Biology 320 Invertebrate Zoology Fall 2005

1. Biology 320Invertebrate ZoologyFall 2005 Chapter 22 – Phylum Gastrotricha and Phylum Nematoda

2. Phylum Gastrotricha • 500 species • Found in all three habitat types • Marine and FW - interstitially or on plants • Terrestrially - in water film covering soil particles • Microscopic to 4mm long • Eutelic • Genetically predetermined and constant number of cells • Cell size increases, but not cell number

3. Body Form • Bowling-pin-shaped • Name means “hairy belly” • Locomotory cilia on ventral surface • Adhesive tubes located near head and/or on lateral body • Adhesive organs at posterior • All are similar to duo-glands of turbellarians

4. Body Wall • Cuticle • Not chitinous • Not molted • Epidermis • Musculature • Circular • Longitudinal

5. Organ Systems • No hemal system • Acoelomate, so don’t even possess a hemocoel • No respiratory system • Nervous system • Brain • Pair of ventrolateral nerve cords • Sensory organs • Cerebral organs possess all three types of receptors • Sensory bristles found on body surface • Excretory system • One to several pairs of protonephridia • Nephridiopores open ventrolaterally • Osmoregulatory in function • Ammonotelic, so ammonia diffuses across body surfaces

7. Movement • Ciliary gliding for forward movement • Rapid rearward withdrawal as an escape response • Can use a combination of adhesion and muscular contractions to: • Inchworm • Somersault

8. Nutrition • Gut lacks stomach • Large muscular pharynx • Y-shaped in some • Possess pharyngeal pores that open to surface and release excess ingested water • Feed on small organic particles (live or dead) • Bacteria and protozoans

9. Reproduction • Hermaphroditic with indirect sperm transfer • Posterior copulatory organ that is loaded with sperm from anterior male gonopore • Spermatophore transferred to seminal receptacle via posterior female gonopore • Internal fertilization

10. Fertilized eggs are released by rupturing body wall • Some species are parthenogenic • Can produce two types of eggs • Summer • Winter (resting) • Direct development • Sexual maturity is reached in about three days • Life span is approximately 40 days

11. Phylum Nematoda • Roundworms • 20,000 described species • May be the largest animal phylum • Found worldwide and live in all habitat types • Interstitially • Inside of animals and plants • 53°C hot springs • Epiphytic bromeliads • Very abundant • One cubic meter of mud off of the coast of Holland contains over 4,000,000 nematodes

12. Ecologically important • Link between decomposers and higher trophic levels • Some are excellent decomposers and nutrient cyclers • 90,000 nematodes in one rotting apple • Caenorhabditis elegans is an important model organism for genetics / development studies • Eutelic • C. elegans has 1031 cells

13. Body Form • Vermiform • Tapered at both ends • Important adaptation for living interstitially • Microscopic to 50 cm • One mm is typical • Mouth at anterior end, with three to six lips that bear sensilla • Caudal gland on posterior that is similar to a duo-gland • Lack cilia

14. Body Wall • Cuticle • Not chitinous • Often annulated • Must be molted • Molted four times while growing • Molting ceases upon reaching adulthood • Ecdysone controls molting • Epidermis • Secretes cuticle • Stores nutrients • Endoparasites may absorb nutrients with • Has four longitudinal extensions called epidermal cords • Longitudinal nerve cords housed here • Musculature • Four bands of longitudinal fibers separated by epidermal cords • No circular muscles

16. Locomotion • Use sinusoidal undulations of dorsoventral plane to move forward • Alternate contractions of dorsal and ventral longitudinal muscles • Efficient movement requires a substratum to act against • Removing worms from natural substratum hinders locomotion • Many swim or are capable of swimming • Some crawl like earthworms or inchworms

17. Organ Systems • Hemal system • Large nematodes have a hemocoel (pseudocoel) • Fluid filled and fluid may contain hemoglobin • Functions as hydrostat • Small varieties are acoelomate • No respiratory system • Nervous system • Collar-like brain surrounds pharynx • Dorsal, ventral, and lateral longitudinal nerve cords in epidermal cords • Sensory organs • Papillae – low projections of cuticle on lips and head • Tactile setae • Ocelli – one on each lateral aspect, near pharynx

19. Nutrition • Will eat just about anything • Carnivorous, herbivorous, or omnivorous • Will eat bacteria, protists, fungi, other nematodes, and plant cells • Some are deposit or detritus feeders • Actually feed on bacteria associated with these types of organic matter • Some fungi actually prey on nematodes • Trap them with hyphal threads

20. Digestive System • Similar to that of gastrotrichs • Cuticle of foregut contains teeth, ridges, rods, or plates • Varies according to feeding habits • Example: Mononchus uses teeth to latch onto other nematodes • Body contents are pumped out • Will eat over 1000 nematodes over its 14 week life span • Diagnostic tool for taxonomists • Herbivores have a stylet for piercing plant cells • Some parasites use body surface to absorb nutrients

21. Excretory System • Ammonotelic • All have one or more excretory glands • Some also have an excretory canal system • Interestingly, is formed from one huge H-shaped cell • Pore opens midventrally near pharynx • The canal system is osmoregulatory in C. elegans, but other nematodes secrete different substances • Gelatinous matrix for eggs • Glycoprotein coat for cuticle • Digestive enzymes to erode host tissue in animal parasites • Molting fluid

22. Reproduction • Most gonochoric • Some hermaphroditic • Some parthenogenic • Internal fertilization with copulation • Sexually dimorphic • Males smaller than female • Male has curled posterior that resembles a hook • Male has a cloaca, as where vagina is located midventrally on the middle of the female’s body • Male has copulatory spicules (resemble curved blades) that are used to hold female gonopore open

23. Both male and female have C-shaped gonads • Females produce pheromones to attract males • Sperm are aflagellate and amoeboid • Eggs have characteristic shapes, and experts can diagnose infections • Some free-living types, such as Turbatrix, are viviparous

24. Hermaphroditic varieties typically self-fertilize and rarely cross-fertilize • Little genetic recombination • Egg numbers vary greatly between species • 50 in some marine species • 200,000 per day in the parasite Ascaris • Eutelic • Around 1000 cells • Number of cells in individual organs is also constant • Cells grow in size, not in number • Direct development • Egg, three juvenile instars, and adult • Four molts (first two of which may occur in egg before hatching) • Molting ceases upon reaching adulthood

25. Parasitism • Can be ectoparasites or endoparasites • Can have one host or multiple hosts • Can infect plants, animals, or both • Juveniles, adults or both can be infective

26. Ascaroid nematodes • Ascaris, hookworms, pinworms, and Trichinella • Infect one host: humans, cats, dogs, pigs, cows, etc. • Infection occurs when eggs or juveniles are ingested • Eggs hatch in intestine • Juveniles penetrate intestinal wall • Juveniles enter hemal system • Juveniles break through alveoli in lungs • They migrate up respiratory tree • Are coughed up in sputum • If sputum is swallowed, end up in intestine

28. Ascaris • Human intestinal worm: Ascaris lumbricoides • Can reach 50 cm in length • Widely distributed, but is found in SW US • Eggs found in soil and are resistant to harsh environmental conditions • Children are susceptible to infection because they put things in their mouths • Feeds on fluid gut contents of host • Can cause malnutrition and death in the event of intestinal blockage • Secrete substances which inhibit host digestive enzymes from harming them

29. Hookworms • Necator americanus • Juveniles enter through skin of foot • Follow typical ascaroid path • Attach to intestinal lining with hooks • Feed on host’s blood • Infections of more than 25 worms can lead to serious blood loss and tissue damage • Common in tropics • 380 million infected worldwide

30. Pinworms • Enterobius vermicularis • Typically infect humans • Worldwide distribution • Adults live in intestine • At night, female crawls out anus and deposits eggs • Scratching traps eggs under fingernails

31. Trichinella spiralis • Infects mammals with a condition known as trichinosis • Juveniles are carried to skeletal muscles by blood • Form calcified cysts in muscle • Transmitted when undercooked flesh is eaten • Example: humans eating undercooked pork • Severe infection causes pain and stiffness

32. The following groups of parasitic nematodes have two hosts (intermediate and definitive) • Filarioids • Dracunculoids • Filarioids • Elephantiasis, heart, and eye worms • Thin, threadlike worms that inhabit the lymphatic system or other tissues • Intermediate host is typically a blood sucking insect • Definitive host is usually a bird or mammal

33. Wuchereria bancrofti • Found mainly in Africa and Asia • Intermediate host is a mosquito, definitive host is a human • Threadlike adults live in lymph glands • Blockage of lymph vessels causes edema • Long term blockage causes a condition known as elephantiasis • Enlargement of appendages, breasts, scrotum, etc… • Life cycle • Eggs hatch into microfilariae that migrate to surface blood vessels at night (when mosquitoes are biting) • Microfilariae migrate from mosquito gut lumen to proboscis • Injected into definitive host

34. Dirofilaria immitis • Canine heartworm • Loa Loa • African eye worm • Sometimes crosses cornea

35. Dracunculus medinensis • A dracunculoid • Guinea worm • Intermediate host is a FW copepod and definitive host is human • Adult female lives below skin of human and produces an ulcer • Juveniles released in water • Ingested by a copepod • Humans ingest copepod by drinking contaminated water • Worms removed surgically or by winding on a stick • Caduceus (symbol of medical profession) is really a nematode curled around a stick