Foveacheles proxima, Zacharda, 2000

Zacharda, Miloslav, 2000, New species of the rhagidiid genus Foveacheles (Acari: Prostigmata: Eupodoidea) with a lyri ® ssure-like structure on the chelicerae, Journal of Natural History 34 (2), pp. 247-265 : 258-264

Foveacheles proxima sp. n.

(®gures 7±9)

Material examined

HOLOTYPE: adult female, deposited in the Canadian National Collection of Insects and Arachnids, Ottawa, in micropreparation, Type No. 22,405; Austria, Tyrol, Oetztal Alps, Obergurgl (11ss02¾E, 46ss52¾N), Obergurgler Schartl- mountain range W of Obergurgl, upper border of alpine subnival zone about 2700 m altitude, under

stones at foot of talus slope partly covered with wet soil with Polytrichum spp. , moss and Salix herbacea , 7 September 1993, coll. M. Zacharda.

D iagnosis

Chelicerae with elongated robust digits and with lyri®ssure-like structure on ®xed digit positioned laterally and slightly distad of articulation of movable digit. Dorsal surface of ®xed digit with distinct rim. Proximal cheliceral seta inserted just distad of articulation of movable digit, its tip not reaching insertion of distal seta. Rhagidial organ II consists of three oblique rhagidial solenidia lying in separate depressions and spiniform famulus, e, positioned laterad of proximal solenidion. Bothridial setae sc 1 reaching, or slightly overlapping disjugal suture. Spiniform solenidia on genua I, II and III each ventral, distomedial. Solenidion on tibia IV lateroventral, medial. D escription

Adult female (one examined). Length of idiosoma 1392 m m. Ratio of leg I length to idiosomal length 1.10.

Gnathosoma . Subcapitulum slender, subtriangular (®gure 8E); ratio of length to breadth 1.35; distal hypostomal lips with spiniform internal malar and serrate external malar processes; adoral setae nude; proximal subcapitular setae ciliate, external pair slightly longer than internal pair. Chelicerae slender, robust, dorsal surface with distinct saddle-shaped depression slightly anterior to bases of digits (®gure 8A); cheliceral digits long, robust, dorsal surface of ®xed digit with distinct narrow rim; ®xed digit smooth along masticatory surface and with distinct laterodorsal longitudinal lyri®ssure-like structure positioned slightly distad of articulation of movable digit; movable digit serrated along approximatel y distal third of masticatory surface. Chelicerae with two setae, proximal seta inserted just distad of articulation of movable digit; tip of proximal seta not reaching insertion of distal seta; tip of distal seta slightly overlaps apex of ®xed digit. Length of chelicera 330, dorsoventral width 132, length of movable digit 135, length of proximal and distal cheliceral setae 33 and 53 m m, respectively, distance between their insertions 53 m m. Ratios: cheliceral length to dorsoventral width 2.50; length of movable digit to length of chelicera 0.41; length of movable digit to dorsoventral width of chelicera 1.02. Palpus robust, with relatively slender tarsus (®gure 8D); ratio of length to width of tarsus 2.53. Length of palpal trochanter, femorogenu, tibia and tarsus 49, 142, 56 and 125 m m, respectively. Number of setae and solenidia (in brackets) on palpal trochanter, femorogenu, tibia and tarsus 0-2-3-10(1), respectively; tarsal solenidion spiniform, erect.

Prodorsum. Naso well-developed, with pair of internal vertical setae v 1. Bothridial setae sc 1 ®liform, ®nely pubescent, reaching or slightly overlapping disjugal suture (®gure 7A). Length of setae: v 1 72, v 2 72, sc 1 138, sc 2 142 m m. A pair of eyes visible beside bases of setae sc 2.

Opisthosomal dorsum. Complement and arrangement of dorsal setae and cupules typical for Rhagidiidae (®gure 7A); three pairs of cupules; ia positioned laterally about midway between setae c 1 and d 1, im lateral and anterior to setae e 1, ip anterior to f 2. Setae c 1, d 1, e 1 and f 1 reach about 0.30, 0.32, 0.24 and 0.62 of distance to insertion of successive seta, respectively. Length of setae: c 1 63, c 2 182, d 1 66, e 1 63, f 1 119, f 2 56, h 1 148, h 2 92 m m.

Podosoma. Coxisternal plates (epimeres) I, II, III, IV with 3-1-5/6-3 ®nely pubescent setae, respectively (®gure 7B).

Genital region. Genital valves each with ®ve ®nely pubescent setae of similar length, about 43±46 m m, arranged evenly along medial edge of valve. Five pairs of aggenital (paragenital) setae of similar length, about 59±63 m m. Length of genital valves 165 m m (®gure 7B). Cupules ih positioned ventrolaterally, almost laterad of posteriormost pair of aggenital setae.

L egs. Leg I 1536 m m long, about 1.10 as long as idiosoma. Empodia of all legs setulose, broadly oval in dorsoventral view, slightly longer than claws; claws each with small clawlet ventrobasally. Number of setae and solenidia (solenidia and famulus, e, bracketed), respectively, on legs I-II-III-IV: trochanters 1-1-2-2; basif emora +telofemora 5 +5-6 +5-4 +4-3 +4; genua 11(1)-9(1)-8 (1)-6; tibiae 11 (2)-7 (2)-7(2)-7 (1); tarsi 19 (4 + e)-16(3 + e)-14-14 (®gure 9). Genua I, II and III each with one erect spiniform medioventral solenidion. Tibia I with one laterodorsal proximal erect spiniform solenidion and one dorsodistal rhagidial solenidion; tibia II with one laterodorsal proximal spiniform erect solenidion and one small lanceolate dorsodistal solenidion recessed in deep pit with small surface pore; tibia III with two erect spiniform laterodorsal proximal solenidia arranged in tandem; tibia IV with one erect spiniform lateroventral, proximal solenidion. Tarsus I slender, its tip abruptly truncated in lateral view, ratio length to width 5.1, with four rhagidial solenidia lying obliquely in separate depressions, stellate famulus, e, inserted between ®rst and second proximal rhagidial solenidia antaxially (®gure 8B); tarsus II with three rhagidial solenidia lying in separate slightly oblique depressions and small spiniform famulus, e, inserted antaxiall y near base of proximal solenidion (®gure 8C).

A nities

See A nities above for Foveacheles gigantea n. sp. and key to species of the gigantea -species group below.

Etymology

The name proxima (in Latin, proximus means very similar) reēcts the morphological similarity of this species with F. gigantea .

Remarks and de®nition of the gigantea-species group

The genus Foveacheles was proposed by Zacharda (1980) for species of rhagidiid mites with the following characteristics: ®liform trichobothria; typical chelicerae with a distinct dorsal saddle-shaped depression and ®xed digits with soft, weakly sclerotized, sharp dorsal rim (as seen in lateral aspect) under which the distal seta is inserted dorsolaterally in a proximally open depression, whilst the proximal seta is inserted dorsally; rhagidial organs on leg tarsi I and II each with three to ®ve rhagidial solenidia and one stellate or spiniform famulus, e; epimeral formula 3-1-5-3, 3-1-6-3, or, exceptionally, 3-1-6-4; claws on leg tarsi with distinct ventrobasa l clawlets.

However, later three species, F. paralleloseta Zacharda, 1985 ; F. troglodyta Zacharda, 1988 and F. halltalensis n. sp., having no ventrobasal clawlets on claws, were discovered. Hence it is proposed to alter the previous de®nition of the genus Foveacheles and omit`the presence of ventrobasa l clawlets on claws’ in this de®nition.

Recently it has been discovered that some large representatives (idiosomal length 1000± 1600 m m) of the genus Foveacheles have a distinct antaxial, laterodorsal lyri®ssure-like structure of unknown ultrastructure and function which is positioned slightly distad of the articulation of the cheliceral digits. This structure strongly resembles the antero-lateral of the two lyri®ssures which occur on the chelicera of anactinotrichid opilioacarid and mesostigmatic mites ( Grandjean, 1935; Evans and Till, 1978). To date, these structures have been discovered in Foveacheles gigantea n. sp., F. halltalensis n. sp. and F. proxima n. sp., all of which live in subterranean spaces between fragments of talus slopes, and in the troglobitic and troglomorphic F. troglodyta from the Stratenska  jeskyneÏ-cave in the western Carpathians ( Zacharda, 1988). These lyri®ssure-like structures were also found on the chelicerae of the troglobitic and troglomorphic rhagidiid mite Traegaardhia vicenzaensis Zacharda, 1994 from a cave located in northern Italy ( Zacharda, 1994).

Van der Hammen (1969) presented lists of`primitive and original, exclusively Actinotrichid and Anactinotrichid characters’, and according to him, only in Anactinotrichida, and not in Actinotrichida where the Rhagidiidae are placed, are lyri®ssures present on the chelicerae. Lindquist and Palacios-Vargas (1991) in their study of the curious endeostigmatic mite Proterorhagia oztotloica Lindquist and Palacios-Vargas, 1991 (Proterorhagiidae) did not mention any lyri®ssures on the chelicerae among plesiomorphic structures that are`typical of various members of the assemblage of ancient families’ of the prostigmatic mites. Baker (1990) in her survey of external morphology of mites of the superfamily Eupodoidea presented no observations about cheliceral lyri®ssures. However, Grandjean (1935, 1938) reported a slit-like lyri®ssure, designated as i a, being located laterally antaxially on the cheliceral ®xed digit in the prostigmati c mite Cyta latirostris (Herm.) (Bdellidae) , and later ( Grandjean, 1944) also in a representative of the genus Caeculus (Caeculidae) . Coineau (1974) in his monograph on mites of the family Caeculidae mentioned the cheliceral lyri®ssures in the representatives of the genera Allocaeculus , Procaeculus , Caeculus , Neocaeculus and Andocaeculus . Thus, in the light of our present knowledge of external morphology of prostigmatic mites, it seems unwise to homologize these cheliceral slit-like structures with the typical lateral and dorsal lyri®ssures which occur on the cheliceral ®xed digit in the Opilioacarida and Mesostigmata. However, there is a possibility that these inconspicuous tiny structures have been overlooked or unrecognized in various other groups of Prostigmata with chelate chelicerae.

Lindquist (pers. comm.) commented on the discovery of these lyri®ssure-like structures in rhagidiids as follows:`Curiously, Grandjean noted that he has never observed such lyri®ssures among oribatid (or apparently astigmatic) mites. One might suggest, therefore, that their presence is basic to the lineage of Prostigmata (or perhaps Trombidiformes ) but not to that of the Sarcoptiformes (Oribatei and Astigmata) . This may possibly be an apomorphy for Prostigmata as a whole, based on their presence in relatively early derivative families of both major groupings of Prostigmata , i.e. Caeculidae in Anystina and Bdellidae and (some) Rhagidiidae in Eupodina (see the dendrogram of Prostigmata in Lindquist (1998). If so, then its presence is plesiomorphic within the Prostigmata’.

There is no reason to doubt that the gigantea -species group is a natural grouping, which can be diagnosed as follows: (1) epigean, with no morphological adaptations to life in caves; (2) length of idiosoma over 1000 m m; (3) unusually enlarged and strongly chelate chelicerae with the proximal seta inserted always distad of the articulation of the movable digit; (4) the lyri®ssure-like structure positioned on the chelicera; (5) rhagidial organs I and II consisting of four and three rhagidial solenidia, respectively.

At present, these particular lyri®ssure-like structures, which are quite unusual in the Rhagidiidae , and Prostigmata in general, can be considered to be a synapomorphy of this natural species-level grouping. However, if the homology between the slit-like structures and lyri®ssures is con®rmed, then the above interpretation must be changed. Presence, or a greater number, of lyri®ssures are generally considered to be the plesiomorphic condition (Van der Hammen, 1969; Lindquist and Palacios-Vargas, 1991), and in species of the gigantea -species group these lyri®ssurelike structures could then be evaluated as a symplesiomorphy which only characterizes the interspeci®c external resemblance between members of the gigantea -species group.

Foveacheles (Spelaeocheles) troglodyta has the lyri®ssure-like structure positioned on the chelicera also, but in comparison with representatives of the gigantea -species group, it is a troglobitic species having distinct morphological adaptations to living in caves ( Zacharda, 1988), i.e. troglomorphisms ( Zacharda, 1979). This is the reason why F. troglodyta is not placed in the gigantea -species group.

Similarly Traegaardhia vicenzaensis is a troglobitic species that is morphologically considerably derived compared to the representatives of the above-mentione d gigantea -species group. Though this species is outside the present concept of the genus Foveacheles , the lyri®ssure-like structure on its chelicera suggests a possible phylogenetic relationship between T.vicenzaensis , F. troglodyta and members of the gigantea - species group. Alternatively, this may also be evidence of a plesiomorphy that persists among unrelated or distantly related taxa. This question can probably be resolved only by means of a detailed study of the occurrence and ultrastructure of these lyri®ssure-like structures and, perhaps, molecular taxonomy ( Symondson and Hemingway, 1997).

It should also be veri®ed whether Foveacheles (Hirschmannetta) magna Zacharda, 1980 is related to the gigantea -species group. This species was described on the basis of the holotype in a micropreparation ( Zacharda, 1980) and the small lyri®ssurelike structure may have been overlooked. The chelicerae in F. magna , with strong elongated digits and with the proximal seta inserted distinctly distad of the articulation of the movable digit, and the rhagidial organs are strikingly similar to those in representatives of the gigantea -species group. Unfortunately, I have had no opportunity to study the holotype of F. magna again to resolve this question.

Key to adults of the Foveacheles -species with the lyri®ssure-like structure on the chelicerae

1 Five and four rhagidial solenidia in rhagidial organs I and II, respectively. Troglobitic,

the Stratenska jeskyne-cave, western Carpathians, Slovakia.................... F.(Spelaeocheles) troglodyta Zacharda, 1988 ± Four and three rhagidial solenidia in rhagidial organ I and II, respectively (the gigantea - species group).................... 2

2 Rhagidial solenidia in rhagidial organ II arranged in tandem in conūent depressions;

spiniform famulus, e, subtending proximal rhagidial solenidion. Spiniform solenidia on genua I and II dorsal............ F. halltalensis n. sp.

± Rhagidial solenidia in rhagidial organ II oblique or in tandem in separate depressions; spiniform famulus, e, lateral to, or subtending proximal rhagidial solenidion. Spiniform solenidia on genua I and II ventral.............. 3

3 Apex of proximal cheliceral seta almost reaching insertion of distal seta; spiniform

famulus, e, in rhagidial organ II subtending proximal rhagidial solenidion; spiniform solenidion on tibia IV laterodorsal.......... F. gigantea n. sp.

± Apex of proximal cheliceral seta distinctly short of reaching insertion of distal seta; spiniform famulus, e, in rhagidial organ II lateral to proximal rhagidial solenidion; spiniform solenidion on tibia IV lateroventral....... F. proxima n. sp.