The Coelomate Bauplan

THE COELOMATE BAUPLAN EVOLUTION OF BODY CAVITY Triploblastic Bauplans Acoelomate Bauplan     Problems associated with acoelomate bauplan: Body organs cannot move freely but are embedded in solid mesoderm tissue. Difficult for materials to move from the gut to the body wall. These evolutionary constraints called for development of a body cavity, called a coelom Coelomate Bauplan     A coelom is a body cavity which lies between the body wall and the digestive system This body cavity is filled …coelomic fluid Movement of the body wall becomes independent of the digestive system This led to development of tube-within-atube body design Advantages of a coelom 1. 2. 3. Coelom separates gut from the body wall and this allows muscles of the digestive system to push food independently of the movement of the body. Animal gains internal space into which can bulge digestive organs, gonads, and developing embryos. Coelomic fluid bathes and lubricates all organs Advantages of a coelom 4. 5. 6. Coelomic fluid functions as transport system to distribute O2, nutrients and hormones throughout body Metabolic wastes are also carried to the body surface more efficiently by fluid than by solid mesoderm. Hydrostatic skeleton- fluid in coelom may function as a lever around which muscles of body contract This leads to more effective locomotory systems.  The Result - Faster locomotion and Larger body size possible.  Advantages of a coelom In addition to having a body cavity, organisms with coelom also have a complete digestive tract Porifera, Cnidaria and Flatworms had Two way digestive systems. Rondworms have a 1 way system. ANUS digestive MOUTH Food enters the worms MOUTH, and exits through the Advantages of a coelom   This digestive system has a mouth and anus. This makes digestion and feeding more efficient because animal can eat before it has finished digesting its previous meal. Advantages of a coelom   Absorption of larger amounts of nutrients is possible with a complete tract and therefore bigger and more complex species can develop. digestion is more efficient, since it provides different sites with different physical and chemical conditions (mouth, stomach, bowels) for the action of different complementary digestive enzyme systems. Types of body cavities  There are two types of body cavities: Pseudocoelom Coelom True The Pseudocoelom Bauplan     Pseudocoelom is a body cavity derived from a persistent blastocoel It is lined by material derived from mesoderm germinal layer only on one side (outside). This is a tube-within-a-tube design, the outer tube being the body wall and underlying muscles and the inner tube being the digestive tract Pseudocoelom is filled with coelomic fluid and it contains reproductive system and other structures The Pseudocoelom Bauplan  Pseudocoelomates have a complete digestive system  It also allow the system to be specialized The Pseudocoelom Bauplan The Pseudocoelom Bauplan Advantages of pseudocoelom 1. 2. 3. 4. Pseudocoelom provides space for internal organs. Pseudocoelomic fluid serves as ‘hydrostatic skeleton’ during locomotion. The coelomic fluid protects the internal organs from mechanical shocks. The coelomic fluid helps in distribution of the nutrients, collection and storage of nitrogenous wastes fill the time of excretion. Pseudocoelomate Phyla         Acanthocephala -- spiny-headed worms; about 1150 spp Chaetognatha -- arrowworms; about 70 species. Cycliophora -- cycliophorans; 1 species known Gastrotricha -- gastrotrichs; about 430 species known Kinorhyncha -- kinorhynchs; about 150 species known Loricifera -- loriciferans; about 10 species described Nematoda -- nematodes or roundworms; about 12,000 spp Nematomorpha -- horsehair worms; about