Cell

Sponges are mostly asymmetrical, i.e. any plane that passes through the centre does not divide them into equal halves.

Ctenoplana belongs to phylum Ctenophora. It body bears eight external rows of ciliated comb plates, which help in locomotion.

In coelenterates, the arrangement of cells is more complex. Here, the cells performing the same function are arranged into tissues, hence is called tissue level of organization.

Those animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm, are called triploblastic animals e.g. platyhelminthes to chordates.

Specialised cells called flame cells that help in osmoregulation and excretion are present in flatworms (platyhelminthes).

Meandrina is called as Brain coral.

Those cnidarians which exist in both forms exhibit alternation of generation, known as Metagenesis, i.e. polyps produce medusae asexually and medusae form the polyps sexually (e.g. Obelia).

Silkworm (Bombyx) belongs to phylum Arthopoda.

Arthropods are bilaterally symmetrical, triploblastic, segmented and coelomate animals.

Salpa belongs to Urochordata. In Urochordata, notochord is present only in larval tail.

Hagfish (Myxine) belongs to Class–Cyclostomata. Theirbody is devoid of scales and paired fins.

Pharynx is perforated by gill slits in chordates while gill slits are absent in non-chordates.

Crocodile belongs to Class–Reptilia. Heart is usually three-chambered, but four-chambered in crocodiles.

Pristis (Saw fish) belongs to Class–Chondrichthyes. Theyhave internal fertilisation and many of them are viviparous.

The most distinctive feature of echinoderms is the presence of water vascular system which helps in locomotion, capture and transport of food and respiration.

All mammals are viviparous with few exceptions e.g. Ornithorhynchus (Platypus).