Arthropoda General Characteristics, Classification and Examples

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Arthropoda General Characteristics

Arthropods are the largest phylum of animals and they have jointed legs
Body is divided into head, thorax and abdomen
Head and thorax may be united to form cephalothroax
Jointed appendages which were used for locomotion, feeding, defense and sensory purposes
They body of arthropods is covered by chitinous exoskeleton
Exoskeleton does not grow and must be shed at intervals called molting or ecdysis
Sensory organs like eyes, antennae, statocyst and anal cerci are found
Digestive system is complete. it has 2 openings mouth and anus.
Respiratory system is well developed and respiration occurs through body surface, gills, trachea, book lung or book gills
Arthropods have an open circulatory system
Blood flows in open tissue spaces and hemocoel.
The perivisceral body cavity is called haemocoel as it is full of haemolymph
Excretion is brought about usually by green glands in aquatic forms and malpighian tubules in terrestrial animals.
Nervous system comprises of a nerve ring and double ventral nerve cord
Reproduction is sexual method
Arthropods are unisexuals and exhibit the phenomenon of sexual dimorphism.
Fertilization is usually internal but few aquatic form has external fertilization
Development may be direct or indirect
In direct development, the young resembles the adults and occur in the same habitat
In indirect development, independent larval stages occur which often show different feeding habits, live in different habitats and do not resemble the adults.
Parthenogenesis is also met in some insects like honey bees

Classification of Arthropoda

Class 1. Onychophora
Body is divisible into head and trunk.
Respiration: Tracheae. Excretion: nephridia. E.g. Peripatus

Class 2. Merostomata
Body is divisible into cephalothorax and abdomen.
Respiration: Book gills. Excretion: Coxal gland.
E.g. Limulus

Class 3. Arachnida
Body is divisible into cephalothorax and abdomen
Respiration: Book lungs. Excretion: Coxal glands and Malphigian tubules. E.g. scorpions, ticks, mites and spiders

Class 4. Crustacea
Body is divisible into cephalothorax and abdomen
Respiration: Gills or body surface. Excretion: Green glands
E.g. prawns, crabs, lobsters

Class 5. Chilopoda
Body is divisible into head and trunk
Respiration: Tracheae. Excretion: Malphigian tubules
E.g. centipedes

Class 6. Diplopoda
Body is divisible into head, thorax and trunk
Respiration: Tracheae. Excretion: Malphigian tubules
E.g. millipedes

Class 7. Insecta
Body is divisible into head, thorax and abdomen.
Respiration: Tracheae. Excretion: Malphigian tubules
E.g. Musca, Lepisma

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