Freshwater AnimalsNote Ctenophores and Echinodermata are marine phyla; all other phyla have representatives in freshwater.

Phylum Porifera: The sponges

• Sponges are mainly marine but there are ~25 freshwater species described.

• Primitive multicellular animals; do not have organs, but do have specialized cells for feeding, digestion.

• Filter feeders; sieve particles from the water as it flows into pores.

• Some species have symbiotic algae (similar to corals), mainly green algae Chlorella.

Can be important consumers of microbes as small as bacteria

Cnidaria: Celenterates(Hydra & Jellies)

• Most species marine; all display radial symmetry and possess nematocysts (defense cells).

• Hydra is probably most common freshwater cnidarian:– May have symbiotic algae, Chlorella.

– Most often sessile; epiphytic

Platyhelminthes and Nemertea: • Turbellaria (free-living flatworms) are most common in freshwater benthic habitats or epiphytic.

• Some planaria acquire nematocysts for defense by ingesting hydra (marine forms do so as well).

• Trematoda (flukes), a major group of animal parasites; some with aquatic phase in life cycle.

• Schistosomiasis is a disease of the human intestinal tract caused by a Schistosoma fluke. A similar fluke causes swimmers itch in humans we get infected as an alternate host (normally water fowl).

• Nemertea have an anus and closed circulatory system.

Schistosoma life history:

Nematoda: The roundworms• Non-segmented roundworms;

common in all kinds of aquatic habitats (damp soil, freshwater, marine).

• Generally benthic infauna (within sediments).

• Feeding strategy varied: detrivores, herbivores, carnivores (including predation on other nematodes).

• Some species are common and important parasites of animals (including humans), often using insects as host vectors. (e.g. “river blindness”, onchocerciasis transmitted by blackfly (Simuliidae).

(and rotifers)

Rotatoria (Rotifers)• 2000 freshwater species, more diverse than in marine

habitats!

• Possess an advanced digestive system including mastax (to grind food down), stomach, intestine, anus. Possess a nervous system and sensory organs (eyes).

• Sexual reproduction produces a dormant cyst and several species can survive years of drought.

• “Wheel organ” is ciliated and creates a whirlpool-like flow to bring prey to mouth. Some modified for ambush capture.

• Predators of bacteria and small protists like nanoflagellates.

• May be planktonic or attached by “foot” (with “toes”).

Mollusca Soft-bodied, unsegmented; possess a head, muscular foot, stomach/viscera, and often grow a calcareous shell.

• Class Gastropoda: snails and limpets– 500 species of freshwater snails

– One-piece shell and a radula (file-like structure) that is used to scrape food from surfaces

– Snails are important grazers of periphyton (epilithic algae, bacteria, etc.) but also feed upon detritus, macrophytes, and dead tissue

Conical shell Spiral shell

• Class Bivalvia: clams and mussels– Bivalves have a shell with two

halves and gills specialized for filter feeding.

– Found in the benthos, either burrowed in sediments or attached to substrate.

– Adults can withstand periods of drought by closing shell.

– Some have specialized larval stages with interesting dispersal characteristics.

– Some bivalve species are important invaders of North American aquatic systems (alien species: Asiatic clam, zebra mussles) with serious ecological implications.

Annelida: Segmented worms• Tubular, segmented body with

specialized digestive system, terminal mouth and anus. Familiar representatives include oligocheates, leeches.

• Oligocheates (like familiar earth worms): benthic, burrow through sediment.– Most ingest organic particles in

sediments (important connection in food chain); some algal grazers or predators.

– Resistant to low oxygen and polluted conditions (good indicator species; Tubifex).

– Vectors of some important parasites, e.g. Whirling Disease

Hirudinea (Leeches)

Whirling Disease of Trout

Tubifex sp.

Myxobolus cerebralis

Arthropoda

• Ubiquitous in all continental surface waters.

• Important in linkages of ecosystems. (aquatic and terrestrial)

• All arthropods characterized by:

– Chitinous exoskeleton

– Stiff jointed appendages (mouth, legs, etc.)

Arachnida: Mites and Spiders• No true aquatic spiders; some able to utilize the

environment on occasion.

• Water mites are diverse and inhabit most surface waters.

• Mostly benthic, but some pelagic species in lakes.

• Almost all predatory (mainly on insects) but some parasitic (often in larval stage).

Mouth

Six pairs of appendages,4 pairs of legs most conspicuous

Fused cephalothorax and abdomen

Subphylum Insecta• Ten orders contain aquatic species; majority are aquatic

as larvae, emerge as adults.• Characterized by:

– body divided into head, thorax (three segments), and abdomen– Single pair antennae, compound eyes, specialized mouthparts

• Order Collembola (springtails): Not true insects.– Wingless, often eyeless.– Mostly terrestrial or semiaquatic, often in lakes– Poorly studied

Order Plecoptera• Stoneflies most common in streams; some predators

and others detritivores.• Sensitive to pollution and low oxygen levels, therefore

used as an indicator species.• Similar in appearance to mayfly larvae except only have

two cerci (filaments) on posterior end, and tend to be mostly flattened.

• Incomplete metamorphosis

Incomplete Metamorphosis

Order Ephemeroptera: Mayflies• Aquatic only as larvae; common in streams and in lake

benthos. Feed by scraping, collecting, some predatory• Many species, typically divided by habitat interaction or

behavior: swimmers, clingers, crawlers, burrowers. Body shape reflects lifestyle:– Clingers flattened dorso-ventrally– Swimmers round & streamlined– Burrowers often have tusk-like mandibles– Crawlers have more streamlined gills than burrowers

Three filaments

Gills

Mayfly life cycle:

1) Eggs hatch in water, larvae grows.

2) Larvae swims to surface and emerges; metamorphoses into sub-adult (subimago) form.

3) Subimago matures into adult. Adult mates, female lays eggs in water, dies.

Order Odonata: dragonflies, damselflies

• Aquatic as larvae in both streams and lakes (more in lakes and slow waters). Important predators of other insect larvae.

• Move by crawling, some by swimming. Prefer thick aquatic vegetation for cover, debris/litter, rocky cobble, or burrow in sediments.

• Three-stage lifecycle similar to mayflies. This lifecycle is termed incomplete metamorphosis.

Order Trichoptera• Caddisflies mostly lotic, a few lentic species; aquatic as

larvae and pupae• Variety of lifestyles habits:

– Some build protective cases from materials in the environment, crawl and graze on periphyton or leaf litter

– Some construct nets for filter-feeding– Others free-living, predatory

Complete Metamorphosis

Order Megaloptera• Dobsonflies, alderflies; aquatic as larvae, pupae• Often large larvae with large mandibles; all predators.• Aquatic period of life cycle can last several years before

emerging as adults.• Occur in both lotic and lentic systems.

Order Heteroptera• The true bugs are mostly terrestrial; aquatic species live

either on surface or submersed.• Inhabit both lentic and lotic environments; many possess

specialized appendages adapted for swimming or to facilitate air breathing.

Order Lepidoptera• Very few aquatic species of moths or butterflies; usually

associated with ponds with dense macrophyte populations. Some lotic species grazers of periphyton.

• Complete metamorphosis.

Paired, filamentous gills

Order Coleoptera

• Though only about 3% of beetles aquatic, there are so many species of beetles that this still represents a significant order of aquatic insects.

• Some submerge water bubbles for air breathing.• Includes predators, periphyton and macrophyte grazers.

Order Diptera: True Flies

• Largest group of aquatic insects, dominated by family Chironomidae (midges).

• Also includes nuisances like mosquitoes, black flies…• Some midge larvae possess hemoglobin as an

adaptation for survival in low oxygen environments.

Subphylum Crustacea

• 4000 species of crustaceans found in freshwaters; although most are marine.

• Includes many important food chain links:– Zooplankton species are key as primary consumers (plankton

grazers)– Benthic omnivores which feed upon detritus, carrion, etc.

• Characterized by:– Respiration across gills or body surface– Chitinous exoskeleton, two pairs antennae, paired and jointed

appendages

Ostracoda• “Seed shrimp” are benthic species covered by carapace made of mix of chitin

and calcium carbonate.

• Mostly graze algae or eat detritus.

• When ostracod dies, carapace resists dissolution; can be found in sediment cores, fossils.

• Isotopic composition of recovered carapace can reveal past climate patterns (temperature).

Copepoda• Important pelagic zooplankton, but other

species also benthic in streams, lakes and groundwater, or parasitic.

• Sexual reproduction, characterized by a many-staged development process divided between 6 naupliar (analogous to larval) and 6 copepodite (juvenile) stages.

• Interesting patterns of diverse morphology, adaptations and speciation.

Branchiopoda • Diverse group including

Cladocera, tadpole shrimp, brine shrimp, etc.

• Usually found in lentic environments. Some benthic, some planktonic.

• Many species have an egg stage that is resistant to drying and can withstand long periods out of water.

Decapoda• Includes many large (macroinvertebrate) species such as crayfish,

shrimp, crabs.

• Inhabit lentic and lotic environments, including caves, groundwaters, wetlands.

• Some species have high value as food for humans; these are often cultured and harvested.

• Crayfish are omnivorous and important benthic consumers; shrimp are primarily grazers or detritivores.

• Important as both consumers and as prey for larger vertebrates.

Isopoda• Pillbugs, sowbugs;

terrestrial, marine and freshwater species.

• Often found in clean, oxygenated water (springs, streams, groundwaters).

• Detritivores and scavengers.

Amphipoda• Scuds and side-swimmers; resemble isopods

but are flattened laterally, not dorso-ventrally.• Omnivorous scavengers; some important

shredders of CPOM; mainly benthic.

The Vertebrates• In freshwaters, fish are considered the most important

vertebrate species.• Most diverse aquatic vertebrates, over 24,000 species

described; ~ half found in freshwater.• Dominant classes:

– Superclass Pertomyzontiformes, jawless fishes (lampreys)

– Class Chondrichthyes, cartilaginous fishes– Class Osteichthyes, bony fishes

• Fish can be found as predators, grazers, scrapers…

• Body form is adapted and specialized toward certain lifestyle / behavior:

– Streamlined fishes are specialized for near constant swimming for locating and pursuing prey

– Elongate, torpedo-shaped fishes specialized as sit-and-wait ambush predators; built for burst speed.

– Benthic species often flattened dorso-ventrally, with under-slung mouths

– Deep-bodied, ventrally flattened fish are specialized for maneuvering in tight quarters

– Eels are adapted for moving through narrow spaces

TetrapodsOther aquatic vertebrates include amphibians, reptiles, birds and

mammals.

• Amphibians include salamanders, frogs; mostly predators but some are algal grazers and detritivores (especially as larvae).– Amphibians have recently gained much attention as

indicator species of aquatic pollution and environmental changes.– Recent evidence suggests a worldwide decline in amphibian

diversity; some correlations to climate change, global warming processes.

Reptiles, Birds and Mammals

• Many familiar representatives including:– Turtles, Water snakes, Crocodilians– Pelicans, ducks, some raptors– Dolphins, bats, beavers, hippopotamus

These animals are often of interest as high-order predators, or for ways in which they alter their environment.

Mostly associated with shallow habitats and aquatic-terrestrial interface.