C R I S T I N A M A R T I9 B

Arachnid/Myriapod

Reason for the name

Arachnid: Greek words ἀράχνη (aráchnē), meaning spider.

Myriapoda: Greek mrias, ten thousand. Podos: foot.

Number of species currently existing

Arachnid include over 100,000 species.Spiders, scorpions, harvestmen, ticks, and

mites.

Myriapoda contains 13,000 species Millipedes, centipedes.

Internal structure of cartilage-like tissue called the endosternite.

Pincer-like jaws, with poison glands.

One pair of legs per body segment.

Characteristics

Arachnid MyriapodAlmost all are terrestrial Terrestrial

Eight legs Range from having over 750 legs to having fewer than ten legs

No antennae or wings Have a single pair of antennae

Usually lay yolky eggs Abundant in moist forests

Body is divided into two parts: anterior and posterior

Majority are detritivorous

Often hunt or wait for small animals such as insects.

Many species possess repugnatorial glands.

Arachnids have an exoskeleton. When the egg is hatched, only some come out with their complete set of legs.

1st appeared on earth “Fossil record”

Silurian Period

Generalized life cycle and life expectancy

Produces an egg sac that can contains up to a thousand eggs.

Baby spiders hatch from the eggs. Some are on their own and receive no care from

their mother. Other spiders climb onto their mother's back

after hatching, where she feeds them. In some species, the mother dies when the young

are ready to go off on their own, and they eat her carcass.

Life expectancy varies greatly.

Eat and digestive system

Most Arachnid are carnivorous and feed on pre-digested bodies

Give off venom from specialized glandsPour digestive juices over their prey after

killing itTurn the prey into nutrients. Stomach has a tubular shape, with various

diverticula throughout the body. These both produce digestive enzymes and absorb nutrients from the food.

Respiratory and circulatory systems

Internal respiratory surfaces in the form of tracheae

Internal vascular lamellae used for gas exchange with the air

Blood varies depending on the respiration. May have a reduced circulatory system. Heart is located in the forward part of the

abdomen. Some mites have no heart at all.

Sensory systems

Fine sensory hairs that cover the body and give it its sense of touch.

Many also have more complex structures, called trichobothria.

Slit sense organs are pits covered with a thin membrane. Inside, a small hair touches the underside of the membrane, and detects its motion.

Slit sense organs are believed to be involved in hearing.