Phylum Cnidaria A highly diverse assemblage that includes
Phylum Cnidaria • A highly diverse assemblage that includes jellyfish, sea anemonies, corals and hydras.
Characteristics of Cnidaria • Diplobastic Metazoa (Ectoderm and Endoderm). • Radialy Symmetrical. • Specialized Cells Cnidocytes for Feeding. • Two Body Types. 1) Polyp: Benthic. 2) Medusa: Pelagic.
CNIDARIA: HYDROZOA HYDRA SP. BUDDING FROM NEBRASKA LINCOLN: POLYP FORM
HYDRA SP. TOP VIEW
UPSIDEDOWN JELLYFISH: MEDUSA FORM Cassiopea frondosa
Tissue Layers Diploblastic = 2 germ layers • endoderm gastrodermis • ectoderm epidermis mesoglea • gelatinous matrix between the 2 layers epidermis gastrovascular cavity mesoglea gastrodermis
General Body Plan • sac-like body (only 1 opening) • Food and waste go in/out the same opening no anus! • water within GVC acts as a hydrostatic skeleton oral surface gastrodermis mesoglea epidermis aboral surface mouth Gastrovascular cavity
General Life Cycle
HYDRA SP. FEEDING A B C D
Nematocysts • specialized stinging organelles • found within cnidocytes (cells) • cnidocytes are located in epidermis A cnidocyte with a nematocyst within it
Nematocysts • nematocysts are like “mini-harpoons” • cnidocil senses movement & acts like a “trigger” • can inject poison, coil around prey, or be adhesive • functions: - prey capture; defense nematocyst cnidocil cnidocyte Undischarged Discharged
Nematocyst Types
HYDRA SP. UNDISCHARGED STENOTELE NEMATOCYSTS
DS DS HYDRA SP. UNDISCHARGED AND DISCHARGED STENOTELE NEMATOCYSTS
A S HYDRA SP. UNDISCHARGED STENOTELE AND ATRICHOUS ISORHIZA NEMATOCYSTS
A S HYDRA SP. DISCHARGED STENOTELE AND ATRICHOUS ISORHIZA NEMATOCYSTS
Nematocyst Discharge
Biology Feeding – nematocysts within cnidocytes – tentacles Digestion – extracellular (in GVC) – intracellular (by gastrodermal cells) – incomplete system (no anus) Gas exchange & Excretion – these systems are absent
Structure Nervous System – nerve net (no central nervous system= no brain) – sense organs – statocysts (equilibrium organs) – ocelli (photosensitive organs) Skeletal System – Mesoglea; water in GVC acts as a hydrostatic skeleton, and some external skeletal system.
Reproduction Asexual – budding – longitudinal fission
Reproduction Sexual – usually dioecious (separate sexes e. g. humans) – monoecious (both male + female gonads in 1 individual) – results in Planula larva
Phylum Cnidaria Class Hydrozoa: Freshwater and marine. Class Scyphozoa: Jellyfish, all marine. Class Anthozoa: Corals and Anemones, all marine. Class Cubozoa: Box jellyfish and Sea Wasps, all marine.
Class Hydrozoa • medusa & polyp body forms Fire coral Millepora
Class Hydrozoa • medusa & polyp body forms (medusa with velum) • most are colonial colonies are formed of individual zooids a single zooid
Class Hydrozoa • many of these colonies show polymorphism this is where there are several different types of polyps/zooid and each type is specialized for a different function e. g. gastrozooids = feeding polyps e. g. dactylzooids = defense polyps all the zooids within a colony are genetically identical these different zooids work together in the colony
Class Hydrozoa - a sessile colony showing polymorphism gastrozooid gonozooid entire colony
Class Hydrozoa - a Portuguese Man-o-war (Physalia) is a floating hydrozoan colony showing polymorphism Float entire colony gastrozooid dactylzooid
Portuguese Man-o-war Victims
Fire coral victim!
Class Hydrozoa- life cycle sexual reproduction asexual reproduction
Class Hydrozoa • Hydra is an example of a solitary, freshwater hydrozoan sexual reproduction gonads asexual No Medusa Stage reproduction bud
Class Hydrozoa • Hydra is an example of a solitary, freshwater hydrozoan asexual reproduction bud
Great Plains Hydrozoans
Chlorohydra viridissima: The Green Hydra The green color arises from Chlorella-like unicellular algae each occupying a vacuole in the endodermal cells.
Hydra vulgaris The common Hydra
Craspedacusta sowerbii Velum
Lives predominantly as a polyp in small lakes, ponds, and old water filled quarries the medusa stage occurs during July-October.
Three ways of asexual reproduction #1) Polyp budding. #2) Non ciliated planulalike buds may be produced.
Three ways of asexual reproduction #3) Production of medusa buds.
Sexual Reproduction Asexual Reproduction
Polypodium hydriforme The most bizarre of the freshwater cnidarians and one of the most unusual species of ALL Cnidarians!!
Polypodium spends almost all of its pre -adult life as a parasite of Acipenseriform fishes.
LIFE CYCLE
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