Ereynetinae Oudemans, 1931

Waki, Tsukasa & Shimano, Satoshi, 2019, Redescription of the Snail Mite Riccardoella reaumuri (Acariformes: Prostigmata: Ereynetidae), Species Diversity 24, pp. 97-102 : 97-99

Subfamily Ereynetinae Oudemans, 1931 Genus Riccardoella Berlese, 1923 Subgenus Proriccardoella Fain and van Goethem, 1986 Riccardoella (Proriccardoella) reaumuri Fain and van Goethem, 1986 ( Figs 1–7 ; Table 1)

Diagnosis. Body (gnathosoma and idiosoma, length×width) 378×277. Color orangish-white under a stereomicroscope. Surface of idiosoma, gnathosoma, and legs folded by cuticle containing striation. No eyespot. Oval idiosoma with barbed and cylindrical setae, except long sensillae sci and f 2. Lyrifissures (im, ip, and ih) present. Aggenital region with 2 pairs of genital papillae. Palp with 3 segments. Palptarsus with 3 setae. Tibia I with 5 setae. Femur I with 1 seta. Trochanters I and III each with 1 seta. Coxae I and III each with 2 setae. One subcylindrical solenidion (ω) present in each tarsi I and II, inserted in almost dorsal position, close to seta ft ″. Length of solenidia 7. Tibia I with forked famulus (k ″) being as long as ca. 60% of the length of its guard seta (l ″). All setae on idiosoma, palptarsi and legs not prolonged with apical filament.

Description. Body (gnathosoma and idiosoma) ( Fig. 2 ). Length excluding legs×width 378×277.

Integuments. Color orangish-white under a compound microscope. Surface of idiosoma, gnathosoma, and legs with striated cuticle.

Idiosoma ( Figs 2 , 7A, B ). Idiosoma oval. Idiosoma length×width 352×277. Lengths of dorsal idiosomal setae vi 30; ve 9; sci 95; sce 32; c 1 26; c 2 33; d 1 27; e 1 30; f 1 29; f 2 73; h 1 25; h 2 21. Lengths of ventral idiosomal setae 1a 13; 3a 12; 4a 13. Setae f 2 and sci long and narrow, ve short, and others subcylindrical ( Figs 2 , 7A, B ). Three pairs of lyrifissures (im, ip and ih) present ( Figs 2B , 7H–J ).

Aggenital region ( Fig. 3 ). Setae making 2 pairs rows. Based on seta base, genital area with external row (aggenital setae (ag )) of 5 setae and internal row (genital setae (g )) of 5–6 setae ( Fig. 3 ). Defluxion of seta found right g 1 and ag 4. Right g 4 adjacent to g 5 probably due to variation. Lengths of ag 1 – ag 6 10–14. Lengths of g 1 –g 5 6–9. Two pairs of pseudanal setae (ps) present and lengths of ps 1 and ps 2 10. Two pairs of genital papillae present.

Gnathosoma ( Fig. 4 ). No eyespot. Length×width 52×73. All setae not prolonged with apical filament. Palptarsus with 3 barbed setae and 1 solenidion (ω) ( Fig. 7F, G ).

Legs ( Figs 5 , 6 , 7C–E ; Table 1). Claws as long as ca. 10 times its width and containing inconspicuous dents. Femur IV subdivided ( Fig. 5D ). All legs setae not prolonged with apical filament. Setation on legs as follows (I-II-III-IV, solenidia and famulus in parenthes): tarsi 12(ω)-9(ω)-8-8; tibiae 5(k ″, φ)-3-3-3; genua 4-4-3-3; femora 6-4-3-3; trochanters 1-1-1-0; coxae 2-1-2-1. Solenidial complement on Tarsi 1-1- 0-0 ( Fig. 7C ). Subcylindrical solenidion on tarsi I-II and inserted dorsally, near seta ft ″ ( Fig. 7C ). Length of solenidia on tarsi I and II 7 and 6–8, respectively. Leg chaetotaxy and solenidiotaxy in Table 1. Setae p ″ on tarsus II, (p) on tarsi III-IV, and u ′ on tarsus IV wider than other leg setae ( Figs 5B–D , 6B–D ). Setae (p), (u), (pv) well barbed on ventral side, except p ′ on tarsi III-IV and u ′ on tarsus IV. Setae on coxa III shortest among epimeral setae, and 3c shorter than 3b. Ereynetal organ (φ) on tibia I oval ( Fig. 7D ). Ereynetal organ with famulus (k ″) 13 long and ordinally seta (l ″), named guard seta, 21 long: length of famulus 59% of length of guard seta ( Figs 5A , 7E ). Famulus (k ″) forked distally ( Figs 5A , 7E ). Eupathidion unclear.

Distribution. Jura near Pontarlier, France ( Fain and van Goethem 1986).

Host. Arianta arbustorum Linnaeus, 1758 in Fain and van Goethem (1986).

Type materials and deposition. Adult female (holotype), adult female and male (paratypes) collected from Arianta arbustorum Linnaeus, 1758 in Jura near Pontarlier, France (23 April 1963) are deposited in the collection of the Royal Belgian Institute of Natural Sciences , Brussel, Belgium (coll. RBINS) with accession numbers 5-10-19, 5-10-17 and 5-10-18, respectively .

Remarks. This species belongs to the genus Riccardoella Berlese, 1923 because of the following morphological characteristics ( Fain and van Goethem 1986; Fain and Barker 2003; André et al. 2004; Waki et al. 2018a): palp with 3 segments; tibia I with 5 setae; femur IV with 3 setae; lyrifissure im present; idiosoma with two pairs of long and narrow setae. R. reaumuri belongs to the subgenus Proriccardoella Fain and van Goethem, 1986 since it has following morphological features ( Fain and van Goethem 1986): trochanter III with one seta; coxa I with two setae; tarsus I with famulus (k ″) consisting ca. 60% the length of its guard seta (l ″); all setae on idiosoma palptarsi and legs not prolonged with apical filament.

This species can be morphologically distinguished from the other seven Riccardoella species based on the following features: idiosoma and leg setae not prolonged with apical filament; palptarsus with 3 setae; tibia I with 5 setae; femora

Redescription of Riccardoella reaumuri 99

I with 1 seta; trochanters I and III each with 1 seta; coxae I and III each with 2 setae; famulus forked distally and ca. 60% long of its guard seta; 2 pairs of pseudanal setae.

Riccardoella reaumuri resembles Riccardoella oudemansi Thor, 1932 because both species have 3 setae on palptarsus, 6 setae on tibia I, 1 seta on trochanter I. However, R. reaumuri is distinguished from R. oudemansi in having the following features: 2 setae on coxa III; famulus ca. 60% long of its guard seta (3 setae and famulus slightly shorter than its guard seta in R. oudemansi ). Riccardoella reaumuri also resembled Riccardoella canadensis Fain and van Goethem, 1986 because both species have 6 setae on tibia I, 1 seta on trochanter I and forked famulus on tibia I; however, these two species are distinguished since R. reaumuri has 3 setae on palptarusus and famulus ca. 60% long of its guard seta (palptarsus with 4 setae and famulus as long as its guard seta in R. canadensis ).

Figures

Fig. 1. Holotype of Riccardoella (Proriccardoella) reaumuri: A. Slide with mounted holotype. B. Body in dorsal view. Scale bar 100µm.

Fig. 2. Riccardoella (Proriccardoella) reaumuri: holotype, female. A. Body in ventral view. B. Dorsal view of idiosoma. Scale bar 100µm. Arrow: base lacking setae 1a.

Fig. 3. Riccardoella (Proriccardoella) reaumuri: holotype, female. Aggenital region. Scale bar 50µm. Arrows: bases lacking setae. Open arrow:right g4 adjacent to right g5.

Fig. 4. Riccardoella (Proriccardoella) reaumuri: holotype, female. Gnathosoma in ventral view. Scale bar 50µm.

Fig. 5. Riccardoella (Proriccardoella) reaumuri: holotype, female. A–D:Leg I–IV without coxae.Scale bar 50µm.

Fig. 6. Riccardoella (Proriccardoella) reaumuri: holotype, female. Tarsi I–IV in lateral view (A–D). Scale bar 20µm.

Fig. 7. Riccardoella (Proriccardoella) reaumuri: holotype, female. Setae, ereynetal organ and lyrifissures. A. setae f1 and f2. B. setae ve. C. solenidion ω and seta ft′ on tarsus I. D. erenynetal organ φ on tibia I. E. famulus k″ and guard seta l″ on tibia I. F–G. solenidion ω and seta (arrows: d, l′ and l″) on palptarsus. H–J. lyrifissures im, ip, and ih (arrows). Scale bars 20µm (A–G) and 5µm (H–J).