Direct Development:
Advantages:
1. The young ones resemble the adult directly and no larval stages occur.
2. The eggs of these animals have lot of yolk for the young ones to grow or are fed by the mother's tissues. (human being) in the larval stages.
3. Parental care is seen in many cases.
Disadvantages:
1. Since the parents and young ones are found in the same habitat. they have to share the same resources.
2. In case of calamities/disasters, they will perish together.
Indirect Development: Advantages:
1. The larval forms are much different from the adult and thrive on different food resources
2. They also grow in a different ecological habitat. Hence in case of calamities, they may continue to exist even if the adults Perish.
3. Indirect development is a better means for the species to survive.
Disadvantages:
1. Chances of all larvae developing into adult cannot be assumed.
2. Eggs have very little yolk.
3. Parental care is not seen.

[Ans.(a)]

1. Bioluminescence (the ability of a living organism to emit light) is well marked in Ctenophores.
2. They lack nematocyte but possess special cells called lasso cells or colloblasts to capture food.
3. They show indirect development and the larva is called cydippid. Eg: Pleurobrachia.

1. All chordates possess a notochord.
2. All chordates possess a dorsal, hollow, nerve cord.
3. All chordates possess pharyngeal gill clefts in some stage of their life cycle.
4. Possess a post-anal tail.

The Ctenophores have eight external rows of ciliated comb plates (comb jellies) in the mesoglea which help in locomotion. Hence they are commonly called as comb jellies or sea walnuts.

Some Cnidarians exhibit two phases in their life cycle. Asexual phase called polyp and sexual phase called medusa. They thus show alternation of generation or metagenesis.

1. Eucoelom or true coelom is a fluid-filled cavity that develops within the mesoderm and is lined by mesodermal epithelium called peritoneum.
2. Such animals with a true body cavity are called eucoelomates
3. Based on the mode of formation of coelom, the eucoelomates are classified into two types,
i) Schizocoelomate animals - In these animals the body cavity is formed by splitting of mesoderm. Eg: Annelids, Arthropods, Molluscs.
ii) Enterocoelomate animals - In these animals the body cavity is formed from the mesodermal pouches of archenteron. Eg: Echinoderms, hemichordates and chordates.

(i) Round worm (Ascaris): body is unsegmented, anterior and posterior ends are tapered, no circular muscles, body has 4 bundled musculature, intestinal worm spreads Ascariasis by contamination.
(ii) Pseudocoelomates: Coelom is filled by loosely arranged mesenchyme.
(iii) Digestive tract is reduced or absent.
(iv) Cuticle above the epidermis protects the animal from the effect of digestive juice of hosts.
(v) It is an endoparasite, living in jejunum and ileum of small intestine of human.
(vi) It exhibits sexual dimorphism
(vii) Male measures 9 cm long, its tail is curved and provided with the cloaca and a paired copulatory spicules.
(viii) Female measures 14 cm long, its tail is straight and provided with anus and excretory pore without copulatory spicules.