6. Animal Classification

Phylum Cnidaria (Coelenterata) – for example, Hydra and jellyfish.

Star fish (Phylum Echinodermata).

Phylum Aschelminthes – I am Ascaris, the intestinal round worm.

Phylum Porifera (sponges, with cellular grade organization).

• Cellular grade organization; the body is asymmetrical.
• The body has many pores (ostia and oscula), and special collar cells.
• It is marine and sedentary (attached to the substratum).
• Its body is supported by fibres of spongin.

• It has jointed appendages and a chitinous exoskeleton.
• The body is triploblastic, eucoelomate, bilaterally symmetrical and segmented.
• It has organ-system grade organization and is unisexual.

• It is a cold-blooded, fresh-water animal.
• Its body is spindle-shaped, with paired and unpaired fins.
• It has an exoskeleton of scales and a bony endoskeleton.
• It respires through gills.

• It is warm-blooded, with an exoskeleton of feathers.
• Its jaws are modified into a beak and its forelimbs into wings. The penguin uses its wings as flippers for swimming.
• It has a neck between the head and trunk. Its digits bear claws.

• Its larva (tadpole) lives in water. The adult lives on land and in water.
• Its skin is moist and without scales. There is no neck and no external ear, but a tympanum is present.
• It has two pairs of limbs; the digits have no claws.

• It is cold-blooded, with dry, scaly skin.
• It creeps on land, as its body cannot be lifted up.
• It has a neck, no external ear, and claws on its digits.

• It has mammary glands and feeds its young on milk.
• It is warm-blooded, with an exoskeleton of hair.
• Its body is divided into head, neck, trunk and tail. Its digits bear nails.

• Its body is umbrella-like (medusa), and it lives in the sea.
• It is radially symmetrical and diploblastic, with cell-tissue grade organization.
• Tentacles with cnidoblasts around the mouth capture prey and inject toxin.

Thus, with new developments in science, the criteria of classification kept changing and became more scientific.

1. Calcareous spines are present on the body; hence they are called echinoderms.
2. They are found only in the ocean.
3. They are radially symmetrical as adults but bilaterally symmetrical as larvae.
4. They move and capture prey with tube feet, and have good regeneration ability.

The cockroach belongs to Phylum Arthropoda, because:

1. It has jointed appendages (legs and antennae).
2. Its body is covered with a chitinous exoskeleton.
3. Its body is triploblastic, eucoelomate, bilaterally symmetrical and segmented (head, thorax, abdomen).
4. It is unisexual.

• Amphibians have moist skin without scales, an aquatic larval stage, and digits without claws.
• A tortoise has dry, scaly skin and a hard shell. It has no larval stage, breathes only through lungs, and its digits bear claws.
• These are characters of Class Reptilia.

So although the tortoise lives on land and in water, it is a reptile, not an amphibian.

• Jellyfish belong to Phylum Cnidaria. Their tentacles bear stinging cells called cnidoblasts.
• When our skin touches the tentacles, the cnidoblasts inject toxin into it.

So our skin gets irritated, burns and itches.

• All animals that have a notochord at some stage of life are chordates. Phylum Chordata has three subphyla: Urochordata, Cephalochordata and Vertebrata.
• In vertebrates the notochord is replaced by a vertebral column, so all vertebrates are chordates.
• But urochordates (Herdmania) and cephalochordates (Amphioxus) keep the notochord and never form a vertebral column.

So all chordates are not vertebrates.

• Like chordates: Balanoglossus has pharyngeal gill slits and a notochord (in the proboscis region only).
• Like non-chordates: it has a worm-like body, and its notochord is not present along the whole body.

Because it shows characters of both groups, it is considered a connecting link between non-chordates and chordates.

• Reptiles are cold-blooded animals (poikilotherms).
• They have no mechanism to keep their body temperature constant.
• Their body temperature changes with the temperature of the surroundings. That is why they bask in the sun to warm up and hide in the shade when it is hot.

The four animals in the pictures are:

1. Jellyfish (Aurelia) – Phylum Cnidaria. Label: bell (umbrella), tentacles, oral arms, mouth.
2. Nereis – Phylum Annelida. Label: head, tentacles, segments, parapodia.
3. Flatworm (Planaria) – Phylum Platyhelminthes. Label: head, eye spots, flat body.
4. Bony fish (Rohu) – Class Pisces. Labels are shown below.

While analysing, note: which animals are seen in all seasons, which appear only in the monsoon (frogs, earthworms, many insects), and which birds come only in winter.