Cnidaria Notes September 24, 2024 PDF

1 OUTLINE Phylum Cnidaria - Jellyfish, Sea anemones, Corals 1. Introduction 2. Body Forms and Structure 3. Cnidae (e.g.: nematocysts) 4. Nerve Net / Muscles 2 INTRODUCTION...

1 OUTLINE Phylum Cnidaria - Jellyfish, Sea anemones, Corals 1. Introduction 2. Body Forms and Structure 3. Cnidae (e.g.: nematocysts) 4. Nerve Net / Muscles 2 INTRODUCTION Chordates Arthropods Hemichordates Annelids Brachiopods Echinoderms Mollusks Bryozoans Nematodes Nemerteans Gastrotrichs Rotifers Flatworms Cnidarians ✓ Sponges Ancestral Metazoan ✓ Unicellular Eukaryotes 3 INTRODUCTION - polymorphic: 2 body forms (polyp, medusa) - 2 germ layers (ectoderm, endoderm) - radial symmetry - Gastrovascular cavity (enteron) with single opening, surrounded by tentacles - Cnidocytes (contain cnidae)  4 INTRODUCTION Phylum Cnidaria Class Hydrozoa Scyphozoa Cubozoa Anthozoa Staurozoa Myxozoa Lifestyle solitary or solitary solitary solitary or solitary parasitic colonial colonial Body form 1. Polyp present reduced reduced present present (absent?) (absent?) 2. Medusae present present present absent absent 5 BODY FORMS Cnidarians fit into one of two morphological types – i.e. dimorphism mouth anus gastrovascular cavity (enteron) epidermis mesoglea gastrodermis anus diploblastic mouth 1. Polyp Morph 2. Medusa Morph 6 BODY FORMS Sessile polymorphic colonial forms (e.g: Obelia) Class: Hydrozoa Gastrozooid polyps - feeding polyps with mouth and tentacles for prey capture Dactylozooid polyps - naked polyps without mouth - functions for defense of colony Gonozooid polyps basal stolon - reproductive naked polyps without mouth Mutualistic hydrozoan colony on hermit crab shell - produce male or female gametes/medusae 7 BODY FORMS Free living polymorphic colonial forms – Physalia physalis Class: Hydrozoa; (Portuguese Man-of-War) Gas-filled float (modified polyp), pneumatophore Polyp morphs gonozooids - male and female gastrozooids - with tentacle - terminal mouth for feeding dactylozooids - with highly retractable tentacle 8  9 Distinguishing free living medusae forms Hydrozoan (e.g. Obelia) Scyphozoan (e.g. Aurelia) radial canal 2 Gastric pouch 3 3 ring canal 2 1 3 radial canals ring canal 1 velum present 1 velum absent 2 manubrium present 2 manubrium absent [4 large oral arms] 3 gastrovascular cavity connects to 4 radial canals, a ring canal and 3 4 gastric pouches connect to a complex system of radial tentacles canals and a ring canal/tentacles 10 BODY FORMS 3 Cubozoa Gastric filaments 1 velarium present (similar to velum, functions in swimming) 6 2 Manubrium present 2 Radial pouch 3 3 Gastric pouch connects with gastric filaments and radial pouch 4 base of each tentacle differentiated into a 1 blade-like pedalium 4 5 a tentacle (or group of tentacles) at each “corner” of the bell margin 5 6 umbrella (or bell) almost square 11 BODY FORMS Cubozoa Chironex fleckeri (sea wasp or box jellyfish) - Up to 15 tentacles on each corner (60 total) - each tentacle up to 3 m long when feeding - contact with just 3 cm of tentacle can kill an adult human 12 CNIDAE: NEMATOCYSTS Nematocyst – the most common type of cnida, a stinging organelle contained within a cnidocyte. - abundant on tentacles - discharge stimulated by chemical and/or physical contact nematocyst cnidocyte cnidocil operculum 13 CNIDAE: NEMATOCYSTS nematocyst cnidocil cnidocyte operculum Discharged nematocyst 14 Nematocyst discharge: 15 16 NERVE NET A. Hydra nerve net Diffuse nervous system - found at base of epidermis and base of gastrodermis (interconnected) - bidirectional transmission of impulses - nerve processes synapse or junction with: 1. (neuro)sensory cells 2. epitheliomuscular cells 3. nutritive-muscular cells - important landmark in the evolution of nervous systems B. Nerve net of Guinea pig intestine 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