i-da) (Gr. hex, six, + aktis, ray) (Hyalospongiae) Have six-rayed, siliceous spicules extending at right angles from a central point; spicules often united to form a network; body often cylindrical or funnel-shaped. Flagellated chambers in simple syconoid or leuconoid arrangement. Habitat mostly deep water; all marine. Examples: Venus’ flower basket (Euplectella), Hyalonema. Class Demospongiae (de-mo-spun’jē) (tolerated misspelling of Gr. desmos, chain, tie, bond, + spongos, sponge). Have skeleton of siliceous spicules that are not six-rayed, or spongin, or both. Leuconoid-type canal systems. One family found in fresh water; all others marine. Examples: Thenea, Cliona, Spongilla, Myenia, and all bath sponges. Class Homoscleromorpha (hō-mō-skle′-rō-mor-fә) (Gr. homos, same, + skleros, hard, + morphe, form) Previously a subgroup of Demospongiae; spicules may be absent as in Oscarella; if present, spicules are small, simple in shape, and do not form around an axial filament; pinacoderm with a distinct basal lamina. Examples: Oscarella, Corticium. Phylogeny and Adaptive Diversification Phylogeny Sponges originated before the Cambrian period. Two groups of calcareous spongelike organisms occupied early Paleozoic reefs. The Devonian period saw rapid development of many glass sponges. Sponges are the sister taxon to a group comprising all animal phyla Phylogeny The simple body plans of most sponges, aside from hexactinellids, might suggest that sponges share few features with other animals, but this is not true. To form a multicellular body, some cells form layers adhering to other cells, to the ECM, or to both items Some proteins used in cell adhesion and cell signaling in sponges are homologous to those in other metazoans; in fact many of these occur in choanoflagellates, evolving before the last common ancestor of all animals. Phylogeny Sponge development includes the characteristic animal blastula stage, and some sponges actually develop to the two- layered gastrula stage before reorganizing their bodies into asymmetrical adults. It is possible that the sessile lifestyle of sponges favored a deceptively simple body in most species and that a closer look at sponges will reveal more features typical of animals. Adaptive Diversification Porifera are a highly successful group that includes several thousand species in a variety of marine and freshwater habitats. Their diversification centers largely on their unique water current system and its various degrees of complexity. The leuconoid body plan, with its many flagellated chambers, has a relatively large surface area for food capture and gas exchange when compared with the asconoid and syconoid plans; this may account for the large size of leuconoid sponges. Adaptive Diversification One very novel way of feeding has evolved within a family of sponges, called cladorhizids, inhabiting nutrient-poor deepwater caves. Each sponge has a fine coating of tiny, hook-like spicules over its highly branched body. The spicule layer entangles the appendages of tiny crustaceans swimming near the sponge surface. Later, filaments of the sponge body grow over the prey, enveloping and digesting them Adaptive Diversification These animals are carnivores, not suspension feeders; they lack choanocytes and internal canals but have siliceous spicules like typical members of class Demospongiae. In addition to capturing prey, some augment their diets with nutrients obtained from symbiotic methanotrophic bacteria. To colonize such a nutrient-poor habitat initially, the ancestors of this group must have had at least one alternative feeding system, either carnivory or chemoautotrophy, already in place.  Adaptive Diversification Presumably, after the alternative method of food capture was in use, the choanocytes and internal canals were no longer formed. Further body modifications in this lineage might make it difficult to identify descendants as sponges The discovery of the deep-sea harp sponge, Chondrocladia lyra shows us the complexity of a predatory sponge.  Adaptive Diversification This animal has multiple veins, each with a basal stolon close to 40 cm in length, anchored by rhizoids. Vertical branches extend nearly 20 cm upward from stolons. Small prey, often copepods are captured on branches and consumed by phagocytosis. Terminal balls on each branch contain spermatophores; eggs are held midway up the branches. Body form varies from stalked and spherical to branching in the 36 other species in this genus. Summary  Sponges (phylum Porifera) are an abundant marine group with some freshwater representatives. They have various specialized cells; these cells are not organized into tissues or organs in most sponges, but the pinacoderm approaches a true tissue in one class, Homoscleromorpha. Sponges depend on the flagellar beat of their choanocytes to circulate water through their bodies for gathering food and exchanging respiratory gases. They are supported by secreted skeletons of fibrillar collagen, collagen in the form of large fibers or filaments (spongin), calcareous or siliceous spicules, or a combination of spicules and spongin in most species  One sponge class, Homoscleromorpha, is interesting because only its members have type IV collagen characteristic of other animals Most sponges are monoecious but produce sperm and oocytes at different times. Embryogenesis is unusual because flagellated cells migrate from the embryo surface to the interior of the larva. The larva is typically a free-swimming parenchymula.  Sponges have great regenerative capabilities and may reproduce asexually by budding, fragmentation, or gemmules (internal buds). Sponges are an ancient group present before the Cambrian. Their adaptive diversification is centered on elaboration of the water circulation and filter-feeding system, with the exception of a unique group of cavedwelling, carnivorous sponges (cladorhizids) that do not filter-feed.