Cnidaria

General Information  Eumetazoans  (true animals) all animals other than sponges-have both tissues and symmetry  When eumetazoans develop-they develop three embryonic tissue types  Ectoderm  outer layer-gives rise to outer covering of body and nervous system  Mesoderm  middle layer-gives rise to skeleton and muscles  Endoderm  inner layer-gives rise to digestive organs

Cnidaria Characteristics  Includes jellyfish, hydra, sea anemones, and corals  All radially symmetrical  All are carnivorous-capture prey with tentacles around the mouth  Evolved a digestive cavity  Two body forms  Medusa  (sexual) free floating, umbrella shape  Polyp  (asexual) cylindrical, attached to rocks

Cont…  Single opening (mouth/anus) to gastrovascular cavity where food & water enter & wastes leave; called one-way digestive system  Have a simple nerve net (only travels one way) to help with movement & senses

Reproductive Life Cycle  Alternate generations between polyp and medusa form Planula (larval form) Polyp Medusa Egg Sperm Zygote + Asexual - budding Sexual

Stinging Cells  Tentacles have stinging cells called cnidocytes  Each cnidocyte has nematocyst that are barbed and are used to spear the prey

Feeding  Use cnidocytes to stun or kill prey  Tentacles contract to bring food to mouth  Food is digested in gastrovascular cavity

Three Classes of Cnidaria  Hydrozoa  Polyp dominant which is larger than medusa  Scyphozoa  Medusa dominant and it is larger than polyp  Anthozoa  Only polyps no medusa forms

Hydrozoa  Hydrozoans   Have both medusa and polyp stages  EX: Hydra  freshwater- no medusa stage- solitary polyp- lives in quiet ponds, lakes, and streams- attaches to rocks with sticky basal disk  EX: Portuguese Man of War  marine-medusa and polyps- colony of organisms-gas filled balloon floats on surface and dangling below are the tentacles with stinging cells-prey is entangled in the tentacles

Hydrozoan Reproduction  Most hydrozoan reproduce asexually by forming small buds on the outside of their bodies-these buds develop into miniature polyps-  Hydrozoan can also reproduce sexually-the polyps produces male and female medusa that release egg and sperm in water-the egg and sperm form a larvae called a planulae the eventually settles to the bottom and forms a polyp. Bud

Colonization  Some Hydrozoans produce colonies in which different polyps have a different specialization.  Some specialized in feeding, reproduction, and protection

Scyphozoan  Scyphozoan  cup animal  Jellyfish  live most of their life as medusa  Active predators-hunt food  Sea wasp-deadly  Reproduce much like hydrozoans but male and female medusa mate and form planulae which settles to bottom and forms polyp. Polyp grows it and buds off to form medusa

Anthozoans  Anthozoans  largest class of Cnidaria – name means flower animal-DO NOT form medusa – Show neoteny (sexual maturity during the larval stage)  Sea Anemones  soft bodied polyps-coastal- feed on fish-when touched they retract their tentacles-Symbiotic  Corals  live in colonies-polyp secretes a hard outer covering which make up coral reefs-

Three types of Reefs  Fringing-close to beach-Florida  Barrier-form in deeper water farther out from the shore-Great Barrier Reef in Australia  Atoll-coral island that form far out at sea and grow into a ring shape with a lagoon in the center.

Homework 1.What are some differences between the three different classes discussed? 2.Why would it be of an advantage to switch from polyp to medusa for vise verse? 3.Why would it be of an advantage to have specialization in colonies?