1. Animals which possess two pairs of symmetrical sides are said to be biradially symmetrlcal
2. Biradial symmetry is a combination of radial and bilateral symmetry as seen in ctenephores

The lungs are light spongy tissues enclosed in the thoracic cavity surrounded by an air tight space. It is bound dorsally by the vertebral column and ventrally by the sternum, laterally by the ribs and on the lower side by the dome shaped diaphragm.

The diffusion membrane of the alveolus is made up of three layers.
They are:
(i) The thin squamous epithelial cells of the alveoli.
(ii) The endothelium of the alveolar capillaries and
(iii) The basement substance found in between them.

The male and female sex organs mature at different times. Sperms develops earlier than the production of ova (protandrous). Hence, self-fertilization does not take place in earthworm.

The body of helminth parasites is covered by a thick covering called tegument. This protects the worms. They have hooks, suckers or both for attachment.

Heparin is an anticoagulant produced in small quantities by mast cells of connective tissue which prevents coagulation in small blood vessels.

Cockroaches are generally oviparous, but the Diploptera punctata is a viviparous cockroach found in Myanmar, China, Fiji, Hawaii, and India.

Ehler's -Danlos syndrome: Defect in the synthesis of collagen in the joints, heart valves, organ walls and arterial walls.
Stickler syndrome: Affects collagen and results in facial abnormalities.
Rhabdomyosarcoma: Life-threatening soft tissue tumour of head, neck and urinogenital tract.

The Areolar connective tissue beneath the skin acts as a support framework for epithelium and acts as a reservoir of water and salts for the surrounding body tissues, hence aptly called tissue fluid.

(i) Each tooth is embedded in a socket in the jaw bone; this type of attachment is called thecodont.
(ii) Human beings and many mammals form two sets of teeth during their lifetime, a set of 20 temporary milk teeth (deciduous teeth) which gets replaced by a set of 32 permanent teeth (adult teeth). This type of dentition is called diphyodont.
(iii) The permanent teeth are of four different types (heterodont), namely, Incisors (I) chisel like cutting teeth, Canines (C) dagger shaped tearing teeth, Pre molars (PM) for grinding, and I Molars (M) for grinding and crushing.

Animal tissues are classified according to the size, shape and function of the cells. There are four primary (basic) tissue types that interweave to form the 'fabric' of the body. They are, the epithelial tissue (covering), the connective tissue (support), the muscle tissue (movement) and the nervous tissue (control).

(i) To identify and differentiate closely related species.
(ii) To know the variation among the species.
(iii) To understand the evolution of the species.
(iv) To create a phylogenetic tree among the different groups
(v) To conveniently study the living organisms.

Classification is a process by which things are grouped in convenient categories, based on easily observable characters. The scientific term used for these categories is taxa.

Ecosystem is a community of living organisms (plants and animals), non-living environment (including minerals, climate, soil, water, sunlight) and their interrelationships.

They are simple tubular intestinal glands which occur throughout small intestine between villi and secrete enzyme and mucus.

Autopsy is a post-mortem (dissection of a dead body) examination to discover the cause of death or the extent of disease.

Eczema, Psoriasis, Epithelial carcinoma and severe Asthma.

The left ovary is well developed while the right ovary is atrophied.

(i) The Phylum hemichordata consists of a small group of worm like soft marine animals, and tubiculous. Such animals are called tongue worms.
(ii) Eg: Balanoglossus. Saccoglossus, Ptychodera flava, etc.

The term 'Echinos' means spiny and 'dermos' means skin. These animals have a mesodermal endoskeleton of calcareous ossicles and hence they are called echinoderms or spiny skinned animals.

1. The female are longer than males.
2. The hind end of the male worm is curved.

e-Taxonomic resources - INOTAXA is an electronic resource for digital images and description about the species which was developed by Natural History Museum, London. INOTAXA means INtegrated Open TAXonomic Access

1. DNA barcoding
2. DNA hybridization
3. DNA Finger printing
4. Marine parks
5. Restriction Fragment Length Polymorphisms analysis.