Anatomy of finfish and shellfish

Unit 12 - Arthropoda

12.1. General characters of Arthropoda

• Arthropods are triploblastic, bilaterally symmetrical, metabolically segmented animals.
• Body is covered with a thick chitinous cuticle forming an exoskeleton.
• Body segments usually bear paired lateral and jointed appendages.
• Musculature is not continuous but comprises separate 'striped muscles.
• Body cavity is haemocoel. The true coelom is reduced to the spaces of the genital and excretory organs.
• Digestive tract is complete; mouth and anus lie at opposite ends of the body.
• Circulatory system is open with dorsal heart and arteries but without capillaries.
• Respiration through general body surface, by gills in aquatic forms, tracheae or book lungs in terrestrial forms.
• True nephritic are absent. Excretion by coelomoducts or Malpighian tubules or green or coxal lands.
• Cilia are entirely absent from all parts of the body.
• Sexes are generally separate and sexual dimorphism is often exhibited by several forms.
• Fertilization is internal. Development is usually indirect through larval stages.
• Parental cave is also often well marked in many arthropods.