Ancestral animals with marginal importance in freshwater systems

Phylum Cnidaria

•Hydras, Jellyfishes, Corals, Man-o-war

•Mostly marine

–Hydras & related “jellyfishes”

•True tissues, Rudimentary organs

•True symmetry (radial)

Basic Morphology

•3 germ layers

–Epidermis – outer layer

–Gastrodermis – lining gastrovascular cavity

–Mesoglea – non cellular, gelatinous layer between Epidermis and Gastrodermis

•2 basic body types

–Polyp – sessile, stalk w/ oral opening surrounded by tentacles

•Mostly small, mesoglea thin

•Mostly asexual reproduction

–Medusa – planktonic, free-swimming, bell-shaped, also w/ oral opening surrounded by tentacles

•Mesoglea >80% of mass

•Mostly sexual reproduction

5 cell types

•Epithelio-muscle cells – cover body, contract for movement

•Interstitial cells – middle layer, produces gametes

•Mucous cells – attachment, protection, feeding

•Nerve cells – sense environment

•Cnidoblasts/cnidocytes – on tentacles, have trigger (cnidocil) which fires nematocysts (barbed “spear” w/ toxin & tether)

–Defense and feeding

Alternation of Generations

•Many Cnidarians alternate between asexual polyp and sexual medusa

3 Classes

•Anthozoa – corals & anemones (all marine)

•Scyphozoa – jellyfishes (all marine)

•Hydrozoa – hydras & FW jellyfish (99% marine), monophyly?

–All NA FW hydra & jellyfish in this taxon

NA FW Hydrozoa

•FW Jellyfish – Craspedacusta sowerbii

–Exotic – native to Asia

–Alternation of generations

–Medusa occasionally extremely abundant and conspicuous in ponds, lakes, reservoirs

•<1.5 cm diameter

–Harmless

NA FW Hydra

•Hydra – many species native to NA FW

–Microscopic (1-20 mm)

–Polyp only

–Attach to rocks, logs, plants, or other hard substrate

–Feed by tentacles capturing food

•Brought into coelenteron & chemically digested by enzymes

•Detach & relocate if >12 hrs w/o food

•Some w/ symbiotic green algae

–Regeneration after mutilation

–Reproduce asexually by budding

–Reproduce sexually by ovaries & spermaries

Phylum Platyhelminthes

•Flatworms

•Free-living & parasitic

•Marine, FW, moist soils, GI tract & accessory organs in most major animal lineages

•Bilateral symmetry

•Monoecious (male & female organs in same individual)

–Pair & cross fertilize

–Zygotes can aestivate during winter

Bilateral Symmetry

•Efficient locomotion

•Cephalization – anterior concentration of nervous tissue and senses

Basic Morphology

•Lack coelom

•Triploblastic

–Ectoderm – outer layer

–Endoderm – gut

–Mesoderm – most of body mass b/w Ecto & Endo

•True organs, rudimentary systems

•Flattened body, diffusion & osmosis largely responsible for transport

•Incomplete or lacking digestive system

4 classes

•Turbellaria – free-living flatworms

•Trematoda – internal parasitic flukes

–Many parasitize aquatic snails

•Monogenea – external parasitic flukes

–Many parasitize fish gills

•Cestoda – tapeworms

Turbellaria

•200 species in North America

–All aquatic or at least found in moist soil

–Most freshwater in genus Planaria

•Cilia & mucous glands on ventral surface

–Locomotion

•Muscles longitudinal & transverse

–Complex motion

•Marginal ecological importance in FW systems

“Pseudocoelomates”

•Body cavity b/w endoderm & mesoderm

•Most likely not monophyletic

•Only common characteristics plesiomorphic

•Relationships uncertain

•Roundworms

•Rotifers

•Gastrotrichs

•Horse-hair worms

Phylum Rotifera

•Ciliated crown

•Very small 0.04 – 3 mm

•~2000 species worldwide

•Mostly FW, some marine & terrestrial

•Cosmopolitan

•Free-swimming & attached

Basic Morphology

•Covered w/ cuticle (spines, hairs & plates)

•Head

–corona w/ cilia – feeding & locomotion

–Mastax – muscular pharynx used for feeding

•Contains hard structures used in identification

•Trunk

–Complete GI tract

–Excretory system

–Reproductive system

•Foot

–Toe - attachment

Reproduction

•Dioecious

–Sexual dimorphism (females larger)

•Some species lack males

–Amictic females – reproduce asexually

–Environmental stimulus causes production of haploid eggs

•Develop into “male” offspring or remain haploid eggs

–“male” produces haploid sperm fertilizing haploid eggs

•Zygote becomes amictic female

Phylum Gastrotricha

•Resemble rotifers

–Lack corona & mastax

–Have scales & spines

•Often found w/ rotifers

•Also w/ unusual reproductive cycle

•~500 species (100 in NA)

•Marine & FW

•Move by crawling along substrate or aquatic plants

Phylum Nematoda

•Roundworms

•10,000 described species

–Probably >500,000

–Few morphological features useful for traditional systematics

•Truly cosmopolitan (found in all imaginable habitats)

•Incredibly abundant

•Dioecious

•Sexually dimorphic (males smaller, hooked posteriorly)

Basic Morphology

•Vermiform

•Longitudinal muscles only

–Thrashing movement

•Cuticle = tough outer layer

•Epidermis below cuticle

•Fluid filled pseudocoel

–Hydrostatic skeleton

•Complete digestive system

Phylum Nematomorpha

•Horse-hair worms

•Poorly studied

•Parasitic larvae

•Free-living adults

–Many don’t feed

•Cuticle covered

•Often more common in degraded habitats

•Dioecious