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)

Major Aquatic Invertebrate Taxa

Review of major invert classifications

--Radially symmetrical animalsPhylum: 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

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)

Major Aquatic Invertebrate Taxa

Phylum: Porifera

About 5,000 species worldwide

About 25 species are freshwater

Collection and Identification of sponges

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.

General physiology

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 speciesClass Cubozoa (sea wasps)Class Scyphozoa (jellyfishes)Class Anthozoa (sea anemones and corals)

polyp medusa

Dimorphism in Cnidaria

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 free-swimming 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

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)

Major Aquatic Invertebrate Taxa

Review of major invert classifications

--Radially symmetrical animalsPhylum: 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 living- Class Turbellaria (planarians)

mostly predaceousfree livingepidermal rhabdites

Parasitic – Class Trematoda (internal flukes)

exclusively parasiticcomplicated life-cycles

Class Cestoda (tapeworms)exclusively parasitic

Platyhelminthes (flatworms):

Trematodes --- ‘black spot disease’; ‘yellow grub’

PlanarianDugesia

Phylum: Platyhelminthes

About 200 species in N. America

Turbellarians: General morphology

epidermis

mesenchyme

gut

rhabditesneoblasts

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

Simple intestine

3-lobed intestine

Many-lobed intestine

Acoela 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. Short-lived, nonfeeding stage.

--Can produce asexually by fission, fragmentation or both.

Life history and ecology

Some species are univoltine:

produce one generation a year

Most turbellarians are multivoltine:

produce several generations a year

--Widely distributed in N. America

--Occur in both lakes and streamsStream-dwelling species more

differentiated than lake species

--Species diversity increases in temperate areas 20 to 60 species per lake

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.

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)

Major Aquatic Invertebrate Taxa

Review of major invert classifications

--Radially symmetrical animalsPhylum: 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 speciesFewer 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.

OPSITACHY(2N)

(N)

Gastrotrich reproduction

juvenile

parthenogenetic

hermaphroditic

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 region2) 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) Bdelloidea2) 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.

--2 types of females: Amictic and dimictic. Morphologically indistinguishable, but functionally distinct.

Rotifer life-cycle

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 layerMatrix layerBasal layer

CuticleEpidermisMuscle processExcretory canalPharyngeal 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 diseasespinwormwhipwormhookwormintestinal roundwormTrichinellaOnchocerca “river blindness”Filaria “elephantiasis”