Introduction to Vertebrates:

Vertebrata:

Vertebrata is the subphylum of Phylum Chordata. Chordates have notochord, flexible rod of tightly packed cells, tubular nerve cord (dorsal) and gill slits at some stage in the life histories. Backbone or vertebral column replaces notochord in vertebrates.

Features:

i) The bilaterally symmetrical body, separated into head, trunk and tail. In many vertebrates, the neck joins head to trunk. The internal skeleton or endoskeleton of bone and cartilage, with backbone or vertebral column composed of series of small bones known as vertebrae.

ii) The well-developed central nervous system with the brain (within brain case) and spinal chord (dorsal position). Well-developed sense organs. The 'closed' blood system composed of the muscular heart (ventral position).

iii) 2 pairs of limbs (tetrapods.)

iv) Kidneys for eliminating body wastes.

v) Skin may be naked or include the covering of scales, feathers or hairs.

Vertebrates are separated into 5 classes:

• Pisces
• Amphibia
• Reptilia
• Aves, and
• Mammalia.

Pisces (Fishes):

These are fishes that are all aquatic. Jawless fishes like hagfish and lamprey are most primitive. They include sucker-like mouths and no paired fins. Cartilaginous fishes such as sharks, skates and rays have jaws and paired fins, but the skeletons are composed of cartilage such as jawless fishes. Bony fishes like Tilapia and carp are largest and most successful group features. It is cold-blooded (poikilothermic) animal, i.e. body temperature differs with that of the surroundings. Its body is enclosed with scales (absent in jawless fishes) and layer of slime. The cartilaginous fish has sharp, tooth-like scales which don't overlap, while the bony fish has thin, flat rounded scales which overlap. It contains fins. Paired fins are adaptations of fore-and hind limbs. It performs gaseous exchange by gills. The bony fish has gill covers where as cartilaginous fish does not. It includes well-developed sense of smell, and lateral line system that allows it to notice movements and changes in water pressure. It contains inner ears. The bony fish has a swim bladder, gas-filled sac that permits it to control the density so that it can remain still at any depth in water.

It contains the two-chambered heart. Fertilization is generally external. Eggs are tiny and may grow directly into the young fish or pass through larval stage.

Adaptive Features of Fishes:

Living organisms are located in several kinds of ecosystems. Environment in ecosystem differs considerably. Usually, organisms demonstrate features which allow them to go live successfully and reproduce in the particular environment. These characteristics may be functional, structural or behavioral. These features are called as adaptations. Adaptations to the particular environment are developed over the long period of time.

Nature of Medium:

Water is denser medium than air. It is hard to move rapidly through it. As the result active aquatic animals such as fish have streamlined bodies. Water, though, assists to support body mass of large aquatic animals.

Osmoregulation and Water Loss:

Many marine organisms contain body fluids which are nearly same concentration as sea water in which they exist. So rate at which water enters and leaves body cells is same. Though, body fluids of freshwater organisms are at much higher concentration than surrounding water. So much water enters body cells than leaves them. Successful freshwater organisms contain osmoregulatory structures which get rid of excess water which enters body cells. Bony fishes are most successful aquatic organisms. Body fluid of marine bony fish is less concentrated than the surrounding water, while body fluid of freshwater bony fish is more concentrated.

Movement:

Aquatic organisms which move keenly use appendages like fins that are altered for swimming.

Adaptations of Fish:

Fish show structural adaptations to life in water. It has streamlined body shape without neck which allows them to move effortlessly through water. Tail and tail fin of fish are special adaptive structures for swimming. Gills are gaseous exchange organs which are adapted for aquatic environment. They are found in fish.

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