BIOL 3454 1st Edition Lecture 10 I Cnidarians Ctenophorans natures dart gun cnidarians have nematocysts specialized organelles that require phylum cnidaria greek knide nettle latin aria suffix for plural cnidocytes all have stinging organelle nematocysts are a type of cnidocyte fastest animal motion recorded longest fossil history of any animal 700my all aquatic prefer shallow warm water most are sessile most slow or slightly swim many exist in symbiotic relationships mutualistic commensalistic parasitic common to name after ships Relationship mutualism both indiv benefit commensalism one benefits one has no effect parasitism one benefits the other losses economic importance most cnidarians of minimal economic consequence except for corals reefs provide food and tourism coral reefs are the most diverse aquatic ecosystem 50 all marine species 1 of ocean area Characteristics test question about non living part of cnidarian cnidocytes present usually nematocysts aquatic readially or birdially symmetrical have polyps medusae diploblastic wiht mesoglea extracellular digestion These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute simple nerve net no excretory or respiratory system no coelomic cavity polyps vs medusae cnidarians have two polyp sessile hydroid medusa jellyfish mobile seem different but both have a saclike body plan medusa is just an unattached polyp polyps reproduce asexually budding fussion pedal laceration exhibit strong phenotypic plasticity or polymorphism single genotype can have multiple phenotypes hydrozoa hydrnths vs gonagia Medusae free swimming with bell or umbrella shaped bodies tetramerous symmetry body parts in fours statocysts for orientation and ocelli for light reception sense gravity statocysts Cnidarian life cycles polyps an medusae play different roles lots of variation between taxonomic groups poly usually sessile some collections of polyps and medusae polyps asexual medusa sexual why the variation phylogenetic constraint anthozoans branch off before medusa evolves true loss of character state hydrozoans probably lost the medusa some may have medusa reduction so drastic it appears as loss all based on nich and evolution only need 1 way of reproducing Body Wall outer endodermis inner gastrodermis mesoglea between no true muscle cells mesoglea covers body thickest in stalk thinnest in tentacles gives support through hydrostatic pressure acts like an elastic skeleton jelly in the jellyfish Cnidocytes unique cell type to the phylum several types adhesive recoiling nematocysts cnidoblast during development cnidae organelle are discharged cell is resorbed nematocyst specialized type of cnidae with chitin like material covered by operculum hydrostatic pressure differences trigger called a cnidocil modified cilium 2 ways to make something hard chitin or NaCl nematocyte feeding digestion polyps carnivorous tentacles capture prey and suck into gastrovascular cavity digestion is internal but extracellular medusa usually filter feeders but not always end of mouth or mouth tube called manubrium corals usually supplement diet with symbiotic algae coral bleaching water gets too warm algae evicted from corral polyps if water cools can return if water doesnt cool coral dies from starvation expected to result in the destruction of most coral reefs by 2050 nerve net diverse simple NS base of epidermis and base of gastrodermis 2 nets that interconnect two way transmission vesicles only on one side of synapse in most animals on both sides in cnidarians no myelin only group animal that have 2 way nerve single no myelin neuromuscular system combination of sensory and nerve cells still represented in all animals digestive system in annelids nerve plexuses in mammals no centralization although some have rhopalia cluster of sensory cells precursor to centralization Class Hydrozoa basic terms polyp base salk one or more zooids hydrorohiza base like a root stolon hyrocauli stalks cellular part called the coenosarc covering called the perisarc individual polyps attached to hydrocaulus hydranths or gastrozooids for feeding thecate covered or athecate naked polyps obelia life cycle germ cell zygote fertilization asexual reproduction budding reproductive polyp meiosis Tubalaria life cycle actinula emerges actinula young polyp adult polyp gonophores larva developing in gonophore Class Hydrozoa basic terms medusa velum margin of the bell that projects inward entocodon developmental layer from ectoderm unique to hydrozoa differentiates into muscles Hydra sp cnidaria that is not a corral 16 species in N America live on underside of aquatic leaves 3cm body is a slender stalk with tentacles at one end and a basal disc for attachment mouth located on top of a conelike structure called a hypostome catches prey with nematocysts on tentacles reproduces sexually asexually hydra anatomy EM Epitheliomuscular cells for covering contraction interstitial cells undifferentiated stem cells everything but EM cells gland cells secrete the adhesive that allows the Hydra to attach found around the foot cnidocytes through the whole epidermis Sensory cells in the epidermis have synapse on one end and a flagellum on the other nerve cells both one way and two way Physalia man o war pneumaatophore sail for floatation drift with the currents dactylooids fishing tentacles gonozooids or gonophores sacs containing empty space ovaries or testes