Zoo-Lab (Sem-1) - Exercise 13: Phylum Nemathelminthes (Nematoda)

Phylum Nemathelminthes (Nematoda)

unsegmented roundworms; bilaterally symmetrical; usually so elongated and slender that they are called thread/hair worms; complete digestive system; covered with a tough cuticle and sensory organs; free-living in soil and water, parasitic to animals

amphids

anterior sensory organs

phasmids

posterior sensory organs

Phasmida; Aphasmida

representative classes of Phylum Nematoda

Class Phasmida

parasitic roundworms that live in the intestine of mammals, including man; both amphids and phasmids present

Ascaris lumbricoides

human Ascaris; cylindrical body with four longitudinal lines running from the anterior to the posterior end

median dorsal line; medial ventral line; two lateral lines

four longitudinal lines of the Ascaris

mouth

part of the Ascaris; at the anterior end, bordered by 3 lip-folds: one dorsal, two ventral lips

gonophore/reproductive pore

a tiny opening; situated at the mid-ventral line about one third from the anterior end of the female; the equivalent for males is the anus, which lie on the ventral line also

pineal setae

in males; a pair of needle-like chitinoid bodies; may project from the anus

Ascaris lumbricoides (male)

smaller than the female; curved ventrally at its posterior end

Ascaris lumbricoides (female)

larger than the male; have two big mass: uteri; distinguishable oviducts and ovaries

Turbatrix aceti

vinegar eel; non-parasitic nematode found in native vinegar; ovoviviparous animal; female bigger than male; cylindrical body

Class Aphasmida

posterior sense organs are absent; only amphids are present; they possess caudal adhesive glands

Trichiuris trichiura

whipworm; small nematode in which the esophagus is not muscular but consists of a long chain of cells forming a narrow tube; body is made up of 2 portions, a very slender anterior portion (esophagus), and a thick posterior portion containing the reproductive organs

spicule

structural elements found in most sponges; the meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators