This document summarizes Chapter 7 of the textbook BIOL 201: Invertebrate Zoology, which covers the phylum Cnidaria. Cnidaria includes jellyfish, sea anemones, corals, and hydroids. They have radial symmetry, two tissue layers, and a gastrovascular cavity. Their defining feature is cnidocytes, which are stinging cells used for defense and prey capture. Cnidarians can be colonial or solitary and have either a polyp or medusa body form. The document then describes key characteristics of major cnidarian classes including Anthozoa, Scyphozoa, and Hydrozoa. It provides examples of orders within each class and details their anatomy, life
9. Colonial
Cnidarians
Reproduce via
budding, but buds
don’t separate
Produce zooids that
resemble juveniles
Small zooids have
large SA:V
Fillter-feeding:
many mouths &
tentacles, broad
distribution, small
size
9
10. Types of
Colonies
Stolonate: have
stolons (strawberry
runners)
Coenosarc: have
coenosarc & solenia
(hollow tubes)
Fruticose: upright &
branching; plantlike
or feathery
Budding: fixed-length
(Obelia) & axial-polyp
10
14. Diversity of
Movement
Polyps: shorten,
extend, & bend
Medusae:
constrict bells for
swimming
Some polyps inch-
worm &
somersault!
Tentacles move
for prey
manipulation
Subumbrella
retracts in polyps
& medusae 14
16. Nervous
Systems
Two nerve nets:
base of epidermis &
gastrodermis; joined
by nerve bridges
across mesoglea
Nerve impulses can
travel any direction
(radial sensory
system)
Medusae: nerve
rings, musculature,
ganglia, & sense
organs around bell
Statocysts, ocelli,
chemoreceptors, &
mechanoreceptors 16
17. Cnidocytes
Used for prey capture
& defense
Cnidocytes (cells)
contain cnida (fluid-
filled capsule with
tubule)
Nematocytes contain
nematocyst that stings
& releases toxins
Spirocytes contain
spirocyst that contains
sticky threads for
adhesion
17
18. Cnidocytes,
cont.
Cnidocytes: abundant
in epidermis, on
tentacles, in
gastrodermis
Chemical &
mechanical cues
from prey trigger
firing of nematocyst
Toxins interfere with
Na+/K+ pumps or
degrade cell
membranes
Hydra discharges 25%
of nematocysts eating
1 brine shrimp
(replaced in 24hr) 18
20. Nutrition &
Internal
Transport
Coelenteron (GVC):
blind gut
Septa increase SA for
digestion, absorption,
gas exchange,
excretion, repro,
hydrostatic skeleton
Radial & ring canals in
medusae radiate out
from central stomach
Coelenteron often
branches into each
tentacle
20
22. Feeding
Prey is caught, mouth
opens, tentacles stuff
prey inside, &
enzymes digest
extracellulary
Gastrodermis absorbs
nutrients & larger
particles are digested
intracellularly
Slow process, taking
several days
Wastes ejected out
through mouth
22
23. Nutrition &
Circulation
Many species have
PSN endosymbionts
May account for
90% of nutrition in
some species
Often defined
patterns of fluid
circulation around
coelenteron
Ciliated
gastrodermis;
muscular
contractions 23
24. Gas &
Waste
Exchange
Gas exchange occurs
across general body
surfaces: tentacles,
body wall
Waste exchange
(excretion) occurs
across body wall
Ammonia is primary
waste product
Terrestrial inverts are
adapted for
conserving water
during excretion
24
27. Sexual
Reproduction
Sexual repro in most:
some monoecious
(hermaphroditic); most
dioecious
Germ cells develop in
gastrodermis &
gametes released into
coelenteron
Most have external
fertilization; some
internal fertilization
Zygote develops into
planula larva, settles
with aboral end down,
& develops into
juvenile polyp 27
29. Anthozoan
Body Form
Long pharynx
attached to
coelenteron
Many septa, 6-192
depending on
species size
Some have acontia:
stringy filaments
attached near septa
base
Heavily armed: spew
from mouth as
anemone deflates
29
33. Subclass
Zoantharia:
Order Actiniaria
Hexamarous symmetry:
septa & tentacles in
multiples of 6
Sea anemones: 1350 sp;
brightly colored; most
<10 cm
Some have unique
methods of locomotion
Burrowing via
peristalsis; walking on
tentacles; swimming by
thrashing tentacles
33
34. Order
Actiniaria:
Traits
Carnivorous suspension
feeders: mucus traps
particles on tentacles,
moved to mouth
Photosynthate: may
have 2 sets of tentacles:
false for PSN (exposed
during day) & true
(exposed during night)
Clonal repro via pedal
laceration
Gonads located in septa
34
35. Order
Actiniaria:
Ecology
Hermit crabs wear
anemone on shell &
will transfer to new
shells
Anemone gets
substrate, food,
protection, access to
mates; Crab gets
camouflage &
protection
Clownfish has
protective surface
mucus
Anemone gets food,
removal of sediment
& necrotic tissue;
Clownfish gets
protection & food
scraps 35
39. Subclass
Zoantharia:
Order
Scleractinia
Corals are often very
colorful due to PSN
endosymbionts
Algae often released
in conjunction with
gametes
Coral bleaching can
occur under stressful
environmental
conditions
Incorrect light/UV
intensity, salinity,
temp (even 1°C)
39
44. Medusozoa
Medusa phase in
life cycle: planula
polyp medusa
Tetramerous radial
symmetry:
multiples of 4
Cnidae are all
nematocysts
2 major classes:
Scyphozoa (large
jellies) & Hydrozoa
(small jellies - Hydra,
& hydroids) 44
45. Class
Scyphozoa
200 sp of large jellies
Polyps: small &
funnel-shaped
(scyphistomae)
Coelenteron divided
by 4 septa
Have 4 septal funnels
that circulate water to
gonads in adults
45
49. Class
Scyphozoa:
Body Form
Coelenteron divided
by septa into 4 gastric
pockets
4 pairs of gonads in
septa & 4 septal
funnels
Many have radial
canals & marginal
canals
Gastrodermal cilia
circulate water
49
50. Class
Scyphozoa:
Body Form,
cont.
Lappets: rounded lobes
on umbrella margin
Rhopalia: sensory
organs in grooves b/w
lappets
Statocysts:
mechanoreceptors
(also chemoreceptors
& photoreceptors)
Nerve net & nerve ring
50
54. Class
Hydrozoa
Hydra & hydroids, fire
corals, & Portuguese
man-of-war; 3000 sp
Most are colonies of
polyp & medusa
zooids
Medusa often form as
buds, but are not
released from colony
Hydra life cycle does
not include medusa
phase
54
55. Hydrozoan
Body Plans
Two types of polyps:
Athecate (A-form) &
Thecate (L-form)
Zooids 1mm or
smaller in length
Large SA:Vol
No gastrodermal
septa
55
56. Hydrozoan
Body Plans
Medusae arise
from colony as
lateral buds (not
via strobilation)
Velum: iris
diaphragm on
subumbrellar
margin for
swimming
Hydroid colonies
are sessile &
benthic (seaweed-
like)
3 colony forms:
stolonate,
coenosarcal, or
fruticose 56
59. Zooid
Terminology
Monomorphic
colonies: 1 type of
zooid
Gastrozooids: feeding
hydranths
Polymorphic colonies:
several types of zooids
Gonozooids:
reproductive polyps
Dactylozooids: have
nematocysts for
protection & food
capture
59
61. Class
Hydrozoa:
Order
Anthoathecatae
Hydra: both clonal &
sexual repro, but no
medusa stage
Fire corals: reef builders
with nasty sting
Velella: by-the-wind
sailor with a float & sail;
extreme polymorphism,
with zooids suspended
mouth-down61 Hydra
68. 68
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