2. Cnidarians

2. Cnidarians Next evolutionary jump Sometimes called coelenterates Cells form tissues that perform specific functions Sometimes called coelenterates Include sea anemones, jellyfish, and corals

Cnidarians: Structure Finally, we see a pie that can be sliced! Cnidarians actually exhibit radial symmetry in which similar body parts can be grouped around a central axis. If cut like a pizza, all slices would be similar Look the same from all sides No head, front, or back

Cnidarians: Structure and Function Oral surface and aboral surface Central mouth with tentacles Mouth open into a gut (only one opening) Capture prey with nematocysts (stinging structures found within tentacles) When cells are touched, water pressure causes nematocysts to protrude Cnidocytes – cells which contain nematocysts

Discharged nematocysts, stingingcells used for defense and prey capture, have been the plague of more than fish. Stings from certain jellyfish have resulted in death in a matter of hours, especially for infants.

Carukia barnesi: the badest of the bad! Irukandji syndrome: A sting from this little guy can cause the following: “It begins with a mild sting, followed by severe lower back pain, muscle cramps in arms, legs, stomach and chest. It causes sweating, anxiety, nausea, vomiting, headaches and palpitations, and has also been known to cause cardiac failure.”

Cnidarian: Structure and Function Feeding and Digestion Carnivores Use nematocysts to capture prey Each contain fluid filled capsule containing thread that is ejected May be spines or long tube that wraps around prey Toxic

Cnidarian: Structure and Function Feeding and Digestion Extracellular digestion – outside of the cells Intracellullar digestion – within cells in the lining of the gut

Cnidarian: Structure and Function Behavior Lack brain and true nerves Nerve cells interconnect forming nerve net that transmits impulses in all directions Sea anemones can tell if other member is from same clone Known to attack and even kill anemones from other clones

Cnidarian: Structure and Function Behavior Some medusae have primitive eyes Medusae have statocysts, small calcareous bodies in fluid-filled chambers surrounded by sensitive hairs, to help with balance

Cnidarians: Structure and Function 1. Polyp: a sac-like attached stage with a mouth and tentacles (mostly sessile) 2. Medusa: a mobile bell-like upside down polyp (jellyfish).

Cnidarians: Structure and Function Larva is called planula, ciliated stage with two cell layers Settles and metamorphoses into a polyp or develops into medusa

Cnidarians: Structure and Function Two layer of cells form body wall; one is epidermis (“skin”) and other is gastrodermis (gut lining) Gelatinous middle layer is mesoglea, does not contain cells In medusa this layer expands to form gelatinous domed bell

Types of Cnidaria Cnidaria come in all shapes and sizes. Sea fan Cnidaria come in all shapes and sizes. Hydrozoans- feathery hydroids Scyphozoans- large jellyfish Anthozoan-sea anemones and coral Most of the animals found within Cnidaria are all carnivores.

Cnidarian Types Hydrozoans (class Hydrozoa) Feathery or bushy colonies of tiny polyps attached to pilings, shells, seaweeds, and other surfaces Polyps may be specialized for feeding, defense, or reproduction Reproductive polyps produce minute, planktonic medusae

Cnidarian Types Hydrozoans (class Hydrozoa) Medusae release gametes & fertilized eggs develop into free swimming planula larvae Each planula larvae settles and develops into a polyp The poylp divides repeatedly and develops into a colony Some lack poylp stage and develop into a medusae Few lack medusae stage and develop into gamete producing polyps

Cnidarian Types Scyphozoans (class Scyphozoa) Larger jellyfish Large medusae are dominate stage in life cycle Polyps small & release juvenile medusae Few lack polyp stage Bell diameter ranges from 2-3 meters, depending on water depth

Cnidarian Types Scyphozoans (class Scyphozoa) Swim with rhythmic contractions of bell but easily carried by currents Some species stings range from rash to fatalities Cubomedusae once classified as Scyphozoa now in own class Cubozoa (box jelly)

Cnidarian Types Anthozoans (class Anthozoa) Anemones and corals Solitary or colonial polyps that lack medusae stage Largest number of species Polyps are more complex Gut contain septa increasing surface area for digestion of large prey Septa provide support for larger species Sea anemones have large polyps

Cnidarian Types Anthozoans (class Anthozoa) Corals – colonial anthozoans Carbonate skeletons Occur in cold waters; tropical waters form reefs Gorgonians (sea fans) secrete branching skeleton made of protein Precious corals gorgonians are fused with red or pink calcareous spicules in addition to protein skeletons

Cnidarian Types Anthozoans (class Anthozoa) Black Corals secrete hard, black protein skeleton Used for jewelry

3. Comb jellies: Ctenophora Similar to cnidarians in most respects. Nearly 100 spp.- all marine Contain ciliary combs which assist in prey capture and mobility.

3. Comb jellies: Ctenophora Gelatinous body with 8 rows of combs that beat in waves Beating of combs refracts light creating multicolor effect Body length range from few millimeters to 2 m http://www.youtube.com/watch?v=G7WT81ukHZE

3. Comb jellies: Ctenophora Found in warm and cold waters Carnivores Swarms consume large numbers of fish larvae and other plankton Capture prey with long tentacles with colloblasts (sticky cells) Few have nematocysts