337
9.5.2.1 Phoresy in the Fossil Record
The oldest putative example of phoresy is an oribatid from the Carboniferous (ca.
320 Ma) of Xiaheyan in China (Robin 2021; Robin et al. 2016) found on the thorax
of a grasshopper-like insect in the extinct order Archaeorthoptera. The mite was
assigned to the Mixonomata clade, the authors noting there was no indication of
parasitism and that this was probably an example of phoresy instead. Phoresy is
uncommon among oribatid mites today, but mixonomatids have been reported phoretic on, e.g., harvestmen (Townsend Jr et al. 2008) in modern ecosystems. The
phoretic deutonymph of an astigmatan mite (possibly Histiostomatidae) was documented from Eocene Baltic amber attached to a woodlouse spider (Dysderidae) by
Dunlop et al. (2012). Again, spiders are not the usual host of these mites, but such
associations are known today (see discussion in Dunlop et al. 2012). It should be
added that computer tomography (μCT) was particularly helpful in resolving morphological details such as the underside of the astigmatid’s body with its characteristic sucker plate. This methodology may be applicable to other phoretic mites both
in sediments and amber; see also comments in De Baets and Littlewood (2015).
Other apparently phoretic acariform mites from Baltic amber were figured by
Eichmann (2002), although as the author noted himself some of them may actually
be parasites as its sometimes difficult to determine whether the mite is using its
mouthparts.
Among the parasitiform mites there are phoretic examples of mesostigmatids in
Cretaceous Burmese amber (unpublished observations). Deutonymphs of tortoise
mites (Urodinychidae) were documented from Rovno and Baltic ambers (Lyubarsky
and Perkovsky 2012; Dunlop et al. 2013). In both cases the juvenile mites were
hosted by beetles (Coleoptera: Cryptophagidae and Cerambycidae), and the characteristic stalk-like anal pedicel which they use for attachment was clearly visible
(Fig. 9.6c). The Baltic amber beetles also carried tentative records of Microgynioidea
and Ascidae, leading Dunlop et al. (2013) to suggest that the rarity of fossil mesostigmatid mites may be an artefact and that further taxa may be found by searching
for parasitic or phoretic mites attached to their more mobile hosts, which are more
likely to have come into contact with sticky tree resin.
9.6 Chelicerates as Victims
Finally, chelicerates, are also affected by parasites. Horseshoe crabs can host a
diverse fauna of epibionts (Botton et al. 2003; Leibovitz and Lewbart 2003) including cnidarians, bryozoans, bivalves and barnacles, as well as algal infections
(Braverman et al. 2012). While many of these organisms are commensal animals,
rather than parasites, heavy infestation of attached or encrusting animals probably
hinders the crab to some extent. True parasites of horseshoe crabs can be found
attacking the haemolymph-rich gills, and include certain protozoans and turbellarid
worms, while a nematode is known to burrow into the cuticle. Of particular note is
9 Chelicerates as Parasites
9.5.2.1 Phoresy in the Fossil Record
The oldest putative example of phoresy is an oribatid from the Carboniferous (ca.
320 Ma) of Xiaheyan in China (Robin 2021; Robin et al. 2016) found on the thorax
of a grasshopper-like insect in the extinct order Archaeorthoptera. The mite was
assigned to the Mixonomata clade, the authors noting there was no indication of
parasitism and that this was probably an example of phoresy instead. Phoresy is
uncommon among oribatid mites today, but mixonomatids have been reported phoretic on, e.g., harvestmen (Townsend Jr et al. 2008) in modern ecosystems. The
phoretic deutonymph of an astigmatan mite (possibly Histiostomatidae) was documented from Eocene Baltic amber attached to a woodlouse spider (Dysderidae) by
Dunlop et al. (2012). Again, spiders are not the usual host of these mites, but such
associations are known today (see discussion in Dunlop et al. 2012). It should be
added that computer tomography (μCT) was particularly helpful in resolving morphological details such as the underside of the astigmatid’s body with its characteristic sucker plate. This methodology may be applicable to other phoretic mites both
in sediments and amber; see also comments in De Baets and Littlewood (2015).
Other apparently phoretic acariform mites from Baltic amber were figured by
Eichmann (2002), although as the author noted himself some of them may actually
be parasites as its sometimes difficult to determine whether the mite is using its
mouthparts.
Among the parasitiform mites there are phoretic examples of mesostigmatids in
Cretaceous Burmese amber (unpublished observations). Deutonymphs of tortoise
mites (Urodinychidae) were documented from Rovno and Baltic ambers (Lyubarsky
and Perkovsky 2012; Dunlop et al. 2013). In both cases the juvenile mites were
hosted by beetles (Coleoptera: Cryptophagidae and Cerambycidae), and the characteristic stalk-like anal pedicel which they use for attachment was clearly visible
(Fig. 9.6c). The Baltic amber beetles also carried tentative records of Microgynioidea
and Ascidae, leading Dunlop et al. (2013) to suggest that the rarity of fossil mesostigmatid mites may be an artefact and that further taxa may be found by searching
for parasitic or phoretic mites attached to their more mobile hosts, which are more
likely to have come into contact with sticky tree resin.
9.6 Chelicerates as Victims
Finally, chelicerates, are also affected by parasites. Horseshoe crabs can host a
diverse fauna of epibionts (Botton et al. 2003; Leibovitz and Lewbart 2003) including cnidarians, bryozoans, bivalves and barnacles, as well as algal infections
(Braverman et al. 2012). While many of these organisms are commensal animals,
rather than parasites, heavy infestation of attached or encrusting animals probably
hinders the crab to some extent. True parasites of horseshoe crabs can be found
attacking the haemolymph-rich gills, and include certain protozoans and turbellarid
worms, while a nematode is known to burrow into the cuticle. Of particular note is
9 Chelicerates as Parasites