Taxonomy and Morphology of Aporomyces ( Laboulbeniales )

Thaxter's original circumscription of Aporomyces (Laboulbeniales) is emended in this study of the eight known species of the genus, three of them new: A. byrrhini, A. lutrochi, and A. physemi. The new species, as well as A. subulatus, A. szaboi, A. trinitatis, and A. unif/agel/atus (type), are dioecious and occur on beetles belonging to the Limnichidae (Coleoptera: Dryopoidea). The eighth species, A. perpusillus, appears to be monoecious and occurs on Staphylinidae (Coleoptera: Staphylinoidea). All taxa are described and illustrated with line drawings and/or photographs. Aspects ofthalloid structure and development are summarized. Aporomyces is removed from tribe Euphoriomyceteae (as subtribe Aporomycetinae) and elevated to the rank of tribe, Aporomyceteae.


INTRODUCTION
The genus Aporomyces was described by Thaxter (1931) to accommodate three new taxa, A. subulatus, A. trinitatis, and A. uniflagellatus, found on beetles then included in the family Byrrhidae (Coleoptera).The first two species, on hosts identified simply as species of Limnichus Latreille, were clearly dioecious; each perithecial individual was accompanied by a diminutive male consisting of three superposed cells terminated by a single antheridium.Antheridia were not found on any of the similar small individuals associated with the perithecium-bearing thalli of A. subulatus, on Byrrhinus punctatus Pic, so the dioecious nature of this fungus, although indicated, could not be firmly established.Banhegyi (1944) added a fourth species of Aporomyces, A. szaboi Banhegyi, found on Pelochares versicolor Waltl, also referred at the time to the Byrrhidae, in several localities in the vicinity of Lake Balaton, Hungary.This species bears some resemblance to A. uniflagellatus in the nature of both the female and male thalli.Tavares ( 1981 ), who examined several type collections of Laboulbeniales described by Spegazzini, determined that Ecteinomyces perpusillus Speg.(Spegazzini 191 7), found on a myrmecophilous species of Staphylinidae (Coleoptera), Rhopalopherus gestroi Bemhauer, belonged instead to Aporomyces.Aporomyces perpusillus (Speg.)Tavares differs from other members of the genus in its apparent monoecy; antheridia have not been observed, however.Like many monoecious Laboulbeniales, perithecium-bearing thalli of A. perpusillus often are associated in pairs; diminutive thalli resembling the male or presumed male of the other species of Aporomyces are unknown in A. perpusillus.
With the exception of the staphylinid host of Aporomyces perpusillus, the host genera given for the other four species of Aporomyces, i.e., Limnichus, Byrrhinus Motschulski, and Pelochares Mulsant & Rey, belong to the Limnichidae rather than the Byrrhidae as given by Thaxter ( 19 31) and B{mhegyi ( 1944 ).The placement of the limnichids with the byrrhids, based primarily on certain superficial resemblances of the adults of these insects, has a long history (Hinton 1939a, b).The Limnichidae began as a tribe of the Byrrhidae (Erichson 184 7) but was elevated to the rank offamily and placed near the Dryopidae by Thomson (1860).However, subsequent students usually recognized the group only as a tribe or subfamily of Byrrhidae (Dalla Torre 1911;Leng 1920: 192) until Hinton (1939a, b) carried out detailed studies of external and internal anatomy of members of these taxa and resurrected the family Limnichidae, which he removed from the superfamily Byrrhoidea and placed in the superfamily Dryopoidea near the family Dryopidae, in line with Thomson's earlier opinion.Recognition of the Limnichidae as a family ofDryopoidea now seems well established (Arnett 1962(Arnett , 1985;;Blackwelder 1944;Crowson 1955;Leech and Chandler 1956;Wooldridge 1986).
Limnichid beetles are very small (1-3 mm in length), oval or convex, brownish to blackish, sometimes metallic, and may be invested with dense, fine, golden or grayish hairs.They are mostly riparian and commonly occur in and around debris, among rocks, or on mudflats near the waterline.They may be taken in blacklight traps placed near suitable habitats.
The only other member of the Laboulbeniales described from Limnichidae is Cantharomyces bordei Picard (1912), found on Limnichus sericeus (Duft.) in Algeria.This species also has been reported from Italy on L. incanus Kiesenw.
During my many years of accumulating Laboulbeniales, I have obtained a number offorms representing several genera infesting Limnichidae.It is intended that this material be the subject of several separate studies.My purpose here is to present a taxonomic survey of Aporomyces and to give an account of the morphology and development of representative species.The work includes an emendation ofThaxter's original circumscription of the genus, a key to the species, and descriptions and illustrations of eight taxa, three of them new.

MATERIALS AND METHODS
The hosts bearing Aporomyces were originally received preserved in 50-70% ethyl alcohol, or in the case of those from T. E. Brooks, dry and layered on soft tissue paper in pill boxes.The dried insects were relaxed in 0.3% NaCl in H 2 0 and transferred to 70% ethyl alcohol for ease of manipulation.Collection data are given following the descriptions in the taxonomic section.
Using techniques given previously (Benjamin 1971(Benjamin :101, 1986:247):247), I mounted the fungi on slides in glycerine containing a trace of cotton blue or acid fuchsin.
Through the cooperation of the curator of the Farlow Herbarium, Dr. Donald H. Pfister, I received for study Thaxter's type and other collections of the species of Aporomyces he described.Dra.Irma J. Gamundi de Amos, Instituto de Botanica "Spegazzini," La Plata, Argentina, kindly arranged for me to receive and study Spegazzini's type collection of Ecteinomyces perpusillus, which had been on loan to Dr. Isabelle Tavares at the University of California, Berkeley.
Hosts were kindly identified by Dr. David P. Wooldridge, Department of Biology, The Pennsylvania State University, Ogontz Campus, Abington.
Direct observations and the preparation of drawings and photomicrographs were carried out with the aid of a Leitz Dialux microscope equipped with differential interference contrast optics.Kodak Technical Pan Film #2415, 4 in.x 5 in., was used.The camera was a WILD MPS 15/11 Semiphotomat with ASA settings of 80 or 125.Film was developed for 8 min in Kodak HC-110, Dilution D or F, at 20 C. Prints were made on Kodak Polyfiber FS paper.
Where applicable, terminology and abbreviations used to describe and discuss the fungal thallus are those of Tavares (1985:431-434).Some modifications in terminology were necessitated because of deviations in the development of the perithecium of Aporomyces.TAXONOMY APoROMYCES Thaxter. Mem. Amer. Acad. Arts 16:74. 1931, emended R. K. Benjamin.
Dioecious (or monoecious [?]).Male individual: Consisting of two or three superposed cells terminated by a single simple antheridium; sometimes consisting of a small number of superposed cells without an identifiable antheridium.Female individual: Receptacle at first consisting of three superposed cells, I, II, and III; subsequently consisting of a uniseriate row of few to many cells corresponding to the true basal cell (I), a variable number of cells derived from cell II, and cell III, which subtends a simple or branched, few-celled primary appendage.Simple or branched secondary appendages, if present, arising from cell III and/or cell-II derived cells of the receptacular axis above the perithecium.Perithecium developed from a single terminal or intercalary cell (the perithecial initial) of the receptacular axis derived from cell II; often appearing terminal at maturity; bearing near its base or on its outer, posterior surface the upper part of the receptacular axis and the associated appendages.The lower part of the ascigerous cavity of the mature perithecium bounded below by the adjacent cell of the receptacle and laterally by the lower part of the greatly enlarged perithecial initial.Primary stalk cell (VI) absorbed; secondary stalk cell (VII) persisting in some species and displaced upward posteriorly along with the perithecial basal cells and wall cells.The upper part of the perithecium, enclosed by the distal part of the perithecial initial, consisting of five basal cells and five vertical rows of inner and outer wall cells of two or three cells each.Walls of upper outer wall cells persistent; walls of basal cells and one or more cells of the lower tier of outer wall cells persistent or not.In some species, one upper outer wall cell giving rise to a unicellular prolongation the tip of which protrudes from the open tip of the perithecial initial, which functions as the ostiole.Ascospores 2-celled, elongate fusiform, typically dimorphic.
The number of receptacular cells of Aporomyces varies according to species.Thaxter ( 19 31:7 4) noted that the receptacle elongates secondarily by intercalary division.Although proof was not obtained in my study, I have followed Tavares (1985:60) in her assumption that the lower segment of most laboulbenialean ascospores initially divides and produces a primary receptacle consisting of a basal cell (I), a subbasal cell (II), and a terminal cell (III).Cell I forms the foot.Cell III subtends the primary appendage derived from the upper spore segment.
In some genera cell III may subdivide and contribute to the ultimate shape and size of the receptacle, including the formation of secondary appendages, or it may, as in members of the Stigmatomycetinae, undergo no change save for increase in size.Cell II may give rise directly to the perithecial initial, as in Stigmatomycetinae, or it too may divide or subdivide.The resulting receptacle may be bulky and three dimensional, due to both longitudinal and transverse divisions, or it may be uniseriate as in Aporomyces and several other genera (for examples see Tavares  1985:61).In such genera, including Aporomyces, one or more cell II-derived cells may give rise to perithecia or secondary appendages.Female individual.-Receptacle below the perithecium 27-150 (-195) ~m long, nearly hyaline or pale yellowish, consisting of the basal cell (I) and 4-19 (average 1 0) somewhat flattened or squarish cells derived from cell II, forming a nearly straight or slightly curved perithecial stalk 11-21(-24) ~m wide distally, tapering downward gradually to the elongate basal cell; the latter usually reddish brown, with nearly parallel outer margins, 13-25(-27) x 7-11 ~m; the foot broader, opaque, flat below; receptacle above the perithecium terminated by cell III, which is only slightly longer than broad, 6-10 x 4-9 ~m, and usually two cells derived from cell II.Primary appendage rarely persistent on mature individuals; simple, variable in length, 30-140 x 6-9 ~m; consisting of a variable number (6-9 observed) of elongate cells.Secondary appendages not observed.Perithecium reddish brown, slightly more than twice as long as broad, nearly symmetrical, 30-35 x 14-26 ~m, the lower margins parallel or slightly convex, abruptly tapered to the blunt apex; posterior margin bearing usually only one persistent receptacular cell which is more or less imbedded in the perithecial wall above the middle of the perithecium; walls of secondary stalk cell (VII), basal cells, and the three tiers of outer wall cells inconspicuous but persistent; walls of upper two tiers of inner wall cells persistent.Female ascospores 25-30 x 3 ~m; male ascospores 15-20 x 2~m.
Total length from base of foot to tip ofperithecium: 65-195(-245)  Thaxter's collections of Aporomyces uniflagellatus from the Cameroons, Philippine Islands, and Sumatra, comprise some 23 mature or nearly mature females, 9 immature females, and 15 males.The type collection from the Cameroons includes about half the mature females, 10 males, and all but one of the immature females.My specimens, which compare in all respects with the type, include over 90 mature or nearly mature females, 49 immature females, and 71 males.
Although the number of receptacular cells may vary greatly, the receptacle of A. uniflagellatus usually is long, rather slender, and relatively uniform in width above the narrow, elongate basal cell (Fig. 2, 3, 9).It becomes only moderately widened distally where it joins the perithecium.The mature, nearly symmetrical perithecium, with its long axis in line with that of the receptacle (Fig. 2, 3, 9), typically bears only one large cell on its upper outer surface (Fig. 5-8)-all that remains of the upper part of the young receptacle and the simple, elongate primary appendage (Fig. 1, 9).Aporomyces szaboi, which also occurs on Pelochares, is readily distinguished from A. uniflagellatus by its more inflated perithecium and the several-celled remnant of the upper part of the receptacle, which often bears the broken remains of secondary appendages and the branched primary appendage (Fig. 12; see also Banhegyi 1944, Pl. I, fig. 1, 3-4, and Pl. II, fig. 1, 3).
The presently known distribution of A. uniflagellatus, from Okinawa south ' t Dr. Wooldridge's determination of my hosts to Pelochares spp.suggests that the hosts of Thaxter's collections of A. uniflagellatus may have belonged to Pelochares rather than Limnichus.
I have seen no specimens of Aporomyces szaboi and have had to depend on Banhegyi's original description and illustrations for my interpretation of the species.Banhegyi presented photographs of six mature and one immature individuals, and I have constructed drawings based on two of these (Fig. 11,12).Aporomyces szaboi appears on the basis of its morphology to be more like A. uniflagellatus than any other species of the genus.It differs most noticeably from A. uniflagellatus in the shape of its perithecium and especially in the larger number of upper receptacular cells, which, along with the branched primary appendage and an occasional secondary appendage (Fig. 11 ), surmount the upper posterior surface of the perithecium (Fig. 12; see also Banhegyi 1944, Pl. I, fig. 1, and Pl. II, fig. 1, 3).Female individual.-Receptacle below the perithecium (60-)70-90 ~m long, consisting of the basal cell (I) and 8-10 squarish to more or less flattened cells derived from cell II, broadest distally, 24-31 ~m wide, rather abruptly narrowed downward, 6-10 ~m wide above the basal cell, which is dark yellowish brown, 10-21 x 6-10 ~m distally; the foot broad, flat, marginally opaque, often with a spinose lateral projection; the 3-4 cells above the basal cell dark yellowish brown to reddish brown, often nearly opaque, especially the septa; the remaining cells pale yellowish brown to nearly hyaline; receptacle above the perithecium terminated by cell III, which is only slightly longer than broad, 5-7(-10) x 4-6(-7) Jtm, and a single cell derived from cell II.Primary appendage rarely persistent on mature individuals, hyaline, simple, up to 120 Jtm long, 4-5 Jtm wide near the base, consisting of a small number (2-4 observed) of elongate cells.Secondary appendages few, arising from cell III or the subtending receptacular cell derived from cell II; simple or branched, straight or slightly curved, consisting of 1-4 elongate cells, the longest up to 100 Jtm, 3-5 Jtm wide.Perithecium uniformly reddish brown except for the hyaline tip; broadly rounded below, somewhat asymmetrical; posterior margin more strongly convex than the anterior margin, 40-60 x 30-45 Jtm; tapered to the blunt apex; bearing on the posterior margin the persistent upper receptacular cell, which is more or less imbedded in the perithecial wall at or slightly below the middle of the perithecium, and usually cell III and the remnants of the primary and secondary appendages; walls of secondary stalk cell (VII), basal cells, the three tiers of outer wall cells, and upper two tiers of inner wall cells persistent.Female ascospores 30-40 x 3 Jtm; male ascospores 25-30 x 2 Jtm.

APOROMYCES TRINITATIS
Total length from base offoot to tip ofperithecium: (105-)120-145 Jtm.Thaxter's four slide mounts of Aporomyces trinitatis from Trinidad include 17 mature or nearly mature females, 14 immature females, and 8 males.In all of the female specimens the contents of the immature and mature perithecia are more or less disorganized, a condition I suspect was true when Thaxter studied the material.This would account for his not being able to discern aspects of early stages ofperithecial development {Thaxter 1931:74).Thaxter attributed the host of A. trinitatis to Limnichus; however, this genus of Limnichidae does not occur in the New World (Wooldridge, pers.comm.).Like the hosts of my collections of A. trinitatis from North, Central, and South America, the host of Thaxter's collection doubtless belonged to Limnichoderus, which resembles the Old World Limnichus (Wooldridge 1981).The range of the collections of A. trinitatis cited above suggest that the species is widely distributed on Limnichoderus in the New World.Mature female with associated male (out of focus).-17,18.Two nearly mature perithecia shown in optical section.The positions of the three tiers of inner (p) and outer wall cells (w' , w 2 , w 3 ) , basal cells My specimens of Aporomyces trinitatis include nearly 100 mature or nearly mature females, about 160 immature females, and some 30 males.Not all ofthe material is in the best condition, but many specimens, both immature and mature, are well-preserved and give a good over-all picture of thalloid and perithecial development 17,18,(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79) as will be described in this paper.
The reddish-brown pigmentation of the lower three to four cells of the lower receptacle of Aporomyces trinitatis is perhaps the one characteristic that most readily distinguishes the species from A. uniflagellatus and A. physemi, the only other taxa with which it might be confused.The basal cell of the receptacle may or may not be deeply pigmented.Like A. physemi, the upper cells of the receptacle of A. trinitatis are relatively broad compared to the proximal cells (cf.Fig. 16, 24).The basally inflated, asymmetric, reddish-brown perithecia are similar in the two species, but that of A. trinitatis lacks the narrow, elongate, hyaline termination and slender cellular upgrowth of one terminal outer wall cell of A. physemi (Fig. 24  -2!.Immature female with associated male (mostly out of focus) at base.The receptacle consists of a basal cell (I), a series of superposed cells derived from cell II, and cell III, which subtends the primary appendage (pa).-22.Immature female with associated male (out of cellular perithecial stalk 13-22 p,m wide distally, which tapers downward gradually and is somewhat abruptly narrowed immediately below its juncture with the basal cell; basal cell hyaline, with nearly parallel margins, 14-21 x 6-8 p,m; the foot broader, black, more or less opaque, flat below; receptacle above the perithecium terminated by cell III, which is broader than long, 4 x 5-7 p,m at maturity, and usually two superposed, somewhat flattened cells derived from cell II.Primary appendage rarely persistent on mature individuals; straight or curved, 20-40 p,m long, 3-5 p,m wide; consisting of 2-3 elongate cells.Secondary appendages arising from cell III and the subtending receptacular cell; simple, usually strongly curved; the longest up to 55 p,m long, 3-5 p,m wide; consisting of 1-3 elongate cells.Perithecium dark reddish brown except for the hyaline, somewhat elongate, narrow tip; broadest below, asymmetrical, 34-50 x 19-30 p,m; anterior margin only slightly convex; posterior margin strongly convex, bearing the persistent upper receptacular cells and appendages near the middle of the perithecium; walls of secondary stalk cell (VII), basal cells, the two tiers of outer and inner wall cells persistent; one posterior, upper, outer wall cell giving rise to an elongate, slender, unicellular upgrowth, 10-14 p,m long, which may project slightly beyond the terminal opening.Female ascospores about 25 x 2.5 p,m; male ascospores about 20 x 2 p,m.
Holotype.-U.S.A.The above description of Aporomyces physemi is based on 25 mature (Fig. 24, 25, 32) or nearly mature females and 18 males (Fig. 33) in the cited collections.Seventeen immature females provided material sufficient to study several pertinent stages of development of the thallus and perithecium (Fig. [21][22][23][26][27][28][29][30][31].Details of these observations will be given later. Aporomyces physemi resembles A. trinitatis more closely than any of the other species of the genus but is readily distinguished by its smaller size and differences in perithecial structure, i.e., the attenuate tip and the cellular upgrowth from one upper outer wall cell (compare Fig. 24 with Fig. 16-18).Immature female showing intercalary origin of the perithecium, which is at an early stage of development.The female organ consists of the carpogenic cell (cp) , trichophoric cell (tc), and trichogyne (tr).Arrows indicate dividing receptacular cells.-37.Female and its associated male; the perithecium is at an intermediate stage of development.-38.Mature female with male at base (see Fig. 35).-39.Cluster of small male and large female ascospores.Note extreme spore dimorphism.-40.Upper end of receptacle showing cell III and the primary appendage (pa).Apices of secondary appendages project upward from the lower left.brown in the upper two thirds, except the hyaline tip; broadest below, symmetrical, 59-81 x 43-58 Mm, tapered abruptly to the blunt, barely rounded apex; walls of secondary stalk cell (VII) and basal cells not clearly defined at maturity; walls of the three tiers of outer wall cells and the upper two tiers of inner wall cells persistent.Female ascospores 38-43 x 5 Mm; male ascospores 17-21 x 3 Mm.
Total length from base of foot to tip ofperithecium: 180-225 Mm.
Ten mature females, 14 immature females, and 13 males of Aporomyces lutrochi were found on the upper surface of four of 10 individuals ofthe host, a relatively large, unidentified species of Lutrochus measuring between 2 and 3 mm in length.
The elongate, multicellular receptacle of A. lutrochi is nearly straight before perithecial development begins.Unlike other species of the genus, the perithecium of A. lutrochi always arises from a receptacular cell remote from the upper end of the uniseriate axis (Fig. 36), which is terminated by cell III and the primary appendage (Fig. 40).As the perithecium develops and matures, the upper part of the receptacle is deflected laterally so that it becomes nearly perpendicular to or is at an acute angle to the lower part (Fig. 35,37,38).Secondary appendages arise from the upper, never the lower, surface of a variable number of cells of the upper receptacle (Fig. 35,37,38).As in A. szaboi (Fig. 11,12), the apparent appendage of A. lutrochi consists largely of receptacular cells along with the variably persistent primary and secondary appendages.
The relatively tiny male ascospore always is closely associated with the base of a female ascospore (Fig. 39), and all of the 13 males recovered were still firmly attached to the foot of mature or nearly mature females (Fig. 35, 37, 38).appendages not observed.Perithecium relatively slender, elongate, its axis divergent to nearly 45° from that of the receptacle; broadest near the base, 25-30 ~m wide; gradually tapered, 85-100 ~m long; with an elongate, attenuate termination extending 33-43 ~m beyond the tips of the upper, outer wall cells; secondary stalk cell (VII) persistent, subtending cell III; only the walls of the upper one or two tiers of outer and inner wall cells persistent; one anterior upper, outer wall cell giving rise to an elongate, slender, unicellular upgrowth, 50-65 ~m long, which projects up to 18 ~m beyond the apical opening.Ascospores not precisely measurable within the perithecium; the longest ca.40-45 x 3 ~m.
Total length from base of foot to tip ofperithecium: 120-145 ~m.Thaxter's type material is in excellent condition, and, if one may judge by comparing them with his drawings, the specimens appear to have remained unchanged during the nearly 60 years since Thaxter prepared his illustrations and description.The material consists of 25 mature females (Fig. 59, 60), 1 nearly mature female, 13 immature females in various stages of development (Fig. 41-46, 54-58), and 9 males (Fig. 47-48), none possessing an identifiable, clearly differentiated antheridium.
Aporomyces subulatus and A. byrrhini are morphologically very different from the species of Aporomyces discussed to this point.In both, the perithecium with its greatly prolonged beak terminates that part of the short receptacle derived from cell II of the young receptacle.The secondary stalk cell (VII) of the perithecium persists in the lower posterior part of the ascigerous cavity where it subtends cell III.The latter cell never is subtended by one or more receptacular cells derived from cell II as in the other species on Limnichidae.
The perithecial apex of Aporomyces physemi bears some resemblance to that of A. subulatus and A. byrrhini in extending well beyond the tips of the upper outer wall cells, although to a lesser degree.Like these species, one upper outer wall cell of A. physemi forms a cellular prolongation that projects through the ostiole (Fig. 24, 32).Benjamin, Mas  Female individual.-Hyaline.Receptacle below the perithecium 52-60 ttm long, straight; consisting of the basal cell (I) and two superposed cells derived from cell II; 18-20 ttm wide immediately below the perithecium; tapered gradually downward to the base, which is somewhat constricted, ca. 9 ttm wide immediately above the blackish, nearly opaque foot; the latter with a conspicuous posterior spinose projection; basal cell (I) 25-35 ttm long, 15-20 ttm wide distally; the succeeding two cells subequal, cylindrical, 10-15 ttm long, 16-19 ttm wide; receptacle above the perithecium consisting only of cell III, which is elongate, straight, 17-26 x 5-7 ttm.Primary appendage subtended by cell III, simple, in excess of 150 ttm long (observed examples with tip missing); composed of several elongate, slender cells, ca. 5 ttm wide near the base.Secondary appendages not observed.Perithecium slender, elongate, its axis in line with that of the receptacle; broadest near the base, 18-19 ttm wide, straight; gradually tapered to the tip, 85-90 ttm long; with an elongate, attenuate termination extending ca. 25 ttm beyond the tips of the upper, outer wall cells; secondary stalk cell (VII) small, persistent, subtending cell III; only the walls of the upper one or two tiers of outer and inner wall cells persistent; one distal outer wall cell giving rise to an elongate, slender, unicellular upgrowth which reaches the apical opening.Ascospores not precisely measurable within the perithecium; the longest ca.35-40 x 2 ttm.

Aporomyces byrrhini
Total length from base of foot to tip of perithecium: 145-150 ttm.
I have described Aporomyces byrrhini on the basis of only five specimens: one mature with numerous ascospores in the perithecium (Fig. 61); four in several stages of perithecial immaturity.The receptacles of three of the immature specimens are mature in that their dimensions are comparable to those of the mature individual.Additional collections of this taxon are needed to establish better its dimensions.
Aporomyces byrrhini resembles A. subulatus but differs markedly in overall habit, especially in the shape of the receptacle and cell III.The attenuated perithecial termination in A. subulatus is more abruptly narrowed near its base than it is in A. byrrhini (compare Fig. 60 and 61).
The host genus, Byrrhinus, is one of only two genera ofLimnichidae known to occur in both the Old World and New World (Wooldridge 1987), the other being Paralimnichus Deleve (Wooldridge 1983).Presumably monoecious, but antheridia not observed.Hyaline.Receptacle below the perithecium 18-20 ~-tm long; consisting of the basal cell (I) and two superposed, somewhat flattened, externally rounded cells derived from cell II; broadest below the perithecium, 10-11 ~-tm wide; abruptly tapered downward to the blackened foot; basal cell longer than wide, about as long as the combined lengths of the two receptacular cells above; receptacle above the perithecium consisting of two superposed cells, a single cell derived from cell II, and cell III, the latter about twice as long as broad, 6-8 x 3-4 ~-tm.Primary appendage up to 25 ~-tm long, 2 ~-tm wide; consisting of a small number (?2-3) of elongate cells, usually broken near the base of a proximal cell and renewed by proliferation.Secondary appendages not observed.Perithecium stout, elongate, its long axis strongly divergent; broadest near the base, 12-13 ~-tm wide; nearly symmetrical, about 30 ~-tm long, its lower margins convex, tapered distally and forming an attenuated termination extending 8-10 ~-tm beyond the tips of the upper, outer wall cells; only the walls of the upper two or three tiers of outer and inner wall cells persistent; one anterior upper, outer wall cell giving rise to an elongate, slightly curved, acuminate, unicellular upgrowth 13-15 ~-tm long, which projects slightly beyond the apical opening.Ascospores not precisely measurable.

+of female individual depicted in
Total length from base of foot to tip of perithecium 35-40 ~-tm.
Specimens examined.-ARGENTINA.Buenos Aires (Escuela Regional de Santa Catalina), Florencio Varela, andLa Plata, 1913-1916, on  Spegazzini's specimens are mounted in diaphane.The high refractive index of this substance made it difficult to resolve details of thallus structure except for thickened cell walls (65)(66).Aspects of cellular structure in immature perithecia could not be determined.
Although Aporomyces perpusillus parasitizes a host taxonomically far removed from those bearing all other known species of Aporomyces, Tavares's transfer of Spegazzini's taxon to this genus appears correct.Paired perithecial thalli of A. perpusillus indicate that the species may be monoecious although no indication of an antheridium on any of the thalli studied, immature or mature, was found.In the 3-celled receptacle and cellular extension of one upper, outer wall cell, the mature thallus of A. perpusillus (Fig. 51-53) bears closer resemblance to the female thalli of Aporomyces spp. on Byrrhinus (Fig. 60-61) than to those on other genera of Limnichidae.
There is a discrepancy between the dimensions given for A. perpusillus by Spegazzini and those obtained by me from an examination of his specimens.Spegazzini's figures for the total height of the thallus (60-65 ~m) and the size of the perithecium (45-48 x 17-18 ~m) are considerably larger than mine.
I have in my collection one mature and two immature specimens (RKB 1965(RKB , 1966) ) in rather poor condition of an Aporomyces that is nearly identical to A. perpusillus in its general morphology, although it is somewhat larger.The mature individual has a total length of 78 ~m and a perithecium measuring 48 ~m long and 25 ~m wide.These specimens were found on the club of the left antenna of an unidentified beetle belonging to the Histeridae (Coleoptera: Histeroidea) collected by Hugh B. Leech (California Academy of Sciences, Golden Gate Park, San Francisco) near "Potrero," Mexico, 17 Dec 1948.The exact locality of "Potrero" is unknown, for the state in which this site is located was not given on the field-collection label.Further collections of this fungus and its host are to be desired, for the histerid beetle may, like the staphylinid host of A. perpusillus, be myrmecophilous.It is possible that A. perpusillus can infect hosts of at least two distinct families of beetles that share the same restricted habitat.Such a relationship of a species of Laboulbeniales, Laboulbenia ecitonis Blum (=L.adinventa Blum) with staphylinid and histerid hosts is known (Blum 1924;Rossi 1980).

Ascospores
The ascospores of Aporomyces species are hyaline, elongate, more or less fusiform, and two-celled.Except for A. trinitatis (Fig. 19) and A. lutrochi (Fig. 39) measurements were made of ascospores inside perithecia.This was necessitated by a desire not to break specimens oflimited material for the purpose ofliberating spores.The cross wall of the ascospore is nearly median in the female ascospore of A. lutrochi (Fig. 39).In the male spore of this species (Fig. 39) and in both female and male spores of A. unif/agellatus (Fig. 6), A. trinitatis (Fig. 19), and A. physemi the longest cell, which is uppermost in the perithecium prior to discharge, is ca.60% of the total length of the spore.Banhegyi (1944) did not give the proportions of the two cells of the ascospore in A. szaboi and I could not determine this statistic for A. subulatus, A. byrrhini, and A. perpusillus.
The ascospores of A. unif/agellatus, A. szaboi, A. trinitatis, and A. lutrochi are dimorphic.The spore giving rise to female individuals always is larger than that giving rise to males and ranges from about 20% greater in length in A. physemi and A. trinitatis (Fig. 17-19), 30% in A. szaboi, 35% in A. uniflagellatus (Fig. 6), to slightly over 50% in A. lutrochi (Fig. 39).In the last species, the relatively tiny male ascospore appears to be embedded in the gelatinous envelope surrounding the female spore (Fig. 39).Ascospore dimorphism, if it exists, could not be determined for A. subulatus, A. byrrhini, and A. perpusillus.

Thallus of Aporomyces perpusillus
Spegazzini's specimens of Aporomyces perpusillus included a number of pairs of perithecium-bearing individuals in several stages of development.There was no evidence of males like those of other species of the genus, and nothing resembling an antheridium was observed on any thallus.The receptacle invariably consisted of three cells subtending the perithecium which, in tum, subtended the relatively large cell III bearing a simple, several-celled appendage (usually broken) 66).There was a hint of structural organization (Fig. 65) inside the perithecium of many of the immature individuals, but details of development could not be inferred.
Because of their thickened walls, the upper outer and inner wall cells of A. perpusillus could be observed without difficulty in mature individuals, as well as the single, elongate, cellular projection of one of the outer wall cells (Fig. 51-53).Ascospores and gross aspects of the centrum could be seen in vague outline (Fig. 66).
An identifiable antheridium was not found on any of the presumed males of A. subulatus (Fig. 4 7,48,(54)(55)(56) or A. byrrhini (Fig. 61).The upper part of the presumptive male thallus of these species, which corresponds to the primary appendage of the female individual, consists of a small number of elongate cells; this is simple in A. byrrhini but is occasionally once-branched in A. subulatus.The upper part of this appendage was missing in the presumably mature individuals observed, but the remnant of the distal cell showed no evidence of differentiation into an antheridium.

Female individual. -Receptacle:
The foot of the receptacle begins differentiating prior to any division of the basal cell of the young individual derived from the ascospore (Fig. 20).The next-youngest individuals found among all the material studied were represented by germlings of A. physemi (Fig. 26) and A. subulatus (Fig. 41) showing an immature receptacle already composed of several superposed cells: the foot-forming basal cell (I); an upper cell (Ill) subtending the primary appendage (pa); and several intercalary cells resulting from the multiplication of cell II.Elongation of the receptacle varied according to the species and took place by intercalary division of cell 11-derived cells (arrows: Fig. 27, 36).
Secondary appendages: Secondary appendages were not found in Aporomyces byrrhini, A. perpusillus, A. subulatus, and A. uniflagellatus, but were observed in the other species.Banhegyi (1944, Pl. II, fig. 1) illustrated a mature specimen of A. szaboi with secondary appendages arising from all but the lowermost cell of the receptacular axis surmounting the perithecium, but in his photographs of other mature specimens (Banhegyi 1944, Pl. I, fig. 3, 4, Pl. II, fig. 3) secondary appendages were absent from all but the uppermost cells of this part of the receptacle.Secondary appendages (sa) also arose not only from cell III but also from one or more cell 11-derived cells of the axis distal to the perithecium in A. trinitatis, A. physemi, and A. lutrochi.These appendages were simple or sparingly branched, composed of only one to three or four cells, and were straight, flexuous, or strongly curved in A. trinitatis (Fig. 13-15;Thaxter 1931, Pl. 14, fig. 4-8) and A. physemi (Fig. 22-25,28,29,31, 32).They were somewhatlongerandmore highly branched in A. lutrochi where single appendages arose from the upper surface of four to seven cells of the laterally projecting axis (Fig. 35,37,38).
As cell d enlarges, its divergent or upwardly growing, rounded or acute apex may become more or less elongate before the first division of its protoplast takes place (Fig. 28,43,65,68).The cell increases in size as perithecial development proceeds and its outer wall eventually encloses the true stalk cells, basal cells, and wall cells of the perithecium as they develop from the original protoplast, which often was more or less withdrawn from the cell wall (Fig. 28, 43, 67, 68), undoubtedly due to inadequate fixation of material studied.
Division of the protoplast of cell d gives rise to the primordial cell of the perithecium (h) and the primordial cell of the procarp (i) (Fig. 69).Celli divides and forms the carpogonial cell (cp) below and the trichogyne initial (e) above (Fig. 44, 70).Cell h divides by the formation of a diagonal cross wall and forms a lower cell k and an upper cell j (Fig. 71).Cell k cuts off two anterolateral cells (basal cells m and m'), one on each side, and becomes the primary stalk cell (VI) (Fig. 72).Cellj also cuts off two anterolateral cells (basal cells nand n'), one on each side, and becomes the secondary stalk cell (VII) (Fig. 29,72,73).Cell m delimits a small cell, the auxiliary basal cell (mac), that lies between cells m and m' (Fig. 44, 73).The relationship of the five basal cells to one another and to cells VI and VII in a mature perithecium is shown in posterior and anterior views, respectively, in Figure 77 and 78 where septal pores between VII and cells nand n' and between cells m and mac are indicated (upper arrowheads).It is possible in some mature perithecia to detect the remnants of the septal pores between the lumen of what was once cell VI, which has enlarged and formed the greater part of the venter, and cells m and m' (Fig. 78, lower arrowheads).
Cell e, the trichogyne initial, grows upward, penetrates the wall at the tip of the perithecial initial (Fig. 72, 73) and becomes the trichophoric cell (tc) after giving rise to the trichogyne (tr) above (Fig. 1 , 36, 45, 46, 57, 74).The latter may consist of several elongate cells and form one to several branches.The trichogyne of immature individuals of A. uniflagellatus was seen to bend sharply near the tip of the young perithecium and extend downward in the direction of the foot.In the specimen shown in Figure 1, the trichogyne doubtless was displaced upward when the specimen was mounted (see Thaxter 1931, Pl. 14, fig. 15).
Each of the five basal cells (m, m', mac, n, m') surrounding the lower end of the carpogenic cell (cp) (Fig. 44, 73) cuts off the first inner and outer wall cells (o) (Fig. 74).Development of the perithecium involves the upward growth of the five inner and outer rows of wall cells around the maturing female apparatus (Fig. 13-15, 23, 31, 45, 46, 54-56, 62-64, 75, 76).The trichogyne persists to at least the two-outer-wall-cell stage in A. subulatus (Fig. 45,46).The degree of persistence of this structure in the other species could not be determined.
Development of the centrum could not be studied precisely, but a possible reformed trichophoric cell (tc') (combination of the trichophoric cell and carpogenic cell [see Tavares 1985]) was observed in A. physemi (Fig. 31) and A. trinitatis (Fig. 14,75).As formation of the perithecial walls and centrum proceeds inside the outer wall of the expanding perithecial initial (Fig. 76), the region occupied by the original cell VI enlarges and eventually forms the major portion of the perithecial venter enclosing the ascogenous cells and developing and maturing asci (17)(18)24,25,32,35,38,60,61).Cell VII and the basal and wall cells are displaced upward.All but the lowermost inner wall cells may persist in their entirety in :A.trinitatis (Fig. 17-18), :A.physemi (Fig. 32), :A.uniflagellatus (Fig. 5-8), and possibly :A.lutrochi, whereas only cell VII and the upper inner and outer wall cells appear to persist in :A.byrrhini and :A.subulatus.Only the upper two or three tiers of outer and inner wall cells appear to persist in :A.perpusillus (Fig. 51-53).
One upper outer wall cell of the perithecia of:Aporomyces physemi, :A.subulatus, :A.byrrhini, and :A.perpusillus forms a slender cellular extension that grows upward through the ruptured tip of the perithecial initial, the greatly enlarged wall of which now encloses the true walls ofthe perithecium (Fig. 24,32,(51)(52)(53)59,60).This apical opening, which sometimes has a jagged or uneven margin, functions as the ostiole in these species where the true ostiole formed by the upper true wall cells lies some distance below.In the other species the true ostiole is emergent or nearly so, e.g., :A.uniflagellatus (Fig. 5-8), :A.trinitatis (Fig. 16-18, 77-79), :A.lutrochi (Fig. 35-38), and possibly :A.szaboi (Fig. 12).An early stage of development of the cellular upgrowth in :A.subulatus is shown in Figure 58.The fully developed upgrowth in this species after its separation from the mother cell by a cross wall is shown in Figures 59 and 60.
There are only two tiers of outer wall cells in the mature perithecium of :A.physemi; cells of the upper tier are nearly twice as long as those of the lower tier (Fig. 32).There are three tiers of outer wall cells in :A.uniflagellatus (Fig. 5-8), :A.trinitatis and A. lutrochi (Fig. 35,38); cells of the upper tier are about equal in length to those of the subterminal tier.There may be only two tiers in A. byrrhini, A. subulatus (Fig. 59, 60), and A. perpusillus (Fig. 51-53), but this could not be firmly established due to the ephemeral nature of the basal cells and perhaps the cells above.

DISCUSSION
Dioecious species of Laboulbeniales having dimorphic ascospores first were reported in Dioicomyces Thaxter (1908:293, Pl. XLII, fig. 24, 25, 29) where the female spore may be considerably larger than the male (see also Benjamin 1970, fig.3D).Thaxter did not comment on this phenomenon in connection with other dioecious taxa including the species of Aporomyces he described (Thaxter 1931), but Banhegyi (1944:51) noted a marked difference in the size of the ascospores of A. szaboi.As shown in this study, spore dimorphism is a feature of other species of the genus as well, reaching its greatest extreme in A. lutrochi.Except for Dioicomyces, I have not seen dimorphic ascospores in any other of the dioecious Laboulbeniales I have studied including Laboulbeniaformicarum Thaxter, (Benjamin and Shanor 1950), Rhizopodomyces Thaxter (Benjamin 1979), Triceromyces Majewski p. p. (Benjamin 1986), and others in my collection for which I have unpublished observations.Ascosporic dimorphism is perhaps a derived condition in Aporomyces and Dioicomyces, but when one considers other aspects of thalloid morphology it probably is a feature having little or no bearing on a close phylogenetic relationship of these genera.
In a few genera of Ceratomycetaceae an extra stalk cell or basal cell may be formed (see discussion in Tavares, 1985:67-68), but the number of complete rows of wall cells has been regarded as fixed at four in all members of the order up to now.
In two genera, Hydrophilomyces Thaxter (1908) and Kyphomyces Tavares (1985), an accessory cell, similar to that in Aporomyces, is formed along with the three basal cells that give rise to the four vertical rows of inner and outer wall cells.This accessory cell, however, grows upward and forms only an elongate, uninucleate cell separating the two anterior cells ofthe lowermost tier of outer wall cells and often the lower ends of the neighboring cells of the subbasal tier (Tavares 1985;Benjamin, unpubl. obs.).The accessory cell in Hydrophilomyces and Kyphomyces does not function as an extra basal cell giving rise to an additional row of inner and outer wall cells as in Aporomyces.
The trichogyne of Aporomyces emerges through the tip of the perithecial initial during an early stage of perithecial development.The ruptured tip later serves as the ostiole in several species ofthe genus, such as A. subulatus for example, where the true ostiole formed by the distal perithecial wall cells does not reach the level of this opening as it does in other species, such as A. trinitatis.
In Aporomyces there is no trichogynic scar, which represents the persistent base ofthe degenerated trichogyne, on the upper, outer wall below the mature perithecial apex.Such a trichogynic remnant is found on the surface of the perithecium in many genera of Laboulbeniales in which the trichogyne is deflected laterally from its initial, more or less terminal position as the perithecium develops and forms an ostiole some distance removed from the original trichogynic orifice, as in Synandromyces (Benjamin 1984) andTriceromyces (Benjamin 1986).Thaxter (1931:74) believed that the prolonged tip of the perithecium of Aporomyces, as in A. subulatus, represented the base of the trichogyne.However, young specimens of this species clearly show that the juncture between the true base of the trichogyne and the upper end of the trichophoric cell may lie some distance below the open tip, which shows no evidence of having been continuous with the wall of the basal cell of the trichogyne.
The venter of the perithecium of Aporomyces was thought by Thaxter (1931: 74) to derive from the absorption not only of the walls of the basal cells of the perithecium but also the walls of one or more of the adjacent receptacular cells.As shown in this study, the basal cells do disappear in A. subulatus, A. byrrhini, A. perpusillus, and possibly A. lutrochi, but they persist in other species, including A. uniflagellatus, A. trinitatis, and A. physemi.The greater part of the ascigerous cavity appears to develop from enlargement of the portion of the perithecial initial occupied originally by cell VI (the primary stalk cell), at least the upper part of which breaks down.The developing centrum intrudes into the space formerly occupied by cell VI.I found no evidence that any cell of the receptacle other than the lower part of the perithecial initial contributed to the formation of the perithecial venter.
In the upgrowth of the perithecial wall cells around the carpogonium, Aporomyces clearly is a member of suborder Laboulbeniineae according to the classi- fication of Tavares (1985).Also, the formation of simple antheridia (phialides) places the genus in her subfamily Laboulbenioideae.However, perithecial development in Aporomyces is unique among all other genera in the suborder, as far as is known, in having five complete rows of inner and outer wall cells derived from five basal cells.Thaxter (1931:74) thought Aporomyces bore little resemblance to other dioecious genera ofLaboulbeniales and stated that it seemed unrelated to any ofthem.Tavares (1985) agreed with Thaxter but suggested that, because of the apparent disappearance of the basal cells and presumably the secondary stalk cell (VII) (which actually persists in all but one species [A.perpusillus]) the genus might somehow be related to Euphoriomyces Thaxter (1931) and certain other genera she allied with Euphoriomyces (Carpophoromyces Thaxter [1931], Meionomyces Thaxter [1931]), Phaulomyces Thaxter [1931], and Siemaszkoa Tavares & Majewski [ 197 6]) in a subtribe Euphoriomycetinae of her tribe Euphoriomyceteae.However, she separated Aporomyces into her monotypic subtribe Aporomycetinae, within this tribe.In view of differences in perithecial structure (i.e., five vertical rows of inner and outer wall cells in Aporomyces [Aporomycetinae] vs. four rows in members of Euphoriomycetinae), I here propose that Aporomyces be removed from the Euphoriomyceteae and placed in a separate tribe Aporomyceteae (Tavares) Benjamin, stat. nov. (basionym: Aporomycetinae Tavares, Mycol. Mem., No. 9:98, 1985).