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 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