First record of Harpellales, Orphellales (Kickxellomycotina) and Amoebidiales (Mesomycetozoea) from Bulgaria, including a new species of Glotzia

Abstract This paper presents the results obtained from a short survey performed in Bulgaria, southeast Europe, where the trichomycetes (sensu lato), an ecological group of arthropod gut endosymbionts, were previously completely unknown. The present study initiates the comprehension of these cryptic organisms, members of the Kickxellomycotina (Harpellales, Orphellales) and the Mesomycetozoea (Amoebidiales), in this Balkan country. Eighteen new geographic records for Bulgaria are reported, including 10 species of Harpellales, three species of Orphellales and five species of Amoebidiales. Within the Harpellales, the species Glotzia balkanensissp. nov. is described. This new species is most related to the rare species G. centroptili Gauthier ex Manier & Lichtw. and G. stenospora White & Lichtw., but is differentiated by spore and thallial characteristics. Photographs are provided and biogeographic implications of these records are discussed.


Introduction
The ecological group trichomycetes includes filamentous or sac-like protozoan organisms (Mesomycetozoea Order Eccrinales and Amoebidiales) (Benny and O'Donnell 2000;Ustinova et al. 2000;Lutzoni et al. 2004;Tanabe et al. 2004;Adl et al. 2005;Cafaro 2005) and filamentous Fungi (Zoopagomycota, Kickxellomycotina, O. Harpellales and Asellariales) (Hibbet et al. 2007), all of them sharing the same ecological behaviour and living symbiotically inside the gut of arthropod hosts. The intense conditions and constrictions of this peculiar environment have shaped the convergent evolution, resulting in parallel morphology for all members in this ecological assemblage of organisms, explaining the previous classification of these phylogenetically unrelated orders within the Class Trichomycetes (Lichtwardt 1986). The Order Harpellales is the most diverse and well-known within the trichomycetes, with nearly 250 species, living associated mainly with immature stages of aquatic insects (Lichtwardt et al. 2001). Recently, a new order has been raised from within the Harpellales: the Orphellales L.G. Valle, M.M. White, Strongman & Lichtw to include the Plecopteran-associated genus, Orphella, with unusual characteristics in its sexual spores, amongst other particularities that make this genus exceptional within the Kickxellomycotina (White et al. 2018). The relationship between trichomycetes and their hosts is considered commensalistic, since they feed on the digestive content transiting those portions of the insect gut where most of the nutrients have already been absorbed by the animal (Misra 2001). However, they can behave mutualistically in some developmental and environmental conditions (Horn and Lichtwardt 1981), while other species may be deleterious to their hosts, like a few dipteranassociated species of Smittium which can be lethal to mosquitoes (Dubitskii 1978;Sweeney 1981;López-Lastra 1990) and may have an added interest for mosquitocontrol research.
Bulgaria is a biogeographically attractive region and, like most other Oriental European countries, it has not, until now, been studied by trichomycetologists. Europe transitions to Asia through the Balkans, acting as a connecting corridor, with Siberian and central European fauna and flora, together with Mediterranean components. This, combined with other geological factors, makes the Balkan Peninsula one of the two -together with the Iberian Peninsula-most interesting biogeographic regions in Europe, both being considered hotspots of biodiversity (Griffiths et al. 2004;Popov and Fet 2007). Bulgaria is actually the best-studied of all Balkan countries concerning biodiversity, because of the great tradition of zoological and botanical research (Popov and Fet 2007). With all these concurrent factors, it is our wish to contribute to the biodiversity data of the country with this preliminary study of arthropod endosymbionts.
At present, there are 54 species of trichomycetes documented from the Iberian Peninsula (Casas et al. 2019, Valle 2004, 2014a, 2014b, Valle and Santamaria 2002, 2004; it can be used as an indicator of what the diversity might be like in Bulgaria if more collections of trichomycetes are made in the future.

Material and methods
All taxa reported here were collected from diverse localities (Table 1) in Bulgaria, most of them in the Provinces of Sofia and Pernik, since fresh material was processed in the laboratory of the Institute of Biodiversity and Ecosystem Research of the Bulgarian Academy of Sciences, in Sofia. Consequently, collecting trips where done not far away from the capital. Arthropod hosts, mainly aquatic insect larvae, nymphs and some aquatic isopods, were captured following the methods described by Lichtwardt et al. (2001), using aquatic dip nets and/or by hand-picking from stones, pebbles and vegetation. Hosts were transported to the lab in jars containing stream water on ice. Insect guts were dissected in water on microscope slides using a stereomicroscope and the gut symbionts transferred to a drop of water on another slide with the aid of ultrafine forceps and entomological needles. Lactophenol cotton-blue was used as the mounting medium for semi-permanent voucher slides, then these were sealed with clear finger- To reference the microscopic slides (specimens), a reference number was selected for each locality, preceded with the geographic reference BUL (Bulgaria: BUL-1, BUL-2 etc…). A second number was assigned sequentially for each microscope slide within the corresponding site (i.e. BUL-1-1: site 1, slide 1). See Table 1 for collecting sites details. All specimens collected by the authors (Leg.). All measurements, length × width in micrometres, for Orphella zygospores and diameter of the major outer spore coil × spore width (in micrometres) were made. Other measurements, as indicated in the text.
Notes. The genus Glotzia has nine species (including that described here), all of them sharing the characteristic cylindrical trichospores with a slightly globose cap and the peculiar 3-appendage arrangement observed also in G. balkanensis. This new species mostly resembles the type species G. centroptili described by Gauthier (1936) in French pools and streams of Dauphiné province (south-eastern France) from Centroptilum luteolum nymphs (Baetidae). This French species was recently rediscovered in Catalonia (Spain) also within Centroptilum sp. nymphs (Busquets et al. 2018). This second observation in Spain was important for providing new material to complete the original description, which was scant and had no photographs, only a drawing of a single specimen (Gauthier 1936). The specimens from Bulgaria can be differentiated from G. centroptili by spore characteristics. Trichospores of the Bulgarian species are longer than those observed in France or Spain (40 × 4 μm according to Gauthier (1936); 35-43 × 4-6 μm according to Busquets et al. (2018), up to 56 μm in the specimens reported here). All the fertile branches observed had a maximum of four generative cells in G. balkanensis, while up to seven have been reported in G. centroptili. Zygospores of G. balkanensis are quite similar to those of G. centroptili in length, but they have significantly larger diameter in the French species, 15 μm diameter (according to Gauthier 1936), while only 7.5-9.5 μm (8.4 μm average) in G. balkanensis. Unfortunately, the specimens of Glotzia centroptili collected from Spain, had no zygospores to compare with the new species, only trichospores were observed and, thus, we do not have a broad perspective of the zygosporic variation in this species, because apparently, the description of the type species was based on just a few specimens (Busquets et al. 2018). The presence of a collar on released zygospores was not described by Gauthier in G. centroptili. The species described here has a quite variable collar length, but in most zygospores, it is rather short (5-10 μm). Regarding thallial characteristics, both species are quite similar, but there are major differences in their fertile branches, generative cells and in the basal cell. The basal cell is much more swollen in the Bulgarian species, resembling (but not identical to) that of the Italian species Glotzia distorta LG Valle, Santam. & W Rossi which has different spore features (Valle et al. 2014). Most species of Glotzia are associated with Baetidae (Ephemeroptera), except for one species recorded in a New Zealand Plecoptera nymph, Glotzia plecopterorum Lichtw. (Williams and Lichtwardt 1990) and another species living within Dixidae (Diptera) larvae Glotzia incilis Strongman & MM White, (Strongman and White 2008). Actually, Glotzia is one of the Harpellid genera with a wider host range. Glotzia centroptili was recorded from Centroptilum (Baetidae) in France and Spain and G. distorta from the related Procleon pennulatum (= Centroptilum pennulatum) (Valle et al. 2014). However, Glotzia balkanensis has been recorded from a different host, Baetis melanonyx, but in the same family Baetidae. In fact, this is the first record of a Harpellid fungus within this host species.
Notes. This species is characterised by the unusual formation of vegetative propagules from the bulbous basal cells (Fig. 12), a feature only shared with the related genus Gauthieromyces (Lichtwardt 1983). Graminella bulbosa was described from France (Léger and Gauthier 1937;Manier 1962). The species is also known from Spain (Valle 2007), Portugal (Valle 2013a) and Italy (Valle et al. 2013). Graminella bulbosa has been reported associated with various species of Baetis and related genera, very frequently within the hindgut of B. rhodani (Pictet). This species of mayfly is common and widespread in Europe and it also hosted Bulgarian specimens of G. bulbosa in the surveyed rivers, together with B. alpinus (Pictet). In fact, the genus Baetis bears different Harpellid species, including the more common Legeriomyces ramosus, occasionally sharing the same gut lumen with Graminella bulbosa. Bulgarian specimens of G. bulbosa show the typical small and numerous trichospores (Fig. 13), measuring 8 -11 × 2 μm in our collections. These measurements are midway between G. bulbosa and G. microsporus (see discussion for further information). Unfortunately, only immature zygospores were observed (Fig. 11 arrowhead).
Note. This species was obtained from the hindgut lining of Simuliidae larvae. Most of the observed specimens of S. microsporus were attached to thalli of both Genistellospora homothallica (Fig. 2) and Paramoebidium chattoni. All the individuals had trichospores and one of the specimens showed also the typical type-I zygospores' young ( Fig. 2). All characteristics and measurements of Bulgarian S. microsporus match that of previous descriptions of the species in Europe (Moss 1970;Valle 2004, White andLichtwardt 2004). This species, discovered in the USA (Lichtwardt 1972), has a sub-cosmopolitan distribution (see Lichtwardt et al. 2001), with a patchy distribution in the Northern Hemisphere and also Australia (Lichtwardt and Williams 1992).

Spartiella barbata Tuzet & Manier ex Manier, 1968.
Notes. This species was described from France (Tuzet and Manier 1950) in the hindgut of Baetidae nymphs. Spartiella barbata is distinguished by its lobulate basal cell, obpyriform trichospores, measuring 21-26.5 × 6.5-7.5 μm in our specimens (Fig.  18) and the presence of one appendage tightly coiled just after release and then eventually uncoiling into a long delicate filiform structure. Spartiella barbata seems to be more common in Europe, where it has been recorded from France Manier 1950, Manier 1962b), United Kingdom (Lichtwardt 1986) and Spain (Valle 2007), with only one report of the species from North America, in Canada (Strongman 2010).

Stipella vigilans Léger & Gauthier, 1932.
Notes. Stipella vigilans was originally described from the French Alps in the hindgut of Simuliidae, together with the protozoan Paramoebidium sp. (Léger and Gauthier 1932). This species was also reported from Spain (Valle 2007), England (Moss 1970), Armenia (Nelder et al. 2005), Thailand (Hapsari et al. 2009). The species is easily distinguished by the particular basal cell, simple or forked, verrucose and narrowing in the most basal section, attached to the hindgut by means of a mucilaginous adhesive substance (holdfast) (Fig. 20). The trichospores of S. vigilans are also very characteristic, almost cylindrical, measuring 35-50 × 3-4.5 μm in our collections, although probably somewhat young, they fit the original description, according to . Various species of Harpellales. 17 Smittium dipterorum from Chironomidae larvae; thallus overview with fertile branches and trichospores 18 Spartiell barbata from Baetidae nymphs, fertile branches with trichospores 19 Stachylina nana from Chironomidae larvae, thallus overview with trichospores 20 Stipella vigilans from Simuliidae larvae, thallus with mucilaginous material at the basal cell (arrow). Scale bars: 25 μm in all figures. Gauthier (1932). We did not see released trichospores, since none of them was mature enough in our collections. Trichospores in this species bear three petaloid appendages, which are visible inside the generative cells before detachment.
Notes. We found this species associated with Leuctra hippopus (Kempny 1899) in two Bulgarian rivers and streams. The specimens examined had the typical characteristics of the species, including the straight trichospores measuring 47-56 × 5-7 μm in our collections, with generative cells 21-26 μm long and a supporting cell 6-8 μm length (Fig. 21). All the characters of trichospores and accompanying cells fit the description of the species (Santamaria and Girbal 1998). Zygospores were not seen on this occasion. This species was described from Catalonia, Spain Girbal 1998, Valle andSantamaria 2005) and has been reported also from Norway (White and Lichtwardt 2004), France (Valle 2013b) and Italy (Valle et al. 2014).
Notes. Species were obtained from the hindgut lining of Leuctridae nymphs (mainly Leuctra hippopus). We found several thalli, most of them producing trichospores and one also bearing helicoidal zygospores, formed homothallically, measuring 25-27 × 5.5-6.5 μm, growing on a fusiform zygosporophore measuring 20-23 × 7-8.5 μm, with a 3 μm long supporting cell and a sigmoid or reflexed intermediate cell about 20-24 μm long in the specimens seen (Fig. 24). All the characteristics of spores and accompanying cells fit those of the specimens reported from other localities in Europe, including Spain (Santamaria and Girbal 1998;Valle and Santamaria 2005), Norway (White and Lichtwardt 2004); Italy (Valle et al. 2013). Thallus has the characteristic basal cell (Fig. 25) and lateral subsidiary branches.

Order Amoebidiales (Mesomycetozoea)
Paramoebidium angulatum Valle, 2014a. Fig. 26 Specimens examined. Site 4: slide BUL-4-2 Notes. This species is characterised by having a thallus bent approximately at a right angle about one-quarter up the thallus from the holdfast; no other described species shares this feature. This species was originally described from the stonefly family Taeniopterygidae. Our specimens were observed in Nemouridae, a different family in the same Order of insects sharing all characteristics with P. angulatum, although most individuals were immature, measuring 350-380 × 29-33 μm, with the typical thallus with the right angle bend and discoid acellular holdfast, known previously only from France (Valle 2014a). Fig. 27 Specimens examined. Site 2: slide BUL-2-6.

Paramoebidium chattoni Léger & Duboscq ex LG Valle, 2014b
Notes. This species of Paramoebidium is common within Simuliidae hosts and is identifiable by having the widest diameter of thallus at the basal to middle sections, slightly tapering towards the distal end. It has a non-cellular holdfast located at the proximal end smaller in diameter (12-27 μm) than the thallus, cylindrical or slightly campanulate (Valle 2014b). Bulgarian species perfectly match with the original description (Léger and Duboscq 1948) and with that provided in the validation of the species by Valle (2014b). The species was recently reported from Colombia (Barón and Valle 2018). In our collections, Simuliomyces microsporus was often found attached to the thalli of this Paramoebidium (Fig. 27).

Paramoebidium hamatum Bench & MM White, 2012
Notes. Paramoebidium hamatum was described originally from USA in Chironomidae, Ameletidae and Baetidae (Ephemeroptera). In Bulgaria, it is associated with Baetidae nymphs (Baetis sp. B. rhodani and B. melanonyx). The species was recorded before in Europe (Spain, Busquets et al. 2018). Bulgarian specimens measured 180-300 × 12-25 μm, with the broader diameter at the proximal end, near the holdfast, thinner at the distal end (Fig. 29); cystospores observed, measuring about 10 × 4-4.5 μm. The species was identified by the curved portion at the basal one-eighth to one-third of the thallial length and by its holdfast characteristics (Bench and White 2012). Fig. 30 Specimens examined. Site 4: slide BUL-4-6.

Paramoebidium inflexum Léger & Duboscq, 1929
Notes. Species observed attached to the hindgut lining of Protonemura montana, measuring 280-340 × 40-60 μm in our collections. This species was described from France, associated with Nemoura variegata nymphs, in the stonefly family Nemouridae. The species has three different thallial morphologies Duboscq 1929b, Duboscq et al. 1948). Subsequent to the revision of the species by Duboscq et al. (1948), this endobiont was not reported again, until now, probably because of the thallus variability and, thus, relatively difficult identification. We only saw one of the thallial morphologies described for the species, this being the stouter and shorter thallus type. The other two morphological types show longer and incurved thalli, one type being wider than the other (Duboscq et al. 1948). Neither was observed in our collections.

Discussion
The new species, Glotzia balkanensis, was the most remarkable taxon recorded in this study. As noted above, it is morphologically close to G. centroptili (Gauthier ex Manier and Lichtw.), recorded from the western Mediterranean (Gauthier 1936, Busquets et al. 2018) and to G. distorta from Italy (Valle et al. 2014), both species from Centroptilum hosts. The new Bulgarian species is justified on the basis of spore and thallial characteristics and was found associated with a different host, Baetis melanonyx, in two distant sites in the Province of Sofia. Both sites were permanent non-tidal, smooth-flowing watercourses (EUNIS habitat type code C2.3, see Table 1). Moreover, both localities, where the new species was found, had in common a water pH of 7.2, the highest of all the watercourses we surveyed in Bulgaria, but different water temperatures (see Table  1). Another species of the genus Glotzia with similar characteristics is Glotzia stenospora MM White & Lichtw., from Norway. However this species has larger trichospores measuring 60-68 × 3-5 μm, with a higher length/width ratio (White and Lichtwardt 2004). Additionally, G. stenospora has larger zygospores than G. balkanensis (61-72 × 11-14 μm, according to White and Lichtwardt 2004). The other non-European species of Glotzia have smaller zygospores and most of them (except G. coloradense William & Lichtw.) also have smaller trichospores (Lichtwardt et al. 2001).
We gathered other Harpellid species from the guts of Baetidae nymphs, including Graminella bulbosa, Legeriomyces ramosus and Spartiella barbata and the Amoebidiales P. hamatum. The species Graminella bulbosa has been reported from western Europe, in France Gauthier 1937, Manier 1962a), Spain (Valle 2003(Valle , 2007, Portugal (Valle 2013a) and Italy (Valle et al. 2014), with this being the first report in eastern Europe. The characteristics of the Bulgarian specimens are interesting indeed, since trichospore morphology is intermediate between two species: G. bulbosa and G. microspora. We have assigned the specimens to G. bulbosa, the type species, which probably is variable enough to actually include both species, as suggested by Valle (2004). Trichospores of G. microspora measure 6-8.5 x 2-2.5 μm, according to Lichtwardt and Moss (1984), while trichospores of Bulgarian G. bulbosa measure 8-11 × 2 μm. According to Léger and Gauthier (1937) and later validated by Manier (1962aManier ( , 1970, trichospores of French G. bulbosa measure 9-17 × 2-3 μm. Bulgarian specimens, like many other specimens collected by one of the authors (LGV) in diverse European localities, overlap the measurements of both species. This question will be addressed further in an upcoming paper. Graminella is very peculiar amongst Harpellales for its vegetative propagules, originated at, or near, the basal cell. Bulgarian specimens of G. bulbosa also had these swollen basal cells, which can extrude their cellular contents to act as vegetative propagules within the same gut. Our specimens were associated with Baetis rhodani (Pictet) and B. alpinus, both common hosts previously reported with this fungus.
Legeriomyces ramosus is a common endosymbiont of Baetidae nymphs and has a broad distribution, especially in the Northern Hemisphere (Lichtwardt et al. 2001). The Bulgarian specimens had the characteristic attributes of the species, including trichospore and zygospore morphology and thallial features. Spartiella barbata is often seen together with L. ramosus, both sharing the same host, as observed in some of our collections, although S. barbata is not as prevalent as L. ramosus. The trichospores of S. barbata are somewhat similar to those of L. ramosus, but more ovoidal and have a single appendage initially folded showing a knob at the proximal end (Manier 1968, Valle 2007. The basal cell of S. barbata is also characteristic, with bulbous swellings around the zone of attachment to the host cuticle, a feature not present in L. ramosus (Manier 1968, Valle andSantamaria 2002). Spartiella barbata has a noticeable preference for calcareous watercourses, but in this study, even though calcareous rocks were present on the river substrate, as in collection site 10 (see Table 1), the water where S. barbata specimens were collected, had a slightly acidic pH (6.8 in site 7 and 6.1 in site 10).
Amongst the Amoebidiales inhabiting Ephemeropteran nymphs, we collected and recognised P. hamatum from Baetidae hosts. This species described from America (Bench and White 2012) was recorded before from Europe in Italy (Valle et al. 2014) and then Spain (Busquets et al. 2018). Léger and Duboscq (1929b), in a paper dealing with Paramoebidium, named P. arcuatum from Baetidae nymphs, without providing additional information on the species (no description or illustrations). Subsequently, Duboscq et al. (1948) provided more information on this species, including the identity of Baetidae hosts where it was observed, a description and some line drawings (Duboscq et al. 1948). The characteristics of this species, described from France earlier, are like those of P. hamatum and, consequently, very similar to the specimens we have collected within Baetidae hosts in Bulgaria. Probably, P. hamatum is the same species named P. arcuatum (regarded as nomen nudum by Lichtwardt et al. 2001), but further investigation is needed to resolve this question. There are some other Paramoebidium species that were named by French authors at the first half of the 20th century, but were not validated or lacked a complete description, making a clear, conclusive identification very difficult.
Other species of Paramoebidium were observed from different Ephemeropteran families, including Leptophlebiidae (with some specimens resembling P. hamatum), Caenidae and Heptageniidae, but were not identified for the lack of enough material or mature specimens for study. These mayfly nymphs did not have associated Harpellales.
The examined Bulgarian Simuliidae (Diptera) held various species of Harpellales and Amoebidiales. Larval black flies inhabit a wide range of flowing waters, from the smallest streams to the largest rivers (Nelder et al. 2006) and have been collected in nearly all surveyed watercourses with high enough flow velocity (not in lentic and slow moving watercourses). Amongst the trichomycetes they had in our collections, Genistellospora homothallica was the most prevalent in the hindgut, occasionally accompanied by Simuliomyces microsporus, a smaller species growing epithallically on the robust structure of G. homothallica. On the other hand, Harpella melusinae was the most common in the mid-gut, attached to the chitinous peritrophic matrix. Harpella melusinae is unbranched, placed within the family Harpellaceae and easily identifiable by the coiled trichospores in a series of long generative cells (Lichtwardt et al. 2001). Stipella vigilans is not as common as G. homothallica, but both species share the hindgut of Simuliidae. The former species can be identified by the mucilaginous substance embedding the basal cell and type I zygospores, according to zygospore types designated by Moss (1975).
In the hindgut, near the anal gills or attached to them, Paramoebidium curvum appears also commonly in Simuliidae, this being identifiable by its curved and robust sac-like thallus with a prominent and eccentric holdfast (Dang and Lichtwardt 1979). Another Paramoebidium observed within Simuliidae hindguts in Bulgaria was P. chattoni, with a longer, arched thallus. Both species of Paramoebidium are quite common in various Simuliidae species and have been reported from different countries (Lichtwardt et al. 2001, Valle 2014b. We also collected symbionts of Chironomidae larvae, but just two species: Stachylina nana from the mid-gut and Smittium dipterorum from the hindgut, both in Chironomus larvae. Smittium dipterorum was described from Costa Rica (Lichtwardt 1997) and then reported from the Dominican Republic and Mexico Cafaro 2010, Valle et al. 2011). It was also recorded from Europe, in Spain (Valle 2007) and it is probably a widespread species, like Stachylina nana, but more rare (less prevalent), especially in Europe. There are insufficient data to determine whether this is or is not a cosmopolitan species.
The genus Orphella (Orphellales) is associated with Plecopteran nymphs, a host also present in our collections, especially in pristine, high altitude or mountain watercourses, since stoneflies nymphs are very susceptible to water pollution and also water temperature, preferring cold and clean streams and rivers with running water and aquatic vegetation and often pebble stones (Berthélemy 1963 (White et al. 2018). The Bulgarian O. coronata had slightly smaller trichospores and zygospores than reported before, but differences are not significant; all other characters of accompanying cells and thallial structure matched the description of the species, taking into consideration all recorded geographic variability (White et al. 2018). Orphella catalaunica was associated with Leuctra hippopus nymphs and most of the observed thalli were immature, except for a couple producing trichospores. No zygospores were observed, but the straight cylindrical trichospores, accompanying cells in fertile cap and thallial characteristics of Bulgarian specimens, fit with those of the original description and later records (Santamaria and Girbal 1998, Valle 2004, White et al. 2018. Orphella helicospora was also associated with Leuctridae hosts, in the same species as O. catalaunica, sometimes sharing the same gut, which is common for these species. In the case of O. helicospora, both trichospores and zygospores were observed and were in accordance with previous descriptions of the species, which has been reported before from various western and central European countries (Lichtwardt et al. 2001). Two species of Paramoebidium were also identified within Plecopteran hosts. P. angulatum, described from France in Taeniopterygidae has been documented here from a different plecopteran family, the second record of the species. On the other hand, P. inflexum, is a rare species described from France that has not been documented until now since Dubosq et al. (1948), in both occasions from Nemouridae nymphs. This is an interesting addition and probably further studies and surveys will allow the possibility of gathering the three different thallial structures described for P. inflexum, since only one was observed in our Bulgarian collections.

Conclusions
This short survey provided 18 new taxa for both Bulgaria and the Balkan Peninsula, including one new species, Glotzia balkanensis, with sporic features that allow a clear differentiation from other described species of the genus and which also shares characteristics with the other two European species. The morphological characteristics of Graminella bulbosa, collected in Bulgaria, have intermediate spore and thallial characteristics between those of G. microspora and G. bulbosa, as previously reported by Valle (2004), making mandatory a revision of the European species of the genus. Some rare or poorly known taxa were recovered, including Paramoebidium inflexum and P. angulatum. Amongst the Orphellales, three species have been reported from Bulgaria (O. catalaunica, O. coronata, O helicospora). They seem to have a broad distribution in Europe, from the western Mediterranean to the Balkans. Some other taxa, reported here, have a cosmopolitan distribution, such as those associated with Simuliidae larvae, including Harpella melusinae, Genistellospora homothallica and Simuliomyces microsporus. The species associated with the dipteran Chironomidae, Stachylina nana have a wide geographic distribution and that is possibly also true for Smittium dipterorum; unfortunately, it seems to be less prevalent and there are few reports for this species described in Costa Rica. Our findings support previous observations, revealing that dipteran hosts generally bear endosymbiont species more widely distributed than other insect groups. This may be related to the possibility of adult-mediated transport of fungal diaspores Descals 1986, Labeyrie et al. 1996) and also the more restricted flight and dispersal capacity of stonefly and mayfly adults. Amongst Plecopteran hosts, there seems to be a more manifest species delimitation between the Old and New world, as in the case of Orphella (White et al. 2018) and also between the North and South Hemispheres. Similarly, the geographic distribution of Ephemeropteran endobionts may be important, but not so evident, as in Plecopteran-associated endobionts. However, these are general tendencies and much more effort has to be spent to improve our knowledge of this poorly-known group of cryptic organisms, regarding diversity, ecology, biology and biogeography. It is our aim to increase the knowledge of trichomycetes in this very interesting biogeographic region.