The monograph lacks formal diagnoses, which makes it impossible to comment on the definitions of taxa outright. To compare the composition of a given taxon to its definition, we reconstructed the intended diagnoses by using the keys to trace the characters leading to a given taxon. Fig. 1 provides a summary of how species previously assigned to Metrodora conform to the diagnostic characters specified in the key to Metrodorina genera. All characters leading to any genus in the key were recorded and marked green whenever observed in a given species, red whenever not observed and yellow whenever the character state could not be clearly assessed.

On average, approximately 70% of character states assigned to a genus were found to be unambiguous, with others being either absent or ambiguous in the species of that genus. This percentage varies considerably: 92% of entries are consistent for Platytettix species, whereas only around 50% are consistent for Metrodora, Hebardidora and Tylotettix species. This analysis demonstrates that the descriptions in the key do not consistently reflect the morphologies of the species whose identification the key is intended to facilitate. This assessment does not determine whether correctly described characters actually delimit genera (see Discussion).

There are three things to note here. First, Metrodora colombiae Günther, 1939 was not treated in the monograph.

Second, we found some of the characters insufficiently defined to be used in diagnosing taxa. For example, we considered the definition of the character concerning the width and length of the infrascapular area impractical because we found it to be very difficult to accurately evaluate from the presented photographs and to vary strongly within genera as they are currently defined. Another example is the scutellum width, which was not defined in relation to any other character, for example to the width of the antennal groove. When coding our table (Fig. 1), we adopted a conservative interpretation, interpreting “wide scutellum” as “noticeably wider than the antennal groove” and “narrow scutellum” as “approximately as wide as the antennal groove or narrower”. However, for Metrodora, the key in the monograph states “scutellum almost narrow”. We found it very difficult to interpret the statement of “almost narrow”, as it blurs the difference between the “narrow” and “wide” states. In fact, in Metrodora rana Bolivar, 1887 (the only species assigned to Metrodora in the monograph), this character resembles the state found in P. uniformis, H. kasaloi and T. simplex, all of which are characterised in the monograph as having a wide scutellum, but which should actually be considered narrow by any consistent definition. Yet another example is the character “anterior margin of pronotum rounded”. Many species lack dorsal photographs; hence, it is unclear how species with only holotypes available were coded for this character. It cannot be coded from lateral photos as the anterior margin can also be pointed as in Bolivaridora parisae Cadena-Castañeda & Tavares, 2025, which would look rounded in the lateral view.

The third and, in our view, most important observation is that we found virtually none of the genera to consistently satisfy all proposed diagnostic characters. Based on our re-examination, nearly every genus contains a few species that do not conform to the diagnosis given in the monograph and, in some cases—particularly Hebardidora and Tylotettix—the majority of included species fail to conform to proposed characters. Combined with the diagnostic issues documented below, we found it largely impossible to reliably apply the keys to identify the species included in the corresponding genera.

We found the newly-proposed generic and suprageneric taxa to lack morphological consistency and to be accompanied by contradictory (or missing) diagnoses. This undermines the usability of the taxonomic system proposed in the monograph until extensive revisions are undertaken. Therefore, as an interim measure, we propose a tentative solution by synonymising taxa lacking meaningful differentiating characters in their definitions. While some taxa may later be validated through diligent research, this approach prioritises clarity and taxonomic stability.

First, we deal with an unsupported synonymisation of a Metrodora species. Since the publication of the monograph, another short paper was published by Cadena-Castañeda et al. (2025a) in which they synonymised two Metrodora species published by Kasalo et al. (2025), which was published days after the publication of the monograph. Cadena-Castañeda et al. (2025a) proposed the Synonymization of Metrodora ala Kasalo & Skejo, 2025 with Hebardidora kasaloi, which is justified since the type localities of these two species are relatively close to each other and no significant morphological differences between holotypes are apparent.

Cadena-Castañeda et al. (2025a) also proposed the synonymisation of Metrodora mollilobata Kasalo & Skejo, 2025 with Hebardidora harroweri (Hebard, 1924). Their justification in the monograph states:

The only notable variation between Metrodora mollilobata syn. nov. and H. harroweri is a slightly more pronounced hump in the former; however, its overall shape remains similar, suggesting intraspecific variation.

This understates how different the crest of M. mollilobata is from that of H. harroweri. As stated in the diagnosis by Kasalo et al. (2025), the crest of M. mollilobata is very similar to the crests of Platytettix gibbosulus and Platytettix arcuatus—it is quite elevated with a sharply sloping caudal part. In comparison, the crest of H. harroweri is visibly lower and has a gentle slope. The shape of the crest is one of the most important characters used in descriptions of Metrodorinae (utilised extensively in the monograph as well) and it cannot be ignored by pronouncing it “intraspecific variation” between morphologically and spatially distant specimens, at least before more specimens have been analysed or before genetic analyses shed more light on the matter. For this reason, we reinstate Metrodora mollilobata stat. resurr. as a valid species.

Second, as demonstrated in Fig. 1 and the accompanying text, we found the definitions of genera within Metrodorina as given in the monograph very confusing and diagnosing them through identification keys led to inconsistent results. The monograph resurrected Platytettix Hancock, 1906 and Tylotettix Morse, 1900 without clear diagnoses. Hebardidora was compared to other genera mostly by the shape of the median carina of the pronotum and infrascapular area, both of which vary significantly within genera as currently defined, so these diagnoses cannot meaningfully separate genera. The monograph differentiated Bolivaridora from Metrodora and Platytettix only by the shape of the fastigium which was stated to be “conspicuously protruding” in Bolivaridora and not in the other two genera. However, there is a large variation in this character within Bolivaridora, with its type species being very similar to Metrodora, both with regard to this character and in general morphology. To avoid guesswork, we consider all of them to be synonymous with Metrodora until proper diagnoses are established. We propose the following taxonomic acts:

• Platytettix syn. of Metrodora;
• Tylotettix syn. of Metrodora;
• Hebardidora syn. nov. of Metrodora;
• Bolivaridora syn. nov. of Metrodora.

The genus Morseidora Cadena-Castañeda & Tavares, 2025 is a special case. The comparison section for this genus states only the general shape of the pronotum as a clear differentiating character from other Metrodorina genera, but our examination showed that the way the pronotum is undulated is very similar to Armasius Perez-Gelabert & Yong, 2014, i.e. the provided information cannot be used to differentiate the two. Therefore, we propose the following:

Morseidora syn. nov. of Armasius, resulting in a new combination Armasius acutus comb. nov. of Metrodora acuta Günther, 1939. The genus Armasius is hereby transferred to the subtribe Metrodorina.

Furthermore, as will be discussed in a later section, Devrieseium Cadena-Castañeda & Tavares, 2025 and Stalitettix Cadena-Castañeda & Tavares, 2025 lack a clear distinction from Chiriquia. Thus, we propose the following:

• Devrieseium syn. nov. of Chiriquia;
• Stalitettix syn. nov. of Chiriquia.

The descriptions of the new tribes Otumbini and Garciaitettigini in the monograph were not accompanied by diagnoses at all, with the reader being referred to the key to the tribes. We already discussed the lack of consistency of the keys in this monograph, so here we stress just a few important non-distinctions. The monograph separated Otumbini from Garciaitettigini and Metrodorini only by the shape of the carinae of the vertex and the width of the scutellum, both of which have exceptions that were admitted in the key itself: “Carinae of the vertex produced in different levels” for Garciaitettigini + Metrodorini and “medial carina not strongly expressed” for Garciaitettigini. We believe that the carinae of the vertex could certainly be one diagnostic criterion for tribes, but by no means the only one, because there is no uniform separation of its states between the proposed groups. Following this, the monograph differentiates Garciaitettigini from Metrodorini based on: (i) the medial carina not being strongly expressed in Garciaitettigini (identical to the state of that character in the type species of Metrodorini: Metrodora); (ii) Garciaitettigini having a concave vertex and Metrodorini having a convex vertex (not true, discussed later) and (iii) pronotum mostly flat with undulations in Garciaitettigini and arcuate with crests in Metrodorini (we see no meaningful distinction between these descriptions, see the following sections). These proposed groups are highly important for the definition of Metrodorinae; clear evidence is required for their definitions and descriptions. Before they are properly evaluated, we propose to consider them synonyms of Metrodorini, as we failed to find any practical characters for their differentiation in the definitions given in the monograph. We propose the following:

• Garciaitettigini syn. nov. of Metrodorini;
• Otumbini syn. nov. of Metrodorini.

Finally, we did not find any justification for the transfer of Platythorus Morse, 1900 to Metrodorinae given in the monograph. As its facial morphology conforms to Tetriginae and contradicts the diagnosis of Otumbini (see Discussion), we hereby place it in the subfamily Tetriginae, without tribal placement.

Tumbrinckitettix syn. nov. of Cryptotettix Hancock, 1900

In the monograph, the new genus Tumbrinckitettix was erected for Cryptotettix impennis Günther, 1939, the only nanopronotal species of Cryptotettix. Cryptotettix is clearly not monophyletic and has been poorly differentiated from Oxytettix since their original description, when only the type species was known, which is why we believe that erecting a new genus in this context will likely create more confusion than clarification. We were unable to confirm the diagnostic characters given in the monograph for defining Tumbrinckitettix. The first character given is: the pronotum does not noticeably surpass the apex of the femora in lateral view. This is typical for nanopronotal species, where the pronotum is not fully developed (as in nymphs). It is the case with most species of Oxytettix (except the macropronotal O. arius (Rehn, 1930)), which are nanopronotal. However, the same is true even in macropronotal Cryptotettix fanovana Günther, 1974 and C. similis Günther, 1974 (see the drawings in Günther (1974)). The second character given is: the space between the eyes is wider than in the other two genera. We found this not to be the case. Günther gave measurements (in his case, the ratio width of one eye/width of the fastigium): 24:33 and 24:37 for T. impennis, 22:33 and 25:34 for C. spinilobus, 19:24 and from 19:26 to 21:24 for C. imerina, 17:18 and 17.5:20 for O. cataphractus, 18:24 for O. macrocerus, 21:25 for O. arius, 20–24.5 for O. lathraeospanius, 17:24 and 19:29 for C. insularis, 22:27 for C. fanovana and 20–26 and 23:27 for C. similis. According to these measurements, T. impennis has a broad fastigium, but not noticeably different from C. spinilobus or O. lathraeospanius.

As we are not aware of other differences, Tumbrinckitettix is not different from Cryptotettix and we consider it a synonym of this genus.

Holocerus and Notocerus

In the monograph, Holocerus devriesei was transferred to Notocerus Hancock, 1900. The monograph argues that the prehumeral tubercle present in Holocerus and absent in Notocerus is not a generic character, but without providing any justification for this claim. This is indeed the case after having transferred H. devriesei to Notocerus, but not based on the earlier definitions of these genera. The monograph did not refer in any way to the comparative diagnosis for these genera provided by Skejo et al. (2020), which includes another clearly visible character: in Notocerus, the pronotum is elevated between the lateral spines, connecting them (visible in frontal view), while in Holocerus, the spines are separate. Therefore, the monograph ignores two established diagnostic characters, providing none to replace them, making another unfounded taxonomic change that makes it impossible to objectively differentiate Notocerus from Holocerus. The prehumeral tubercle character was then used to separate the species in the key, which is a common practice employed in the monograph (see Discussion).

Hereby, we return Holocerus devriesei comb. rev. to its original combination.

Guntheritettiginae

As the monograph states, an informal group of genera from Madagascar was recognised by Günther (1939, 1959, 1974), Devriese (1991) and Skejo et al. (2020). The literature contains a lot of discussion about the groupings proposed, which one can fall back on to incorporate into one’s own perspective. However, we found that several relevant publications and previously proposed groupings are not discussed when introducing the new classification in the monograph. The subfamily Guntheritettiginae is now formally described, although its composition is not completely the same as that given by Günther (1979), which also comprised Agkistropleuron Bruner, 1910, Isandrus Rehn, 1930 and Pterotettix Bolivar, 1887. There is no explanation why these have been excluded. Apart from the monograph having chosen a not well known representative genus as its type, the most concerning fact is that the synapomorphy which all previous authors have mentioned as typical for the group—the absence of an elytral sinus together with the small and narrow elytra in the macropronotal form—is mentioned in the monograph as “weakly developed” in the description and not at all in the comparison with other subfamilies (or unassigned tribes and genera).

The choice of type genera in the new subfamily Guntheritettiginae and its tribes does not follow recommendation 64A of the ICZN, that genera should be chosen that are both well-known and representative of the family-group taxon. Two new genera were described, Guntheritettix Cadena-Castañeda & Tavares, 2025 and Tumbrinckitettix Cadena-Castañeda & Tavares, 2025 for species known from one or two places in Madagascar and they were designated the type genera for the new tribes. As discussed above, we were unable to identify characters that differentiate the new genus Tumbrinckitettix from Cryptotettix Hancock, 1900 and Oxytettix Rehn, 1930. Therefore, we propose to synonymise it with Cryptotettix, in which the type species was originally described.

In summary, we find both the description and the comparison insufficient for taxonomic differentiation. Of course, the fact that Cladonotinae and Metrodorinae are polyphyletic and that some tribes are unassigned complicates comparisons, but this does not mean that comparison should not have been performed in the monograph. The question arises whether it was opportune to create the subfamily.

Guntheritettigini and Tumbrinckitettigini

These tribes have been distinguished as informal groups by Devriese (1991). The main differences between both tribes have already been relatively well described (Devriese 1991), but it is useful to further clarify them here.

In Guntheritettigini, the transverse carina of the pronotum (CT) is absent; significant are the presence of (sometimes spectacular) elevations on the lateral carina of the pronotum (CL) and sometimes on the median carina (CM) in this tribe, the large head with relatively small eyes (ratio total head width/fastigium width > 2) and the quadrangular lobes of the pronotum that are projecting outwards. All known species are macropronotal.

The genera and species of Tumbrinckitettigini are either nanopronotal or macropronotal, have transverse carinae, no elevations on the lateral carinae, a narrower head (ratio total head width/fastigium > 1.5) and, in most species, spines on the lateral lobes of the pronotum.

Pterotettigini

The position of Pterotettix Bolívar, 1887 has always been unclear. Günther (1939) found resemblances with Morphopus Bolívar, 1905 and Discotettix Costa, 1864 and synonymised Tetticerus Hancock, 1900 with it. Later, he (Günther 1974) placed it in the group of Holocerus-Andriana (the present Guntheritettigini).

While the resurrection of Tetticerus in the monograph has some merits, no analysis is provided for Ocytettix, only the photograph of the type of Ocytettix latihumerus Hancock, 1907 being provided. From all the pictures and descriptions in the literature, it is clear that at least Pterotettix and Tetticerus have no elytral sinus and very narrow elytra, which places these genera in Guntheritettiginae according to the current classification.

We, therefore, formally place Pterotettigini in Guntheritettiginae.

It is not clear to us, whether all the species within the newly-created tribe have similar characters. However, until additional material can be studied, we abstain from proposing changes that could only complicate matters for future study.

Günther (1974) changed his opinion on the synonyms of the species of Pterotettix that he did not see himself (Amorphopus simplex, Tetrix belphegor and Tetrix asmodeus). However, Cadena-Castañeda et al. (2025b) synonymise humilis (and alluaudi) with belphegor and simplex with andrei, on the authority of Günther, although this author was never explicit about this. As we have not seen the material ourselves, we cannot confirm or dispute these synonymisations.

Hildegardiinae

The creation of a separate subfamily for Hildegardia is, in our opinion, pre-emptive. The only autapomorphy we could identify is the antennae having lateral apical extensions on the antennomeres. We do not find that they “have an incredible appearance that is not seen in any other Tetrigid”, as proposed in the monograph. We do not see any justification in creating a separate subfamily for this genus. Its sister group is still an enigma, but this can be said for a lot of genera, chiefly because nobody has yet made the effort to make a thorough analysis of possible candidates in African and Asian faunas. It is difficult to make a decision about the status of this subfamily, as much research is needed to identify the potential relatives of Hildegardia.

The study of the Metrodorinae of Madagascar and the Indian Ocean Islands was based solely on a bibliographic study and on a study of a limited number of photographs and lacks a comparative approach. We believe it was premature to present a complete revision on this basis. However, some taxonomic novelties can be accepted as they formalise opinions by other authors.

In our view, the taxonomy is as follows:

Guntheritettiginae Cadena-Castañeda

Guntheritettigini Cadena-Castañeda

Type genus. Guntheritettix Cadena-Castañeda & Tavares.

Tumbrinckitettigini Cadena-Castañeda

Type genus. Tumbrinckitettix Cadena-Castañeda & Tavares (= syn. nov. of Cryptotettix Hancock).

Pterotettigini Cadena-Castañeda

Type genus. Pterotettix Bolivar.

Unassigned genera (in Tetrigidae)

Arexion Rehn, Hildegardia Günther, Isandrus Rehn, Storozhenkoium Cadena-Castañeda

The monograph begins with a re-description of the subfamily Metrodorinae, followed immediately by the re-description of the nominotypical tribe Metrodorini. A large number of morphological features were treated in this description, though mostly in a very general manner, for example, “specimens slender or robust”, “face generally ovoid or subrectangular”, “fore- and mid-femora compressed, with or without conspicuous undulations”. No specific diagnostic characters were described or highlighted. As a result, we found it very difficult to impossible to actually apply this description to any specimen. Which of the many listed characters apply to all members of the group? Which are more reliable than others? What makes Metrodorini Metrodorini?

According to the International Code of Zoological Nomenclature (ICZN 1999) Article 13.1.1., every new name should

be accompanied by a description or definition that states in words characters that are purported to differentiate the taxon.

This is further elaborated in Recommendation 13A:

Intent to differentiate. When describing a new nominal taxon, an author should make clear his or her purpose to differentiate the taxon by including with it a diagnosis, that is to say, a summary of the characters that differentiate the new nominal taxon from related or similar taxa.

Even though names accompanied solely by general descriptions are technically valid under the ICZN (1999), formal differential diagnoses are strongly recommended. A lengthy description does not necessarily serve this purpose more effectively. In fact, a concise, well-founded diagnosis—even a single sentence when properly justified—often proves more useful.

The taxonomic treatments in the monograph do not consistently follow this good practice. References to diagnostic characters are infrequent and unsystematic, providing insufficient differentiation of the proposed taxa. Rather than stating diagnoses directly, the monograph employs identification keys at individual taxonomic levels, which are referenced as if they were diagnoses. In the case of the genus Otumba, two species groups are established solely within the key, without any mention in the text.

This approach creates a significant problem—readers must work backwards through the keys to reconstruct the intended diagnoses, which unnecessarily complicates the primary purpose of any taxonomic revision. If taxa can be separated by a key, there logically must be a combination of characters that defines each taxon. These should be explicitly stated.

A related issue is that we found numerous cases in which the differentiating characters stated in the keys do not correspond to the morphology visible in the cited taxa.

First, one of the diagnostic characters stated for Metrodorini is: “vertex convex”. A convex vertex is a diagnostic character for Cladonotinae (e.g. Kasalo et al. (2023)), while in Metrodorini, it is flat with its carinae elevated (see the figure in a later section). Another character stated for Metrodorini is “median carinae of pronotum arcuate, mostly forming a crest in different shapes”. This description contains two significant issues: there is only one median carina, not multiple; and within the circumscription of Metrodorini given in the monograph, several genera lack both crests and the described arcuation of the median carina. Furthermore, this character was invoked to separate Metrodorini from Garciaitettigini Cadena-Castañeda, 2025, although many Garciaitettigini members possess crests formed by median carina elevation.

Second, for the genus Tylotettix Morse, 1900, one stated character is: “infrascapular area with medium width, reaching up to the fourth to sixth abdominal segment”. In T. simplex Hebard, 1924, the infrascapular area clearly surpasses the body and is notably narrow (Fig. 2A), particularly in comparison to other genera. In the two remaining Tylotettix species, the infrascapular areas are partially obscured by hind legs, though at least in T. sinuata Morse, 1900, the character appears comparable to that in T. simplex.

Third, for the genus Hebardidora Cadena-Castañeda & Tavares, 2025, the key states: “crest wavy, formed by the elevated wavy median carina”. Neither the type species (H. harroweri) nor H. panamae (Hebard, 1924) exhibits a wavy crest; only H. kasaloi Cadena-Castañeda & Tavares, 2025 does (Fig. 2B).

Fourth, for Otumba dentata Hancock, 1907, the key states: “fascial carina diverging on the level of the lower edge of the eyes”. The bifurcation of the frontal costa in this species (and in all other species of Otumba Morse, 1900) is at around the middle of eye height (Fig. 2C).

These examples, presented as representative rather than exhaustive, illustrate instances in which the character states listed in the keys differ from those observed by us in the taxa concerned.

Possibly as a consequence of the use of identification keys instead of formal diagnoses and the misinterpretation of differentiating characters, we found several instances in the monograph where mutually exclusive character states of the same character were used to establish taxa at different hierarchical levels. Here, we provide three examples.

First, in the key to tribes, “medial carina strongly expressed” is meant to differentiate Metrodorini from other tribes; however, deeper within the key to Metrodorina, the statement “Carinae of vertex [which includes the medial carina] low, not protruding between the eyes” leads to Metrodora, the type genus. This means that the primary diagnostic character for Metrodorini does not apply to its own type genus. This is not merely imprecise phrasing; according to our re-examination, the vertex carinae in Metrodora possess nearly identical dimensions and form to those in certain Garciaitettigini, for example, Stalitettix and Garciaitettix Cadena-Castañeda & Tavares, 2025.

Second, in the key to tribes, Garciaitettigini is characterised by: “median carinae of pronotum slightly elevated in some sections, pronotal disc mostly flat but with mid-sized undulations”. Subsequently, in the key to Garciaitettigini genera, the following is stated: “undulations of the median carina of the pronotal disc low and moderately elevated”. The first diagnosis suggests to us that the median carina is sometimes just barely elevated, while the surface of the pronotum can form wave-like shapes. The diagnosis in the second key then claims that the median carina forms moderate elevations, which is confusing. It is unclear to us what the intended difference between an undulation and a median carina elevation is or if there is any. Furthermore, it is unclear why these undulations in Garciaitettigini are not called “crests” like in Metrodorini even though they are both formed by the elevations of the median carina. This difference in nomenclature implies a greater degree of difference than we could actually confirm—we consider the shape and the position of the median carina elevation in Metrodora rana (Metrodorini) and in Stalitettix spinifrons (Stål, 1861) (Garciaitettigini) identical. It would have been very useful if the monograph had dedicated some space to the discussion of the ways in which the crests of Metrodorini and Garciaitettigini actually differ and why these differences are phylogenetically important.

Third, in the key to genera of Metrodorina, the state “lateral lobes of the pronotum with the lower margin pointed” leads to Bolivaridora Cadena-Castañeda & Tavares, 2025. Then, the first entry in the key to Bolivaridora species states: “lower margin of the lobes rounded”.

Exceptions to general trends amongst members of taxa, especially higher taxa, are not uncommon. This makes writing short and practical keys difficult and is the very reason why (differential) diagnoses and notes are necessary. They not only provide the general pattern of characters and character states, but also explain that, although characters occasionally deviate from the typical state, the character itself is still useful to define the taxon. When it comes to providing differential diagnosis, the monograph occasionally contains “comparison” sections, but exclusively for newly-named genera, not for established genera or genera that were reinstated.

In the previous section, we documented shortcomings in the definitions of taxa across all hierarchical levels. Here, we document how numerous Metrodora s.l. species do not conform to the diagnostic characters associated with the genera to which they are assigned. We demonstrate this in Fig. 1 and discuss five more examples to provide evidence for this concern.

The first example involves the new monotypic genus Grantiatra Cadena-Castañeda & Tavares, 2025, classified within the subtribe Miriatrina Cadena-Castañeda & Cardona, 2015. However, within the subtribe Metrodorina, the monograph describes Bolivaridora parisae, which differs markedly from other Bolivaridora species and could readily be considered either a Grantiatra species or a closely-related genus. Both taxa possess sharp, similarly-shaped lateral lobes; both have pointed anterior pronotal margins; both possess similarly-formed infrascapular areas; both appear dorsoventrally flattened; and both share comparable vertex morphology (although B. parisae exhibits a proportionally wider vertex). Despite sharing all these morphological features, these taxa were placed in distantly positioned taxonomic groups in the monograph. If Metrodorina and Miriatrina are as readily confused as such overlap suggests, what justifies their retention as separate subtribes? This leads us back to the earlier question of higher taxa diagnoses. It is unclear to us which characters are supposed to differentiate Metrodorina and Miriatrina. None of the diagnostic characters for Miriatrina is unique to that group (our comments in square brackets):

Carinae of the vertex conspicuously produced [same in Metrodorina]. Scutellum almost narrow, delimited by the frontal costa with its nearly straight branches [narrow scutellum observable in many Metrodorina]. Median carinae of the pronotum not arcuate, with pronotal disc generally flat, without conspicuous crests [a very similar description is used for Bolivaridora in Metrodorina, while Grantiatra in Miriatrina has an elevated median carina]. Wings well-developed, as long as the pronotum or slightly exceeding it [Grantiatra and Rehniatra in Miriatrina are wingless]. Genicular tooth of hind femora poorly developed [varies between species in both groups]”.

Based on the characters provided in the monograph, we were unable to identify a clear basis for assigning genera to one subtribe rather than the other.

The second example is the position of Bolivaridora tani Cadena-Castañeda & Tavares, 2025, which the monograph describes under Metrodorina, although it does not have its medial carina projecting in front of the vertex. Rather, its entire vertex is projected forwards, much like in Rehniatra Cadena-Castañeda & Tavares, 2025, which is placed under Miriatrina. Both B. tani and Rehniatra brevifastigiata (Cadena-Castañeda & Cardona, 2015) also have a shorter third tarsal segment of the hind leg, short antennae and a low median carina. Regardless of whether R. brevifastigiata and B. tani are actually congeneric or closely related or if perhaps the entire Bolivaridora genus is related to Rehniatra, these similarities are not discussed in the monograph and we were unable to determine how they were weighted relative to the characters used for classification.

The third example is the placement of Platythorus Morse, 1900 in the tribe Otumbini Cadena-Castañeda, 2025. In the Discussion, the monograph states the following:

The tribe Otumbini trib. nov., unlike the previous tribes, camouflaging among bryophytes has not been observed. However, they have cryptic colors in shades of brown, gray, and black. Its appearance is slender, and most of its taxa are winged (except Platythorus), which can be confused with some Tetriginae. However, upon careful observation, its morphology conforms to what is proposed here for the American metrodorines.

This “careful observation” is not supported—a clear description of these characters is required. Platythorus has the bifurcation of its frontal costa placed very high on its face, i.e. the frontal costa is extremely short. The same is true for other Tetriginae (e.g. Devriese et al. (2023)). Notably, Cotys Bolívar, 1887 not only has identical facial morphology to Platythorus, but it has a small crest in the same place as it is in Platythorus, as well as plenty of other important similarities, like the short third segment of the hind tarsus. The monograph transferred Cotys to Tetriginae, while Platythorus was assigned to Metrodorinae without providing any supportive data. More problematically, Platythorus (which has the frontal costa bifurcation at the dorsal margin of the eyes) was assigned to Otumbini in the monograph, which was characterised (incorrectly) as containing species with the frontal costa bifurcation positioned at the ventral margin of the eyes.

The fourth example is the placement of a new Otumbini genus, Bruneritettix, described for Allotettix fuscipennis Bruner, 1910. The remarks section for the genus contains the following:

It is differentiated by the structure of the maxillary palps, conspicuous eyes (Fig. 119D), and lower margin of the lateral lobes of the pronotum expanded to the sides (Figs 119A, B). Due to the characteristics described here, this new genus fits the characteristics of the new tribe Otumbini trib. nov.

Two concerns merit attention. First, none of the characters cited here constitutes part of the proposed Otumbini diagnosis (given within a key), raising questions about their relevance to tribal placement. Second, Bruneritettix fits the diagnostic characters of Garciaitettigini provided in the key, which reads:

Carinae of the vertex produced in different levels, mostly conspicuous, with lateral carinae forming more or less pronounced horns and medial carina visibly compresso-elevated. Frontal costa rounded or divergent, rarely straight.

As in previously discussed examples, the monograph here asserts that taxa “fit the diagnosis” or “conform” to specific morphologies without providing either the diagnosis itself or the precise characters demonstrating this conformity.

The fifth example is the composition of Garciaitettigini. Two new genera were described in the monograph: Devrieseium Cadena-Castañeda & Tavares, 2025 and Stalitettix Cadena-Castañeda & Tavares, 2025, for two species that were previously assigned to Chiriquia Morse, 1900. They were differentiated by slight differences in the medial carina elevation, slight differences in the pronotal humps and the shape of the tegmina. We propose that the differences in these characters are more pronounced amongst Chiriquia species than they are between these two genera. The monograph even partially suggests this in the comparison section regarding these genera:

Devrieseium gen. nov. differs from Garciaitettix gen. nov. and from most species of Chiriquia for the pronotum extending well beyond the apex of the abdomen and hind femur.

If Devrieseium differs only from most Chiriquia species, this raises the question of whether it truly warrants generic status separate from Chiriquia. Alternatively, should those Chiriquia species with similar characteristics be reclassified as Devrieseium? Furthermore, the genus Otumba exhibits comparable morphological diversity encompassing the characters used to differentiate Devrieseium and Stalitettix, yet Otumba species are not similarly subdivided. The same applies to median and medial carina variation within certain Metrodorina genera. A much greater consistency in the application of generic criteria and the discussion of these decisions is needed.

In all these examples, we found it difficult to follow the reasoning of the authors of the monograph for defining the taxa in question. A priori designation of species and genera to predetermined groups, followed by post-hoc attempts to circumscribe these groups, would be a plausible explanation. If this was the approach to taxon definition taken in the monograph, the conformity to good scientific practice would have to be called into question.

A well-executed taxonomic revision re-examines previously gathered data on the group of interest and provides an updated interpretation. In certain cases, the group has received limited historical examination and a revision provides the first comprehensive interpretation of its taxonomy (e.g. Tumbrinck (2014); Kasalo and Skejo (2024)). In other instances, extensive literature exists on the group, requiring the revision to critically examine available data and synthesise it meaningfully (e.g. Tumbrinck (2018); Skejo et al. (2022)). When prior literature is disregarded, a revision becomes incomplete, necessitating subsequent work that addresses unresolved questions. In this section, we discuss examples from this monograph in which existing literature is disregarded or misinterpreted and insufficient context to substantiate proposals is provided. The monograph extensively refers to a publication by Kasalo et al. (2023) and misinterprets many of its claims, so we provide a comparative overview of these claims here. In the later sections regarding Malagasy Metrodorinae, several more examples of literature misinterpretation are presented.

In a relatively minor publication by Kasalo et al. (2023), the tribe Metrodorini was formally defined and diagnosed for the first time, despite its status as the nominotypical tribe of Metrodorinae. Kasalo et al. (2023) synonymised the tribes Miriatrini Cadena-Castañeda & Cardona, 2015 and Mucrotettigini Cadena-Castañeda & Silva, 2019 with Metrodorini, as their diagnoses could not be meaningfully separated at that time—all three were composed of Metrodora-like taxa with the medial carina projected in front of the head. Additionally, Kasalo et al. (2023) transferred Eleleus Bolívar, 1887 to Cladonotinae. The objective was to provide a working definition of core Metrodorinae against which other groups could be compared, facilitating eventual clarification of the subfamily’s composition.

The monograph’s Introduction contains the following:

More recently, the tribe Mucrotettigini was transferred from Cladonotinae into Metrodorini (Kasalo et al., 2023a), although Silva et al. (2019) had previously discussed this possibility.

It is unclear what the Silva et al. (2019) citation refers to. The paper in question (Silva et al. 2019) mentions Metrodorinae exactly once, as a part of the list of subfamilies that occur in the Neotropical Region. Metrodora Bolivar, 1887 is mentioned in comparison to Cota Bolivar, 1887 (which is very explicitly considered separate from Mucrotettigini) and the taxonomic placement of the Mucrotettigini tribe is not discussed after describing it in Cladonotinae, an entirely different subfamily.

The monograph’s Discussion contains the following:

Therefore, the decision of Silva et al. 2019 should not be considered a “failure”, as mentioned by Kasalo et al. (2023a); the tribes that Silva et al. (2019) described only remained within the subfamily Cladonotinae awaiting future contributions. In the same way that other authors did, it is important to avoid making drastic changes without a complete picture or enough evidence. For instance, Adžic et al. (2020) preferred to keep the tribes Thoradontini and Criotettigini outside of Scelimeninae (Tetrigidae). This position is valid and conservative and seeks to reduce noise in the classification. Still, if the status of Thoradontini and Criotettigini is resolved in the future, it would not be correct to mention that the authors “failed” to exclude those tribes from the subfamily in which they traditionally grouped once they followed the information and evidence available at the time.

This response addresses the following statement from Kasalo et al. (2023):

The original diagnosis by Silva et al. (2019) compares the tribe Mucrotettigini only to the tribe Choriphyllini (Cladonotinae), noting that they are easily separated because the latter tribe exhibits leaf-like morphology. That diagnosis does not take into account the type specimens of either Metrodorinae or Cladonotinae and thus fails to provide evidence for the subfamilial classification of Mucrotettigini.

The comment in Kasalo et al. (2023) simply indicates that, without comparison to type specimens, the original diagnosis lacks the information necessary to determine subfamily placement, i.e. the diagnosis fails to separate subfamilies. The authors’ extended response appears to address what they perceive as a personal attack, concluding that errors are not shameful. We concur—errors are inevitable in complex research. Taxonomy requires iterative refinement and new data can substantially alter previous conclusions. Such errors are valuable when the work is conducted diligently, accompanied by transparent reasoning and integrated with established knowledge.

However, the authors themselves state that “it is important to avoid making drastic changes without a complete picture or enough evidence”—a principle that, we suggest, is not consistently applied in their monograph.

Yet another instance of misinterpretation is the following section of the monograph:

Kasalo et al. (2023) proposed keeping Eleleus Bolívar, 1887 within Cladonotinae (without tribal assignment) due to the non-development of the vertex carinae, in contrast to the other genera with which it was previously associated. Nevertheless, the development of the vertex carinae can be variable, very conspicuous like Miriatra, or moderate like Metrodora. However, Hottettix has an organization of the vertex carinae similar to Eleleus, which would conflict with the proposal of Kasalo et al. (2023).

In Kasalo et al. (2023), the following was proposed regarding Eleleus curtus Bolívar, 1887:

However, this species has the vertex bulging in the same way as in Cladonotini and Choriphyllini, without well-defined carinae of the vertex.

Kasalo et al. (2023) focus extensively on the bulging shape of the vertex as a diagnostic character shared by Cladonotinae and this is illustrated in the paper’s only figure. The monograph does not address this central point and instead focuses on the degree of carina development. The monograph claims that Hottettix Perez-Gelabert et al., 1998 has a similar vertex to Eleleus and that this conflicts with the proposal in Kasalo et al. (2023). First, the lateral carinae of the vertex in Hottettix are a little elevated and the vertex appears somewhat concave between them, unlike in Eleleus, in which the vertex appears uniformly rounded (Fig. 3). Second, if Hottettix is indeed similar to Eleleus, this does not conflict with the transfer of the latter to Cladonotinae; rather, it would suggest that Hottettix should similarly be transferred to Cladonotinae.

Taxonomy and systematics should strive to reflect evolutionary and phylogenetic relationships by assigning names to monophyletic groups. Therefore, if a subfamily is reviewed and new tribes (and even subfamilies) are described, it would be valuable to at least provide a short discussion on how these taxa may be related. The monograph assigns five tribes, mostly newly described, to “core” Metrodorinae, but there is no attempt to establish any relationships between them. This is a revision of Metrodorinae and, hence, Metrodorinae need to be defined and discussed clearly.

The two new subfamilies described in the monograph receive similarly minimal treatment. More problematically, the abstract states: “Two new subfamilies closely related to Metrodorinae are described”. This proposed close relatedness is not elaborated in the text, despite carrying significant implications for Tetrigidae evolution. How can Hildegardiinae Cadena-Castañeda, 2025 be simultaneously closely related to Metrodorinae and “notably differentiated from the rest of the world tetrigids”? If both new subfamilies are closely related to Metrodorinae, they should share notable similarities worthy of discussion. If they form a monophyletic group, which subfamily do the authors propose as their closest relative? What implications do these new subfamilies carry for the morphological characters currently distinguishing tetrigid subfamilies?

The authors have declared that no competing interests exist.

No ethical statement was reported.

Regarding the use of AI in the preparation of this manuscript, the authors declare the following: AI was used for language editing. No content was generated using AI.

No funding was reported.

NK, HD, LD-G, SH, and JS conducted the analysis and wrote the first draft of the manuscript and are authors of equal contribution. The other authors provided smaller additions to the text and contributed to forming the final draft of the manuscript.

N. Kasalo https://orcid.org/0000-0002-3139-6349

H. Devriese https://orcid.org/0000-0003-4011-8225

L. Desutter-Grandcolas https://orcid.org/0000-0002-7781-3451

S. Hugel https://orcid.org/0000-0003-2464-3601

M. Husemann https://orcid.org/0000-0001-5536-6681

S.W. Heads https://orcid.org/0000-0002-3141-1940

M.J. Thomas https://orcid.org/0000-0002-4514-7757

G. Doucet https://orcid.org/0009-0003-8544-411X

F.M. Buzzetti https://orcid.org/0000-0003-4061-5192

R.R. Patano Jr. https://orcid.org/0000-0001-5020-6048

M. Subedi https://orcid.org/0000-0001-8660-1314

D. Bhaskar https://orcid.org/0000-0002-5398-6470

P. Kočárek https://orcid.org/0000-0002-1739-0143

T. Fite https://orcid.org/0000-0003-3492-4933

J. Skejo https://orcid.org/0000-0002-2554-4499

All of the data that support the findings of this study are available in the main text.