Download II. Phylum Cnidaria [nettle]

II. Phylum Cnidaria [nettle]
Also called Coelenterata [hollow body]
A. examples: (9,000 species)
jellyfish,
Man-of-War,
hydra,
sea,
coral
intro
nemo
B. radial symmetry
No front or back
simpler to keep track of, only 2 ends
1. Oral = mouth end
2. Aboral = not mouth end
3. sensory organs are evenly
distributed so can respond to
stimuli from all directions
C. mostly marine
1. very important to
formation of coral reef
2. ocean takes care of support (buoyant),
diffusion of oxygen, removal of wastes, diffusion
of carbon dioxide
D. structure
p. 271
1. diploblastic – made of only two layers of
tissues, not three
a. ectoderm - outer layer (epidermis)
b. endoderm - inner layer (gastrodermis)
c. mesoglea- not cell layer,
filling between, jellylike fluid
Simpliest type of tissue organization
Structure (con’t)
2. gastrovascular cavity = one opening gut
a. advantage: allows for rapid diffusion of
nutrients/gases to cells (close proximity)
b. disadvantage: less efficient digestion,
food, digestive wastes, and gametes
enter/leave cavity through mouth
Structure (con’t)
3. tentacles ( not appendages)
a. flexible, extendible
b. “nerve net” in epidermis;
most primitive nervous
system;
coordinates movement,
response
sensitive to touch and
various chemicals
c. cells called cnidocytes
contain nematocysts
(stinging cells)
defense, food gathering,
attachment
the barb is coiled up
inside a capsule.
When a nematocyst
touches something the
barb uncoils and fires
from the capsule along
with venom.
Nematocyst (video link is picture)
eating
•More than 100 species are
toxic to humans.
Jellyfish stings usually are mild,
except those caused by species in the
South Pacific, such as the box jellyfish
or Portuguese man-of-war.
Can cause: rashes abdominal muscle
rigidity, vomiting, profuse sweating,
and excessive shaking to cardiovascular
and respiratory collapse.
• described as feeling like being struck
by a lightning bolt.
Deadliest jellyfish
box jellyfish
Some are paralyzing,
some are very toxic
(box jelly of Indian
Ocean near Australia
fatal in matter of
seconds)
More people die from
jellyfish stings than
shark attacks
box jellyfish
Chironex fleckeri
An extremely poisonous jellyfish - one
individual has enough venom to kill 60
adult humans. Some animals like the
sea turtles can eat the box jellyfish
without being stung.
WORD BANK
Gastrovascular cavity
Tentacle
Cnidocyte
Ectoderm
Endoderm
Mesoglea
Ovary/Teste
Bud
Nematocyst
Mouth
Basal Disk
d. after food is harpooned, tentacles
contract to draw it in the mouth
e. gastrodermal cells secrete
enzymes to break the food down
extracellular digestion –
“pre”digestion; break food
particles down small enough to
diffuse into the cells then finish
breaking them down in
mitochondria or lysosomes
E. locomotion
1. limited - some are primarily
sessile, others can “swim” by
contracting muscle tissue against
hydrostatic skeleton to draw
water in or push it out
2. some float passively on
current using a “sail”
3. Polyp form can somersault
or glide along substrate
flexing
F. Reproduction
1. most are dioecious [separate genders]
2. usually sperm & eggs are made inside
the gastrovascular cavity
3. gametes usually released out the mouth
4. Some environmental trigger causes
spawning. This increases the chance of
success
5. a planula is a free swimming larva that
disperses the species
p. 272
G. two common body forms
1. medusa–dioecious
stage, oral down
[dangling tentacles like
Medusa’s snakes]
- free swimming
2. polyp – asexual,
Sessile, attached at
aboral end
Body Plans in general
medusa (more mesoglea)
polyp (less)
H. Alternation of Generations
I. five (5) classes based
primarily on which body
forms are present or dominant
1. class Hydrozoa
2. class Scyphozoa
3. class Anthozoa
4. class Ctenophora
5. class Cubozoa