oxford views updated May 17 2018
One of the specialized silk-handling devices found in spiders. In general there are four pairs, two pairs on the tenth abdominal segment and two pairs on the eleventh, although few spiders retain the maximum complement in the adult stage. The anterior median pair is usually lost, but sometimes a remnant may remain in the form of a median cone (colulus) whose function is unclear. In some cases the anterior median pair fuse during embryonic development to form an oval plate covered with thousands of tiny spigots (the cribellum). Some spiders retain only two pairs of spinnerets, losing both the anterior median and posterior lateral pairs. Spinnerets are movable, sclerotized tubes composed of several segments; they vary in size, and are mostly conical in web-spinning species. The silk glands produce a protein (fibroin) as a liquid which is emitted through tiny spigots on the ends and ventral sides of the spinnerets. Polymerization of the liquid silk is not an oxidative or evaporative process, but relies on tension.
oxford views updated May 14 2018
A small tubular appendage from which silk
is produced in spiders and some insects. Spiders have four to six spinnerets on the hind part of the abdomen, into which numerous silk glands open. The silk is secreted as a fluid and hardens on contact with the air. Various types of silk are produced depending on its use (e.g. for webs, egg cocoons, etc.). The spinnerets that produce the cocoons of insects are not homologous with those of spiders. For example, the spinneret of the silkworm is in the pharynx and the silk is produced by modified salivary glands
oxford views updated May 23 2018
spin·ner·et / ˌspinəˈret/ •
n. Zool. any of a number of different organs through which the silk, gossamer, or thread of spiders, silkworms, and certain other insects is produced. ∎ (in the production of man-made fibers) a cap or plate with a number of small holes through which a fiber-forming solution is forced.