Phylum Porifera (sponges) Cnidaria (hydra & jellyfish) Platyhelminthes (flatworms)

Major Aquatic Invertebrate Taxa 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)

Review of major invert classifications --Radially symmetrical animals Phylum: 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 About 5,000 species worldwide About 25 species are freshwater

Collection and Identification of sponges

General physiology 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.

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

Dimorphismin Cnidaria polyp medusa

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

Platyhelminthes (flatworms): Free living- Class Turbellaria (planarians) mostly predaceous free living epidermal rhabdites Parasitic – Class Trematoda (internal flukes) exclusively parasitic complicated life-cycles Class Cestoda (tapeworms) exclusively parasitic

Platyhelminthes (flatworms): Trematodes --- ‘black spot disease’; ‘yellow grub’

Phylum: Platyhelminthes Planarian Dugesia About 200 species in N. America

Turbellarians: General morphology gut epidermis mesenchyme neoblasts rhabdites

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 --Widely distributed in N. America --Occur in both lakes and streams Stream-dwelling species more differentiated than lake species --Species diversity increases in temperate areas 20 to 60 species per lake Some species are univoltine: produce one generation a year Most turbellarians are multivoltine: produce several generations a year

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: Gastrotricha About 450 species Fewer 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.

Gastrotrich reproduction OPSI TACHY (2N) juvenile parthenogenetic (N) 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 region 2) 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) Bdelloidea 2) 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.

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

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

Phylum Porifera (sponges) Cnidaria (hydra & jellyfish) Platyhelminthes (flatworms)