Kalmar "littafin huhu" tana nufin sashin numfashi da ake samu a cikin wasu arachnids, kamar gizo-gizo da kunamai. Ana kiran wannan gaɓar “littafin huhu” domin tana ɗauke da jerin faranti masu sirara da sirara waɗanda aka jeri kamar shafukan littafi. Wadannan faranti suna da wadata a cikin jini kuma suna ba da izinin musayar iskar gas, yana barin arachnid ya shakar iskar oxygen daga iska. Sunan "littafin huhu" ya fito ne daga kamannin waɗannan sifofin numfashi zuwa shafukan littafi.