SUBPHYLA: TRILOBITA, CRUSTACEA, CHELICERATA, AND UNIRAMIA ARTHROPODS SUBPHYLA: TRILOBITA, CRUSTACEA, CHELICERATA, AND UNIRAMIA

Phylum Arthropoda “jointed feet” Characteristics: segmentation Jointed, paire appendages Exoskeleton – chitin Cephalization Compound eyes Coelom Open circulatory system Ventral nerve cord

The Exoskelton The exoskelton is composted of the polysaccharide chitin. An arthropod can not grow without periodically shedding the exoskeleton. This process is called molting or edcysis. During the few days following the replacement of the exoskeleton, the animal is extremely vulnerable and must hide from predators. There is also the problem of desiccation.

Advantages & Disadvantages of the Exoskelton Protection Support Site for muscle attachment Flexible at the joints Disadvantages Heavy Must be molted

Subphylum Trilobita All members of this phylum are extinct

Subphylum Crustacea Only arthopods with 2 pair of appendages on their head that serve as feelers Most have 16-20 segments which are fused into several tagmata Most have gills for respiration Most have a free-swimming larva called a nauplius

Crustacean Diversity

Subphylum Chelicerata Have piercing and sucking mouth parts called chelicerae

Class Arachnida Include: spiders, scorpions, mites and ticks Cephalothorax and abdomen Cephalothorax – 6 pairs of jointed appendages 1 pair of chelicerae (used to inject venom into prey) 1 pair of pedipalps (holding food, chewing, & reproduction 4 pairs of walking legs 8 simple eyes at anterior end

Abdomen Spinnerets Respiration Excretory organs Book lung Tracheae and spiracles Excretory organs Malpighian tubules Coxal glands

Mites and Ticks Most abundant and specialized archnids Completely fused head and cephalothorax

Subphylum Uniramia Classes Insecta Diplopoda Millipedes 2 pair of legs on each body segment Rounded bodies Poor vision with a good sense of smell Feed on plants or decaying plant matter Secrete a noxious fluid that contains cyanide when threatened

Chilopoda Flattened bodies with one pair of legs per segment ( except first and last 2 segments) May have 15 – 175 pairs of legs The appendages on the first segment are modified into a pair of poison claws Long antennae and two clusters of simple eyes Move quickly and feed mostly on earthworms and other insects