Marine Biology Exam 2

Dr. Traci Erin Cox's Marine Biology at LSUNO

Phylum Cnidaria

• Have Ecto & Endo Derm tissue layers

• Often Radial Symmetry (oral - aboral body axis)

• Stinging/Adhesive structured called cnidocytes containing nematocysts cells

• Exhibit alternation of asexual polypoid & sexual medusoid generations

• SImple Nerve Net nervous system

• Have Planula Larvae

• Osmoregulation through body wall

Cnidaria Body Plan

• Poses a medusa, polyp or both.

• Mesoglea from ectoderm

• Tentacled & a mouth lead to gastrovascular cavity that responsible for digestion and circulation

• Have a Hyrdrostatic Skeleton (water supported)

Cnidocyte aka Nematocysts

Cnidocil is triggered - the operculum opend and the coiled shaft is everted exposing stylet w spines- may have stinging toxins released

How to Cnidaria Feed?

• Carnivores or parasites that use tentacled to capture food and bring to mouth (some w oral disk that closes on food) use a mucus net suspension feeding

• Have a symbiotic relationships with zooxanthellae and digest extracellularly

Class Anthozoa - Phylum Cnidaria

• Anemones, corals, sea pens and sea pansy (exclusively marine)

• Lack Medusa stage ARE Benthic Polyps most w 8 tentacles

• Gastrovascular cavity lined w ciliated ,cnidae & gland cells called mesentary filaments (string-like internal tissue folds that corals can extend out of their mouths to digest food, clean surfaces, or attack neighboring competitors)

• Pharynx is a flagellated groove

• Polyps thats reproduce xesually and asexually (releasing gametes thru cavity)

Anemone Structure- Anthozoa - Cnidaria

Acontia are filaments that are used in defense and feeding … may have defensive structures around oral tentacles to fight with neighbors

Individual polyps in a colony are called zooids which connect thru the mesoglea

Two Types of Coral

• Those that build reefs are called Hermatypic- these harbor zooxanthellae (symbiodium)

• Ahermatypic corals lack zooxanthellea and fully rely on capturing food (can also be solitary)

Direct / Vertical Transfer Coral (anthozoa) Symbionts

Asexually = symbiont released in egg from mother or are obtained thru phagocytosis from the coral or be infiltrated by the zooxanthellae containing cytoplasmic extensions of the coral cells

Indirect / Horizontal Transfer of Coral (Anthozoa) Symbionts

Are absorbed by environment motile zooxanthellae can show positive chemotaxis in the direction of corals with zero or lower concentrations of zooxanthellae

Corals can obtain zooxanthellae indirectly through the ingestion of fecal matter excreted by corallivores.

Class Scyphozoa - Phylum Cnidaria

• True Jellyfish (exclusively marine) cane be both benthic and planktonic bc of medusa and polyp life stages (may even lack polyp stage)

• Medusa stage is large - Polyps are small, inconspicuous & can be long lived

• Polyps produce Medusa throu asexual budding called strobilation

• Have THICK mesoglea

• Medusas move by moscular contraction of the bell

Scyphozoa Structure

Scyphozoa Reproduction

Class Hydrozoa - Phylum Cnidaria

• Hydrozoids

• Usually colonial & polymorphic Polyps

• Medusa and Polyps can be present

• Reproduction involves medusa usually involved in production of gametes & polyp asexual budding

• Medusa can be retained on polyp

• Medusa has a structure called a velum that tends to be clear

• Protein exoskeleton usually chiton called a perisarc and living tissue called coenosar