Hairs on trigonotarbid mouth parts
deutsche Version
Trigonotarbids resemble spiders not only in their aspect and their predatory way of life but assumedly also in their eating habits. They are supposed to not really eat their prey but liquefy the eatable parts and imbibe the nutrient-rich liquid, as it is known from spiders [1]. Variously arranged hairs near the mouth are sometimes interpreted as filtering systems preventing solid prey fragments from entering.
Attention is drawn here to the fact that there is another effect of hairs arranged in a brush-like way: They can ease the handling of liquids, which is important with sub-mm-size phenomena like the small-scale transport of liquid considered here, where surface tension is the dominating force. The trigonotarbid must not get soiled by the sticky liquid, be it as separate droplets or as a fluid layer on the partially liquefied prey [1].  
Suitably arranged hairs with non-wetting surface can keep the liquid at a distance from the body and thus prevent contact.

Image: Sharply pointed fang (chelicera) of a Devonian trigonotarbid, nearby hairs probably facilitating the transport of nutrient-rich liquid. Rhynie chert, image width 1.2mm.

Sample: Rh9/58.1 (0.21kg), Part 1, found by S.W. in 2004.

H.-J. Weiss       2020

[1]  W.G. Eberhard, G. Barrancs, Ju-Lin Weng: The mystery of how spiders extract food without masticating prey.  
      Bull. Br. arachnol. Soc. 13(2006) (9), 372-376.
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