Two novel adaptations for dispersal in the mite family Histiostomatidae (Astigmata)

Abstract

Two unique morphological adaptations for phoretic attachment to arthropod hosts by deutonymphs of the family Histiostomatidae are described. The deutonymphal attachment plate of Creutzeria from Madagascar and Seychelles has well developed suckers for attachment to smooth cuticle, as well as modifications that allow for ‘grasping’. The conoidal setae are located on the posterior margin with apices modified into trifurcate, claw-like projections. Although the modified conoids are retracted and separated when the sucker plate is relaxed and flat, deutonymphs can fold the sucker plate medially and simultaneously extend the modified conoids. This action causes the medial conoids to merge and interlock their trifurcated tips above a furrow formed from the plate fold. In all probability, these deutonymphs are both entomophilous and pilicolous. The deutonymphal attachment plate of Ceylanoetus is enlarged, covering a significant portion of the paraproctal region. Although it has typical conoidal setae, the anterior suckers are greatly reduced and the medial suckers vestigial. The idiosoma has a truncated rear margin bearing flap-like lateral extensions that curve ventrally and surround the attachment organ. When dispersing, a deutonymph wraps the flaplike lateral extensions of its idiosoma around the anterior margin of the beetle host‘s tibia, thereby completely surrounding it. Although the ridged conoids probably help the deutonymph to hold its position, the ancestral attachment method by means of suckers has been lost in this genus. The term ‘crurophilous’ is proposed for this unique form of deutonymphal attachment.