Mr. Bastin - Cnidarians

Taxonomy

Domain: Eukarya

Kingdom: Animalia

Phylum: Cnidaria (from Greek "nettle"

Cnidarian Basics (includes, live with anyone, feeding, where they live)

-most marine

-includes hydras, jellyfish, sea anemones, coral

-some colonial

-carnivorous w/ stinging tentacles

Structure

-simplest animals to have body symmetry + specialized tissues

-radial symmetry (can respond to stimuli from all directions

-central opening surrounded by tentacles (functions as bot mouth/anus)

Life cycle

-typically dimorphic (2 stages)

Polyp: cylindrical body w/ tentacles

-usually sessile + adheres to substratum

- Mouth/anus points up

Medusa: bell-shaped body

-motile by drifting + weak contractions

- Mouth/anus points down

-both polyp and medusa have 2 tissue layers (diploblastic)

2 tissue layers (diploblastic)

-both the polyp and medusa have

-epiderm(is): outer layer of cells

-gastroderm(is): inner layer of cells lining gastrovascular cavity

-mesoglea: layer between

Feeding

sperm/egg

zygote

larva

polyp

budding polyp

young madusa

adult madusa

Response

-simple nerve net but lacks brain

-nerve net = loosely organized network of cells

-eyespots detect light

Movement

-microfilaments arranged into contractile fibers

-gastrovascular cavity acts as hydrostatic skeleton when filled w/ water

>enables body to change shape

>allows medusa to move by jet propulsion

Reproduction

-both asexual and sexual

Asexual: polyps clone by budding

-swell to form new polyp

-seperate to form tiny medusas

-polyps also clone by splitting

Sexual:

-individuals usually male + female

-external fertilization in water (sperm and egg released by parents) (usually Medusa)

-zygote becomes free swimming larva

-larva attaches to hard surface to form polyps

-polyps form medusas

Class Hydrozoa

-freshwater hydras to colonial marine taxa

Hydra:

-solitary polyps

-lack medusa stage

Obelia

Portuguese man-o-war

-colony of medusas+polyps

tentacles up to 20 meters long

-sting painful to fatal

Class Scyphozoa

-jellyfishes (cup animals)

-medusa most prominent stage

-sting for feeding + defense (painful to fatal)

Class Anthrozoa

-sea anemones and corals

-only occur as polyps (lack a medusa stage)

Sea anemones:

-solitary polyps

-capture prey with nematocysts

-fight for space with other anemones

-some symbiotic with:

> Algae (food and oxygen)

>crabs (motility)

>fish (nutrients, defense)

Corals:

-colonial polyps

>motile larva settle onto hard surface

>developer into polyps

>produce colony by budding

-secrete skeletons of CaCo3 (calcium carbonate)

>cement to adjacent polyps

>over time, build up rocklike formations called coral reefs

>three types of reefs

-distrabution determined by water temp and light

-rely on symbiotic zooxanthellae

Types of reefs

Fringing: near coastline and around islands/continents

Barrier: parallel to coastline but are separated by deeper, wider lagoons

Atolls: rings of coral that create protected lagoons

Corals rely on symbiotic zooxanthellae for?

-its a type of algae

-provides oxygen

-aids in CaCo3 (calcium carbonate) production

Threats to coral reefs

-Siltation: the sand/soil blocks the coral from light

-Ocean warming

> Coral expel zooxanthellae

>results in coral bleaching (coral loses color without zooxanthellae)