Patterns of problems
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Animal Kingdom

- Hit the perfect ace in exams by getting acquainted with the different ways or patterns of the questions asked for a particular concept
Topic- Basis of Classification

Description - Despite the differences in structures and forms of different animals, there are some common features among them which form the basis for animal classification. These features are -
  • Arrangement of cells - cellular level, tissue level, organ level and organ system level (complete and incomplete)
  • Body symmetry - Categorized under asymmetrical, radial and bilateral symmetry.
  • Nature of coelom - Coelomates (presence of coelom), Acoelomates (absence of coelom) and Pseudocoelomates (false coelom)
  • Germinal layers - Cells are arranged in three embryonic layers, external ectoderm, internal endoderm and a middle mesoderm . Organisms with only ectoderm and endoderm are called diploblastic and with all three layers are called triploblastic.
  • Segmentation - The body possesses a serial repetition of body segments, called metameric segmentation.
  • Notochord - Mesodermally derived rod-liked structures are formed during embryonic development in some animals, they are called chordates. Animals that do not form this structure are called non-chordates.
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Topic - Non-chordates
Description - Non-chordates are animals without a notochord (a cartilaginous rod-like structure that supports the body). These include phyla such as Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata.
Some of the key features are - Central nervous system is ventral, solid and double. Gill slits are absent. Mostly, sexes cannot be distinguished among the members. These animals respire through gills, trachea or body surface. Heart usually absent and if present then dorsal placement and post-anal tail is absent in all of them. They generally have open type of circulatory system.
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Topic - Hemichordata
Description- This is a phylum that contains marine deuterostome animals. They are considered as connecting link between phylum Echinodermata and Phylum Chordata. Phylum Hemichordata is a small phylum with animals having a worm-like appearance. Some species may be solitary or some occur in colonies. These animals are also called as Acorn Worms. They were initially grouped under Phylum Chordata. But, research has proven that none of these organisms has a post-anal tail or even the notochord, which is a distinguishing feature of chordates. Hence, these animals have been given a separate phylum, called the Hemichordata. They have stomochord.
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Topic - Chordates
Description - Chordates are animals with the presence of notochord at some stage during their development. Members possess a hollow nerve cord and pharyngeal gill slits, central nerve system is dorsal, hollow and single. Pharynx is perforated by gill slits. Heart is ventral and post - anal part is present. Circulatory system is closed type. Phylum Chordata is divided into three subphyla: Urochordata, Cephalochordata, and Vertebrata.
Subphylum Urochordata and Cephalochordata are often referred as Protochordata and are only seen in marine water bodies. In urochordates, notochord is present only in larval tail, while in cephalochordates, it extends from head to tail region and is persistent throughout their life.
Examples include - Urochordata - Ascidia, Doliolum, Salpa; Cephalochordata - Amphioxus or lancelet.
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Topic - Vertebrates
Description- Vertebrates possess notochord during the embryonic period. The notochord is replaced by a cartilaginous or bony vertebral column in the adult. Vertebrates have a ventral muscular heart with two, three or four chambers,they have kidneys for excretion and osmoregulation. Paired appendages are present as fins or limbs. The subphylum Vertebrata is divided into Pisces, Amphibia, Reptilia, Aves and Mammalia.
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