Porifera & Cnidaria (Z 101) Lecture Notes PDF

(Z 101) Prof. Dr. Hala Ali  Sponges are the most primitive multicellular animals belonging to Phylum Porifera.  Porifera means,. “pore bearers”.  Sponges (15,000 species), they are mostly found in marine water.  Only a few are found in freshwater.  They are sessile. General chara...

(Z 101) Prof. Dr. Hala Ali  Sponges are the most primitive multicellular animals belonging to Phylum Porifera.  Porifera means,. “pore bearers”.  Sponges (15,000 species), they are mostly found in marine water.  Only a few are found in freshwater.  They are sessile. General characters of Sponges:  They are the most primitive metazoans (multicellular animals), their cells lacking specialized tissues or organs.  Most are asymmetrical, and some are radially symmetrical.  Body with many pores or ostia through which water flows.  They are holozoic with no mouth, no digestive system and digestion is intracellular.  They respire and excrete by simple diffusion. General characters of Sponges:  The central cavity is called spongocoel or atrium which opens to the outside through the osculum.  The spongocoel lined with choanocytes (collared flagellated cells). Reproduction is by asexual and sexual means  Asexual Reproduction A-External budding B- Regeneration C-Internal budding (gemmules formation in fresh water sponge  Sexual reproduction The development is indirect due to the presence of larva Structure of the body wall  Structure of the body wall 1-The body wall is pierced by many incurrent openings or pores (ostia) that extend from the external surface to the central cavity. Each pore is a canal through a tubular cell, or porocyte found in the outer layer. 2-A gelatinous material is mesenchyme (mesoglea), containing: A- Skeletal components may be spicules (calcareous or siliceous spicules), and also it may be spongin fibers. (calcareous or siliceous spicules), and also it may be spongin fibers B- Amoebocytes.  B-Amoebocytes are found A-Archaeocytes 2-Scleroblasts -Innerregion, gastral layer, consisting of collared flagellated cells or choanocytes  Skeleton of sponge It used in taxonomic identification of the different types of sponges  Types of Sponges Ascon type Sycon type Leucon type Ex. Leucosolenia, Ascetta Ex. Sycon, Grantia Ex. Bath sponge Euspongia  Types of Sponges Ascon type Sycon type Leucon type This is the simplest type; The The body wall has been folded The body wall is very thick and body wall is thin, the ostia lead horizontally and as a result two highly folded resulting in the directly into the spongocoel, types of canals. These canals formation of many small then water is finally driven to are: rounded flagellated chambers, outside through the osculum. 1-Inhalant canals (that lined while the spongocoel cavity is with pinacocytes and open to very much reduced the outside by ostia). 2-The flagellated chambers (that lined with choanocytes and opened into spongocoel through apopyles). -The inhalant canals communicate with flagellated chambers through pores called prosopyles  Water flow Ascon type Sycon type Leucon type Water Ostia Water Ostia Water ostia Subdermal cavities Inhalant canal Inhalant canal Spongocoel Flagellated chambers Flagellated chambers osculum Spongocoel Exhalant canal Osculum Outside Osculum outside Outside  Animal Kingdom Subkingdom Metazoa Branch Eumetazoa (Enterozoa) Division Radiata (Diploblastica) Phylum Cnidaria (Coelenterata) Phylum Cnidaria Hydrozoa Scyphozoa Cubozoa Anthozoa Ex.: Hydra, Ex. Aurelia. Ex. Box jellies Obelia.. Subclass:  General characters of Cnidarians They are solitary or colonial, sedentary or free swimming. They are aquatic, mostly marine, some are fresh water. The body is radially symmetrical. Most cnidarians are carnivorous.  The mouth is surrounded by tentacles arranged in one or more whorls. The tentacles help in food capture, ingestion and for defense.  General characters of Cnidarians Body wall has peculiar stinging cells called cnidocytes which are more abundant on the tentacles. There is a central gastro-vascular cavity (coelenteron or enteron) which is communicated with the exterior by a single opening, the mouth. Digestion is extracellular in the gastro-vascular cavity and then intracellular inside the endodermal cells.  General characters of Cnidarians No respiratory, circulatory and excretory systems. Sense organs are simple or complicated, e.g. ocelli and statocysts. Nervous system consists of one or more nerve nets made up of nerve cells and nerve fibers. The individuals are of two types: the attached polyp and free-swimming medusa.  General characters of Cnidarians Reproduction occurs by both asexual and sexual. Asexual reproduction by budding and regeneration. Sexual reproduction by gametes to form a uniformly ciliated planula larva. Life cycle exhibits metagenesis (alternation of generation) in which sexual medusoid generation alternates with asexual colonial polypoid generation. The occurrence of more than one type of structurally and functionally different individuals within a in a single species during its life cycle is called polymorphism. -Two basic forms of individuals, the polyps and the medusae occur. -Polyp is concerned with feeding, protection and asexual reproduction, while medusae are concerned with sexual reproduction  Locomotion Actual locomotion is achieved by the following various methods:  Structure of body wall It consist of two body layers ectoderm and endoderm. 1-Outer layer Jellylike material , including: Mesoglea - Epithelio-muscular this is non-cellular cells, Mucous- -it is traversed by secreting cells. migrating cell and - Interstitial cells. crossed by nerve fibers. - Sensory cells. - Nerve cells - Cnidocytes (forming a nematocyst) The ectoderm, has cells 2-Inner layer, Gastrodermis that aid in capturing food -It lines the gastrovascular and cells that secrete -it is mainly nutritive in function mucus. The endoderm, including: has cells that produce -Musculo-nutritive cells digestive enzymes and -Glandular cells break up food particles -Mucous-secreting cells -Sensory cells and Nerve cells