ZOOPLANKTON DIVERSITY

Most zooplankton are derived from marine ancestors (not aquatic spiders, mites, insects, pulmonate gastropods, rotifers
        and perhaps cladocera)
Freshwater plankton don’t bioluminesce
I. Kingdom Protista (microzooplankton) – single celled eukaryotic organisms
    A. Taxonomic groups
        1. Subphylum Mastigophora (flagellates)

        2. Subphylum Sarcodina (amoeboid forms)
            1) Amoeba
            2) Difflugia
                a) makes a hard case called a test of sand grains
                b) migrates vertically by regulating density by altering lipid content
                c) often get large Difflugia blooms in the great lakes in the spring
            3) Heliozoans
        3. Phylum Ciliophora (ciliates)
           Paramecium

    B. Miscellaneous
        1. Less work done on the ecology of individual microzooplankton protists than other zooplankton
        2. Many tolerate low oxygen concentrations
    C. Life history
        1. Reproduction by conjugation
        2. Some can reproduce asexually by fision
        3. Many forms can produce resistant protective cysts induced by drying, excessive heat or cold, lack of food
                (some viable for over 40 years)
    D. Feeding
        1. Mastigophora consume small algae, bacteria and detritus
        2. Ciliophora and Sarcodina can also consume mastigophora
        3. Cilia and flagella are used both for motility and to set up food currents
        4. Sarcodina have pseudopodia that engulf food
        5. Are themselves eaten by other zooplankton

Kingdom Animalia (metazoans)

II. Phylum Cnidaria (Coelenterata)
    A. Taxonomic Groups
        1. medusa
           Craspedacusta
    B. Miscellaneous
        1. Medusa forms are fairly rare, poor swimmers
        2. Radially symmetrical
    C. Life history –
        1. Medusas have a polyp stage
        2. The benthic cnidarian, Hydra, has lost medusa stage – when reproduce sexually they make eggs
            that when fertilized by sperm produce new polyps
    D. Feeding –
        1. Eat zooplankton and sometimes small larval fish
        2. Have stinging cells (cnidoblasts/nematocysts) for catching prey – shoot out a sticky thread; some have neurotoxins

III. Phylum Platyhelminthes (flatworms), Class Turbellaria
     A. Taxonomy
        1. Rhabdocoels (order)
    B. Miscellaneous
        1. Move by cilia and muscular undulation
        2. Gut opening in the center of body
    C. Life History
        1. Are hermaphrodites with internal fertilization
        2. Direct development
    D. Feeding
        1. Predators and scavengers
        2. Rise up from lake bottom at night and eat other zooplankton
          (Case et al. 1979. Flatworms control density of mosquito larvae in rice paddies)

IV. Phylum Mollusca
    A. Taxonomic Groups – adult mollusks are benthic, but some bivalves have planktonic larvae
    B. Miscellaneous
        1. Glochidium (larval form) found in the plankton
            a. Most glochidia are parasitic and attach to fish
            b. Later encyst
            c. Metamorphose into mussels and sink to the bottom
        3. Veliger larva of zebra and quagga mussels live in the plankton (disperse)
    C. Life history
        1. adult unionid mussels (native) release large numbers of small glochidia larvae
        2. zebra mussel (exotic) veligers live in the plankton for ~10 days
    D. Feeding
        1. veligers consume algae (adults filter algae, microzooplankton and detritus from the water)
V. Phylum Rotifera (Rotatoria)
    A. Taxonomy
        1. Class Bdellioda
            a.~200 species; very difficult to tell apart
            b. ID them by their trophi (jaws)
        2. Class Monogonata
            a. 90% of the species
            b. representative genera
                i. Keratella
                ii. Brachionus
                iii. Conochilus
                iv. Asplanchna
    B. Miscellaneous
        1. small: 30 mm (include the smallest metazoan) in tropics to 1 mm
        2. most morphologically diverse group of freshwater plankton
        3. some species are sessile (attached), but many are purely planktonic
        4. most abundant in freshwater; evolved in freshwater
        5. can have a hard case called a lorica (same name as for some algae);
        6. have eutely – cell constancy – no cell division in any somatic cells
        7. cilia band is known as a corona
        8. jaws are called trophi and are made of chitin
        9. often fairly abundant (200-300/L up to 5000/L)
    C. Life History
        1. Bdelloid males are never seen (no sex for 40 million years)
        2. Monogonata are cyclical parthenogens

Monogonata rotifer life cycle
        1. fast generation times – a few days to 2 weeks/generation
        2. some species are viviparous
        3. most lay 1 egg at a time and then carry it for 1-3 days
        4. male production
            a. males are haploid (produced by meiosis)
            b. stimulus for male production -- sometimes diet shift, sometimes crowding
            c. resting eggs
                (1). Monogonata
                (2). Bdelloids never have males and don’t have resting eggs; the adults can withstand desiccation

    D. Feeding
        a. the rotifers use their cilia to create currents around their anterior ends
        b. some are predatory; some eat algae; some eat protozoans
        c. Trophi (jaws):
            (1) malleate – designed to mash food; algae eaters
            (2) virgate – designed to suck in food or puncture tissue and suck up contents
            (3) forcipate – designed to extend out of mouth

VI. Phylum Arthropoda, Class Crustacea, Order Branchiopoda
     A. Taxonomy
        1. Cladocera
            a) Daphnia – water flea
            b) Bosmina
            c) Leptodora
            d) Cercopagis
    B. Miscellaneous
        1. 300 mm to 1 cm long
        2. Have a bivalve carapace with a gap
        3. Herbivorous cladocera have paddle-shaped legs and draw water currents into carapace
    C. Life History
        1. rapid life cycles – 1 to 2 weeks per generation
        2. most often are parthenogenic – cyclical parthenogens
        3. direct development -- no distinctive change in morphology associated with each instar
        4. clutch size variable
            a. related to age (body size), instar, food levels
            b. eggs produced after each adult molt
        5. cues for male and haploid egg production – crowding (excretion products), decreased food, light decreases, temperature decreases
        6. Sexual reproduction results in diapause eggs -- ephippia (saddle)
        7. arctic daphnids can often produce resting eggs without males (asexually)
        8. Some daphnid species and clones never make resting eggs
        9. some cladocera overwinter as adults in the lake

Daphnia life cycle
    D. Feeding
        1. most are herbivorous
        2. some predaceous (Leptodora, Polyphemus, Bythotrephes)
        3. some can feed on bacteria

VII. Phylum Arthropoda, Class Crustacea, Order Copepoda
     A. Taxonomy
        1. Suborder Cyclopoida – short antennae

        2. Suborder Calanoida – long antennae
            a. Diaptomus

        3. Suborder Harpacticoida -- mostly littoral and benthic; some parasitic

    B. Miscellaneous
        1. widely distributed in all freshwaters
            a. from tropical to arctic regions
            b. from low ionic strength to salty
        2. Will accumulate different lipids if are in cold versus in warm environments
        3. Body size -- 300 mm to 5 mm
    C. Life History
        1. Sexual reproduction only – males and females
        2. Indirect development –
            a) juvenile – nauplius
            b) copepodid stage – metamorphosis to this stage
        3. Cyclopoida
            a. eggs are carried by the females in egg sacs
            b. mating behavior
                i. male make spermatophores (packages of nonflagellated sperm)
                ii. males must give spermatophores to the females (mating pheromones and behavior)
                iii. males have ‘geniculate’ antennae that are used to deposit spermatophore on female (true for calanoids as well)
            c. relatively short generation time, several per year
                1) 1-2 months per generation
                2) generation time affected strongly by temperature
            d. resting stages
                1) in some species the eggs can be dried and hatch when wet
                2) diapause in copepodite IV stage, not as a resting egg
                3) encyst in sediments in fall and undergo stasis for the winter
                4) diapause is broken by temperature or light in the spring
        2. Calanoida
            a. relatively long generation time, 1 to 2 per year
            b. most carry eggs in a sac or deposit them into water
            c. no diapause stage as a copepodite
            d. production of morphologically distinct resting eggs
                1) normal hatching eggs have a thin shell and the nauplii develop (rate proportional to temperature)
                2) diapause (resting) eggs have a thicker shell and can withstand desiccation.
                3) one type has a 2-layer integument or shell, mostly in Northern populations (arctic), some temperate, not tropical
                4) cues for hatching related to temperature and light

    D. Feeding
        1. Cyclopoida
            a. predaceous/omnivorous
                (1) can feed on algae or other animals
                (2) nauplii (juveniles) are generally herbivorous and there is an ontogenetic (developmental)
                    switch from herbivory to predation as they metamorphose to adult copepods
            b. no elaborate modifications for feeding

        2. Calanoida
            a. set up feeding currents and remove particles – can select their food
            b. mostly herbivorous; large forms like Epischura are sometimes predaceous (but are herbivorous as nauplii)
            c. mouthparts of some modified for filter feeding
        3. how do they find food?
            i. Mechanoreception – setae on antennae
            ii. Chemoreception
        4. Harpacticoids
            a. mouthparts adapted for seizing and scraping particles from the sediments and macrovegetation
            b. parasitic on fish

VIII. Phylum Arthropoda, Class Crustacea, Order Malacostraca
    A. Taxonomy
        i. Mysidacea - mysids
            (1) Glacial relicts
            (2) Long lived
            (3) omnivores
        ii. Amphipoda

IX. Phylum Arthropoda, Class Crustacea, Eubranchiopoda
    In temporary bodies of water without fish
    Eat algae, bacteria, protozoans, rotifers, detritus
    Have resting eggs

    A. Anostraca - Fairy shrimp
        Swim on backs (‘like tiny walruses’)

    B. Notostraca – tadpole shrimp (Triops)
        Notostraca will also eat dead animals or are sometimes predaceous

X. Phylum Arthropoda, Class Crustacea, Order Ostracoda
        Mostly benthic
        Herbivorous
        Resting eggs
        Sexual or asexual reproduction

XI. Phylum Arthropoda, Class Insecta
    A. Taxonomy
        1. Dipteran (true fly) larvae
            a) Chaoborus – voracious predator
          
        2. Predators
        3. Larval stage of flies
 

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