Phylum Arthropoda includes lobsters, spiders, scorpions, millipedes, and insects. It contains over 1,000,000 species, which is a lot, but scientists believe that only 1/10th of the species have been discovered. It is the most abundant of all the animals.
Why should we study this phylum? They live virtually everywhere and their influence upon man and the environment cannot be ignored. They can destroy crops; produce things like wax, drugs, and silk; help maintain cross fertilization; transmit deadly diseases; and some, like spiders, eat mosquitoes!
Characteristics of phylum arthropoda:
They have an exoskeleton.
Scorpion's Exoskeleton
These are made primarily by chitin, a polysaccharide with strong hydrogen bonds.
Because the exoskeleton is non-living and cannot grow, once the arthropod outgrows their home, they must molt, or shed its covering.
Enzymes are produced to eat away at the inside of the old exoskeleton while a new exoskeleton is produced underneath the old one.
A scorpion molting
They have jointed appendages.
Arthropoda means “joint-footed”
The muscles of the arthropod move the limbs from within its exoskeleton.
Variety or forms and functions:
spider/grasshopper: jumping and locomotion
crabs and lobsters: defense
sensory reception, chewing food, sexual reproduction, etc.
Body segmentation.
Arthropods have three body segments:
Head and thorax (cephalothorax)
Abdomen
Open circulatory system
Dorsal heart
Ventral nervous system
Two ganglia joined into a ventral nerve cord. Protected by not only the exoskeleton, but also the bulk of the animal’s body.
Near the appendages for command and coordination.
Antennae: appendages in the head region that provide taste, smell, and touch.
Sensory bristles
Eyes: compound (thousands of individual lenses) or simple (one lens)
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