Chapter 6 PHYLUM NEMATODA Phylum Nematoda • Round or Thread worms • size 1-2 mm mostly but some may reach 60 cm or more • Pseudocoelomates • non-sigmented • Free living and parasitic species • Pointed at both ends • Covered by a thick multilayered cuticle (non-cellular covering) • Epidermis is syncytial (secretes cuticle) 2 Nematode life cycle • Cuticle is shed 4 times during develop ment 3 Musculature • Lack circular muscles • muscular layer (longitudinal muscles) that arrange in 4 groups separated by the dorsal, ventral and lateral hypodermal chords, each muscle cell connected to either the dorsal or ventral nerve chord by muscle cell process; Movement and hydrostatic skeleton • Movement is by thrashing the body into sinusoidal waves generated by alternating contraction of longitudinal muscles on each side of the body. • The round shape of nematodes is due to the hydrostatic pressure generated by celoemic fluid and its opposing rigid cuticle. Nervous system • Nervous system made of brain (nerve ring and associated ganglia and at least 4 longitudinal nerves that run in the dorsal, ventral and lateral nerve chords in the hypodermis • Sense organs include a pair of head chemoreceptive amphids (characteristic feature of all nematodes), other sense organs found in certain groups include: posteriorly located chemoreceptive phasmids, ocelli, cephalic and caudal papillae as well as mechanoceptors Nematode Features II • Eutely: Cell number in adult tissue remain constant throughout life so that the limited increase in size is a function of increase in cell size NOT number). • Tubes within tubes worms, all organ systems tubular; 7 Nematode Features • Digestive system complete with mouth, muscular pharynx (esophagous), intestine and rectum; • Excretory system made of renette glandular cells in most spp; • No specialized gas exchange or circulatory system. 8 Nematode Reproduction & Life Cycle • Worms are mostly dioecious; • Male reproductive system tubular and made of testis, vas deferens, ejaculatory duct that opens in cloaca, many spp. have bursa and 1-2 copulatory spicules; • Female reproductive system tubular and made of one or two ovaries, each leads into oviduct--seminal receptacle—uterus, a vulva leads to female gonopore. • Fertilization internal following copulation or hypodermic impregnation; • Females are oviparous, ovo-viviparous or viviparous; • L.C. involves ecdysis of larval stages controlled by molting hormones with 4 larval stages before worms become adults; some larval stages can molt within the egg shell; Parasitic stages mostly use the third larval stage (L-3) as infective stage to the final host.. 9 10 Classification of parasitic Nematodes • Class Chromadorea (3 sub-classes) Sub-class: Rhabditia • Orders: 1. Rhabditida – • 2. Strongylida - Ancylostoma (hookworm), Enterobius (pin worm) – Sub-class: Spiruria – • Orders: 1. Spirurida - Filarioidea - filarial worms. Wuchereria bancrofti (elephantiasis), Onchocerca volvulus (river blindness), Dirofilaria immitis (dog heartworm). • 2. Ascaridida - intestinal parasites of vertebrates. Ascaris. Ascaris, Toxocara canis (dog ascarid) Debilitating effect of parasitic Nematodes • Blood suction. E.g Hook worms – Suck about 0.6 ml blood/day – 100 worms= 60 ml/day= 180 ml/month • Blocking of intestine and bile ducts. E.g ascaris – In cases of heavy infection. • Blocking of blood or lymphatic system. E.g Filaria – Elephantiasis as in Onchocerca volnulus Trichuris trichura L.C. 13 Hookworm L.C. 14 A. Lumbricoides L. C. 15 E. vermicularis L.C. 16 O. volvulus L.C. 17 Wuchereria bancrofti L.C. 18 .