25.10.2010., ponedjeljak
BODY STRUCTURE AND MORPHOLOGY
 Jaws (chelicerae) Chelicerae consists of the main appendage and foldable jaws. At the tip oft he jaws are fangs through which venom glands are excerted. If a spider cathes pray with chelicerae, the claws penetrate armour or skin, and venom is injected into the body. In most spiders the chelicerae move one towards the other (labidognath), but in Theraposidae and some other Chelicerae groups they lay paralel with the body and fold as a pocket knife (orthognath). Pedipalps Pedipalps resemble shortened walking legs, but are not used for locomotion. They primarily serve as tactile organs, and also help mating organs at the end oft he pedipalps (bulbus), used for sperm transfer. Eyes Spiders have 8 eyes (with the exception of few groups that have only 6). They come in various patterns. Theraphosidae have very small eyes that are very close to each other. Other spiders have much larger eyes, which can be wide apart. Legs Spiders have four pairs of walking legs, consisting of 7 leg joints. On the last joint there are 2 or 3 claws. In addition to that, many spiders have tufts made of tiny hairs, which provide them a foothold on smooth ground with the help of adhesion. Cephalothorax (prosoma) Spiders have a two-part body. The head and thorax have grown into its front part (prosoma, cephalothorax). Abdomen (opisthosoma) The abdomen is not surrounded by hard envelopment as the rest of the body, and it is protected only by skin. This is why it is a very sensitive body part. But on the other hand, the strechable skin allows for the modification in abdomen size for digestion purposes. Spinnerets At the rear of the abdomen spiders have spinnerets which emit silk threads excerting silk glands. Spider silk constains protein, which hardens in contact with air into spinned threads. Hairs The spiders are very hairy. On pedipalps and walking legs they have sensory setae (trichobothria), which are very sensitive to vibrations. They use them for recognizing potential prey in their immediate environment. Some theraposidae spiders have so called irritating setae on their abdomen and when they are in danger, they cast these setae with the back legs and throw them into the air. This can cause skin irritation and cough in people. |
