and exhibit sexual dimorphism; often females are longer than males. Fertilisation is internal; majority are oviparous (e.g. Ascaris ) few are ovoviviparous ( Wuchereria ). Development may be direct or indirect.
Examples. Ascaris lumbricoides (Round worm), Enterobius vermicularis (Pin worm), Wuchereria bancrofti (Filarial worm), Ancylostoma a deuodenale (Hook worm) (Figure . ). .
. Phylum: Annelida (Segmented Worm) (L. annulus -a ring, and G. edios - form) Annelids were the first segmented animals to evolve.
They are aquatic or terrestrial, free living but some are parasitic. They are triploblastic, bilaterally Figure . Examples of Platyhelminthes Planaria Liverfluke Tapeworm Figure . Examples of Aschelminthes Ascaris Filarial worm Hook worm XI Std Biology-Zoology Chapter- symmetrical, schizocoelomates and exhibit organ system level of body organisation.
The coelom with coelomic fluid creates a hydrostatic skeleton and aids in locomotion. Their elongated body is metamerically segmented and the body surface is divided into segment or metameres. Internally the segments are divided from one another by partitions called septa. This phenomenon is known as metamerism .
The longitudinal and circular muscles in the body wall help in locomotion. Aquatic annelids like Nereis have lateral appendages called parapodia , which help in swimming. Chitinous setae in Earthworms, and suckers in Leech help in locomotion. The circulatory system is of closed type and the respiratory pigments are haemoglobin and chlorocruorin .
Nervous system consists of paired ganglion connected by the lateral nerves to the double ventral nerve cord. They reproduce sexually. Development is direct or indirect and includes a trochophore larva . Some are monoecious (earthworms) while some are dioecious (Neries and Leech).
(Figure . ) Examples: Lampito mauritii (earthworm), Neries (sand worm), Hirudinaria (leech). How is cephalisation advantageous to animals in finding food? Filariasis has been a major public health problem in India next only to malaria.
The disease was recorded in India as early as th century B.C. by the famous Indian physician, Susruta in his book Susruta Samhita. In th century A.D., Madhavakara described signs and symptoms of the disese in his treatise ‘ Madhava Nidhana’ which holds good even today.