Transcript Phylum: Cnidaria

Major Aquatic Invertebrate Taxa
Phylum
Porifera
(sponges)
Cnidaria
(hydra & jellyfish)
Platyhelminthes (flatworms)
Gastrotricha
(gastrotrichs)
Rotifera
(rotifers)
Nematoda
(nematodes)
Mollusca
(snails/bivalves)
Annelida
(oligochaetes/leeches)
Bryozoa
(moss animals)
Tardigrada
(water bears)
Arthropoda
(arthropods)
Review of major invert classifications
--Radially symmetrical animals
Phylum: Cnidaria
--Bilaterally symmetrical animals
Acoelomates – animals that lack a body
cavity: Phylum: Platyhelminthes
Pseudocoelomates – animals that have a
body cavity but no peritoneum.
Phlya: Gastrotricha, Nematoda, Rotifer
Coelomates – animals with internal body
cavity lined with peritoneum.
Protostomes:
Phyla: Mollusca, Annelida, Tardigrada,
Arthropoda
Deuterostomes:
Phyla: Echinodermata, ‘Chordata’
Major Aquatic Invertebrate Taxa
Phylum
Porifera
(sponges)
Cnidaria
(hydra & jellyfish)
Platyhelminthes (flatworms)
Gastrotricha
(gastrotrichs)
Rotifera
(rotifers)
Nematoda
(nematodes)
Mollusca
(snails/bivalves)
Annelida
(oligochaetes/leeches)
Bryozoa
(moss animals)
Tardigrada
(water bears)
Arthropoda
(arthropods)
Phylum: Porifera
About 5,000 species worldwide
About 25 species are freshwater
Collection and Identification of sponges
General physiology
Pinacocytes: ‘skin cells’, thin, leathery and tightly
packed.
Choanocytes: striking resemblance to
choanoflagellates(a single-celled protist). Their
function is to create active pumping of water and
major site of nutrient uptake.
Archaeocytes: These cells are “totipotent”. They
can change into all of the other types of cells.
Ingest and digest food caught by choanocyte
collars.
Schlerocytes: Create and excrete spicules.
Reproduction
--All sponges can reproduce sexually
--Generally monoecious and produce eggs and
sperm at different times.
--Produce flagellated parenchymella larva that
exit via exhalent current.
--Larval motility is the principal dispersal
mechanism
--Sponges have great powers of regeneration
Feeding
--Sponges feed on fine particulate material in
the inflowing water.
--Food particles generally range from 5- to 50
µm and are phagocytized by archeocytes.
--After digestion is complete, the archeocytes
and associated wastes are expelled into the
water.
Phylum: Cnidaria
Class Hydrozoa (only freshwater rep)
over 3,000 species
only 14 freshwater species
Class Cubozoa (sea wasps)
Class Scyphozoa (jellyfishes)
Class Anthozoa (sea anemones and corals)
Dimorphism in Cnidaria
polyp
medusa
Reproduction
--Cnidarians reproduce both asexually and
sexually. Medusa are produced by
budding of polyps but not vice versa.
--Generally dioecious and reproduce
sexually during warmer periods.
--Embryos develop into ciliated freeswimming larva called planula.
Crespedacusta bowersi –
the only freshwater “jellyfish”
Feeding
--Cnidarians are carnivorous but have limited
powers of movement.
--Essential to the feeding process are thin,
flexible ‘tentacles’.
--Nematocysts are specialized cells located
on tentacles that aid in capture of prey.
--Amino acids released by prey can trigger
the tentacles to ‘bend’ toward the mouth by
ciliary action.
--Common foods of Hydra include
invertebrates and sometimes small fish.
Nematocycts – Food, protection, anchoring
Major Aquatic Invertebrate Taxa
Phylum
Porifera
(sponges)
Cnidaria
(hydra & jellyfish)
Platyhelminthes (flatworms)
Gastrotricha
(gastrotrichs)
Rotifera
(rotifers)
Nematoda
(nematodes)
Mollusca
(snails/bivalves)
Annelida
(oligochaetes/leeches)
Bryozoa
(moss animals)
Tardigrada
(water bears)
Arthropoda
(arthropods)
Review of major invert classifications
--Radially symmetrical animals
Phylum: Cnidaria
--Bilaterally symmetrical animals
Acoelomates – animals that lack a body
cavity: Phylum: Platyhelminthes
Pseudocoelomates – animals that have a
body cavity but no peritoneum.
Phlya: Gastrotricha, Nematoda, Rotifer
Coelomates – animals with internal body
cavity lined with peritoneum.
Protostomes:
Phyla: Mollusca, Annelida, Tardigrada,
Arthropoda
Deuterostomes:
Phyla: Echinodermata, ‘Chordata’
Platyhelminthes (flatworms):
Free livingClass Turbellaria (planarians)
mostly predaceous
free living
epidermal rhabdites
Parasitic –
Class Trematoda (internal flukes)
exclusively parasitic
complicated life-cycles
Class Cestoda (tapeworms)
exclusively parasitic
Platyhelminthes (flatworms):
Trematodes --- ‘black spot disease’; ‘yellow grub’
Phylum: Platyhelminthes
Planarian
Dugesia
About 200 species in N. America
Turbellarians: General morphology
gut
epidermis
mesenchyme
neoblasts
rhabdites
General physiology
--Triploblastic (3 layers). 0.5 to 5 cm long.
-- Respire/excrete by diffusion.
-- No body cavity other than gut. No anus.
--Rhabdoids: Cells that produce mucus and
poison for prey immobilization/predator
deterrence.
--Neoblasts: Small, ameboid like cells that
initiate regeneration of lost parts.
Identification of planarians
Nutritive
cells
Acoela
Simple
intestine
3-lobed
intestine
Many-lobed
intestine
Neorhabdocoela Tricladids Polycladids
Reproduction
--Most turbellarians are monoecious.
--Penal stylets (Penis) that can be used for both
reproduction and defense.
--Embryos develop into a free-swimming,
ciliated stage called Muller’s larva. Shortlived, nonfeeding stage.
--Can produce asexually by fission, fragmentation
or both.
Life history and ecology
--Widely distributed in N. America
--Occur in both lakes and streams
Stream-dwelling species more
differentiated than lake species
--Species diversity increases in temperate areas
20 to 60 species per lake
Some species are univoltine:
produce one generation a year
Most turbellarians are multivoltine:
produce several generations a year
Feeding
--Effective predators on other invertebrates
including rotifers, nematodes, cnidarians,
bryozoans, small crustaceans, annelids and other
turbellarians.
--Turbellarians use ‘slime’ to entangle prey.
They use a muscular protrusible pharynx to help
ingest prey.
Major Aquatic Invertebrate Taxa
Phylum
Porifera
(sponges)
Cnidaria
(hydra & jellyfish)
Platyhelminthes (flatworms)
Gastrotricha
(gastrotrichs)
Rotifera
(rotifers)
Nematoda
(nematodes)
Mollusca
(snails/bivalves)
Annelida
(oligochaetes/leeches)
Bryozoa
(moss animals)
Tardigrada
(water bears)
Arthropoda
(arthropods)
Review of major invert classifications
--Radially symmetrical animals
Phylum: Cnidaria
--Bilaterally symmetrical animals
Acoelomates – animals that lack a body
cavity: Phylum: Platyhelminthes
Pseudocoelomates – animals that have a
body cavity but no peritoneum.
Phlya: Gastrotricha, Nematoda, Rotifer
Coelomates – animals with internal body
cavity lined with peritoneum.
Protostomes:
Phyla: Mollusca, Annelida, Tardigrada,
Arthropoda
Deuterostomes:
Phyla: Echinodermata, ‘Chordata’
Phylum: Gastrotricha
About 450 species
Fewer than 100 freshwater species
Gastrotrichs
--Nearly ubiquitous in the benthos of
freshwater habitats.
10,000 to 100,000 per m2.
--Colorless animals 50 to 800 um long.
General physiology
--Sensory organs include ventrally located cilia
--Most are photosensitive
--Most species exhibit tactile chemical sense.
--Excretory system consists of a midbody pair
of protonephridia that empty through pores on
the body surface.
--No circulatory or respiratory system per se.
Reproduction
--Believed to produce 3 types of eggs:
2 types are parthenogenic
1) tachyblastic eggs – develop
immediately and hatch quickly (within 1-2 days)
2) opsiblastic eggs – thick shelled ‘resting’
eggs that are very resistent to freezing and drying
1 type of sexual reproduction?
--Newly hatched Gastrotrichs already have
parthenogenetic eggs and reach maturity in several
days.
--No larval stage in gastrotrichs.
Gastrotrich reproduction
juvenile
parthenogenetic
hermaphroditic
OPSI
TACHY
(2N)
(N)
Feeding ecology
--Gastrotrichs typically feed on bacteria, algae,
protozoans, detritus and inorganic particles.
--Bacteria are probably most important.
--Predators include amoeba, cnidarians and
midge larvae.
--We know very little about what controls
gastrotrich populations in the natural
environment.
Phylum:Rotifera
The ‘wheel animals’
Rotifers
--About 2000 species (mostly freshwater)
--Possess 2 distinctive features:
1) ciliated ‘corona’ near head region
2) a muscular pharynx, the ‘mastax’
--Small, (100-1000 um) herbivores and predators.
--Can be very abundant (up to 1000/L) and found
in nearly all habitats from open water to soils and
attached to plants.
--Exhibit cyclomorphosis
--Two major classes:
1) Bdelloidea
2) Monogononta
Rotifer diversity
General Rotifer morphology
Rotifer reproduction
--Rotifers are dioecious and males are always
smaller than females.
--Parthenogenesis predominates, but males do
appear sporadically.
-- Mostly oviparous; producing 3-50 eggs.
--Monogononta have only 1 gonad; Bdelloidea
has paired gonads but no males are known.
Rotifer life-cycle
--2 types of females: Amictic and dimictic.
Morphologically indistinguishable, but
functionally distinct.
Functional role
--Because of their sheer abundance and quick
turnover time, they can exert significant grazing
pressure on phytoplankton.
--Can represent up to 50% of zooplankton
production in lakes/ponds.
--Generally have lower ‘filtering rates’ as compared
to crustacean zooplankton (e.g. cladoceran and
copepods).
Phylum Nematoda
General morphology
mouth
pharynx
gut
Reproductive
tract
anus
Internal characteristics
Lipid layer
Matrix layer
Basal layer
Cuticle
Epidermis
Muscle process
Excretory canal
Pharyngeal muscles
General biology
--Unsegmented, round worms that range in size
from microscopic to 250 um.
--Live almost anywhere and are a major taxa of
sediment fauna. Can even live in hot springs at
62 C!
--Estimates of 10,000 to 30,000 species but may
be up to 20 times higher.
--Many species are parasitic on plants and
animals; feed on a variety of food resources.
--Most are dioeceous and no asexual
reproduction occurs.
--Exhibit sexual dimorphism; males are smaller
and have curved posterior ends
Implications for Humans
--Humans are hosts to about 50 species of parasitic
nematodes:
--Life cycles of parasitic nematodes not as complex
as trematodes because usually involves only 1 host.
--Common human diseases
pinworm
whipworm
hookworm
intestinal roundworm
Trichinella
Onchocerca “river blindness”
Filaria “elephantiasis”