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
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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
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Longitudinal muscles
No circular muscle layer (burrowing impossible)
Body cavity not spacious, filled with organs
Cuticle provides support = hydrostatic
Whiplike undulatory motion
Nematodes feeding on termite
Feeding
• Detritivores, microscavengers: consume
bacteria/fungi on decomposing organic
matter
• Free-living taxa can be carnivores
Digestion
Complete digestive tract: mouth,
pharynx, intestine, anus
Pharynx adds enzymes
Digestion 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