Geology Department - Porifera 33 - Lecture 2 - PDF

Lecture: 2  Kingdom Animalia Division (1): Parazoa Have no real tissues Phylum Porifera (Sponge) "pore bearer" The sponges are placed in a separate group, the Parazoa, due to their great difference from the protozoa (higher than the protozoa in evolution) and...

Lecture: 2  Kingdom Animalia Division (1): Parazoa Have no real tissues Phylum Porifera (Sponge) "pore bearer" The sponges are placed in a separate group, the Parazoa, due to their great difference from the protozoa (higher than the protozoa in evolution) and from metazoa (lower than metazoa in evolution). This phylum contains sponges (= pores) only. Sponges were first to branch off the evolutionary tree from the last common ancestor of all animals, making them the sister group of all other animals.  Characteristic Features of Phylum Porifera *Multicellular metazoans , sitting sessile (always live attached to rocks, coral reefs or any other suitable medium) and mostly marine (warm seas and oceans) except for a very few that live in fresh water. *They vary in their general form; they are spherical, flat, vase-shaped, or irregular in shape. Sponges come in different colors, including red, yellow, orange, purple, green and black. *Symmetry is radial in primitive species, but most sponge species lost this characteristic and became asymmetric. *Body - wall pierced by many tiny pores “(ostia)” (inhalant) which in turn lead to channels and chambers through which water flows in a complex structural system, also one or more large oscula (exhalent). *Cells show some kind of cellular specialization, but they do not form germ layers (an essential feature in true metazoa) and there is no coordination between the activities of these cell groups, and thus they are not true tissues. *Skeleton is in the form of thorns of lime (calcium carbonate CaCO3) or silica SiO2 or in the form of organic fibers (collagen fibers or spongin fibers). *Sponges do not have sensory or nerve cells, so their response to stimuli is limited (not observed). *Nutrition in sponges is holozoic animal nutrition, and sponges do not have a mouth or digestive cavity (digestive canal), Food items are taken into individual cells by phagocytosis and digestion is intracellular. *The body contains a single space called the paragastric cavity, also called spongocoel, which is lined by cells with flagella known as choanocytes. *The processes of respiration and excretion, as in the protozoa, by simple diffusion *Sponges reproduce asexually by budding and forming gemmules, and they have the ability to regeneration, and they reproduce sexually by forming gametes. *Have no circulatory systems or muscles. Instead, most rely on maintaining a constant water flow (created by the choanocytes ) through their bodies to obtain food and oxygen and to remove wastes. Classification of Phylum Porifera There are about 5,000 living species of sponges included in this phylum Porifera. All the species of this phylum are grouped into three classes depending mainly on the nature of the skeleton. The Cellular Structure A sponge's body is hollow and is held in shape by the mesohyl, a jelly-like substance made mainly of collagen and reinforced by a dense network of fibers also made of collagen. The Cellular Structure Sponges have three layers (Dermal and gastral layers) separated by an a cellular jell layer called mesohyl. The body wall of a common sponge consists of three layers which are (i) Pinacoderm (dermal layer) It is an outer cellular layer (ii) Choanoderm (gastral layer) It is inner cellular layer consisting of highly specialized flagellated cells called choanocytes or collar cells. (iii) Mesohyl layer (mesenchyme) It is a non-cellular layer found in between pinacoderm and choanoderm. It has fine dispersed spongin fibers and numerous spicules. 1- The first layer (Pinacoderm) consists of: A- Exopinacocytes External wall cells, flat, overlapping cells, which cover the outer surface of the sponge. B- Endopinacocytes: The cells of the inner lining, the cells are spindle-shaped. Line the incurrent and ex-current canals. C- Basopinacocytes : The cells that are found at the end of the sponge or at the base of the sponge. Cells oflayer Dermal sponges Pinacocytes Sclerocytes (Skeletogenous) Amoebocytes (Archaeocytes) Porocyts Spongocytes Myocytes Gastral layer Choanocytes Amoebocytes are modified into following cells (a) Trophocytes (nurse cells) (b) Thesocytes (c) Gland cells (d) Collencytes (e) Myocytes (f) Germ cells (g) Chromocytes (h) Phagocytes. 1- Pinacocytes "skin cells": They line the exterior of the sponge body wall. They are thin, leathery and tightly packed together. 2- Archaeocytes (amoebocytes): They are amoebic cells that have the ability to give rise to any other type of cell. 3- Sclerocytes: Secrete the spongin skeletal fibers. Responsible for producing spicules of siliceous and calcareous to sponge. 4- Porocytes: which surround canal openings and pores can contract to regulate flow through the sponge. It is characterized as a cylindrical tube that forms the holes in the wall of the sponge and controls the opening and closing of the hole. 5- Choanocytes: Flat cells that are responsible for regulating the entry of water into the aquiferous system. These cells do not work together in a coordinated manner. And their numbers are not equal in different rooms. These cells have a central flagellum that is surrounded by a collar of microvilli. The beating of the choanocytes‟ flagella creates the sponge‟s water current. 6- Spongocytes (lophocyte): they found in mesohyl gel which secrete different substances to form the structure of the sponge. They secrete fibrous collagen called sponging (protein). 7- Myocytes (contractile): conduct signals and cause parts of the animal to contract. It spreads in the gel densely. Skeleton: The structure of the sponge consists of many lime spicules differing in different types and contributed to the formation of the fossil records of the sponge. These spicules are formed within the mesohyl gel layer by sclerocytes, which have the ability to regularly precipitate silica or calcium carbonate grains. These spicules contribute to the support the body and also have an important taxonomic role in differentiating between different species.  Types of structural models Sponges Leucon type Sycon type Ascon type *Ascon type - The simplest model. ‫فُويهه‬ - Small in size. Osculum - Live in marine colonies. -The general shape is tubular, cylindrical, or cup-shaped. -The body wall is thin and perforated with ‫التجويف‬ many tiny holes known as ostia. ‫نظير‬ ‫ثقب‬ - The body wall is surrounded by a central Pore ‫المعدى‬ cavity, the (spongocoel), which is lined by a Pore single layer of collar cells (choanocytes), in which the pores also open. - The paragastric cavity leads to a large opening called the osculum (single opening). - This type of sponge is radially symmetric. Example... Leucosolenia colony. ****Water moving: ostium →spongocoel (over the choanoderm) →osculum. *Sycon type - More advanced than the previous model, as the body wall is thicker and folds several times to form a certain number of parallel chambers. *Sycon type - The body surrounds the central cavity which is the paragastric lumen (narrow). - Each chamber has a closed end from the outside and the other to the inside with a hole towards the paragastric cavity called apopyles. - The chambers are lined with a single row of flagellated cells, and for this they are known as flagellated chambers. Examples… Scypha ciliata Note that, paragastric cavity don’t linned by the collar cell. It lined with pincocytes. Water moving: incurrent (dermal) pore →incurrent canal → prosopyle → choanocyte chamber → apopyle →atrium →osculum. *Leucon type - More developed and more complex ‫فويهه‬ ‫فويهه‬ in structure than the previous models, as most types of sponge belong to, especially those of economic importance. - The body wall is very thick and ‫ثقب شهيقى‬ folds several times to form a very ‫ثقب‬ ‫شهيقى‬ large number of flagellated chambers, which are arranged in groups and dipped in a thick gelatinous substance supported by spongin fibers. - As a result of the thickness of the body wall and the increase in the number of flagellated chambers, the paragastric cavity is significantly reduced in size. Water moving: dermal pore →incurrent canal → prosopyle → choanocyte chamber → apopyle →excurrent canal →osculum. Nutrition in a sponge **Nutrition is holozoic filter feeders in sponge. In most sponges digestion is intracellular, in contrast to most other animals. Food is obtained either by pinocytosis or phagocytosis. ** It does not have a digestive canal, and the water that enters the sponge (created by (the flagellated collar cells) passes through a series of openings acting as a sieve through which microorganisms and organic molecules are filtered. **The flagellae beat regularly, creating a water flow across the microvilli which can then filter nutrients from the water taken from the collar of the sponge. Food particles are then phagocytosed by choanocytes and archaeocytes. Nutrition in a sponge Some sponges feed by predation where you can capture the prey by set of hooks, spicules and tentacles. The prey is surrounded by digestive cells which are digested and absorbed. Respiration Gas exchange occurs by simple diffusion between streams water entering that carrying oxygen and various cells in the body wall. The output process is done by simple diffusion and then out of animal through the oseullum. Excretion The excretory materials are often in the form of ammonia, which is toxic and repellent to many animal organisms that is why it is considered a means of defense that the sponge uses to protect it from enemies. Also, the amoeboid and primitive cells help in the process of excretion by diffusion, the excess water is removed in the fresh water sponges by the contractile vacuoles.  Reproduction Sexual Asexual Budding Fragmentation Reproduction * Asexual:- Budding 1. External (production of external buds that detach or remain to form colonies) 2. Internal (internal buds called gemmules that form during unfavorable periods (Gemmules are aggregates in sponge tissue, covered by a hard coating containing spicules or spongin fibers). These buds are characterized by a high ability to withstand freezing and drought. Reproduction * Asexual: - Fragmentation (regeneration): can regenerate from broken pieces * Sexual: Majority is hermaphroditic; produce sperms and eggs at different times. It also shows distinctive phenomena such as protogyny, in which the maturation of the female reproductive cells takes place before the male or vice versa, and therefore self-fertilization does not occur. Exchange between masculinity or femininity. Fertilization may be external (occurs in the surrounding water) ovipary. Or internal fertilization takes place where the sperm enters through the aqueous system and penetrates the cellular barriers and enters the mesoderm until it reaches the egg (vivipary) and eventually fertilizes it. Fertilized egg develop into mesoglea form blastula, develop to amphiblastula, escape from the osculum, swim hours or days, and then settling on an object. Thanks a lot