•Crustaceans is a very large group ok arthropods, whichincludes: crabs, crayfish, krill and barnacles•They are distinguished from other groups of arthropods for :• possession of two-parted limbs.• the nauplius form of the larvae.•Their fossile apparently unchanged sincethe Triassic periodScientific studies =CARCINOLOGY
Their body is divided into three region :•Head•Thorax•AbdomenIn the head we find also thechefalothorax .The crustacean’s body is entierlycovered by an hard exoskeletron.Each somite, or body segment can bear a pair of appendages: two pairs of antennaeHEAD TORAX the mandibles legs maxillae To walk To feed
Other carachteristic: carachteristic• Appendages are tipicall biramous• The main body cavity is an open circulatory system, where blood is pumped into the haemocoel by a heart located near the dorsum.• The alimentary canal consists of a straight tube for grinding food and a pair of digestive glands that absorb food; this structure goes in a spiral format.• The majority of crustaceans are aquatic, living in either marine or fresh water environments
•Arachnids are a class of joint-legged invertebrate animals inthe subphylum Chelicerata.•They comprise over 100,000named species,including spiders,scorpions, ,ticks, mites and Solifugae.•Basic characteristics ofarachnids include four pairsof legs and a body divided intotwo tagmata: the cephalothoraxand the abdomen.
Head•Eight legs chelicerae pedipalps Prosoma Thorax•Two pairs of appendages• Their body is organized into two tagmata Abdomen Preabdomen Postabdomen
•The excretory glands ofarachnids include four pairsof coxal glands along the sideof the prosoma, and one ortwo pairs of Malpighiantubules;•The blood of arachnids isvariable in composition,depending on the mode ofrespiration;•The heart is located in theforward part of the abdomen.