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