The locking of the jaws
Males and females have extremely long chelicers furnished with internal spines. Males have two pair of additional large and spines protruding from the inside and outside of his chelicers. These spines lock the female's chelicers open during mating. The male's palps are also very long. For a video of a mating pair of Tetragnatha click here and for a fantastic post by Catherine Scott with observations of mating and male competition click here.
Tetragnatha extensa on resting posture on a leaf over the pond water.
Tetragnatha extensa turning on a leaf allowing to see her chelicers.
Tetragnatha extensa on her web over a pond
Female Metellina sp. on her web. Metellina females are quite plump and don't have particularly long legs.
Male Metellina guarding a female's web. Unlike the female, he is slender and looks more similar to Tetragnatha. He will wait until a female catches an insect to mate. For more information on this species mating strategy see this post at Bugblog.