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Phylum Nematoda
Highest abundance of any animal on planet:
4 million / square meter in marine
~ 16,000 species described
> 100,000 predicted taxa
Phylum Nematoda• Triploblastic, bilateral, vermiform, unsegmented• Complete gut • No circulatory or gas exchange structures• Longitudinal muscles ONLY
Dioecious - males have “hooked” posterior
Marine, freshwater, terrestrial
some free-living, some parasitic
Nematoda body wall
• Cuticle secreted by epidermis• Epidermis: syncytial = nuclei not separated by complete cell
membranes
• Longitudinal nerve cords
Support and Locomotion
• Longitudinal muscles • No circular muscle layer (burrowing impossible)• Body cavity not spacious, filled with organs• Cuticle provides support = hydrostatic• Whiplike undulatory motion
Feeding
• Detritivores, microscavengers: consume bacteria/fungi on decomposing organic matter
• Free-living taxa can be carnivores
Nematodes feeding on termite
Digestion
Complete digestive tract: mouth, pharynx, intestine, anus
Pharynx adds enzymesDigestion extracellular
Circulation, Gas Exchange, Excretion, Osmoregulation
• Circulation and gas exchange by diffusion and movement of body cavity fluids
• Excretory system: renette?• Cuticle differentially permeable to water (H2O
in but not out)
Nervous System and Sense Organs
• Cerebral ganglion = nerve ring and ganglia
• Nerves extend from nerve ring• Abundant sense organs = papillae
and setae (tactile receptors)• Amphids - paired organs on head =
chemosensory
Reproduction and Development• Mostly dioecious: sperm amoeboid• Few hermaphroditic (sperm and egg production in same
gonad = ovitestis)• Few parthenogenetic• Female: ovary, oviduct, uterus, vagina, gonopore
Female nematode x-sec
Male– Smaller, curved body– Threadlike tubular testes– Sperm stored in seminal vesicle
Male x-sec
Hookworm: Necator americanus> 1 billion infected worldwide
egg
Pinworm = Enterobius vermicularis~ 20 % US children infected
Cool Nematodes!Guinea worm: female can be 1 m long, just under skin, produces ulcer
that causes opening, release young (to intermediate copepod host)
Chapter 17 Pechenik
Cycloneuralia:Nematomorpha and others
Phylum Nematomorpha
• “thread body” = Hair Worms• 2 orders– marine– freshwater and terrestrial
Hair worms
• ~ 320 species described•5 are marine•Adults all free-living•Adults do not feed = nonfunctional digestive tracts
•Juveniles are internal parasites•Lack digestive tract•Mostly insect hosts•Details of life cycles unknown for most species