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1 Acarologia A quarterly journal of acarology, since 1959 Publishing on all aspects of the Acari All information: acarologia@supagro.inra.fr Acarologia is proudly non-profit, with no page charges and free open access Please help us maintain this system by encouraging your institutes to subscribe to the print version of the journal and by sending us your high quality research on the Acari. Subscriptions: Year 2018 (Volume 58): Previous volumes ( ): 250 / year (4 issues) Acarologia, CBGP, CS 30016, MONTFERRIER-sur-LEZ Cedex, France The digitalization of Acarologia papers prior to 2000 was supported by Agropolis Fondation under the reference ID through the «Investissements d avenir» programme (Labex Agro: ANR-10-LABX ) Acarologia is under free license and distributed under the terms of the Creative Commons-BY-NC-ND which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

2 DESCRIPTION OF A NEW SPECIES, BONOMOIA OPUNTIAE N. SP. (HISTIOSTOMATIDAE, ASTIGMATA), WITH OBSERVATIONS ON THE FUNCTION OF ITS EYES BY S. WIRTH 1 (Accepted November 2005) ISTIOSTOMATIDAE BONOMOIA PHYLOGENY GNATHOSOMA PALPARMEMBRANE DEUTONYMPH LEG SEGMENTS SERIAL HOMOLOGY BONOMOIA OPUNTIAE N. SP. WAVE BEHAVIOR LENTICULUS EYES HISTIOSTOMATIDAE BONOMOIA PHYLOGENIE GNATHOSOMA PALPARMEMBRAN DEUTONYMPHE BEINGLIEDER SERIELLE HOMOLOGIE BONOMOIA OPUNTIAE N. SP., WINK VERHALTEN LENTICULUS AUGEN SUMMARY: Bonomoia opuntiae n. sp., a new species that inhabits rotting Opuntia pieces, is described. In this species, the distal mouthparts (palparmembrane structures) are conspicuously transformed in adaptation to the fluid-like habitat where the species is found. A comparative study of the chemotactic orientation of deutonymphs of Bonomoia opuntiae n. sp. and other histiostomatid species was performed. An up and down movement of legs I ( waving ) to receive scent particles from the air is characteristic of all species of Histiostomatidae. The light sensitive organs of Bonomoia deutonymphs are possibly homologous to the lenticulus of the Oribatida, a type of eye that originated within the paraphyletic Oribatida and probably remained within the Astigmata that phylogenetically come out of the Oribatida. This eye differs completely from the ommatidium type that is usual for other mite groups that exhibit eyes. Experiments demonstrate that Bonomoia opuntiae n. sp. deutonymphs are attracted to light. This is a plesiomorphic character of all Histiostomatidae, but only B. opuntiae n. sp. (or probably Bonomoia in general) is able to recognise slight beam gradients. The special ability to position the body perpendicularly while walking and thereby bring the eyes in a position to receive small spots of light enables the mite easiliy to find the light. The phototactic behavior of B. opuntiae n. sp. is therefore derived and differs from that of other histiostomatids. ZUSAMMENFASSUNG: Die neue Art Bonomoia opuntiae n. sp. wird beschrieben. Die Palparmembran dieser Art, Bestandteil des distalen Gnathosomas, ist in Anpassung an einen besonderen Lebensraum auffällig abgewandelt worden: Die Milbe entwickelt sich inmitten einer flüssigen Bakterienemulsion in verrottenden Stücken von Opuntia. Das chemosensitive Orientierungsverhalten der Deutonymphen von B. opuntiae n. sp. ist mit dem anderer Histiostomatiden verglichen worden. Eine regelmäßige Auf- und Abbewegung des erste Beinpaares ( Wink -Verhalten) unterstützt bei allen Arten die Aufnahme von Duftstoffen. Dieses Verhalten ist bei B. opuntiae n. sp. in Anpassung an den Lebensraum abgewandelt worden und unterscheidet sich von dem anderer Histiostomatiden. Die auffälligen Lichtsinnesorgane der Deutonymphen von Bonomoia sind möglicherweise dem Lenticulus einiger Arten der Oribatida homolog. Der 1. FU Berlin, Institut für Biologie/Zoologie, AG Evolutionsbiologie, Königin-Luise-Str. 1-3, Berlin, Germany. wirthstef@web.de Acarologia, 2004 [2005], XLV, 4 :

3 304 Lenticulus unterscheidet sich in seinem Aufbau grundlegend vom Ommatidien-Typs, der in anderen Milbengruppen häufig ist. Er ist innerhalb der Oribatida entstanden und offensichtlich bei den Astigmata beibehalten worden, die phylogenetisch aus den Oribatida hervorgehen. Untersuchte Histiostomatiden Deutonymphen reagieren mit wenigen Ausnahmen phototaktisch. B. opuntiae n. sp. weist jedoch ein Verhalten auf, das bei Histiostomatiden anderer Grupen nicht zu beobachten ist: Sie verbringt die Augen durch Veränderung der Körperhaltung in eine bessere Position, um diffuse Lichtstrahlen besser wahrnehmen und leichte Lichtgradienten besser unterscheiden zu können. INTRODUCTION Detailed studies on the morphology, phylogeny, and biology of the Histiostomatidae have not been conducted. The most important systematic works were done by SCHEUCHER (1957) and HUGHES and JACKSON (1958). The genus Bonomoia was identified as the most basal branch (WIRTH, 2004). Because of its interesting morphological and biological autapomorphies, a new species of Bonomoia, B. opuntiae n. sp., is described, and its conspicuously derived gnathosoma examined in an attempt to understand its function in a biological context. Biological and behavioral observations of Bonomoia species as well as most histiostomatid species in general do not exist. The interesting chemotactic behavior of this species was observed and comparisons made with observations on other histiostomatid species in order to find new characters that support the argumentation of my reconstructed cladogram. To emphasize the difference between the phoretic transport (the phorets do not feed on the carriers) and parasitism (parasites feed on their hosts), phoretic carriers are called carrier organisms or transporters. This nomenclature follows KIONTKE (1997). Deutonymphs of the taxon Bonomoia possess what appear to be light sensitive structures (eyes) on the lateral margins of the idiosoma (EVANS, 1992). Up to now light sensitive organs of astigmatid mites remained morphologically and functionally unobserved. In contrary eyes of the related and paraphyletic Oribatida are well analyzed and are termed lenticuli. They evolved within that group and differ from the type with rhetinula cells in more basical mite groups (ALBERTI & FERNANDEZ 1988). Experiments with deutonymphs of Bonomoia opuntiae n. sp. compared to experiments using deutonymphs of other histiostomatid species illustrate how these mites react to light stimuli. In addition the current serial homology of setae on the legs of deutonymphal histiostomatids as given by FAIN & ERTELD (1988) is questionable. For this reason another possible homology of these setae is discussed in this paper. MATERIAL AND METHODS Mite cultures were maintained in small bowls (5 cm in diameter). Bonomoia opuntiae n. sp. was fed on pieces of rotting Opuntia sp., the rotting process first stimulated by sprinkling water over fresh, small pieces of plant. Other histiostomatid mites species were fed with potato pieces containing microorganism growth. Specimens for observation under the scanning electron microscope (SEM) were fixed in 100 % ethanol for at least 5 days. Those used to make palparmembrane details visible were critical point dried, whereas those used for examining the eyes were air dried. Both were sputtered with gold prior to examination under the SEM.

4 FIG. 1. A: Total gnathosoma of Bonomoia opuntiae n. sp. in dorsal view. B. Female in dorsal view. C. :in ventral view. D. Deutonymph in dorsal view.

5 FIG. 2.A. Deutonymph in ventral view. B. Larva in dorsal view. d1-d9= dorsal setae; ia, ip= cupules; a1, st1, p1, p2, bcx2, r1, r3= ventral apodemes of deutonymph; cx1, cx3, gp= ventral setae of the deutonymph, homologous to the conoids.

6 RESULTS AND DISCUSSION DESCRIPTION OF BONOMOIA OPUNTIAE n. sp. Deutonymph. Body rhombic in outline (FIG. 1D). Idiosomal length 156 µm, mean and range of 3 specimens 165,6 (160,7-172,6) µm; width 110,8 µm, mean and range 117,2 (110,8-123,6) µm. Dorsal setae short, forming a pattern of seven transverse rows with 12 setae on each side. Pattern similar to that of adults, but presumably setae d5c reduced and therefore not visible. As characteristic of all Bonomoia species, a pair of rounded convex structures on the dorsal anterior hysterosoma (FIG. 1D) presumed to be light sensory organs. Anterior end of the dorsal propodosoma directed downward, enclosing the gnathosomal remnant (FIG. 1D, FIG. 9c). Another characteristic of all Bonomoia species are elongated and not conoidal composed setae cx1, cx3 and gp (FIG. 2A). Sternal 1 apodeme free, not touching r1. Posterior end of sternum 1 divided into three apodemes running parallel to each other, reminiscent of a Neptune-fork (FIG. 2A). A doubled apodeme in position of apodeme bcx2. Apodemes r4 and l4 absent in described Bonomoia species. Punctuation of ventral cuticula, which in described Bonomoia species usually fills the whole area of coxae I, located only on the posterior coxal area I (FIG. 2A). As in all described Bonomoia species, solendidion phi of legs I elongated, however sigma of legs III also elongated in this species. Setae e of legs III as elongated as setae e of legs IV, and legs IV scantly armed with setae (FIG. 4B). ADULT FEMALE. Body balloon-shaped in outline (FIG. 1B). Idiosomal length 359 µm, mean and range of 3 specimens 355,3 ( ) µm; width 244 µm, mean and range 256 ( ) µm. Digitus fixus of typical histiostomatid morphology, however the proximal part differs by forming a simple undivided process followed by about 4 seta-like structures (FIG. 3B). Setae la of legs I and II and setae e of legs III and IV conspicuously elongated. Empodial claws elongated and not much vaulted. Setae surrounding claw conspicuously enlarged (FIG. 4A). Pattern of dorsal setae on idiosoma similar to that 307 of the Malaconothridae ( Oribatida ) (FIG. 1B). Openings of opisthonotal glands located between setae d2 and cp, whereas in all other observed histiostomatid species they are located between setae e1 and d2. All ringorgans enlarged (FIG. 1C). The distal gnathosoma also differs significantly from that of other histiostomatid species. Parts of the proximal pedipalps are conspicuously notched inwards (FIG. 1A). The distal pedipalp articles are shortened and do not project laterally as in other histiostomatids (FIG. 3A). The dorsal guiding structures of the chelicerae are unusually enlarged, highly vaulted and form ridges. Parts of the ventral palparmembrane elongated dorsally, covering both the dorsal pedipalpal articles and parts of the dorsal palparmembrane. These ventral components are divided into hair-like dorsal fringes at the anterior of the gnathosoma (FIG. 3A) and project over its border. The ventral cheliceral guiding structures are enlarged and project conspicuously to anterior. The coxal endites and dorsal guiding structure are anteriorly connected to each other, and in lateral view seem to form one continuous structure (FIG. 3C). In all other histiostomatids, the ventral cheliceral guiding structure (coxal endites) ends at the anterior front more medianly than the dorsal guiding structure. ADULT MALE. Unknown. EGG. Oval in outline. Length ca. 85 µm. LARVA. Length ca. 98 µm; width ca. 55 µm. Dorsal sclerites absent. Dorsal setal pattern typical of larval histiostomatids (FIG. 2B). Ring organs enlarged relative to other species. PROTONYMPH. Length ca. 148 µm; width ca. 83 µm. Idiosoma similar to larva exceptfor arrangement of ring organs which are typical for protonymphal histiostomatids. TRITONYMPH. Length ca. 186 µm; width ca. 108 µm. Idiosoma similar to protonymph and larva. TYPE-LOCALITY AND HABITAT. Specimens were collected from partly rotting pieces of Opuntia sp. in Sardinia, Korsika and Gomera. Mites inhabit the area between the still green plant material and the dark brown rotting material (FIG. 5B). They seldom

7 308 FIG. 3. A-C. Gnathosoma of Bonomoia opuntiae n. sp. (A) in dorsal view, (B) in ventral view, (C) in lateral view.

8 FIG. 4. A: Bonomoia opuntiae n. sp., legs I to IV of the adult female in ventral view. Distal tarsi of legs III and IV depicted in enlarged ventral view. B. Legs I to IV of the deutonymph in ventral view. Distal tarsi of legs II and III depicted in enlarged view. Tarsus II seen from latero dorsally, Tarsus III from ventrally. Letters in black: new serial homologisation of leg setae, gray letters: old homologisation. Letters and arrows point to setae not visible in the depicted view.

9 310 FIG. 5. A. Proximal part of leg III of the deutonymph in a schematic longitudinal section. B. Schematic section through a rotting Opuntia-piece. C. Reconstruction of the lenticulus (after Alberti & Fernandez, 1988):. Ax=photoneurone axons, Co=cuticular cornea, DB=dendrit base, DF=dendritic fibres, EP=epidermis, FB=fat body cells, LB=lamellated body, ONP=optic neuropile, PC=pigment cell, PN=perikaryon of photoneurone. Nomenclature of leg setae after for example Fain and Erteld (1998). feed on the plant s surface and are usually found moving or swimming in the fluid-like material. The type-specimens were collected from cultures derived from specimens found in Sardinia near Olbia where the Opuntia plants were located on a barren plane surrounding a garden that was located near the rocky coast of the sea. The Opuntia material was collected from the ground. TYPUS-MATERIAL. Holotype deutonymph in a glycerine slide deposited in the Museum für Naturkunde, Berlin. 10 paratypes fixed in 99% ethanol and another glycerine slide deposited in the same locality. Diagnosis. Deutonymph: e on legs III conspicuously elongated (as elongated as on legs IV). Sternum 1 ending in a three-pike fork. Ventral punctuation located only in posterior region of coxal field I. Gnathosomal remnant reduced to a small stump, surmounted by anterior parts of the dorsal propodosoma (FIG. 7c). Adults: Only known from females. Short and thick setae on distal tarsi of all legs (FIG. 4A). Body balloon-shaped in outline. Opisthonotal gland openings located between setae d2 and cp. Pedipalps notched inwards, with distal pedipalpal segments shortened. Dorsal and ventral cheliceral guiding structures enlarged and connected to each other. Ventral palparmembrane elongated dorsally and divided into hair-like fringes. BIOLOGY AND ECOLOGY The mode of reproduction: In laboratory cultures, Bonomoia opuntiae n.sp. was observed to undergo

10 311 FIG. 6. Reconstructed cladogram of the Histiostomatidae; 1, 2, 3,4: behavioral apomorphies ( see text ). thelytoky (diploid parthenogenesis) (observed at a cellular level by WITALINSKI, in lit. WITALINSKI, 2003). Thelytoky is not uncommon in the Histiostomatidae, and HUGHES and JACKSON (1959) observed four of twenty species to be thelytokous. They found two species, Histiostoma humiditatis Vitzthum, 1927 and H. feroniarum, to be capable of thelytoky as well as arrhenotoky, with both modes of reproduction appearing in the same habitats and populations. Moreover H. feroniarum is also able to reproduce only by thelytoky (in litt. FASHING, 2003). The cultures of Bonomoia opuntiae n.sp. were reared from only a few specimens found in Sardinia, and it cannot be ruled out that both modes also exist in B. opuntiae n.sp.in the wild. Assumed function of the mouthparts. The following structures are conspicuously derived in Bonomoia opuntiae n. sp.: the dorsal guiding structure is enlarged upwards (FIG. 3B); the ventral cheliceral guiding structure is forwardly elongated (FIG. 3A); the second pedipalpal article is small in relation to other histiostomatid species; the distal pedipalpal articles are strongly shortened, and parts of the ventral palparmembrane are elongated to form dorsal hair-like fringes on their anterior margins (FIG. 3A). Presumably the uptake of microorganisms occurs in a manner that was derived from the usual mechanism where the laterally directed distal pedipalpal segments with ventral lobes function to sweep microorganisms together into mounds in front of the preoral cavity. In usual histiostomatids the function of the laterally arranged pedipalpal articles and their lobes is therefore analogous to that of automobile windshield wipers. Because this Bonomoia species lives submerged in the fluid-like habitat, it cannot funnel the microorganisms into mounds as do many other histiostomatid species. Presumably the ventral lobes and dorsal fringes act together as to pickup the microorganisms from the ground in waterg environment. The food is then transported by the chelicerae to the opening of the pharynx. The transport through the preoral cavity could be supported by the enlarged ventral and dorsal cheliceral guiding structures by preventing the food emulsion from drifting away laterally.

11 312 FIG. 7. A. Deutonymph of Histiostoma straightened up and moving its body alternating to the right and to the left ( wave and wait for the carrier organism). B. Deutonymph of Histiostoma waving with legs I during the walk. C-D. Deutonymph of Bonomoia opuntiae n. sp. (C) fixed on the ground and moving its body around ( wave and wait for the carrier organism), (D) while straightening up its body during the walk ( wave and visual orientation).

12 PHYLOGENETIC POSITION OF BONOMOIA OPUNTIAE n. sp. Arguments for the species status. Bonomoia Oudemans, 1911 is a monophyletic taxon as indicated by the following morphological apomorphies of the deutonymph, which I reconstructed: Light sensory organs ( eyes ) on the anterior hysterosoma-cx1, cx3 and gp elongate setae and not conoidal formed. Area around the anterior sternum armed with lots of cuticula points Solenidia Phi of legs I conspicuously elongated. It is possible that observations in the future will verify that species assigned to Copronomoia Mahunka, 1976 differ distinctly enough from species of Bonomoia (including Probonomoia Fain & Rack, 1987) to substantiate the classification to an own genus. Probably the taxon Copronomoia comes out of Bonomoia or is the sister group caused by the possession of light sensory organs in the deutonymph. ARGUMENTS FOR THE PHYLOGENETIC PLACEMENT OF BONOMOIA. 1) The larvae as well as all other instars of Bonomoia lack dorsal sclerotisations. 2) The stem species of the sister group of Bonomoia consisting of all other histiostomatids developed a symmetric pattern of dorsal sclerites in larval and protonymphal instars. I found only this character to separate Bonomoia from all other groups (WIRTH, 2005b). Using this argument Bonomoia is considered to be the first basal branch within the Histiostomatidae. DEUTONYMPH BEHAVIOR OF BONOMOIA OPUNTIAE N. SP. COMPARED TO OTHER HISTIOSTOMATIDS. Deutonymphs of Bonomoia opuntiae n. sp. demonstrate conspicuous behavioral attributes while moving around. Important structures for chemotactic orientation in all instars are the leg solenidia, with those on legs I and II being the most important (FIG. 9F). A comparative study of waving behavior involving the deutonymphs of several species was performed utilizing two experimental designs. 1. A pattern of fields was arranged on the surface of a piece of dry cardboard, and deutonymphs 313 released at a standardized location. Observations were made for nine minutes, and the distance covered was described by a painted line. 2. A pattern of fields was arranged under a transparent Petri-dish (diagonal 5 cm) filled with 1,5 % agar media, thereby creating a wet surface. The procedure given above was followed. Then the same experiments were performed for a comparative study with the following histiostomatids: Rhopalanoetus sp., Histiostoma sp. (related to H. piceae), H. pulchrum Kramer, 1886, H. sapromyzarum Dufour, 1839, H. maritimum Oudemans, 1914 and H. feroniarum Dufour, Three species of Acarus sp. were observed as outgroup members. For histiostomatid mites in general, leg-waving was observed following a characteristic pattern. Legs I are alternately moved with the right leg being raised and lowered twice followed by the left leg being raised and lowered twice. During this waving of legs I, which happens very rapidly, the deutonymph walks on three pairs of legs, or stops walking for a brief moment (FIG. 7B). Experiment 1. Deutonymphs left the startingpoint quickly, with both rapid and slow walking alternating in a conspicuous manner. The up and down movement of legs I or II for chemosensory reception while walking ( waving ) was in Bonomoia opuntiae n. sp. missing contrary to other histiostomatid genera or outgroup members of Acarus. Deutonymphs regularly stopped walking and attached to the cardboard surface with their suckerplates, positioning the entire body flat on the surface. In this position they used their legs to rotate their bodies around the attached suckerplate in either direction. Only legs I were used for waving (FIG. 7C). 2. Deutonymphs walked slowly and didn t change their speed. After each 2-3 steps they straightened their bodies, being fixed on the agar surface by the sucker plates. In this position they waved (FIG. 7D). Transformations of the waving behavior within the Histiostomatidae. On a dry cardboard and on agar Rhopalanoetus sp. left the release point quickly, waving regularly after each step. Histiostoma spe-

13 314 FIG 8. Deutonymph of B. opuntiae receiving small spots of a beam from distance. cies remained for some time near the starting place where they walked around in a zig-zag manner before leaving. The waving behavior was similar to Rhopalanoetus sp.. Occasionally deutonymphs of Histiostoma straightened up while being fixed on the ground by their sucker-plates. In this position they used all legs to move the whole body alternating to the right and to the left. Meanwhile legs I and sometimes legs II were used to wave (FIG. 7A). This behavior is somewhat different from the straightening up of B. opuntiae n. sp., because Histiostoma deutonymphs remained longer in the described positions in a behavior reminiscent of a dance. Deutonymphs of Acarus immediately left the release point, and waving with legs I occurred often but not in a regular rhythm. Sometimes instead, both legs were stretched upwards at the same time. Possible reasons for the behavior of B. opuntiae. Waving of legs I, also in the non histiostomatid outgroup members, was observed. Therefore it is a plesiomorphic character for the histiostomatid stem species. Bonomoia opuntiae n.sp., however, inhabits a fluid like-habitat. Distance chemoreception via the solenidia of legs I or II is only possible if the deutonymph can elevate its body above the fluid surface. This is one possible explanation for the perpendicular orientation of the body on wet agar under laboratory-conditions. In addition, a light-sensitive function was observed. In the field deutonymphs require a carrier arthropod for dispersal. It is assumed that deutonymphs must leave the rotting area of Opuntia and wait on its dry surface for such a transporter. Rotting Opuntia pieces were primarily found on the ground near the living plant, so the position of a deutonymph on the Opuntia surface would provide maximal exposure to air currents. Pieces in which the mites were found were collected from a barren plane. In such a location it is probably easy to perceive all scents from the surrounding area with minimal movement. It is probably sufficient to remain in a fixed position and occasionally rotate and wave from that position (FIG. 5B). Phylogenetic conclusions. The cladogram of the Histiostomatidae was reconstructed using morphological characters (WIRTH, 2004) (FIG. 6A), and the behavioral characters mapped on this tree. Deutonymphs leaving the release point immediately is considered a plesiomorphy of the stem species of the Histiostomatidae (FIG. 6, no. 1). Released in the experiment could be equated with that point in the field where protonymphs molted into deutonymphs.

14 FIG. 9A. Deutonymph of Bonomoia opuntiae n. sp. in dorsal view. B. Eye enlarged. C. Dorsal anterior propodosoma bearing the gnathosoma of the deutonymph. LB= lamellated body, FB= Fat body cells. D. Proximal leg III. E. Distal secondary articulation. F. An enlarged typical solenidium with pattern of small openings for receiving scent particles. G. Leg III of the deutonymph of Histiostoma palustre treated with lactat during preparation.

15 As an assumed apomorphy of the stem species of the Histiostomatidae, deutonymphs wave after each step (FIG. 6, no. 2). As apomorphies of Histiostoma (FIG.. 6A, no. 4), deutonymphs remain for a period of time at the release point, and sometimes straighten up their bodies while moving alternatingly both to the right and to the left (FIG. 7A). It could not be determined whether the conspicuous behaviors of B. opuntiae to rotate the body on the dry cardboard and regularly to straighten up on the agar surface are apomorphies (FIG. 6, no. 3) of that species or apomorphies of the stem species of Bonomoia. THE LIGHT SENSORY ORGANS OF BONOMOIA OPUNTIAE N. SP. Light sensory organs frequently occur in the Acari, and except for the Oribatida and Astigmata, are commonly located in the propodosomatic region of the prosoma. Propodosomatic eyes were presumably lost within the Oribatida (ALBERTI &FERNAN- DEZ, 1990). A completely different kind of light sensitive organs, the lenticulus, developed within the Oribatida and is located in the hysterosomatic region (ALBERTI & FERNANDEZ, 1990). The clear spots of Oribatida species is interpreted to be homologous to the lenticulus of Hydrozetes lemnae Coggi, 1899, whose eyes were investigated by the authors (ALBERTI & FERNANDEZ, 1988) more precisely (FIG. 5C). The eye structure of H. lemnae probably developed from the clear spot type on the basis of a specialisation of distinct neurones in the synganglion whose dendrites moved to the surface of the central nervous system and finally came to lie close to the dorsal surface of the body (ALBERTI &FERNAN- DEZ, 1988). The lenticulus is a paired organ with two parts being located in close contact (ALBERTI &FER- NANDEZ, 1990). The eye s surface of B. opuntiae n. sp. forms a pattern of small and parallel running grooves (FIG. 9B). The author did not yet conclusively demonstrate that the eyes of Bonomoia are derived from this oribatid eye type. In a SEM view of a section made with a razorblade, a cuticular lens is recognizable as a conspicuous rounded structure that appears to be the photosensitive area and could be homologous to the lamellated body of the lenticulus 316 (FIG. 9B). Then within the Astigmata, the parts of this organ must have migrated away from each other to be located laterally on the hysterosoma as in Bonomoia. Light sensitive behavior of Bonomoia opuntiae n.sp. in comparison to other histiostomatids. To understand the function of the eyes of B. opuntiae n. sp., comparative experiments using deutonymphs of the following mite species were performed: Acarus sp. (outgroup taxa), Bonomoia opuntiae n. sp., Rhopalanoetus sp., Histiostoma sp. (related to H. piceae), H. maritimum and H. feroniarum. These species represent the main groups of the Histiostomatidae. Experiment 1 In this experiment an agar dish (5 cm) was subdivided into a pattern of quadratic fields (0,5x0,5 cm) arranged under the transparent dish. The middle field was illuminated by a beam that lighted its entirety. To avoid warmth that could influence the mite s behaviour, a cold-light-beam for illumination of stereomicroscopes was used. Four different intensities of light could be distinguished. Deutonymphs were released singly at different distances away from the illuminated field and their phototactic behaviour recorded. 20 experiments for each species were performed in this and the following experiment. The duration of each observation was 20 minutes. Regardless of the release distance, deutonymphs of Bonomoia opuntiae n.sp. always moved into the lighted field where they remained for the duration of the trial. Deutonymphs of Histiostoma sp. (related to H. piceae) did not respond either positively or negatively to the light stimulus, and dispersed in all directions regardless of the release distance. Deutonymphs of H. maritimum always avoided the light. Deutonymphs of Acarus sp., Rhopalanoetus sp. and Histiostoma feroniarum were photopositive only when released close to the illuminated field. When released at a distance greater than 1 cm, they moved in all directions, only accidentally reaching the beam. Experiment 2 In a second experiment to determine whether deutonymphs would follow a moved light beam, the position of the beam on the agar plate was changed after five minutes. The new beam position

16 was always 1.5 cm away from the deutonymph. At the beginning of the experiment deutonymphs were released near the first beam position. The experiments were performed for deutonymphs of the following photopositive species: Bonomoia opuntiae n. sp, Rhopalanoetus sp. and Histiostoma feroniarum. Deutonymphs of all three species always went into the illuminated field at the beginning of the experiment, but only Bonomoia opuntiae n. sp. followed the beam to its new locations. The other histiostomatids walked in random directions after the position of the beam was changed. When a deutonymph of B. opuntiae n. sp. was placed at a greater distance from the light source, it walked slowly around in a zig-zag pattern. After about 2 seconds of walking, it straightened its body as described previously. When the deutonymph encountered some diffuse light, it remained in the upright position for a short time and then oriented to the beam. It was observed that the line of walking was corrected at intervals as the deutonymph was illuminated by light rays. They obviously were received by the deutonymph s eyes (FIG. 8). In this way the mite always found the light source after each change. Conclusions. Deutonymphs of the Histiostomatidae and the observed outgroup members behaved photopositive, even if only released close to the illuminated field. That s why the photopositive behavior in general is interpreted to be a plesiomorphic character of the histiostomatid stem species. It is therefore assumed that all species are capable of orienting to light, even those without visible eyes. It is possible that such histiostomatids have rudimentary light sensory organs probably homologous to the eyes of Bonomoia. The behavior of Bonomoia opuntiae n. sp. to regularly upright its body during walking is assumed to be an adaptation that not only maximizes its ability to receive chemical stimuli ( waving ) but also to bring the eyes in a position to maximize the reception of incidence of light. Such behavior would enable this species to differentiate gradients of light much better than other histiostomatid mites. Within the Opuntia pieces Bonomoia opuntiae n. sp. prefers the area with optimal growth of microorganisms, an area which is usually dark-brown in 317 color (FIG. 5B). It is possible that deutonymphs must leave this area and move to the Opuntia surface in order to locate the organisms used for phoresy. The transporter is unknown, and in the rotting tissue below the Opuntia surface adult or juvenile insects that seemed to be attractive carriers for the deutonymphs were never found. In the field the Opuntia surface over the rotting area was always damaged and there were some small splits in the external wall. Deutonymphs presumably need to find these small openings in order to ascend to the outside surface, a probable reason why the light sensory system is so well developed in this Bonomoia species. The second conspicuous behavior of the deutonymph, attaching to the surface and turning around while waving, cannot be explained in the context of visual orientation because it occurs only on the Opuntia surface. It cannot be determined whether this behavior already existed in the stem species of Bonomoia. Other Bonomoia species were not observed. The visible eyes are apomorphic in the stem species of Bonomoia, and comparative studies of deutonymphal behavior are needed. The author observed deutonymphs of other histiostomatid species (and astigmatid mites in general) often develop in insect tunnels that exist inside the dung of mammals or inside logs. That s why it is assumed that they only need to orient to a close light source, and/or that the organism used for dispersal shares a common habitat. Deutonymphs of Histiostoma maritimum in the above experiments were not attracted by light and even seemed to avoid it. This can be explained in regard to their biology. Carrier organisms are the beetles Heterocerus fenestratus and H. fusculus (WIRTH, 2005), and both the adult beetles and mites spend most of their life inside tunnels in mud around fresh waters. Deutonymphs can therefore easily find new carriers without being forced to leave the tunnels. PROBLEMS RELATED TO THE CURRENT SERIAL HOMOLOGISATION OF LEG ARTICLES IN HISTIOSTOMATID DEUTONYMPHS An apomorphy of the Histiostomatidae is six instead of five free articles on legs III and IV of the

17 deutonymph (FIG. 4B). One of the articulations is a secondary, but it is not easy to decide which of the articulations is secondarily formed. A study of the serial homology of the setal pattern could help to determine where it is located, however such a study is difficult to perform due to the reduction in the number of setae of legs III and IV in comparison to legs I and II (FIG. 4B). Usually the last distal visible articulation is interpreted to be secondary (see, for example, FAIN & ERTELD, 1998) (FIG. 9E). The third visible part of these legs from the proximal end is interpreted to be serially homologous to the genu (FIG. 9D), but in my observations this article seems to be a false one and part of the femur (FIG. 5A), because it does not look like a real article and the observation of another species showed that it must be a partly membranous fold of the femur. The third visible part of legs III and IV of Histiostoma palustre Wirth, 2002, a species not closely related to B. opuntiae n. sp., was observed in a SEM study in more detail. After the deutonymph was treated with 90% lactate, this area was folded inwards and nearly invisible (FIG. 9G). That s why it is assumed that the cuticle in this area is thin and membranous. Therefore the author interprets that this portion of the leg belongs partly to the enlarged articulation membrane basal to the genu and partly to the inwardly folded femur. The fact that the questionable proximal part of legs III and IV does not look like a typical article seems to confirm this interpretation (FIG. 9D, FIG. 5A). Having the femur divided into two parts enables the forward directed position of legs III and IV (an apomorphy of the Histiostomatidae) when the deutonymph is attached to the carrier insect. This leg position is a consequence of another apomorphy of the Histiostomatidae: all legs of the deutonymph are elongated in relation to other body parts. In comparative observations concerning the function of elongated legs, it was observed under laboratory conditions that histiostomatid deutonymphs easily right themselves after they have fallen onto their backs. The mobility of these deutonymphs is, for the most part, better developed than in other astigmatic mites. The foreward directed position of legs III and IV probably could support the attachement better than to have them sticking out laterally. 318 The new serial homology of the articles of legs III and IV leads to the assumption that seta d (leg III) and seta r (leg IV) of the old homology must be serially homologous to solenidion phi (leg III and IV) (FIG. 4B). In case of the distal solenidia on legs III and IV, specific solenidial characteristics were not recognised. These solenidia could have lost their chemosensory function because this function is mainly centered on legs I and II. ACKNOWLEDGEMENTS I am grateful to Prof. Dr. W. SUDHAUS and the working group for their helpful and constructive criticism on these observations. I thank my parents R. & G. WIRTH for supporting my work. I thank Dr. N. FASHING for general discussions concerning the Histiostomatidae and correcting the English text version of that manuscript. REFERENCES AESCHLIMANN (A.), What is our current knowledge of acarine embryology? In: Griffiths, D.A. & Bowman, C.E. (eds), Acarology VI, Vol. 1. Ellis Horwood, Chichester, pp ALBERTI (G.)&FERNANDEZ (N.A.), Fine structure of a secondarily developed eye in the freshwater mossmite, Hydrozetes lemnae (Coggi, 1899) (Acari; Oribatida). Protoplasma 146, ALBERTI (G.) & FERNANDEZ (N.A.), Aspects concerning the structure and function of the lenticulus and clear spot of certain oribatids (Acari, Oribatida). Acarologia 31, EVANS (G.O.), Principles of Acarology. University Press, Cambridge. EVANS (G.O.) & TILL (W.M.), Mesostigmatic mites of Britain and Ireland (Chelicerata: Acari: Parasitiformes). An introduction to their external morphology and classification. Transactions of the Zoological Society of London 35, FAIN (A.) &ERTELD (C.), Description of a new species of Histiostoma Kramer, 176 (Acari: Histiostomatidae) phoretic on the solitary bee Halictus sexcinctus (Fabricius, 1775) (Hymenoptera: Apidae: Halictinae). Bull. Annls Societé Belge d Entomologie 134;

18 GRANDJEAN (F.), La chaetotaxie des pattes chez les Acaridiae. Bulletin Soc. Zool. France 64: 50-60; Paris. GRIFFITHS (D. A.), ATYEO (W. T.), NORTON (R. A.) & LYNCH (C. A.), The idiosomal chaetotaxy of astigmated mites. Journal Zoology 220: 1-32; London. HUGHES (R.D.)& JACKSON (C.G.), A review of the Anoetidae (Acari). Virginia Journal of Science 9, KIONTKE (K.), Anhalter und blinde Passagiere Phoresie bei Nematoden und Milben. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin, 36: OCONNOR (B. M.), A systematic revision of the family-group taxa in the non-psoroptidid Astigmata (Acari: Acariformes). doctor thesis. SCHEUCHER (R.), Systematik und Ökologie der deutschen Anoetinen. Beiträge zur Systematik und Ökologie mitteleuropäischer Acarina. 1: WIRTH (S.), Das Stammartmuster der Histiostomatidae (Acari) und Beschreibung der durch zwei Männchen-Typen charakterisierten Histiostoma palustre n. sp.. Acarologia XLII, 3: WIRTH (S.), Phylogeny, biology and character transformations of the Histiostomatidae (Acari, Astigmata). doctor thesis, online publication, Berlin. WIRTH (S.), 2005 a. Phylogeny and characteristic transformations of the Histiostomatidae. Proceedings of the XI International Congress of Acarology, in press. WIRTH (S.), 2005 Phylogeny and necromenic life-strategy of Histiostoma polypori and H. maritimum (Histiostomatidae, Acari). Experimental and Applied Acarology, in press.