Definition noun, plural: chelicerates Any of the species belonging to the subphylum Chelicerata Supplement The chelicerates are species of the subphylum Chelicerata, which in turn, belongs to the largest phylum of the animal kingdom — Arthropoda arthropod s.
The arthropods are characterized by having segmented body or specialized body regions, jointed and paired appendages limb s , and a hard chitin ized exoskeleton. The chelicerates are arthropods that are named for their feeding appendages called chelicera e. The chelicerae are specialized pair of appendages that appear before the mouth. These appendages have become a part of the mouth and in spiders, the chelicerae form fangs. These fangs may be associated with a venom gland and therefore are used to inject venom into a prey or into a potential threat.
Most chelicerates also have pedipalp s. The pedipalps are specialized appendages that are found next to the chelicerae and in front of the first walking legs. The pedipalps may be modified to perform a range of functions including food manipulation and sensing, locomotion, defense, and reproduction. The chelicerates have an open circulatory system just as other arthropod s. Silk Glands -- There are several varieties of silk glands.
The silk they produce differs in strength, slipperiness, etc. Different kinds of webbing are produced for particular circumstances. The tips of the legs are modified for walking on the webs. Economic Importance -- Some species of spiders are poisonous to humans and animals. Spider silk has been used in bombsights during World War II. Order : Scorpiones Scorpionida -- scorpions : These animals have a well marked cephalothorax and segmented abdomen that is equipped with a sting and poison gland at the posterior end.
They can be dangerous in warmer regions. Chelicerae and pedipalps are both chelate. They have book lungs. They feed on other arthropods. They are also viviparous as they bear living young.
Order : Amblypygi. Pedipalpia -- whip spiders and tailless whip scorpions : There is a long tail, large palps and small chelicerae. Order : Pseudoscorpionida -- book scorpions : These are small animals that have the appearance of scorpions because their pedipalps are pincers. The abdomen is rounded but without a sting. They feed on small insects. See Inv for example:. Order : Opiliones Phalangida -- harvestmen : Their extremely long walking legs have earned them the name of " Daddy Long Legs.
They are predators of small insects and other arachnids. Order : Acarina -- mites and ticks : The chelicerae and pedipalps are modified into projections called a hypostome. They are parasites and vectors of disease, and serious pests of vegetable and tree crops. Class Pycnogonida -- sea spiders : These are tiny marine animals. Included are parasites, commensals and free-living predators. These animals have remained essentially unchanged sinde the Paleozoic. They and the Pycnogonida are the only marine arachnids.
They are also the only Arachnida with compound eyes. They usually inhabit shallow waters and feed at night on worms , mussels and other small molluscs.
Below is Tachypleus tridentatus , which is found in the Indo-Pacific. In the mating season horseshoe crabs mate on the shore at high tide in late spring. Gentle, sloping sandy beeches are needed for breeding. The female digs a burrow about 20 cm deep in the sand and lays her eggs. Between 15, and 60, eggs are laid, the amount depends mainly on the size of the female.
The males approach the burrow and add their sperm to the eggs. More than one male may creep up behind the female to add his sperm. The eggs are then covered, and in this position are protected from the waves and warmed by the sun. The larvae hatch at high tide. Males are sexually mature at around 10 years of age, and females at around The life span is not known, but is thought to be 20 - 40 years. Horseshoe crabs blood is blue when exposed to air as it contains hemocyanin - a copper containing protein, whereas our blood is red when exposed to air as it contains haemoglobin - an iron containing protein.
The blood is widely used in medicine to detect bacterial diseases, and enzymes from the blood are used in the International Space Station to test for bacteria and fungi. And as the blood is uniquely sensitive to toxins, it is being used to test vaccines for contaminants. It will be used as one of the tests run on all covid vaccines. The horseshoe crabs are not killed for this blood. Rather like human blood donors, a small amount is taken, and the crabs are released back into the sea.
Limulus polyphemus , above, is found in the Gulf of Mexico and along the northern Atlantic coast of north America. Females are larger than males, and can be up to 60 cm long including the telson.
They also have the unusual ability to regrow lost limbs. The telson, or tail is used to steer the animal through the water, and also to flip it upright if it is upside down. It has two large compound eyes, five simple eyes on its carapace, and 2 simple eyes on its underside, near its mouth.
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