9/23/2023 0 Comments Zebra spider nymphMost species of the Haplogynae have six eyes, although some have eight ( Plectreuridae), four (e.g., Tetrablemma) or even two (most Caponiidae). The specific arrangement of the eyes is one of the features used in classifying different species. Spiders usually have eight eyes, each with a single lens rather than multiple units as in the compound eyes of insects. Main article: Spider vision Multiple eyes of a jumping spider In mesothele and mygalomorph spiders, the maxillae are only slightly modified in araneomorph spiders, the anterior edge is often saw-like and is used in cutting up prey. The basal segments of the pedipalps, the coxae, next to the mouth, are modified to assist with feeding, and are termed maxillae, although they are not homologous with the maxillae of mandibulate arthropods. In adult males, the tarsus of each palp is modified to carry an elaborate and often species-specific structure used for mating (variously called a palpal bulb, palpal organ or copulatory bulb). The pedipalps have only six segments: the metatarsus is missing. Some spiders, such as the Australian crab spider, do not have claws. Since they do not have antennae, spiders use specialised and sensitive setae on their legs to pick up scent, sounds, vibrations and air currents. Spiders that spin webs typically have three claws, the middle one being small hunting spiders typically have only two claws. The tip of the tarsus bears claws, which vary in number and size. Starting from the body end, these are the coxa, trochanter, femur, patella, tibia, metatarsus and tarsus. Spiders' legs are made up of seven segments. They do not have antennae the pair of appendages in front of the legs are the pedipalps (or just palps). Spiders typically have eight walking legs (insects have six). Some spiders, such as the dewdrop spiders ( Argyrodes), even eat the silk of other spider species. However, they are able to eat their own silk to recycle proteins needed in the production of new spider webs. Like other arachnids, spiders are unable to chew their food, so they have a mouth part shaped like a short drinking straw that they use to suck up the liquefied insides of their prey. Most external appendages on the spider are attached to the cephalothorax, including the eyes, chelicerae and other mouthparts, pedipalps and legs. The cephalothorax, also called prosoma, is composed of two primary surfaces: a dorsal carapace and a ventral sternum. Unlike insects, spiders have an endoskeleton in addition to their exoskeleton. The abdomen and cephalothorax are connected by a thin waist called the pedicel. The exception is the Liphistiidae, a basal family, which retains this more primitive character hence they are sometimes called segmented spiders. In the majority of spiders, the abdomen is not externally segmented. The exception to this rule are the assassin spiders in the family Archaeidae, whose cephalothorax is divided into two parts by an elongated "neck". Spiders, unlike insects, have only two main body parts ( tagmata) instead of three: a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (also called an opisthosoma). External anatomy The underside and head of a female spider Many species of spiders exhibit a great deal of sexual dimorphism. Male spiders have specialized pedipalps that are used to transfer sperm to the female during mating. Most spiders possess venom, which is injected into prey (or defensively, when the spider feels threatened) through the fangs of the chelicerae. All spiders are capable of producing silk of various types, which many species use to build webs to ensnare prey. Spiders also have several adaptations that distinguish them from other arachnids. These characteristics include bodies divided into two tagmata (sections or segments), eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed. The anatomy of spiders includes many characteristics shared with other arachnids. The epigastric plates and furrow are visible, as well as the hourglass marking on the underside of the abdomen, which is a characteristic feature of widow spiders. The ventral side of a brown widow spider. Physiology of Spiders (order Araneae) Basic characteristics of arachnids include four pairs of legs (1) and a body divided into two segments: the cephalothorax (2) and the abdomen (3).
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