Fine structure of the chelicera in the spider Nephila clavata

Abstract

The fine structural characteristics of the biting apparatus in the orb‐web spider Nephila clavata were studied using scanning electron microscopy. The main biting apparatuses of spiders are the chelicerae and cheliceral fangs in the cephalothorax. The chelicera of N. clavata is that of the jack‐knife (folding knife) type, which is composed of two segments, and has a labidognathous form that moves at right angles to the body axis. Each chelicera bears a hinged fang that folds into a cheliceral groove. The tips of the fangs are quite sharp, and the spider's body is well adapted to driving the fangs into prey. Just below the fang, each side of the cheliceral groove is covered with a total of seven cuticular teeth (four promarginal teeth and three retromarginal teeth) in two rows. The cheliceral fang has a single aperture at the tip of the posterior surface, and the lower margin of the fang which meets the promarginal teeth is a saw‐like groove. Fine structural observation reveals that each fang has a single venom pore, and each cuticular depressive area on the cheliceral groove has two different types of surface pit. Approximately 40 to 50 spiky protrusions were counted at the cheliceral groove, to hold prey tightly.

Multiscale structural gradients enhance the biomechanical functionality of the spider fang

“…Among their several functions such as those in cleaning behaviour and the widening and opening of the egg sac to release the spiderlings, the mechanically most demanding function of the cheliceral fangs is to puncture the cuticle of prey insects in order to inject the venom 21 22 23 . Spider fangs typically are a few millimetres long, of conical shape, hollow and curved 24 25 . The fang is essentially made of two elements, chitin fibres embedded in a protein-rich matrix, which together form a stiff light-weight structure 26 .…”

Beyond venomous fangs: Uloboridae spiders have lost their venom apparatus but not their toxins

“…Notably, we found that, not only were the venom glands absent, but the opening of the venom duct in the tip of the fangs was also not visible, suggesting a complete loss of the venom apparatus. Nevertheless, we observed the presence of small pores on the fangs, which seem commonly found in spiders (Moon and Yu 2007), but whose function remains unknown. In contrast to the histology results, transcriptomics analysis revealed the expression of genes related to venom components in the prosoma, where venom glands are typically found.…”

“…2B). Similar small cuticular pits have been observed at the fang's tip of the orb-web spider Nephila clavata, although their function remains unknown (Moon and Yu 2007).…”

Morphological Analysis Reveals a Compartmentalized Duct in the Venom Apparatus of the Wasp Spider (Argiope bruennichi)

“…The wasp spider carries ventral cheliceral teeth that accommodate the fang when the venom delivery system is in its resting position. Cheliceral teeth are found in several spider lineages and enable a secure grip on prey [ 48 ]. They are also used to mechanically break up food by species that practice extraintestinal digestion, promoting liquefaction by digestive fluids [ 45 ].…”