Freshwater Animals

1. Freshwater Animals Note Ctenophores and Echinodermata are marine phyla; all other phyla have representatives in freshwater.

2. 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.

3. Can be important consumers of microbes as small as bacteria

4. 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

6. 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.

7. Schistosoma life history:

8. 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)

9. 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”).

11. MolluscaSoft-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

12. 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.

13. 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

14. Hirudinea (Leeches)

15. Whirling Disease of Trout Tubifex sp. Myxobolus cerebralis

16. 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.)

17. 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 Fused cephalothorax and abdomen Six pairs of appendages, 4 pairs of legs most conspicuous

18. 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

19. 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

20. Incomplete Metamorphosis

21. 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 Gills Three filaments

22. Mayfly life cycle: • Eggs hatch in water, larvae grows. • Larvae swims to surface and emerges; metamorphoses into sub-adult (subimago) form. • Subimago matures into adult. Adult mates, female lays eggs in water, dies.

23. 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.

24. 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

25. Complete Metamorphosis

26. 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.

27. 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.

28. 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

29. 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.

30. 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.

31. 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

32. 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).

33. 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.

34. 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.

35. 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.

36. Isopoda • Pillbugs, sowbugs; terrestrial, marine and freshwater species. • Often found in clean, oxygenated water (springs, streams, groundwaters). • Detritivores and scavengers.

37. Amphipoda • Scuds and side-swimmers; resemble isopods but are flattened laterally, not dorso-ventrally. • Omnivorous scavengers; some important shredders of CPOM; mainly benthic.

38. 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

39. 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

40. Tetrapods Other 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.

41. 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.