Glossary: Animal Kingdom | Biology for Grade 11 PDF Download

Classification of Animals

• Cellular level of organisation: In sponges, the cells are arranged as loose cell aggregates, i.e., they exhibit cellular level of organisation.
• Tissue level of organisation: 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 organisation.
• Organ level organisation: Tissues are grouped together to form organs, each specialised for a particular function. e.g., platyhelminthes.
• Organ system level: organs are associated to form functional systems e.g., Annelids, Arthropods, Molluscs, Echinoderms and Chordates.
• Open type circulatory system: Blood pumped out through heart. Not confined to blood vessels. Cells and tissues are directly bathed in it.
• Closed type circulatory system: Blood is circulated through blood vessels (arteries,veins and
• capillaries)
• Asymmetrical: Sponges are mostly asymmetrical, i.e., any plane that passes through the centre does not divide them into equal halves.
• Radial Symmetry: When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry.
• Bilateral Symmetry: Animals like annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry.
• Diploblastic animals: Animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm, are called diploblastic animals, e.g., coelenterates.
• Triploblastic animals: Those animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm, are called triploblastic animals.
• Coelom & Coelomates: The body cavity, which is lined by mesoderm is called coelom. Animals possessing coelom are called coelomates, e.g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates.
• Pseudocoelom & Pseudocoelomates: In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates, e.g., aschelminthes
• Acoelomates: The animals in which the body cavity is absent are called acoelomates, e.g., platyhelminthes.
• Metamerism: In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs. For example, in earthworm, the body shows this pattern called metameric segmentation and the phenomenon is known as metamerism.
• Sea walnuts or comb jellies: Ctenophores, commonly known as sea walnuts or comb jellies.
• Bioluminescence: Bioluminescence (the property of a living organism to emit light) is well-marked in ctenophores.
• Flame cells: Specialised cells called flame cells help in osmoregulation and excretion.
• Malpighian Tubules: Arthropoda Excretion takes place through malpighian tubules.
• Water Vascular System: The most distinctive feature of echinoderms is the presence of water vascular system which helps in locomotion, capture and transport of food and respiration.
• Radula: In mollusca, the mouth contains a file-like rasping organ for feeding, called radula.
• Poikilotherms: An organism that cannot regulate its body temperature except by behavioural means such as basking or burrowing.
• Parapodia: Aquatic annelids like Nereis possess lateral appendages, parapodia, which help in swimming.
• Homoiothermous: They are warm-blooded (homoiothermous) animals, i.eThey are able to maintain a constant body temperature.
• Mammary glands: The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished.