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Phylum Cnidaria (=Jellyfish & Corals) Most Members of the Phylum (Eg

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Phylum Cnidaria (=Jellyfish & Corals) Most Members of the Phylum (Eg Phylum Cnidaria (=Jellyfish & Corals) most members of the phylum (eg. corals) are sessile 9,000 living species, 9,300 fossil species often beautiful and graceful “plant-like” or “flower- like” forms with one or more rows of large include: tentacles extending from body jellyfish sea anemones like sponges, ancient scholars considered them some kind of corals plant sea fans sea whips not considered animals until 1700’s another very ancient group with lots of fossil but some (eg. jellyfish) swim weakly as part of the representatives zooplankton simplest living animals with true tissues though sessile almost all are extremely effective predators longest fossil history of any animal jellyfish are among the longest of animals known fossils are even more ancient than up to 9’ diameter with 120’ tentacles sponges some colonial forms can grow up to 150’ long going back at least 700 M years (plenty of hard parts – corals) as a colony, they rank as some of the longest – lived animals on earth st in terms of evolutionary history they were the 1 animals to appear that had a definite shape eg. a gold coral colony off the coast of Hawaii was recently (2009) dated at 2742 years old radial symmetry eg. a black coral in the same area was dated at 4265 years old all known animals at that time were sessile all are aquatic organisms; cnidaria (jellyfish) may have been the first animals to swim widespread in marine habitats Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 1 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 2 à especially shallow waters, warmer oceans polyp (=hydroid) a few found in freshwaters tubular body all but 1 species of fw cnidarians are polyps usually sessile – though some can move upward facing mouth surrounded by tentacles but there is one small fw jellyfish: Craspedacusta medusa (=jellyfish) many are colonial umbrella shaped à groups of individuals usually living together and mouth facing downward interconnected eg corals often, thick jelly-like layer in body wall à jellyfish eg. a single coral colony can contain millions of individuals motile: contractions of “bell” free floating, pelagic planktonic tissue level of organization polyp medusa more complex than sponges but still very simple sessile motile asexual sexual do have true tissues benthic pelagic body wall is made of 2 layers of tissue Cells & Tissues only a few very simple organs two true tissue layers, not the 3 typical of animals Body Forms =diploblastic many cnidarians are polymorphic epidermis & gastrodermis à with 2 or more separate body forms 2 well defined embryonic layers: ectoderm with an alternation between forms endoderm àthe same species has 2 distinct forms become two adult tissues epidermis Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 3 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 4 gastrodermis most epidermal cells contain contractile fibers and act like muscle cells to produce movement between the two tissues is a jelly layer called mesoglea Cells of Epidermis: à very thick in “jellyfish” a. epitheliomuscular cells covers outside of body nontissue layer of mesoglea in between tall T shaped, columnar cells base elongated with myofibrils in a few species this mesoglea is replaced by 3rd muscular contractions true tissue: b. interstitial cells mesoderm à connective tissue undifferentiated cells can form cnidocytes, nerve cells, sex cells, etc Body Wall but not epitheliomuscular cells c. gland cells epidermis – tissue layer that lines outer surface around basal disc and mouth secretes mucus and adhesives those in basal disc can secrete gas bubble for floating mesoglea – jellylike middle layer; not tissue layer d. cnidocytes gastrodermis – tissue layer that lines GVC stinging cells, more later e. sensory cells 1. Epidermis scattered but especially near mouth and tentacles respond to chemical and tactile stimuli outer “skin” of the animal f. nerve cells most multipolar (3 or more processes) consists of cells that cover and protect form synapses with sensory cells and other nerve cells connect to epitheliomuscular cells and cnidocytes also contain special stinging cells 2. Mesoglea some areas also have gland cells for attachment not really a tissue layer, just a layer of jelly-like secretions contain nervous and sensory cells Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 5 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 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 à can glide on pedal disc à inchworm movements using tentacles these cells also contain contractile fibers for à 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, 2015.9 7 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 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 à highly coiled tubular thread àcontained within a capsule like organelle eg. Portuguese Man-O-War and some corals à 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 à mouth only digestion mostly extracellular, but some intracellular can differentiate between animate and inanimate objects most are predatory à 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, 2015.9 9 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 10 intracellular digestion completes the process at margins of bell often between lappets indigestible material is expelled through mouth contains ocelli à detect light statocysts à balance organs sensory pits à chemoreceptors No respiratory or excretory system Life Spans Coordination and Control little is know of lifespans of cnidaria no head, no cephalization, no CNS but one sea anemone kept in an aquarium lived very simple nervous system, no brain for 80 years until the tank was accidentally drained = nerve net some jellyfish can live up to 10 years mostly for coordinating contractions in body Reproduction diffuse network of nerve fibers connect to: sensory cells both sexual and asexual reproduction cnidocytes epitheliomuscular cells asexual: nutritive muscular cells asexual reproduction usually by budding some simple sense organs: if buds remain connected = colonial statocysts à balance ocelli à light fission sea anemones only polyp pedal laceration simple sensory cells scattered in epidermis sexual: medusae most are dioecious clusters of sense organs = rhopalium Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 11 Animals: Phylum Cnidaria; Ziser Lecture Notes, 2015.9 12 Classification gonads are epidermal in hydrozoa gonads are gastrodermal in other groups Class: Hydrozoa most shed gametes into water, often mass most are marine, a few are freshwater spawnings individuals usually small and inconspicuous polyp is dominant stage, some completely lack medusa but one species of box jellyfish actually have a “wedding dance” medusa when present has velum around margin no septae in GVC, no pharynx (=throat), no cells in mesoglea begins as male takes hold of female tentacle and pulls her most are colonial - small plant-like appearance around in the water most have polymorphism with alternation of generations he then draws her close, male and female become Class: Scyphozoa (true jellyfish) entwined, so that their manubria touch most of the larger jellyfish belong to this group male deposits a spermatophore on one of her tentacles and medusae without velum, cells in mesoglea releases her all are marine solitary polyp stage reduced
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