Phylum Cnidaria Often Beautiful and Graceful “Plant-Like” Or “Flower- (=Jellyfish & Corals) Like” Forms with One Or More Rows of Large Tentacles Extending from Body

Phylum Cnidaria often beautiful and graceful “plant-like” or “flower- (=Jellyfish & Corals) like” forms with one or more rows of large tentacles extending from body 9,000 living, 9,300 fossil like sponges, ancient scholars considered them some kind of plant include: jellyfish not considered animals until 1700’s sea anemones corals but some (eg. jellyfish) swim weakly as part of the sea fans sea whips zooplankton another very ancient group with lots of fossil though sessile almost all are extremely effective representatives predators longest fossil history of any animal jellyfish are among the longest of animals up to 9’ diameter with 120’ tentacles known fossils are even more ancient than sponges some colonial forms can grow up to 150’ long going back at least 700 M years as a colony, they rank as some of the longest – lived (plenty of hard parts – corals) animals on earth in terms of evolutionary history they were the 1st eg. a gold coral colony off the coast of Hawaii was recently animals to appear that had a definite shape (2009) dated at 2742 years old eg. a black coral in the same area was dated at 4265 years old all known animals at that time were sessile organisms; cnidaria (jellyfish) may have been all are aquatic the first animals to swim widespread in marine habitats radial symmetry ! especially shallow waters, warmer oceans most members of the phylum (eg. corals) are sessile a few found in freshwaters Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 1 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 2 tubular body all but 1 species of fw cnidarians are polyps usually sessile – though some can move but there is one small fw jellyfish: Craspedacusta upward facing mouth surrounded by tentacles many are colonial medusa umbrella shaped ! groups of individuals usually living together and interconnected eg corals mouth facing downward often, thick jelly-like layer in body wall eg. a single coral colony can contain millions of individuals ! jellyfish motile: contractions of “bell” tissue level of organization free floating, pelagic planktonic more complex than sponges but still very simple polyp medusa do have true tissues sessile motile asexual sexual only a few very simple organs benthic pelagic Cells & Tissues Body Forms two true tissue layers, not the 3 typical of many cnidarians are polymorphic animals ! with 2 or more separate body forms =diploblastic epidermis & gastrodermis with an alternation between forms 2 well defined germ layers: !the same species has 2 distinct forms ectoderm endoderm polyp (=hydroid) become two adult tissues medusa (=jellyfish) epidermis gastrodermis polyp Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 3 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 4 between the two tissues is a jelly layer called most epidermal cells contain contractile fibers and mesoglea act like muscle cells to produce movement ! very thick in “jellyfish” Cells of Epidermis: nontissue layer of mesoglea in between a. epitheliomuscular cells covers outside of body in a few species this mesoglea is replaced by 3rd tall T shaped, columnar cells true tissue: base elongated with myofibrils muscular contractions mesoderm ! connective tissue b. interstitial cells Body Wall undifferentiated cells can form cnidocytes, nerve cells, sex cells, etc but not epitheliomuscular cells epidermis – tissue layer that lines outer surface c. gland cells around basal disc and mouth mesoglea – jellylike middle layer; not tissue layer secretes mucus and adhesives those in basal disc can secrete gas bubble for floating gastrodermis – tissue layer that lines GVC d. cnidocytes stinging cells, more later 1. Epidermis e. sensory cells scattered but especially near mouth and tentacles outer “skin” of the animal respond to chemical and tactile stimuli consists of cells that cover and protect f. nerve cells most multipolar (3 or more processes) form synapses with sensory cells and other nerve cells also contain special stinging cells connect to epitheliomuscular cells and cnidocytes some areas also have gland cells for attachment 2. Mesoglea contain nervous and sensory cells not really a tissue layer, just a layer of jelly-like secretions Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 5 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 6 very thin layer in polyps; much thicker in medusa cavity in which it lives thus “jellyfish” muscle layers in body wall contract against 3. Gastrodermis hydrostatic skeleton inner lining of the digestive sac some polyps of noncolonial forms are motile mademostly of cells that digest and absorb food eg. fw hydras are not permanently attached ! can glide on pedal disc ! inchworm movements using tentacles these cells also contain contractile fibers for ! gas bubbles and float to surface movement medusae are more mobile Cells of Gastrodermis: have hydrostatic skeleton a. nutritive muscular cells tall T shaped, columnar cells ciliated nerve net controls contractions of bell for base elongated with myofibrils swimming lines GVC in some freshwater species cells contain green algal symbionts Feeding and Digestion in some marine species cells contain dinoflagellate algal symbionts all are carnivores b. Interstitial cells scattered most species have one or more rings of tentacles transform into other cells as needed, see above surrounding mouth c. gland cells in hypostome and scattered throughout armed with cnidocytes (=stinging cells) for some secrete digestive enzymes capturing prey mucous glands around mouth Stinging Cells (cnidocytes) Movement one of the most characteristic features of the typically polyp is sessile and often secretes a cup like phylum Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 7 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 8 most are not harmful to humans used for feeding and defense eg. most sea anemones stings are harmless inside each cell is harpoon-like nematocyst but a few are very painful ! highly coiled tubular thread !contained within a capsule like organelle eg. Portuguese Man-O-War and some corals ! triggerlike cnidocil (tactile trigger) a few can be fatal when triggered can fire in a fraction of a second eg. cubomedusae (box jellies) discharge due to: digestive system is a mouth that opens into a saclike cavity high osmotic pressure within (140 atm; 10x’s sea level) when stimulated to discharge water rushes in = gastrovascular cavity lined with gastrodermis forces thread out with great force – turns inside-out as it extends at 2m/sec causes barb to flick out like tiny switchblades to impale prey single opening = mouth each cell operates independently incomplete digestive tract ! mouth only digestion mostly extracellular, but some intracellular can differentiate between animate and inanimate objects most are predatory ! doesn’t just fire at anything use cnidocytes to capture and paralyze prey use tentacles to move prey toward mouth cnidoblast must grow new nematocyst after firing engulf prey with mouth over 20 different kinds inside GVC gland cells secrete digestive enzymes some wrap around prey or are sticky nutritive muscular cells take in particles by some with tiny barbs that impale prey & inject poison pseudopodia Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 9 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 10 intracellular digestion completes the process at margins of bell often between lappets indigestible material is expelled through mouth contains ocelli ! detect light statocysts ! balance organs sensory pits ! chemoreceptors No respiratory or excretory system Reproduction Coordination and Control both sexual and asexual reproduction no head, no cephalization, no CNS asexual: very simple nervous system, no brain asexual reproduction usually by budding = nerve net if buds remain connected = colonial mostly for coordinating contractions in body fission sea anemones only diffuse network of nerve fibers connect to: pedal laceration sensory cells cnidocytes sexual: epitheliomuscular cells most are dioecious nutritive muscular cells many shed gametes into water gonads are epidermal in hydrozoa some simple sense organs: gonads are gastrodermal in other groups statocysts ! balance ocelli ! light little is know of lifespans but one sea anemone kept in an aquarium lived for 80 years until the tank polyp was accidentally drained simple sensory cells scattered in epidermis some jellyfish can live up to 10 years medusae clusters of sense organs = rhopalium Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 11 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2012.9 12 embryo in marine species is usually a planula Classification in many members of the group there is an Class: Hydrozoa alternation of generations between most are marine, a few are freshwater individuals usually small and inconspicuous polyp which reproduces asexually and the polyp is dominant stage, some completely lack medusa medusa when present has velum around margin medusae which reproduces sexually no septae in GVC, no pharynx (=throat), no cells in mesoglea most are colonial - small plant-like appearance most have polymorphism with alternation of generations Class: Scyphozoa (true jellyfish) most of the larger jellyfish belong to this group medusae without velum, cells in mesoglea all are marine solitary polyp stage reduced or completely absent thick jelly layer (=mesoglea) Class: Cubomedusa (box jellyfish, sea wasps) cubical jellyfish with extremely potent toxins - some lethal Class: Anthozoa (Corals and Sea Anemones) =”flower animals” all are marine polyp

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