PoriferaPoriferaCycliophoraCycliophora CnidariaCnidaria CtenophoraCtenophora SipunculaSipuncula MolluscaMollusca AnnelidaAnnelida OnychophoraOnychophora TardigradaTardigrada BryozoaBryozoa PlatyhelminthesPlatyhelminthes NemerteaNemertea RotiferaRotifera GnathostomulidaGnathostomulida GastrotrichaGastrotricha NematodaNematoda NematomorphaNematomorpha PriapulidaPriapulida KinorhynchaKinorhyncha LoriciferaLoricifera PhoronidaPhoronida BrachiopodaBrachiopoda EchinodermataEchinodermata ChordataChordata HemichordataHemichordata ArthropodaArthropoda Adapted from Lesser Known Protostome Phyla. SICB J.R. Garey. The Ecdysozoa = animals that molt a cuticle by hormonal (steroid) cue

Phylum Nematoda

Nematoda: characteristics non-cellular cuticle in layers shed pseudocoelomate no circular muscles, only longitudinal muscles: hydrostatic skeleton dioecious (amoeboid sperm) little cephalization (nerve ring ~ a brain, amphids) 80,000 spp described (>1M?) most are benign to beneficial, 15,000 are parasitic up to 4M/m 2 in mud, billions in an acre of good farm soil Caenorhabditis elegans is an important model organism

Physiology Specialized buccal cavity for diet –Diatoms, algae, fungi, bacteria –Plant roots, carnivores, internal parasite Pharynx also specialized for diet Excretion by excretory gland (renette cell) and excretory canal (not all nem’s have them) leading to an excretory pore –May also serve other functions (exoenzymes, molting fluid) –It does osmoregulation in C. elegans

Reproduction Separate sexes –but some hermaphroditic (e.g., C. elegans) –others are parthenogenic Internal fertilization

Development Eutely: = growth by increase in cell size, not cell number –E.g. C. elegans: 200 nerve cells, 12 epidermal cells, 172 gut cells…

Human “worm” diseases Acanthocephala7 species Nematoda138 species Nematomorpha24 species Platyhelminthes173 species Digenea113 species Eucestoda57 species Turbellaria3 species TOTAL342 species

Ascaris lumbricoides in intestine of > billion people (64% in pops SE US) Dioecious, sexually dimorphic: F > M each F makes 200,000 eggs/day  feces  ingested  burrow through intestine wall  carried by blood to lungs  alveoli  up mucociliary escalator  swallowed  mature in intestine (30 cm long)

Necator: Hookworm Cut mucosa & feed on blood  anemia Life cycle similar to Ascaris except infective juveniles penetrate into bare feet  burrow into int wall  lungs  swallowed  adults in intestine

Trichinella (disease = trichinosos) in 2.4% of US pop in humans, pigs, rats, cats, dogs Adult in sm int.  live larva  from intestine burrow  blood stream  encyst in muscle tissue  cyst consumed  hatch and live in sm int.

Guinea worm

Elephantiasis

Enterobius: Pinworm in 30% of children & 16% of adults in US Eggs laid around anus at night  itch  spread eggs  ingested  hatch  adult

Crop parasites Of enormous economic impact…e.g. corn soybean ginseng

Fungi that snare nematodes