Classification of Animals Test - 2

Sponges do not have a digestive system. Hence they don't have a mouth and anus. The functions of digestive system are performed by canal system.

Coelenterates have a mouth and anus as they have a gastrovascular cavity. 

Phylum Platyhelminthes has incomplete digestive tract but mouth and anus are present.

Phylum Nemathelminthes has a complete and digestive tract with mouth and anus.

Ascariasis is an intestinal infection that occurs when the eggs of a parasitic roundworm, Ascaris lumbricoides are ingested. There is an increase in the number of WBCs in the body i.e., leucocytosis and decrease in the number of eosinophils (eosinophilia) can be observed. There is a very high fever, restlessness, disturbed sleep, abdominal pain and extensive haemorrhage and inflammation of pancreas can be observed.

Porifera is multicellular organisms, which are sedentary in nature. Most of them are marine.
The body wall is diploblastic, which consists of an outer layer, called as pinacoderm and an inner layer, called as choanoderm.
The canal system mainly comprises of incurrent and excurrent canals, which are lined with pinacocytes and radial canals, which are lined with choanocytes (flagellated cells).
The body walls contain numerous pores, called as Ostia through which water enters the body through a canal system into the central body cavity called as the spongocoel.
Sponges have an exoskeleton, which is made up of either spongin fibers or calcareous/siliceous spicules or a combination of both.

A. Planktonic organisms are the ones that float on the surface of sea water.

B. Nectonic organisms are the ones that swim in the sea water.

C. Neuston organisms are the ones that move on the surface film of the water.

D. Sedentary organisms are the ones that are fixed at a place i.e. they are attached to a substratum.

Sponges are sessile organisms as they are attached to a substratum. Hence, they are sedentary organisms.

Taenia and Fasciola are parasitic Platyhelminthes. Pheretima is an annelid animal. Planaria is a nonparasitic or free-living platyhelminth. Planaria (Dugesia) belong to class Turbellaria of phylum Platyhelminthes. Mostly free-living flatworms are placed in class Turbellaria

Internal fertilization is the fusion of an egg cell with a sperm during sexual reproduction inside the body of a parent. For this to happen there needs to be a method for the male to introduce the sperm into the female's reproductive tract. The same kind of fertilization occurs in Dugesia, Fasciola and Schistosoma. Internal fertilization is one of the main characteristics of platyhelminthes.

The animal phyla Porifera is considered as side line to the major trends of evolution. Porifera have cellular level organisation and their individual cells functioning independently, they lack the coordinated patterns of cell functions seen in more specialized tissues or organs of other animal phyla.

Bilaterally symmetrical means left and right halves of the body has the same design. Dorsiventrally flattened means the front and back of the organism are flat. These two features are present in the organisms belonging to group Platyhelminthes. Liver fluke is one of the examples of group Platyhelminthes. It possesses both features. Hence, the correct answer is option A.

Planarian belongs to class Turbellaria (phylum Platyhelminthes). It is free living. These are flatworms that have a bilaterally symmetrical body. These are acoelomate.

Classification of animals is based on the level of organization as diploblastic or triploblastic based on cellular, tissue, organ, organ system etc on the basis of which the animals are classified under the different phyla. At a very basic level of classification, true animals can be largely divided into three groups based on the type of symmetry of their body plan: radially symmetrical, bilaterally symmetrical, and asymmetrical. On the basis of the Body Cavity or Coelom which is the space between the body wall and the alimentary canal, which is produced by splitting of mesoderm, during embryonic development. On the basis of nature of the coelom, animals are classified into three types. There is no classification on the basis of the nervous system.