Redescription of adults, nymphs and taxonomic notes on the Southern Brazilian mayfly Ulmeritus saopaulensis (Traver, 1946) (Ephemeroptera: Leptophlebiidae)

Traver, 1956 currently includes three species of Neotropical Leptophlebiidae (Ephemeroptera) distributed in southern South America in the Pampean and Atlantic Forest dominions: U. carbonelli (Uruguay), U. balteatus (Brazil and Uruguay) and U. saopaulensis (Brazil). Ulmeritus saopaulensis is a poorly known endemic species from Brazil. Based on material from a single locality in Minas Gerais, we complement the knowledge on this species with a redescription of adults and nymphs and describe the eggs for the first time. The confusing nomenclatural history and the correct spelling of the specific name saopaulensis is discussed in light of International Code of Zoological Nomenclature. This paper points out that in despite of recent advances on the knowledge of this genus a full taxonomic review and phylogenetic analyses are pending to solve species delimitation and evolutionary relationships.

Among the three species of Ulmeritus, little is known about U. saopaulensis. Since the original description, in which only the hind wing and genitalia were illustrated (Figs. 3 to 6 of Traver, 1946), no additional data or even illustrations have been provided for the adults. Importantly, the description was based on a single male and a single female imago, from the states of São Paulo and Minas Gerais, respectively. Later, based on three specimens reared to the adult stage, Da-Silva and Pereira (1992) described the ultimate nymphal instar of this species for the first time, and illustrated it. Notes with biological data were also provided, including the unusual occurrence of the nymphs in lentic habitats.
In the present study, based on extensive material from a single locality in Minas Gerais, we complement the knowledge of this poorly known species by presenting the description of the eggs and subimagos for the first time, and a full taxonomic treatment including synonymy, diagnoses, redescriptions of the imagos and nymphs, as well as a map Redescription of adults, nymphs and taxonomic notes on the Southern Brazilian mayfly Ulmeritus saopaulensis (Traver, 1946) (Brazil). Ulmeritus saopaulensis is a poorly known endemic species from Brazil. Based on material from a single locality in Minas Gerais, we complement the knowledge on this species with a redescription of adults and nymphs and describe the eggs for the first time. The confusing nomenclatural history and the correct spelling of the specific name saopaulensis is discussed in light of International Code of Zoological Nomenclature. This paper points out that in despite of recent advances on the knowledge of this genus a full taxonomic review and phylogenetic analyses are pending to solve species delimitation and evolutionary relationships.
including the distribution of the three species of Ulmeritus. Finally, we also comment on the habitat and life cycle.

Material and methods
Specimens of U. saopaulensis were collected in Paula Cândido municipality, Minas Gerais State, Brazil. The nymphs were captured using a regular aquatic net. Subimagos and imagos were captured using a light sheet trap, while some of them were reared in the laboratory from nymphs. All material was preserved in ethanol 80-100%. Mouthparts and legs of nymphs, as well as male genitalia, were mounted on permanent slides with Canada Balsam or Euparal. Fore and hind wings were dry mounted on slides. General morphological terminology was based on Domínguez et al. (2006) except for the thorax which follows Kluge (2004) and eggs that follows Koss and Edmunds (1974). Images from scanning electron microscope (SEM) were obtained from dissected structures and eggs, transferred from ethanol, and subsequently treated-to be cleaned and dehydrated during 15 minutes to 24 hours-using three distinct chemical solutions: (1) ethanol series (80%-absolute), (2) 100% acetone and (3)  The coordinates of the map of the collecting sites were standardized following the toponyms list of IBGE (2011). The map was elaborated in the QGIS (2022).
Abdomen (Fig. 1E). Terga orange brown, except for a dark brown macula on posterolateral corner of terga I to VII. Sterna orange brown. Caudal filaments orange brown, paler toward apex and region between articulations dark brown.
Genitalia (Figs. 2I, J). Orange brown, styliger plate with area between base of forceps tinged with brown. Forceps orange brown, paler at base. Penis lobe light brown. Ventral projection of penis lobe long and laterally positioned (Fig. 2J), gonopore located at apex of penis lobe.
Male subimago (Fig. 1C). Similar to imago, except for the following characteristics: membrane of fore and hind wings gray, longitudinal veins yellowish white; mesoscutum with mediolongitudinal suture, medioparapsidal suture, area between posterior scutal protuberance, and scutellum broadly tinged with yellowish white, outer half of posterior scutal protuberance yellowish brown.
Female imago (Fig. 1D). Body length: 6.7-8.7 mm; fore wing length: 8.7-9.0 mm; hind wing length: 1.8-2.1 mm. Similar to male except for the following characteristics: body coloration lighter. Head dorsally washed with white and with a black stripe close to posterior margin, compound eye black. Pronotum and membranous areas on mesothorax washed with white.
Head (Figs. 1A, B). Brown, with black marks between compound eyes and ocelli. Ocelli whitish with inner margins black. Eyes of male with upper portions dark orange-brown, lower portion black. Eyes of female black. Antennae yellowish brown.
Mouthparts. Labrum (Fig. 3A), exposed area of mandibles, stipes, paraglossa, and maxillary (Fig. 3F) and labial palp (Fig. 3I) light brown,  remaining parts paler. Basal 2/3 of outer margin of mandibles with few scattered setae, apical 1/3 with two groups of setae: a basal one with few long setae and a distal one with denser and smaller setae (Figs. 4A, E). Tusk on inner apical margin of maxilla small (Fig. 3F). Maxillary palp segment I subequal to segment III, segment II 1.2 times longer than segment III. Thorax (Fig. 1B). Pronotum with lateral black mark and oblique submedian brown band, mesonotum with anterolateral black marks.
Legs (Figs. 5A-L). Yellowish brown. Femur of all legs stained with black at apex. Fore leg with femur with two median maculae, black and smaller on inner margin, dark brown and larger on outer margin; tibia stained with black, darker toward apex; tarsi slightly washed with black, except on base and apex; claw yellowish. Middle and hind leg similar to fore leg, except for smaller size of femoral maculae on middle leg and absence on hind leg, and for tibia completely yellowish brown. Row of pectinate setae on ventral surface of hind tibia mostly single.
Gills (Figs. 1A, B). Gray, tracheae and fimbriae dark gray. Eggs. Size: 250-260 µm in length, 140-150 µm in width. Oval ( Fig. 5M) with polar regions convex, chorionic surface smooth. Knobterminated coiled threads (KCTs) equally distributed, overlapped and completely covering the chorionic surface: when threads are fully coiled, they remain glued to each other. Threads of KCTs long, entirely covering the KCT collar. Slick collar with hexagonal edge; (Fig. 5M). Micropyle present, two, both located close to one of the polar regions (arrows, Fig. 5M) and. located among three KCTs. Distribution (Fig. 6). Brazil. Bahia State: Maracás municipality (-13.440833, -40.430833 Ecological and biological data. In Paula Cândido, nymphs of U. saopaulensis were found in a pond among emergent macrophytes, habitat similar to that described by Da-Silva and Pereira (1992) while originally describing the nymphs. According to these authors, subimagos of the species emerge between 7:00 and 7:30 PM. We have no data on the period of emergence of subimagos, but we observed one subimago emerging at 7:45 PM. Female imagos of U. saopaulensis can carry a mass of eggs (Fig. 1D), similar to females of the closely related Ulmeritoides.

Nomenclatural notes
The nomenclatural history of the specific name saopaulensis is confusing. While there is no dispute that its etymology is a toponym in reference to the type locality in the state of São Paulo, Brazil, its spelling has changed many times. Traver (1946) made the nomen available in combination with the genus Atalophlebioides and used são-paulense as the original spelling. A decade later Traver (1956) transferred it to Ulmeritus changing to the subsequent spelling são-paulensis, and a few years later she returned to sao-paulense, but without the diacritic accent (Traver 1959). The current spelling saopaulensis was first adopted by Hubbard (1982) in his catalog with the combination Ulmeritus (Ulmeritus) saopaulensis, and since of the milestone studies by Domínguez (1991Domínguez ( , 1995, this spelling persists. Hubbard (1982) nor Domínguez (1991Domínguez ( , 1995 justified the emendation. The specific name são-paulense is formed by the stem saopaulplus the suffix -ense on its neuter form, and it can be considered an adjective by affixation. According to the International Code of Zoological Nomenclature (ICZN, 1999, two changes in the original spelling were mandatory-the exclusion of the diacritic mark and hyphen in the stem-to correct it from são-paulense to saopaulense (Art. 32.5.2.). However, the suffix change would be considered not mandatory, thus an unjustified emendation. The genus-group nomen Ulmeritus (masculine) means from Ulmer, a homage to the German entomologist Georg Ulmer , and it was formed by the stem Ulmerplus adjective -itus, -a, -um. Whether saopaulense is considered a declinable adjective based on a blind interpretation of the Code (Art. 31.2 and 34.2) it must agree in gender with the generic name, therefore in this context the correct spelling shall be saopaulensis. Otherwise, the Code is noticeably clear which conditions need to be met for an original spelling to be considered incorrect which does not apply to this case. First, it is not clear in the original publication "itself without recourse to any external source of information, clear evidence of an inadvertent error" (Art. 32.5.1.), nor the original author "indicate whether he or she regarded it as a noun or as an adjective, and where it may be regarded as either and the evidence of usage is not decisive, it is to be treated as a noun in apposition to the name of its genus" (Art. 31.2.2). In addition, in the section "Recommendations on the Formation of Names" of the Appendix D, published in the third edition of the Code there are only general lines to be followed and there no is mentioned that the only suitable suffix is -ensis, indeed it states: "preferably an adjective derived from the geographical name, and ending in a suitable suffix, such as -ensis or -iensis". In short, under absence of any sound evidence and in accordance with the article 33.5 that states in any case of doubt different subsequent spellings should be treated as an incorrect subsequent spelling, one would judge a name in apposition with the original spelling to be correct, thus Ulmeritus saopaulense. However, considering by the stability stated in principle 4 of the Code, we endorse Hubbard's (1982) emendation and considered Ulmeritus saopaulensis the correct spelling for this mayfly species.

Discussion
The nymph of U. saopaulensis have important characteristics to distinguish it from the other species in the genus. Unlike U. carbonelli and U. balteatus, those of U. saopaulensis (1) completely lack denticles on the distal emargination of the labrum, (2) the maxillary tusk is small, and (3) the maxillary palp segment III is shorter than segment II. While the first characteristic is unique among members of the Ulmeritus-Ulmeritoides lineage, the second is observed in some species of Ulmeritoides, and the third in all the species of that genus. Nevertheless, as in U. carbonelli and U. balteatus and unlike the species of Ulmeritoides, the row of setae on the dorsal surface of the labrum is medially interrupted in U. saopaulensis (Fig. 3C). In the nymphal stage, therefore, the most useful characteristics to distinguish Ulmeritus from Ulmeritoides are the dorsal row of setae on the labrum (interrupted in Ulmeritus, continuous in Ulmeritoides) and the development of the denticles of the distal emargination of the labrum (denticles absent to minute and flattened in Ulmeritus, developed in Ulmeritoides).
Adults of U. saopaulensis, male and female (Figs. 1A, C-E, 2C-E), are easily distinguished from its congeners based on having less pigmentation and fewer cross-veins on fore and hind wings. The ventral projection on the male genitalia of U. saopaulensis is also distinct from the remaining species: it is laterally displaced, instead of centrally positioned. According to Domínguez et al. (2006), besides its more lateral position, the projection is shorter than that of U. carbonelli [which agrees with the illustrations provided by Traver (1946)]. On our material, however, the length is similar in both species. A noteworthy aspect about the male genitalia, which has not been mentioned previously for the genus, is the location of the gonopores. They are at the apex of the penis lobe and not at the The eggs of U. saopaulensis can be differentiated from U. carbonelli by the number of micropyles. The first species has two (Fig. 5M) while the last has one. In conclusion, even after a series of recent studies on the group, including phylogenetic analyses proposed by Domínguez (1995) and Salles and Domínguez (2012), some species of the Ulmeritus-Ulmeritoides lineage are still poorly known with inter-and intraspecific variations not fully comprehended. Furthermore, since the last phylogenetic hypothesis and taxonomic revision of the group, 6 species have been described. Therefore, a of taxonomic review plus phylogenetic analyses studies could be very enlightening on this lineage. help with of HDMS treatment and to André L. Martins for help with methodology of SEM. Finally, we would like to thank the two anonymous reviewers of this manuscript for their important contributions.

Conflicts of interest
The authors declare there is no conflicts of interest.

Author contribution statement
VAS and FFS designed the study. All authors made the images and illustrations and contributed equally to the analysis, writing and revision of the manuscript and approved this version.