phylum nematoda highest abundance of any animal on planet: 4 million / square meter in marine ~...

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