Platyhelminthes I Notes Sept 26 2024 PDF

17 NERVE NET- neuromuscular system Lateral nerve net interconnection Contraction of lateral Contraction of longitudinal myofibrils...

17 NERVE NET- neuromuscular system Lateral nerve net interconnection Contraction of lateral Contraction of longitudinal myofibrils permits myofibrils permits body peristaltic-type movement and/or tentacle shortening 18 1 OUTLINE Phylum Platyhelminthes – flatworms, flukes and tapeworms 1. Introduction 2. Body Form and Structure(s) 3. Osmoregulation 4. Nervous Tissue 5. Parasitic strategies 2 INTRODUCTION Chordates Arthropods Hemichordates Annelids Brachiopods Echinoderms Mollusks Bryozoans Nematodes Nemerteans Gastrotrichs Rotifers Flatworms ✓ Cnidarians ✓ Sponges Ancestral Metazoan ✓ Protozoa 3 INTRODUCTION Phylum Platyhelminthes Class Turbellaria Trematoda Monogenea Cestoda Lifestyle free living parasitic parasitic parasitic Parasitic internal external internal mode Digestive present present present absent tract 4 INTRODUCTION Pseudoceros-inhacensis-h01x_jpg A. Bilateral symmetry B. Triploblastic acoelomates 1 3 C. Tissue-organ level of organization 2 5 BODY FORM AND STRUCTURES Cross Section of Planarian (Class: Turbellaria) Pharynx DORSAL (NOT ciliated Epidermis) Intestine VENTRAL (Ciliated Epidermis) Nerve Cord Dual-gland Rhabdite adhesive Cell organ 6 BODY FORM AND STRUCTURES Ciliated Ventral Epidermis Parenchymal muscle Longitudinal muscle Circular muscle Basement membrane Epidermal cell Cilia substratum 7 BODY FORM AND STRUCTURES Specialized Structures in Epidermis 1. Rhabdites : rod shaped fused vesicles from golgi body inside parenchymal cells (Rhabdite cell). - Rhabdite cell inserts into epidermis when Rhabdites formed. 2. Dual-gland adhesive organs: three cell types, mediate attachment and release of epidermis to substrate (aid in locomotion). 8 1. Rhabdites and 2. Dual-gland Parenchymal muscle Longitudinal muscle Circular muscle Basement membrane Epidermal cell Cilia substratum 2. Dual-gland adhesive organ – 1. Rhabdites – released into lobes produce secretions which environment causing a thick are released into environment mucous coat for protection. via extensions. 9 BODY STRUCTURE & LOCOMOTION Locomotion involves each of: A. Ciliated ventral surface B. Subtle muscular contraction C. Dual-gland adhesive organs VENTRAL (Ciliated Epidermis) substratum 10 BODY STRUCTURE & LOCOMOTION A. Ciliated ventral surface B. Subtle muscular contraction C. Dual-gland adhesive organs 1. Paired viscid cells (glands) - produce adhesive secretions that attach anchor cells to substratum 2. Anchor cells - bear strain of attachment & allow subtle muscular contractions to pull the animal forward 3. Releasing cell (gland) substratum - secretes chemicals that release anchor cell attachment  11 OSMOREGULATION Flame cell * Protonephridium [Gk. prōtos, first; nephros, kidney] - an 'inverted' flagellated cell (flame cell) sitting in a 'mesh cup' (tubule end) Flagella Tubule(s) -Mesh (weir) = cellular interdigitation between flame cell and terminal tubule cell * Tubule  12 OSMOREGULATION Flame cell * Protonephridium [Gk. prōtos, first; nephros, kidney] - an 'inverted' flagellated cell (flame cell) sitting in a 'mesh cup' (tubule end) Flagella Tubule(s) -Mesh (weir) = cellular interdigitation between flame cell and terminal tubule cell * Tubule  13 OSMOREGULATION Flame cell * Protonephridium [Gk. prōtos, first; nephros, kidney] - an 'inverted' flagellated cell (flame cell) sitting in a 'mesh cup' (tubule end) Flagella Tubule(s) -Mesh (weir) = cellular interdigitation between flame cell and terminal tubule cell -flagellar beat creates negative pressure and draws fluid in through mesh - fluid is “ultrafiltered”, then further * modified in tubule system - modified fluid is eliminated through Tubule excretory pores; nephridopores 14 Tubule End Cell 15 NERVOUS TISSUE 3 Types of nervous tissue organization 1. Subepidermal nerve plexus - simplest system, resembling the diffuse cnidarian Ringlike Primitive nerve net Brain Cnidarian Platyhelminth 16 NERVOUS TISSUE 2. Subepidermal nerve plexus + longitudinal nerve cords - 1 – 5 nerve cord pairs lying under the musculature cerebral ganglion nerve cord 17 NERVOUS TISSUE auricle cerebral ganglion ring commissures nerve cord 3. Nerve cords + a primitive brain - nerve cords (1 – 3 pairs), with connecting nerves (ring commissures) forming a “ladder-type” pattern 18 NERVOUS TISSUE -ve thigmotactic Auricle (Side of body) 1. tactile receptors 2. chemoreceptors 3. rheoreceptors 4. statocysts (gravity) 5. photoreceptors (ocelli) +ve thigmotactic 3. Nerve cords + a primitive brain - nerve cords (1 – 3 pairs), with connecting nerves (ring commissures) forming a “ladder-type” pattern