Published in Zoology
Sunday, 14 May 2017 15:44
"Aristotle" first described crabs and some decapods. He named them as Malacostraca.
"Linnaeus" kept Malacostraca under insecta. "Lamarck" divided this insecta into three classes.
1) Crustacea 2) Hexapoda and 3) Arachnida.
The name Crustacea was first used by Cuvier.
Von Setbold' in 1845 combined Crustacea, Arachnida and Hexapoda into an independent group. He called this group "Arthropoda".
Arthropoda means "Jointed legs". This phylum includes animals with jointed legs. These animals are metamerically segmented, true coelomate, and bilaterally symmetrical.
This is the biggest phylum and it includes about 80 percent of the known animal species.
Arthropoda is the largest and most successful phylum in terms of number, distribution, and adaptations. It is the dominant group at the present day. This is the only invertebrate phylum which includes flying forms. The segments bear appendages. These appendages are jointed. Hence the name Arthropoda. Their body is covered by chitinous outer exoskeleton. The hard exoskeleton restricts growth, this is overcome by periodic shedding of exoskeleton, which is called ecdysis.In these animals musclesare arranged segmentally. All these muscles are straited muscles.
These animals show definite organ systems. The body cavity contains blood called Haernocoel. Excretion is performed by green glands or malphighian tubules. Nervous system includes brain and double ventral nerve cord. Com­pound eyes are seen in majority of the arthropods. Respiration is by gills, gill books, book Kings, tracheae etc. Sexes are separate; often there is sexual dimorphism. Fertilization is internal.
Arthropods occur on land, in the soil, in fresh water, in sea water and in the bodies of other animals and plants.

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