Chondrichthyes vs Arthropod

Chondrichthyes vs Arthropod

The black widow is most easily recognized by the hourglass marking on the underside of its abdomen. When bitten, a neurotoxin is released that can cause dull pain and cramping in muscles, that can be accompanied by sweating and vomiting. Less than 1% of black widow bites result in death.

Black widow spiders are usually not aggressive. If disturbed, they will retreat to a corner of their web. These spiders are more aggressive if they are protecting an egg sac. The natural habitat of a black widow is outdoors, under rocks, brush or piles of debris. Indoors, these spiders can usually be found behind furniture, in storage boxes, etc.

A black widow's eyes are on top and near the front of its head. They have 8 eyes, arranged in 2 rows of 4 each. Some spiders have better vision than others. For example, hunting spiders have good eyesight at short distances. Their eyesight enables them to form images of their prey and mate. Web-building spiders (the black widow) have poor eyesight. Their eyes are used for detecting changes in light.

A black widow's mouth opening is bellow its eyes. It does not have chewing mouth parts, and they eat only liquids. Various appendages around the mouth opening form a short "straw" through which the spider sucks the body fluid of its victim. The black widow can eat some of the solid tissue of its prey by predigesting it. To do this, the spider sprays digestive juices on the tissue. Chelicerae are a pair of appendages that the spider uses to seize and kill its prey. The chelicerae are above the mouth opening and just below the spider's eyes. Each chelicera ends in a hard, hollow, pointed claw, and these claws are the spider's fangs. An opening in the tip of the fang connects with the poison glands. When the black widow stabs an insect with its chelicerae, poison flows into the wound and paralyzes or kills the victim. The fangs of tarantulas point straight down from the head, and the poison glands are in the chelicerae. In the black widow, the fangs point crosswise, and the poison glands extend back into the cephalothorax. They also crush thier prey with their chelicerae.

Pedipalpi are a pair of appendages that look like small legs. One pedipalp is attached to each side of the spider's mouth, and they form the sides of the mouth.
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