2. •Crustaceans is a very large group ok arthropods, which
includes: 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 since
the Triassic period
Scientific studies =
CARCINOLOGY

3. Their body is divided into three region :
•Head
•Thorax
•Abdomen
In the head we find also the
chefalothorax .
The crustacean’s body is entierly
covered by an hard exoskeletron.
Each somite, or body segment can bear a pair of appendages:
two pairs of antennae
HEAD TORAX
the mandibles
legs
maxillae
To walk To feed

4. 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

5. •Arachnids are a class of joint-
legged invertebrate animals in
the subphylum Chelicerata.
•They comprise over 100,000
named species,including spiders,
scorpions, ,ticks, mites and Solifu
gae.
•Basic characteristics of
arachnids include four pairs
of legs and a body divided into
two tagmata: the cephalothorax
and the abdomen.

6. Head
•Eight legs chelicerae
pedipalps Prosoma Thorax
•Two pairs of appendages
• Their body is organized into two tagmata
Abdomen Preabdomen
Postabdomen

7. •The excretory glands of
arachnids include four pairs
of coxal glands along the side
of the prosoma, and one or
two pairs of Malpighian
tubules;
•The blood of arachnids is
variable in composition,
depending on the mode of
respiration;
•The heart is located in the
forward part of the abdomen.