Porifera

** The Porifera (Sponges) **
“Pore Bearer”  (Meet the real SpongeBob)



(ORS 16) **Phlum Porifera:** Sponges are sessile, permanently fixed, with porous bodies and maintain a flow of water through the. Sponges, on branch parazoa of the phylogenetic tree represent the lineage closest to the colonial choanoflagellates that gave rise to the animal kingdom.

· The diagnostic characteristics that define the group · Acquiring and digesting food · Sensing the environment · Locomotion · Respiration · Metabolic waste removal · Circulation · Self protection · Osmotic balance · Temperature balance



1. **Characteristics of Porifera:** Sponges are immobile invertebrate animals that appear very calm to humans, which explains why the ancient Greeks believed them to be plants. The general body plan consists of two cells layers surrounding a **spongocoel,** the large central cavity. The body wall is approximately two cell layers thick with a gel like substance called the mesohyl in- between. The body wall is perforated by many pores and channels through which water enters the animal, passing into the spongocoel, and exiting through a large opening called the **osculum**. Sponges are unique because of their cell layers, which are loose federations of cells that are not really tissues because of they lack cell specialization. They have no nerves or muscles, but each individual cell can sense and react to changes in the environment. The cells of the body are supported by secreted skeletal elements called **spicules**. (LW)(3)



There are over 9,000 different species of sponges and only 100 of them live in fresh water. Sponges range in height from 1 cm up to 2 meters and vary in shape, color and structural complexity. The body of a simple sponge resembles a sac perforated with holes. Some species become pigmented by symbiotic algae. Sponges have been split up into three different body plans. The first is asconoid. This is a sponge that is shaped like a simple tube but is covered by pores. The internal part of the tube that is open inside is the spongocoel. The one opening to the outside is called the osculum. The next type of body plan is the syconoid and is larger than an asconoid. Although similarly formed with a tube and pores, the wall making up the tube is thicker, therefore making the pores longer. Because the pores are longer, they are more like canals. This body plan also has an osculum. Leuconoids are the last type of body plan and are the most complex. They contain more tissue with many canals that lead to different chambers lined with flagella designed to help move the water along. (NG)([|1]) There are three different types of sponges within the phylum Porifera, their classes being determined by the type of spicules they have. (TM)(13) Poriferans have diverse skeletal elements including calcareous laminae, organic filaments, and siliceous and calcareous spicules as seen below:
 * Calcarea (calacereous sponges) have spicules made from calcium carbonate [All sponges in the calcarea class are marine sponges. The spicules are either single or branched. (MP)[|19]]
 * Hexactinellida (glass sponges) have siliceous spicules that form as six rays intersecting at right angles, (like a toy jack), hence, HEXActinellida [Hexactinellida are noted for their cylinder or funnel shape. Sponges in the class hexactinellida habit mostly in the deep water, and they are all marine sponges. (MP) [|19]]
 * Demospongia which have silicate spicules (that form in 1-4 non right angle ray patterns), spongin fibers, or both. [Most families are found in marine water, but one family can be found in freshwater, which is why sponges are not just marine aquatic (MP) [|19]]

(MC) Adult sponges can be asymmetrical or radially symmetrical and come in a variety of shapes: arboresecent (tree-like), flabellate (fan-shaped), caliculate (cup shaped), tubular (tube shaped), globular (ball shaped), and amorphous (shapeless) among others. (AK) (18)

2. ** Acquisition and digestion of food ** : Almost all sponges are suspension-feeders, also known as filter feeders, which are animals that collect food particles from water passed through food-trapping devices. {Since sponges are filter feeders, they live successfully in habitats with strong currents or wave action. (AC)(22) The food is trapped from the water circulated through its porous body. The flagellated choanocytes, or collar cells, line the inside of a spongocoel. This flagella generates a water current allowing the collars to trap food particles that the choanocytes to ingest via ** Phagocytosis, ** a process in which phagocytes engulf and digest microorganisms and cellular debris. Wandering through the mesophyl are cells called ** Amoebocytes, ** which have many different functions. These functions include taking up food from the ** choanocytes **, digesting the food, and carrying nutrients to other cells. They can also undergo developmental changes to become other cell types that may be required. This allows for the growth and repair for the sponge.(KL)([|2])

3. ** Sensing the environment and Locomotion ** : All sponges live in an aquatic ecosystem. Out of 9,000 different species of sponges, 8,900 of them live in marine environments. Acting like water filter, poriferas simply sway in the water collecting food particles. Once a larva reaches a suitable size and starts to grow, it becomes **sessile** or immobile. However, Porifera Larvae are free swimming. (LW) (11) The sponge body is unique because it continuously remolds itself to fine-tune its filter-feeding system. The constant rearrangement is done by the amoeboid movement (like that of an amoeba) of cells inside the sponge, and their change from one differentiated form to another. (AK) (18) Sponges have no real nervous system, as they contain very limited cell diversification, but it has been shown that they carry the same proteins and enzymes we use in our human nervous systems, outlining the origins of a more complex system. Although they lack a nervous system, some sponges will contract local areas of their body if they are touched. (JS) [|(23)]

**4. Respiration and Circulation:** Sponges filter food from water pumped through their porous bodies. This is accomplished when water is drawn through the sponge’s pores into a central cavity called the spongocoel, then flows out of the sponge through a larger opening called the osculum.

Respiration begins when water makes contact with the pinacocytes on the outer layer of the sponge. The water is then absorbed through porocytes when the morocytes, small muscles, open them. Choanogflagetta, flagellated structures, absorb the oxygen. Archaoecytes transport the oxygen, through canals, to other parts of the sponge. The rest of the oxygen is absorbed directly through the sponge's cells' membranes. Water and gases that are not needed by the sponge are pumped through the atrial cavity and out the osculum. (SI) (12)

5. ** Metabolic waste removal: ** Since the sponges consist of only two cell layers, each cell is able to directly remove waste into the environment and maintain homeostasis. Porifera do not have a mouth or anus. Porifera lack a sophisticated excretory system. All of their waste is removed in one of three ways: diffusion, osmosis, and cell transport. (17)(MF) Porifera have spores on the outer cell layer of their body, which allows them to excrete their waste. They also have very few cell layers (two to three layers) which means that waste can easily travel out of the organism's body. They also have oscula, a large opening that the waste passes through, The size of the oscula ranges, and that determines how much waste travels out of the body. (RG) [|(8)]

6. ** Self Protection: ** Parazoas are peaceful animals that developed certain defenses that are vital for their survival. The amoebocytes also form tough skeletal fibers within the mesohyl. Some fibers have sharp spikes made from calcium carbonate or silica. Other sponges produce more flexible fibers composed of collagen protein, also known as sponging. Amoebocytes are also important defenses against infection for taking up any harmful substances. Another defense many sponges have is the ability to produce toxins which are either on the surface of the sponge or are released into the water by the sponge. By releasing the toxin they can keep away predators that would otherwise eat them. Also used for defense are spicules which are small particles made from either silica or calcium carbonate found protruding through the surface of the sponge. They can be shaped like stars, crosses, or rods, and are used for support along with defense. (RL) (4, 5, 6, 7)

7. ** Osmotic Balance: ** The osmolarity in sponges is the same as in seawater.This means that sponges are isosmotic to their environment, and are osmoconformers. Many freshwater sponges have contractile vacuoles for osmoregulation. These vacuoles collect excess fluid in the protoplasm and pump it into the external environment. (CSR, [|8], [|9], [|10]) The open pores on the surface of the sponge comes in two types. The entry cells are known as ostia while the larger exit cells are known as oscula, or excurrent. Specialized cells called choanocytes allow water into the ostia. Water flows through the body of the sponge, entering the ostia, circulating around the canals and chambers, then leaving from the oscula. The flow of water through the sponge is unidirectional, driven by the beating of the flagella which line the surface of the chambers. The water movement through some sponges is aided by ambient currents passing over oscula. This moving water creates an area of low pressure above the oscula that allows water to be drawn out of the sponge. Sponges are able to regulate the amount of flow through their bodies by constricting various openings. (LW) (14)

8. ** Temperature Balance: ** Sponges are found in places where they have adapted to environmental temperatures.

9. **Reproduction:**

Most sponges are hermaphodites, meaning that each individual functions as both male and female by producing both sperm and eggs. Gametes, a mature sexually reproductive cell, arise from choanocytes or amoebocytes. Eggs rest in the mesophyl while sperm cells are carried of the of the cell by the water current created by the flagella. Fertalization occurs in the mesophyl, where the zygotes develop into flagellated, swimming larvae that disperse from the parent. When a larva reaches a suitable environment, it will start to develop into a sexual reproductive adult sponge. Cross-fertilization occurs when a sperm is drawn into a neighboring sponge. Sponges have the ability to continuously regenerate, replacing lost parts. This regeneration property is also used to reproduce asexually from pieces broken off the parent sponge. Asexual forms include fragmentation, budding and gemmules. Gemmules are reproductive structures in some sponges that remain dormant through the winter and later develops into an individual. (LW) (11) Porifera are hermaphroditic, but they can only be one gender at a time (male, female, or neuter). Some species, like the Halichondria moorei, change color when they change sexes. (21)(SM)

**Picture - The development of a sponge starting with a fertilized zygote. (DB)(24)**

**Review Questions:**

1)How do the body structures, cells and functions of porifera differ from those in species found in the mammalia and amphibia kingdoms? (YA) 2) Since sponges do not move much once they find a suitable substratum, explain how a proifera might become a keystone specie in its surrounding ecosystem? (GR) 3) How do such small, immobile organisms protect themselves from predators and the environment? (MT) 4) Is there a type of environment(temperature range, etc.) that sponges prefer/are better adapted to? (ZXU) 5) how do Porifera(sponges) protect themselves? (ZS) 6) How do Porifera reproduce? What are Gemmules? How is Gemmule development different from other development? (MLK) 7) What "distinct" body systems do porifera lack? What single function compensates for them? Explain how it works.(CW)