Phylum cnidaria




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Lecture 2

PHYLUM CNIDARIA

Tissue level of organization, simple nerve net

Diploblastic – two tissue layers:

Epidermis: outer skin, contains cnidocytes, epitheliomuscular cells, interstitial cells, neurosensory cells

Gastrodermis: lines gastrovascular cavity, nutritive muscular cells, interstitial cells, gland cells

Mesoglea – nonliving gelatinous layer in middle

Mouth serves same function as anus

Circular muscles elongate body

Longitudinal muscles shorten body

Life cycle

Polyp (sessile form) – asexual reproduction

Medusa (mobile form) – sexual stage, gonochoristic

Class Hydrozoa – both stages dominant

Class Schyphozoa – Medusa stage dominant

Class Anthozoa – Only Polyp stage

General life cycle: Sperm and egg meet externally, form zygote, form actinula (or planula) larvae, form polyp stage, asexual buds from polyp form medusa stage and cycle starts over

PHYLUM CNIDARIA

CLASS HYDROZOA – all medusa have characteristic velum

ORDER HYDROIDEA

Hydra – single polyp, no medusa stage

Obelia – colonial organism, feeding polyps called gastrozooids

Reproductive polyps called gonozooids

Both are connected thru gastrovascular cavity

Medusa forms: Leptomedusa – flattened bell (Obelia)

Anthomedusa – domed bell (Gonionemus)



ORDER SIPHONOPHORA

Portugese Man-O-War (colonial organism)

Pneumatophore = “sail”

Hanging morphs called cormidia with gastrozooids

Fishing tentacles

Dactylozooids with cnidocytes

Budding medusae form sexual gonophores, stay in colony

ORDER HYDROCORALLINAE

Hydrozoan corals (colonial organisms)

Calcium carbonate exoskeleton (fire corals – covered in cnidocytes)

Tiny pits in exoskeleton where polyps reside




CLASS SCHYPHOZOA

ORDER SEMOSTOMAE

Typical jellyfish

Life Cycle: Sperm and egg unite to form zygote, planula larvae, polyp form called scyphostoma, forms strobula, forms ephyra (baby medusa), forms adult medusa

CLASS ANTHOZOA (NO MEDUSA STAGE IN THIS CLASS)

SUBCLASS ZOANTHERIA

ORDER ACTINARIA

Sea Anemones, solitary polyps with no exoskeleton



ORDER SCLERACTINIA

True corals, also called hard coral

Calcium carbonate exoskeleton, very few cnidocytes


OMMISSIONS AND SUGGESTIONS

EX. 2 – omit epitheliomuscular cells, gland cells

EX. 4 – living hydra, start this exercise first because they can take some time to capture their prey

EX. 6 & 7 – omit tentaculocysts on live specimens

EX. 8 – omit everything but pneumatophores and fishing tentacles

EX. 9 – omit everything starting after “in one corner of the drawing……”

Only label radial canal

EX. 10 – omit subgenital pits and rhopalia



EX. 11 – omit mesenteries, epidermis, gastrodermis, ostia, stomodaeum, and siphonoglyph

EX. 12 – be sure you label the types of corals you draw on this page


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