Earth Science: Biology – Animals – crustaceans and spiders
Crustaceans and spiders, as well as the ancient scorpions, belong to the phylum Arthropoda or “arthropods.” As close relatives to insects, they share many anatomical features.
There are about 38,000 species of crustaceans, most of which live in water. Crustaceans live in diverse environments and may look very different from each other.
Tiny clam shrimps (Conchostraca) with a two-part shell that are only 0.02 inch (five mm) in size are as much part of the crustaceans as the American lobster (Homarus americanus), which has an elongated body and huge claws and can be longer than three feet (one m). Many crustaceans have two pairs of antennae and biramous legs, that is, legs that branch out into two segments.
Crustaceans are equipped with gills, making them fully adapted to aquatic life. The bodies of spiders consist of two major parts: the cephalothorax at the front, which combines the head (cephalon) and midsection (thorax), as well as the abdomen at the rear.
The front section contains the brain and stomach, eight legs, one pair of chelicerae or jaw-like structures, one pair of pedipalps (legs that can feel), and eyes attached to the front section. The abdomen includes the heart, part of the digestive tract, and the spinnerets, as well as the reproductive and respiratory organs.
Many spiders build webs in order to capture their prey and produce venom for hunting and defense. The majority of spider venoms are actually not dangerous to humans.
Scorpions still have the original form of spiders and there are approximately 2,000 known species in existence. They have large pinchers at the end of their pedipals and a very flexible tail. The tail is made up of five abdominal segments and is often armed with a thick venom gland with a sting at the tip.
The venom of some species may be deadly to humans. Due to their nocturnal lifestyle and a preference for warmer temperatures, scorpions live mainly in tropical and subtropical regions, including deserts. Scorpions are carnivorous and hunt insects using their claws.
TICKS AS DISEASE CARRIERS
Ticks of the genus Ixodes belong to the class of Arachnids, along with spiders and scorpions, and act as carriers for various diseases. One of these is Lyme disease, caused by a bacteria called Borrelia burgdorferi.
Lyme dis- ease may result in arthritis and infections of the heart and nervous system. In Europe, ticks may also carry a virus that causes the life threatening European early summer meningoencephalitis disease.
BASICS
THE AUSTRALIAN FUNNEL WEB spider belongs to the few species that may threaten human life.
When males are searching tor mates they may enter homes and gardens, and de- fend themselves aggressively if disturbed.