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Kingdom Animalia: Classification

Based on the features mentioned in the previous chapter, Kingdom Animalia is classified as follows.

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Phylum – PORIFERA

Poriferans are commonly known as sponges.

Habitat: Sponges are mostly marine. Avery few occupy freshwater habitats.

Examples:

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Spongilla Sycon Leucosolenia

Body plan: Sponges are multicellular and have cellular level of organization.

Symmetry: They are either asymmetrical or radially symmetrical.

Germ layer: Sponges are diploblastic. The body wall is composed of an outer layer of epidermal cells and an inner layer of flagellated collar cells called choanocytes.

Body characteristics:

  • The body is usually cylindrical, tubular or vase-like.
  • Its surface bears minute pores called ostia.
  • There is a central cavity called spongocoel with a terminal large opening called osculum.
  • The body has an external skeleton made of calcareous or siliceous spicules or spongin fibres.

Physiology:

  • The sponges have a water transport system or canal system.
  • Water carrying food and oxygen enters through the ostia into the central spongocoel.
  • The water carrying waste and carbon dioxide moves out through the osculum.
  • This pathway helps in respiration, food intake and waste excretion.
  • Digestion is intracellular.

Reproduction:

  • Sponges are hermaphrodites (sexes are not separate).
  • Both male and female sex organs are present in the same organism. Hence eggs and sperms are produced by the same individual.
  • Asexual reproduction takes place by fragmentation. Sponges have great powers for regeneration.

Embryo Development: Fertilization is internal. Development is indirect with a free-swimming ciliated larva called parenchymula or amphiblastula.

 

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