Life in Freshwater
Lecture 2
Subkingdom Protozoa
·
Characteristics
o Unicellular
(a few unicells)
o Eucaryotic
o Heterotrophic
·
Phylum Sarcomastigophora
(amoeboid and flagellated cells, some have both)
o Subphylum
Mastigophora (flagellates)
§
Properties
·
1 to many flagella
·
many are closely related to algal species
·
food storage as glycogen
·
most are naked (no cell wall)
·
may undergo amoeboid stages
·
strong affinity for solid substrates
§
Representative taxa
·
Peranema
(euglena-like, holozoic = predaceous)
·
Chilomonas (cryptomonad-like, saprozoic:
dissolved organics)
·
Noctiluca (dinoflagellate-like)
·
Choanoflagellates
(filter feeders) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Mastigophora/Codosiga/index.html
·
Trypanosoma, Giardia (endoparasite in
vertebrates)
·
Trichonympha (termite endosymbiont)
§
Reproduction
·
Asexual: binary fission
·
Sexual: rare
o Subphylum
Sarcodina (amoebae)
§
Properties
·
Move by pseudopodia (flowing extensions of
cytoplasm)
·
Generally feed by engulfing particles in pseudopods
·
Some also produce flagella
·
Naked or shelled
§
Representative Taxa
·
Amoeba (large pseudopods,
naked) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Sarcodina/ap/indexE.html
·
Arcella (chitinous shell) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Sarcodina/Arcella/index.html
·
Euglypha (siliceous
shell)
·
Difflugia (cemented
particle shell) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Sarcodina/Difflugia/index.html
·
Heliozoans (naked or scaled with axiopods)
§
Reproduction
·
Asexual (binary fission)
·
Sexual: rare
·
Phylum Ciliophora
o Class
Ciliata
§
Properties
·
Cilia or compound ciliary
structures for locomotion and/or food gathering
·
Two types of nuclei
·
Most are solitary, but some colonial forms
·
Most are holozoic
(particle feeders), but may also be saprozoic
·
Important bacterial grazers in microbial loop
§
Reproduction
·
Asexual: binary fission
·
Sexual: conjugation
§
Representative Taxa
·
Paramecium (figure) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Ciliophora/Paramecium/indexE.html
o Uniform
body ciliation
o Bucal cavity for feeding
o Food
and contractile vacuoles
·
Vorticella (peritrich=cilia concentrated at one end) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Ciliophora/Vorticella/index.html
o Attached
to a solid substrate
o No
body cilia
o Bucal cilia create vortex for drawing in food particles
·
Euplotes (hypotrich=few cilia) http://mtlab.biol.tsukuba.ac.jp/WWW/PDB/Images/Ciliophora/Euplotes/index.html
o Body
ciliature reduced to fused tufts of cilia called
cirri
o Dorsoventrally flattened
o Class
Suctoria
§
Sessile, stalked “ciliates”
§
Distal end bears tentacles
§
No body ciliature when
mature
Phylum Porifera (sponges)
- Only
one family with freshwater sponges
- 170
species (30 in US) found in freshwater out of a total of 4500
- Size
varies greatly as a function of species, age, and environment
- Thin
mat, few cm2, 1 mm thick
- 40
m2, 4 cm thick
- Family
Spongillidae
- Skeleton
of monaxial spicules
(silicious spines) and sponging
- Nutrition
- Particle
feeders up to 50 um
- Water
enters trough ostia by current produced by choanocyte cells
- Bacteria
and bits of detritus caught on sticky surface of choanocyte
collars and absorbed
- Then
passed on to amoebocytes through mesoglea for digestion
- Filtration
rate: 0.01-0.28 mL/sec/ml sponge
- Some
have zoochloroellae
- Reproduction
- Asexual
- Reduction
bodies (blobs of tissue that shrink)
- Fragmentation,
reaggregation
- Gemmules (spheres with hard outer layer, internal
mass of undifferentiated tissue, highly resistant)
- Sexual
- Oogonium is amoebocyte
that grows by absorbing adjacent cells
- Sperm
may develop from other cells and become flagellated
- Flagellated
embryos released and settle on substrate
Phylum Coelenterata (hydroids,
jellyfish)
- 2 life
forms (sessile hydroid, mobile medusa)
- Class
Hydrozoa
- Only
one of the three classes of coelenterates with freshwater representatives
- 20
species in the US:
16 Hydra/Chlorohydra, 1 fw
jelly (Craspedacusta), 1 colonial polyp
- all
sessile except jelly, also may hang from surface film
- most
abundant during summer
- Representative
Taxon
- Hydra
- Radially symmetric morphology, 1-25 mmlong
- External
cell layer (epidermis), internal cell layer (gastrodermis)
- Tentacles
with minute stinging cells (nematocysts)
- Has
only polyp stage
- Nutrition
- Carnivorous
on small metazoans (cladocera, copepods,
insects, annelids, occasionally fish fry)
- Kills
prey with nematocysts, prey fed into opening below the tentacles, prey
may be 4x diameter of Hydra
- Some
Hydra have zoochlorellae which are passed on
in the egg cytoplasm
- Reproduction
- Asexual:
budding
- Sexual
- monoecious or dioecious
- stimulated
by autumn temp declines
- Craspedacusta (freshwater jelly)
- Normally
found in small lakes/ponds in late summer
- 5-22
mm in diameter
- feeds
on zooplankton 0.2-2 mm
- eaten
by crayfish
- also
has a colonial hydroid stage
Phylum Playhelminthes
·
Three classes, two of which are exclusively
parasitic (Cestoda, Trematoda)
·
Class Turbellaria
(flatworms)
o Many
are freshwater
o Elongate,
may be flaggened or cylindrical
o Anterior
end may be differentiated as head
o Some
5-30 mm long (triclads)
o Others
<4 mm long (rhabdocoels)
o Body
surface more or less covered with cilia
o Body
cavity has a single external opening
o Reproduction:
§
Asexual: fission or fragmentation
§
Sexual
·
Hermaphroditic (monoecious):
both sex gonads on the same individual
·
Not self-fertile, must mate with another
individual
·
Sperm held, fertilize eggs as they leave ovary
·
Zygote accumulates yolk cells moving down the
oviduct, zygotes and yolk cells aggregate into a capsule or cocoon of 2-20
zygotes and hundreds of yolk cells (2-4 mm dia),
leaves body attached to a stalk
·
Cocoon resistant to low T, but not to drying
·
“worms” emerge 1-3 mm long, direct development
by enlargement
o Nutrition
§
Suck in soft material, decaying animals, whole
living micrometazoa (rotifers, nematodes, gastrotrichs)
§
May secrete mucous to entangle particles
§
May recycle nematocysts from Hydra
Phylum Nematoda (roundworms)
- Found
in great abundance in sediments/vegetation
- Poorly
known because of small size and difficulties in identification
- 1500
freshwater species described, probably an underestimate
- <1
cm long, protein cuticle shed during growth
- Feeding
- Cover
all food items as a group, but individual species specialize
- Reproduction
- Asexual:
parthenogenic egg development
- Sexual
- Dioecious: separate sexes
- Male
inserts sperm into female
- Fertilization
followed by egg shell formation, embryo hatches in a few days, small,
but fully formed and terminal number of cells
- Undergoes
four molts to reach final size
- Eggs
are highly resistant to dessication and
temperature extremes for up to 10-20 years
- Transported
by wind, animals
Phylum Rotifera
- Phylum
most characteristic of freshwater: 95% of 2500 species are exclusively fw
- Two
classes
- Monogononta: single ovary and lorica
(shell)
- Digononta: paired ovaries, no lorica,
“bdelloid”
- Nutrition
- Omnivorous
particle feeders
- Brachionus, Keratella, Filinia
- Predatory
- Asplanchna, Synchaeta, Trichocerca
- Reproduction
- Asexual:
parthenogenesis (diploid females produce diploid eggs)
- Sexual
- diploid
female undergoes meiosis, produces haploid eggs
- if
haploid eggs unfertilized, produce haploid males which produce haploid
sperm
- if
haploid eggs fertilized by haploid sperm, produce zygotes which hatch
into diploid females
- Bdelloid rotifers may undergo dessication
and remain viable for up to 25 years
Phylum Gastrotricha
- Small
metazoans related to nematodes, rotifers
- 70-600
um (most are 100-300 um)
- body
is flattened strip with enlarged head, narrower neck, enlarged abdomen,
and two tails
- body
is covered with cuticle which may be thickened to form plates
- Feeding
- Browse
on solid substrates (plants, surfaces) ingesting periphyton
(bacteria, algae, small protozoa, organic detritus)
- Head
cilia induce currents
- Reproduction:
- All
known species are parthenogenetic females,
males are unknown
- 1-5
eggs/lifetime
- eggs
very large: 70-80% of adult size
- two
types of eggs
- quick
developing (tachyblastic), hatching in 12-70
hrs
- resistant
(opsiblastic)
- dormancy
2 yrs or more
- survive
desiccation, freezing, high temps
- animal
is large and well-developed at emergence
Phylum Annelida
- Semented structure, true coelom
(tube within a tube), thin cuticle
- Three
classes, one is Polychaeta with is rare in
freshwater although found in the tidal Potomac
- Class
Hirudinea (leeches)
- Dorsoventrally flattened, mouth surrounded by oral
sucker, also large caudal sucker
- All
have 34 segments
- 5
mm to 45 cm long
- Feeding:
scavengers and carnivores mostly (2 US genera suck blood)
- Reproduction:
- Sexual:
hermaphroditic (not self-fertile), cocoon (2-15 mm long) formed around 1
to several eggs and fastened to substrate, young hatch from cocoon and
start to grow
- Class
Oligochaeta (aquatic earthworms)
- Similar
in anatomy to terrestrial earthworms
- Few
setae on segments
- Families:
Aeolosomatidae, Naididae,
Tubificidae
- Feeding:
ingest bulk sediment and detritus, a few are carnivorous
- Reproduction:
- Asexual:
budding in some groups
- Sexual:
hermaphroditic, not self- fertile