A new genus and eight new species of the subtribe Anillina (Carabidae, Trechinae, Bembidiini) from Mexico, with a cladistic analysis and some notes on the evolution of the genus

Abstract One new genus and eight new species of anilline carabids are described from southern Mexico. The new genus, Zapotecanillus gen. n., is established for Z. oaxacanus (type species) sp. n., Z. nanus sp. n., Z. iviei sp. n., Z. ixtlanus sp. n., Z. montanus sp. n., and Z. kavanaughi sp. n. from the Sierra Madre de Oaxaca, Z. pecki sp. n. from the Sierra Madre del Sur, and Z. longinoi sp. n. from the Sierra Madre de Chiapas. A taxonomic key for all described species of Zapotecanillus and a cladistic analysis, based on morphological data, are provided. Morphological, behavioral and biogeographical aspects of the speciation in the genus obtained from the resulting cladogram are discussed.


Introduction
The anilline fauna of Mexico remains extremely inadequately investigated in spite of numerous publications on carabids of the region. Monographs by Jeannel, revising the world fauna of Anillina, contain no information on Mexican representatives (Jeannel 1937(Jeannel , 1963a. To date, only two species from two different genera: Mexanillus sbordonii Vigna Taglianti and Geocharidius zullini Vigna Taglianti, have been recorded from Mexico (Vigna Taglianti 1973). The genus Mexanillus Vigna Taglianti (1973) was established for beetles that were collected in caves and closely resembled troglobitic trechines in several specialized features and peculiar habitus. The genus Geocharidius Jeannel had been established 10 years earlier by Jeannel (1963a) for a Guatemalan Verbatim label data are given for type specimens of all newly described taxa, with label breaks indicated by a slash ("/"). In a case of series of KUNHM specimens with the same geographical labels but differing in various barcode numbers only, these numbers were replaced in the text by periods of ellipsis.
Measurements. All specimens were measured electronically using a Leica M420 microscope equipped with a Syncroscopy AutoMontage Photomicroscopy system (SYNCROSCOPY, Synoptics Ltd.). Measurements for various body parts are encoded as follows: LH = length of head, measured along midline from anterior margin of labrum to the virtual line, connecting posterior supraorbital setae; WH = width of head, at level of anterior supraorbital setae; WPm = maximal width across pronotum; WPa = width across anterior angles of pronotum; WPp = width across posterior angles of pronotum; LP = length of pronotum from base to apex along midline; WE = width of elytra, at level of 4th umbilicate setae; LE = length of the elytra, from apex of scutellum to apex of left elytron; SBL = standardized body length, a sum of LH, LP and LE. SBL measurements are given in mm; others are presented as nine ratios: mean widths-WH/WPm and WPm/WE and body parts-WPa/WPp, WPm/WPp, WPm/LP, WE/LE, LE/SBL, WE/SBL and LP/LE. All values are given as mean ± standard deviation.
Illustrations. Digital photographs of the dorsal habitus of new species were taken with the AutoMontage system using a Leica M420 microscope. Line drawings of selected body parts were made using a camera lucida on an Olympus BX 50 microscope or grids on a Labomed Lx400 compound microscope. Scanning electron micrographs were made either with coating on a LEO 1450VP SEM or without coating using low vacuum mode on an ESEM FEI Quanta 200.
Dissections. Dissections were made using standard technique. Genitalia were dissected from the abdomens of specimens previously softened in boiling water for 20-30 minutes. Contents of the abdomen were cleared using boiling 10% KOH for 2-3 minutes to remove internal tissues, and then washed in hot water before examination. After examination, genitalia were mounted on plastic transparent boards in dimethylhydantoin formaldehyde resin (DMHF) and pinned beneath the specimen. In some species, investigation of body parts was undertaken in the following way. The whole specimen was cleared, using boiling 10% KOH for ~5 minutes, then washed and dissected in the typical way. Disassembled body parts from one specimen were placed on plastic transparent board, properly oriented, mounted in DMHF and pinned together with the specimen labels.
Type material. I had no opportunity to investigate the type material of the Mexican species of Anillina described by A. Vigna Taglianti, so, Mexanillus sbordonii is known to us only by the original description. The concept of Geocharidius used here, is based on the investigation of a long series (>20 specimens) of G. integripennis (Bates) (Terry Erwin's identification) from the Quiché Department of Guatemala, which is not the type locality of the species (the latter is located within neighboring Totonicapán Dept.); but these specimens exhibit features that closely match diagnostic features of the genus, mentioned in the literature (Jeannel 1963a, Vigna Taglianti 1973. Types of the Guatemalan species of Geocharidius described by T. L. Erwin in his revision of Central American Bembidiini (Erwin 1982) were examined.
Terms. Terms used in the paper are largely of general use and follow the literature (Ball and Bousquet 2000;Ball andShpeley 2005, 2009;Erwin 1974;Jeannel 1963a;Shpeley and Ball 2000), except those for ventral surface structures, terms of which follow the Handbook of Zoology (Lawrence et al. 2010).
Species ranking. Species recognition is in accordance with our previous approach (Sokolov et al. 2004).
Arrangement of taxa in the text. Taxonomic treatments of species in the text follow mostly the geographical basis. The species sequence starts with the type species, and each following species is more distant from the latter geographically, and, presumably, genetically. Within the Sierra Madre de Oaxaca the sequence generally corresponds to the virtual movement along the Tuxtepec -Oaxaca road in SW direction.
Descriptions. The scheme of descriptions follows that of Ball andShpeley 2005, 2009).
Maps. Maps were downloaded from the web-site: http://www.maps-for-free.com/ and adjusted with the help of Photoshop software.
Cladistic analysis. Morphological data were used to reconstruct the phylogenetic relationships among species of Zapotecanillus. The analysis was based on the assumption that the ancestral lineage of Mesoamerican anillines was represented by a true litter-dwelling, but not endogean, species. Accordingly, as outgroup taxa, two litter species from the anilline genera Nesamblyops and Geocharidius were chosen for analysis. The geographically proximate Geocharidius phineus Erwin from Guatemala represents the globose species of the genus and is confined to the litter of midaltitudinal forests (Erwin 1982). Geographically distant Nesamblyops sp. from New Zealand, because of the presence of rudiment eyes is considered to be close to the ancestral type of normally blind Anillina (Moore 1980). Furthermore, molecular data, although scarce, suggest that this genus forms a branch on the phylogenetic tree of Trechitae basal to the European and American genera of Anillina (Maddison and Ober 2011). A total of 32 binary or multistate characters (29 parsimony informative) were derived from the external morphological features (22), male genitalia (9), and female genitalia (1) (see Tables 1 and 2 in the Appendix). A character matrix was generated using NEXUS Data Editor 0.5.0. for Windows (Page 2001), and the analysis was performed using PAUP* version 4.0 (Swofford 2002), with heuristic tree searches using random addition sequences (100 replicates), holding 10 trees at each step, swapping on all trees, and excluding parsimony-uninformative characters from the data sets. Character states were treated as unordered and unweighted. Bootstrap analyses (Felsenstein 1985) were conducted with resampling at 1,000 replications using the previously mentioned settings. Branch support was also examined using Bremer support indices (Bremer 1994), calculated using the TreeRot.v3 software (Sorenson and Franzosa 2007).
Labrum. Labrum (l) transverse with straight, entire anterior margin with six setae apically, increasing in size from the central pair outwards (Fig. 5).
Labium. Labium ( Fig. 7) with mental tooth; mentum and submentum fused, without mental-submental suture (ms) and with moderately enlarged lateral mental lobes, which are translucent along the lateral margins (llm). Glossal sclerite (gsc) with short but distinct paraglossae (pg) laterally and with two setae apically. Central area of mental-submental complex with a field of pores and 1-2 pairs of shorter setae additionally (Fig. 11).
Male genitalia . Median lobe of aedeagus anopic, elongate, twisted and slightly arcuate. Internal sac with two groups of copulatory sclerites: dorsal group represented by 2 plates, and ventral group represented by weakly sclerotized fold or folds. Dorsal plate 1 (dp1) in form of an elongate plate, rounded or pointed at basal end, and tapered into a needle-like structure apically. Dorsal plate 2 (dp2) much smaller than plate 1, also needle-attenuated apically, curved and enlarged towards base; coplanarly adjoined to dorsal plate 1 apically in lateral view and divergent from plate 1 basally as a ventrally directed protuberance; can be seen as a separate structure in some species (Figs 54,57). Ventral sclerites (vsc) of varied shape, dependent on development of sclerotization. Additional spines or scaled membranous fields of internal sac are absent. Parameres typically bisetose, except right paramere of Z. pecki 3-setose (Fig. 53). Left paramere large and broad, either evenly tapered to apex (Figs 43,46) or with short attenuation before setal attachment (Figs 37,40). Ring sclerite broadly ovate with transverse handle-like extension of varied length and shape hd).
Geographical distribution. The species of this genus are known from three mountain ranges of Mexico: the Sierra Madre de Oaxaca, the Sierra Madre del Sur and the Sierra Madre de Chiapas, within the states of Oaxaca and Chiapas (Fig. 77). This type of distribution best fits Halffter's (1987) Meso-American Montane Distribution Pattern.
Relationships. The position of Zapotecanillus within the North and Central American Anillina is unclear at present, and awaits molecular data analysis or further discoveries and subsequent morphological analyses of the Middle American anilline taxa. Members of this new genus differ principally from those of the southern stock of Middle American anilline genera (Geocharidius Jeannel, Honduranillus Zaballos, Mexanillus Vigna Taglianti) in having a different arrangement of the last three pores of the umbilicate series and the fused labium, and from geographically proximate Geocharidius and Mexanillus in having distinct paraglossae. They differ from members of the northern stock of North American anilline genera (Anillaspis Casey, Anillinus Casey, Anillodes Jeannel, Micranillodes Jeannel, Serranillus Barr) in lacking fixed discal pores on the elytra.
The key provided below allows distinguishing members of the new genus from those of the other continental North and Middle American anilline genera: Labium fused, without mental-submental suture (Fig. 7). Pores 8 and 9 of umbilicate series geminate, much closer to each other, than 8 th to 7 th (Fig. 3)  Recognition. Adults of this new species can be distinguished easily from those of other species of the genus by the following combination of external characters: bicolored and robust appearance, comparatively small head and distinctly transverse pronotum.
Legs. 1 st male protarsomere only slightly dilated (Fig. 22). Male genitalia. Median lobe of aedeagus ( Fig. 36), with short and transverse apex, broadly rounded at tip. Dorsal plate 1 long, with apical pointed attenuation of moderate length. Dorsal plate 2 joined to plate 1 at its middle ventrally, where it forms a distinct protuberance. Ventral sclerites elongate, with subparallel sides and obliquely stretched from dorsal plates towards ventral margin of median lobe. Right paramere short and moderately wide (Fig. 38). Left paramere with distinct apical constriction (Fig. 37). Ring sclerite with long handle-like extension, widely rounded apically (Fig. 60).
Geographical distribution. This species is known only from the type locality in the Sierra de Juárez Range, a part of the Sierra Madre de Oaxaca, within the high course of the Rio de Valle Nacional (Figs 77 and 94, black quadrangles).
Way of life. Specimens of this species were collected at an altitude of 5200 feet (1600 m).
Relationships. The armature of internal sac of Z. oaxacanus males is nearly indistinguishable from that of Z. nanus and Z. ixtlanus males, described below, clearly suggesting both of them as closest relatives. The former species is sympatric with Z. oaxacanus and, based on the same label data, may also be syntopic (i.e., their members may occur together in the same habitat). See also Fig. 90  Specific epithet. The specific epithet is a Latin adjective, nanus, in the masculine form, meaning dwarf, miniature, and refers to the small size of the beetles.
Recognition. Adults of this new species are distinguished from those of other species of the genus by the combination of small size and brunneorufous color; and males can be further distinguished by the shape of the median lobe (Fig. 39).
Elytra. Slightly convex, not depressed along suture, comparatively wide (WE/LE 0.72±0.025). Margins rounded, moderately divergent in basal half, evenly rounded to apex in apical third, maximal width of elytra slightly behind the midpoint.
Geographical distribution. The species is known from a few localities in the Sierra de Juárez Range, a part of the Sierra Madre de Oaxaca, along the ~5km stretch of the Rio de Valle Nacional (Figs 77 and 94, white triangles).
Way of life. According to the label data, the elevations of localities range from 4000' to 5200' (1200-1600 m).
Elytra. Convex, not depressed along suture, of moderate width (WE/LE 0.70±0.023). Margins subparallel at middle, slightly divergent in basal third, evenly rounded to apex in apical third, maximal width of elytra slightly behind midpoint.
Female genitalia. Spermatheca standard for genus. Geographical distribution. The species is known only from the type locality in the Sierra Juárez Range, a part of the Sierra Madre de Oaxaca (Figs 77 and 94, white circle).
Relationships. Aedeagal characters (shape of the median lobe and dorsal plates) suggest that Z. ixtlanus is closely related to Z. oaxacanus and Z. nanus. See also Fig. 90 for cladistic affinities.
Recognition. Adults of this new species can be distinguished from those of other species of the genus by the combination of elongate habitus and comparatively narrow pronotum; and males can be further distinguished by the shape of the copulatory sclerites of the median lobe (Fig. 45).
Elytra. Slightly convex, not depressed along suture, rather narrow (WE/LE 0.66±0.019). Margins subparallel at middle, slightly divergent in basal forth, evenly rounded to apex in apical forth, maximal width of elytra at midpoint.
Female genitalia. Spermatheca (Fig. 74) standard for genus. Geographical distribution. The species is known only from the type locality in the Sierra Juárez Range, a part of the Sierra Madre de Oaxaca (Figs 77 and 94 black star).
Way of life. According to the label data (elevation ranges 2600-2700m), these beetles inhabit the pine-oak forest zone of the Sierra Madre de Oaxaca.
Relationships. Externally, adults of Z. iviei are similar to those of Z. kavanaughi, Z. pecki and Z. montanus, described below, but the armature of the internal sac of the median lobe suggests closer relatedness to Z. oaxacanus, Z. nanus and Z. ixtlanus. See also Fig. 90  Specific epithet. The specific epithet is a Latinized eponym in the genitive case, and is based on the surname of David H. Kavanaugh, Senior Curator of the Entomology Department of the California Academy of Sciences, whose enthusiastic efforts in locating and borrowing the material for the current investigation were so magnanimous and productive.
Type locality. Mexico, Oaxaca, 14 km N San Juan del Estado.
Recognition. Adults of this new species are distinguished from those of other species of the genus by the combination of elongate habitus and comparatively narrow pronotum; and males can be further distinguished by the shape of median lobe (Fig. 54).
Elytra. Slightly convex, not depressed along suture, rather narrow (WE/LE 0.66±0.023). Margins almost subparallel, slightly divergent in basal half, evenly rounded to apex in apical third, maximal width of elytra posterior to midpoint.
Geographical distribution. The species is known only from the type locality in the Sierra Aloapaneca Range, a part of the Sierra Madre de Oaxaca (Figs 77 and 94, black circle).
Way of life. All beetles were collected at an elevation of 2600 m. Relationships. Externally, adults of Z. kavanaughi are similar to those of Z. iviei, Z. pecki and Z. montanus, described below, but males and females differ from those of these species in features of the median lobe and shape of the spermatheca, respectively. See also Fig. 90  Specific epithet. The specific epithet is a Latin adjective from mons (= mountain), in the masculine form, meaning mountain-dwelling, and refers to the altitudinal data of the species locality.
Type locality. Mexico, Oaxaca, 52 miles N of Oaxaca.
Recognition. Males of this new species are distinguished from those of other species of the genus by the combination of elongate habitus and shape of the median lobe (Fig. 48).
Female genitalia. Spermatheca standard for genus. Geographical distribution. The species is known only from the type locality in the Sierra Juárez Range, a part of the Sierra Madre de Oaxaca (Figs 77 and 94, white quadrangle).
Way of life. Specimens of this species were collected at 2900-3000m, which is the highest locality known among the Zapotecanillus species. The collection site was located in a limestone area with sinkholes and karst topography, covered with a pine-oak forest. Soil temperature at the time of collection was 48°F (S.Peck, pers. comm.).
Relationships. Externally, adults of Z. montanus are similar to those of Z. kavanaughi, Z. iviei and Z. pecki, but males of Z. montanus may be distinguished from those of the other species by the shape of the median lobe (Fig. 48). See also Fig. 90 for cladistic affinities.  Type locality. Mexico, Oaxaca, 3.5miles S of Suchixtepec. Recognition. Males of this new species are distinguished from those of other species of the genus by the shape of the median lobe (Fig. 51).
Elytra. Slightly convex, not depressed along suture, of moderate width (WE/LE 0.70±0.022). Margins subparallel at middle, slightly divergent in basal half, evenly rounded to apex in apical half, maximal width of elytra at midpoint.
Female genitalia. Spermatheca standard for genus. Geographical distribution. The species is known only from the type locality in the Sierra Madre del Sur, in the surroundings of Suchixtepec (Figs 77 and 94, black flower).
Way of life. Members of this species live at elevations of 8000-9500' (2440-2900 m). At 8000' (= 2440 m), beetles were collected in mixed pine-oak forest with Alnus, Carpinus, etc, and soil temperature at the time of collection was 56°F (S. B. Peck, pers. comm.).
Relationships. Males of this species are easily distinguished from those of other members of the genus by the structure of the median lobe (Fig. 51) and setation of the right paramere (Fig. 53); and the geographical distribution of this species sets it apart from all its congeners. See also Fig. 90 for cladistic affinities.  Recognition. Adults of this new species can be distinguished from those of other species of the genus by the combination of small size and rufotestaceous color; and males can be further distinguished by the shape of the median lobe (Fig. 57).
Elytra. Slightly convex, not depressed along suture, of moderate width (WE/ LE 0.69±0.015). Margins nearly subparallel, slightly divergent in basal forth, evenly rounded to apex in apical third, maximal width of elytra near midpoint.
Geographical distribution. The species is known only from the type locality in the Sierra Madre de Chiapas (Figs 77 and 94, black triangles).
Way of life. According to the label data, these beetles inhabit mesophyll and mixed oak/pine forests at low elevations.
Relationships. In the structure of median lobe of males and geographical distribution, this species is only remotely related to its congeners. See also Fig. 90 for cladistic affinities.
Zapotecanillus sp. Among the materials at hands, these two teneral specimens remain unidentified because of insufficient material for investigation. They were collected in the cloud forest near Custepec in the Sierra Madre de Chiapas (Fig. 77, white star). Both specimens resemble Z. longinoi adults externally but are larger in size, and cannot be identified unambiguously. This locality represents the most southern point of the known range of Zapotecanillus.

Results of cladistic analysis
The parsimony analysis resulted in two most parsimonious trees (L=53; CI=0.74; RI=0.76); the 75% majority-rule consensus cladogram of these trees is presented in Fig. 90, with the characters and support values mapped on the corresponding internal branches. The main basal nodes of the cladogram are highly supported by Bootstrap and Bremer indices, whereas a part of the terminal nodes is inadequately supported, which results in collapsed branches. The Zapotecanillus species form a well-supported monophyletic group (clade A, bootstrap value=100). Their monophyly is supported by the derived states for characters 4 (labial mental suture), 12 (additional apicolateral pronotal setae), 18 (positions of 7, 8, and 9 pores of umbilicate series), 19 (elytral subapical sinuation), 20 (shape of the intercoxal process of the abdomen), 21(shape of the metendoventrite) and 32 (shape of the spermatheca). Within the genus, a basal clade is presented by Z. oaxacanus, which is morphologically the closest species to the outgroup taxa (the latter selected from the litter species of anilline genera Geocharidius and Nesamblyops, Figs 78 and 79, respectively). Clade B is characterized by few traits, highlighting changes in the species' appearance-notably the proportional reduction in the size of pronotum (character 3) and the shifting of the pronotal hind angles in a forward direction (characters 10 and 11); also the apex of median lobe is getting smaller (character 26). Clade C includes species with derived shared characters, which intensify the habitual dissimilarity with outgroup taxa. The pronotum in members of these species is proportionally shorter (character 6) and the elytra are narrower (character 15); also, internal parts of the male genitalia, namely the ring sclerite (characters 23 and 24), and parameres (character 31), are reduced. Clade D includes the species that are most unlike the basal taxa externally. Members of species in this clade have slightly convex bodies (character 1) and are completely yellow in color (characters 14 and 16). Members of Clade E species share a narrow pronotum with a shallow sinuation of the lateral margins anterior to the hind angles (characters 8 and 9). Thus, the cladogram of species' relationships primarily reflects the gradual changes in external characteristics from basal to terminal clades, incorporating some changes in genitalic structures. The trend in changes in external form on the cladogram (from ovoid and pigmented towards elongate and depigmented beetles) reflects evolutionary adaptations for a more endogean way of life.

Taxonomic and evolutionary issues
New data enable us to discuss several taxonomical and evolutionary issues, despite the limited material available for Zapotecanillus.

Taxonomical notes
Remarks on Geocharidius larva. Ten years ago, a description of the first-instar larva of Geocharidius was published (Grebennikov 2002), and since then, it has remained the only larva of Anillina known from the New World. Material from the locality where the larva was collected also contained adults of Anillina and was labeled: "MEX: Oaxaca, 17.6mi S Ixtlán de Juárez…" (l.c.). The larva was identified as Geocharidius larva by association with adults, first by Vasily Grebennikov (Ottawa Plant Laboratory, Canadian Food Inspection Agency), and later by Terry Erwin (Smithsonian Institute), who approved the identification (l.c.). Based on data available now, Geocharidius species do not occur in the state of Oaxaca, whereas Zapotecanillus species do occur there. Thus, it is likely that the larva described in 2002 is of a Zapotecanillus species, rather than a Geocharidius species. Erwin did not distinguish the two genera, so his labeling the representatives of Zapotecanillus as Geocharidius sp. is understandable. Notes about Zapotecanillus. As previously mentioned, it is difficult to assess relationships of the new genus to the other North and Central American Anillina without a modern revision of the latter. Therefore, the conclusions drawn below should be treated as preliminary and speculative.
Externally, the absence of discal setae is a feature that members of this new genus share with those of the southern stock of genera, like Geocharidius, Mexanillus and Honduranillus Zaballos (Zaballos 1997). The enigmatic Honduranillus, described from one female, is the only genus of Anillina in North and Central America whose members lack elytral discal pores but have distinct paraglossae, traits shared with Zapotecanillus members. However, the differences in arrangement of the last umbilicate pores and the length of the apical palpomere of the maxillae suggest that these similarities may be convergent. Historically, great importance has been given to the arrangement of setae in the apical portion of the umbilicate series. The above-mentioned southern stock of anilline genera belongs to the "scotodipnienne" evolutionary lineage, members of which have pores 7 and 8, and 8 and 9 separated from each other by equal distances ("Type B" of Jeannel's classification), whereas Zapotecanillus is formally a representative of another evolutionary lineage of Anillina, the "anillienne" lineage, in which pores 8 and 9 are distinctly closer to each other than pore 7 is to pore 8 (the so-called" geminate" arrangement, "Type A" of Jeannel (1963a)). Recently, Giachino and Vailati (Giachino and Vailati 2011), treating the anilline fauna of Greece, discovered that representatives of the "anillienne" genus Prioniomus Jeannel demonstrate great variation in the positions of pores 8 and 9. This discovery led the authors to propose a scheme of positional rearrangements of the setae of umbilicate series, leading from the "scotodipnienne" to the "anillienne" arrangement of pores. Similar rearrangements in the position of the 7 th through 9 th pores of the umbilicate series may well have occurred with the evolution of Zapotecanillus species. If so, Zapotecanillus may be the sister-taxon of Geocharidius; and the diversification of each genus may then be associated with one of two mountainous regions-namely, Oaxaca and Nuclear Middle America-which are separated by the Isthmus of Tehuantepec (Fig. 77), an important biogeographical barrier in the region under question (Ball 1968;Halffter 1987;Marshall and Liebherr 2000). In this case, the common ancestor of both genera would have been characterized as an anilline beetle with the "scotodipnienne" type of umbilicate series, as well as it would also lack discal pores on the elytra, and would have long last maxillary palpomeres, distinct paraglossae, free labial complex (i.e., mentum and submentum not fused), and simple metendoventrite. Subsequent evolution led to independent modifications of these traits and resulted in the origin of these two genera, members of which are morphologically very dissimilar. Presumably, we can tie the divergence of the two genera to the middle Pliocene, c. 3.1-3.5 Ma, when the Isthmus was replaced by a marine embayment (Barrier et al. 1998). Molecular analyses of many taxa among reptiles (Castoe et al. 2009;Daza et al. 2010), birds (Barber and Klicka 2010), and rodents (Hardy et al. 2013;Ornelas et al. 2013) provide evidence that this time is a historic milestone for Mesoamerican faunal diversification.
To confirm or reject the proposed phylogenetic relationship of Zapotecanillus within the North and Central American Anillina, the regional fauna requires further investigation, including analyses of additional morphological and, hopefully, molecular data.

Evolutionary notes
Although cladistic analysis does not allow us to fully resolve phylogenetic relationships, some evolutional trends of Zapotecanillus, evident from the resulting cladogram, are worth examining.
Deviations from the form of the pronotum of litter species, such as the reduction in the overall size of the pronotum and forward shift of the hind angles (Fig. 90, clade  B), reflect an increase in flexibility of the pronotal-elytral joint. A more flexible joint can potentially expand the number of accessible niches, enabling their bearers to live in a greater number of structurally different litter or soil interspace habitats. It seems that, among the litter-dwelling ancestors of Zapotecanillus, adaptations for living in a new environment were restricted by two major directions of species evolution.
The first direction, a syntopic habitat expansion, can be characterized as the intensification of local litter resource exploitation, presumably by means of niche differentiation.
The structural complexity of the litter, undergoing decomposition, produces a graded series of overlapping planes interspersed with intertwined gaps, both of which tend to become smaller as one travels downwards toward the soil (Kaspari and Weiser 2007). In this case, new pronotal features enabling the species to move deeper, downwards through the intertwining environment, resulted in the differentiation of a miniature species Z. nanus (Fig. 91), which co-occurred with its relatively larger and morphologically closest relative, Z. oaxacanus. Syntopic miniaturization, producing a certain number of related species differing in size can be considered a common evolutionary trend within the anilline world. Pairs of syntopic small/large species pairs are known among the Central American Geocharidius (G. phineus-G. romeoi Erwin) (Erwin 1982), the North American Anillodes (A. walkeri Jeannel-A. minutus Jeannel) (Jeannel 1963a(Jeannel , 1963b, Anillinus (A. lescheni Sokolov and Carlton-A. stephani Sokolov and Carlton) (Sokolov et al. 2004), and the European Typhlocharis Dieck (Pérez-Gonzáles and Zaballos 2013a). In some cases, even more than two species of anillines may be syntopic, as it was shown for the Pyrenean Typhlocharis Dieck, among which three species, well-differentiated in size, co-occur (Pérez-Gonzáles and Zaballos 2013b). The evolution of Z. longinoi, another miniature species of Zapotecanillus, also matches the proposed scheme of evolution, except that, in this case, the role of the large species is played by a representative of another genus, Geocharidius.
The second direction of evolution among Zapotecanillus species was connected with the altitudinal expansion of the genus and subsequent adaptations to the endogean way of life. In Clade C (Fig. 90), pronotal and elytral morphology have undergone additional modifications. Most of the species of this clade live at elevations above 2400m, as exemplified by Z. ixtlanus (Fig. 92). The ability to live at high elevation implies adaptations to withstand daily and seasonal variations in temperature and humidity. One solution to this challenge is the acquisition of adaptations that facilitate vertical migrations, from the litter down into the soil and back to the litter again to track favorable and escape from unacceptable microclimatic shifts (e.g., regular frosts at high elevations of the Sierra de Juárez). Also, changes in forest communities along the elevation gradient can play an additional role in the evolution of species adaptations. In the Sierra Madre de Oaxaca, the humid montane cloud forests at elevations of 1200-1600m are characterized by the dominance of broadleaf tree species, such as Quercus, Liquidambar, Carpinus, and Fagus (Flores and Manzanero 1999), while in the temperate high-elevation forests at altitudes of 2200m to 2800m, the dominant tree species are various species of Pinus , Saynes et al. 2012, presumably with corresponding changes in the forest litter composition and structure. Such features of high-altitude anillines as elongate habitus together with small pronotum with an oblique basal margin, may represent adaptations to differences in the important climatic and vegetation parameters along the altitudinal gradient such as those mentioned above. Changes in the states of characters in Clade D (Fig. 90), including depigmentation and flattening of the body, may reflect and support the transition from the litter to the endogean way of life among the high-altitude Zapotecanillus. The same situation was recorded for the high-altitude Appalachian Anillinus moseleyaegroup of species, Sokolov 2011). All terminals of clade D on the cladogram (Fig. 90) are represented by species (Figs 27-31) whose morphology suggests an endogean way of life (at least temporarily); and in one case (Z. montanus) we have a straight reference to habitat ("sink litter"), which can be treated as support for the proposed speculations.

Distributional notes
A review of the overall distribution of genus Zapotecanillus shows that species with endogean lifestyles are distributed across the whole range of the genus (Fig. 90, SMS, SMO, SMC), while litter-dwelling species are restricted to only the eastern slopes of the Sierra Madre de Oaxaca (Fig. 90, SMO). A priori, one might expect that litterdwelling forms would be more broadly distributed than endogean forms, but within Zapotecanillus, this does not appear to be so. Perhaps additional litter-dwelling species of the genus remain undiscovered or have gone extinct in this region, but the extensive overall distribution of endogean species clearly suggests a role for them in the expansion and the shape of the modern geographical range of the genus. For instance, in the Sierra Madre de Chiapas, adults of Z. longinoi and Z. sp., both of the endogean morphological type, were collected at altitudes of 1330m to 2140m, which are approximately the same elevations at which low-altitude Z. oaxacanus and Z. nanus were collected in the Sierra de Juárez (Sierra Madre de Oaxaca). If a litter-dwelling ancestral Zapotecanillus species had dispersed from the Sierra Madre de Oaxaca to the Sierra Madre de Chiapas, one would expect members of the Chiapan descendant species to be similar in life-style and appearance to those of the Oaxacan ancestral form because low elevations are primarily occupied by litter species. However, adults of Z. longinoi and Z. sp., are flattened and depigmented, and quite different from the convex and pigmented litter-dwelling Zapotecanillus forms, as well as from litter-dwelling Geocharidius species. It is perhaps significant that Z. longinoi and Z. sp. members are syntopic with litter-dwelling species of Geocharidius in the Sierra Madre de Chiapas. It may be that the presence of two species of Zapotecanillus with endogean morphology at low elevations in the Sierra Madre de Chiapas represents a secondary occupation of the region by endogean forms, thus, supporting the idea that at least some endogean Zapotecanillus forms are capable of significant dispersal.
If we consider that the endogean way of life of the Zapotecanillus species was triggered by changes in microclimate parameters, then regional dispersal of the depigmented and only slightly convex Zapotecanillus species also could have been connected with certain climate changes. Such dispersal likely occurred during one or more of the Pleistocene glacial cycles, which enabled species with endogean life-styles to cross the Isthmus of Tehuantepec, and, perhaps, the Central Valleys of Oaxaca, and to establish populations in the Sierra Madre de Chiapas and the Sierra Madre del Sur, respectively (Fig. 93). Evidence that the Isthmus served as a corridor connecting Oaxaca and Chiapas Sierras during Pleistocene glaciations has been shown for some bird species (García-Moreno et al. 2004;Barber and Klicka 2010) as well as cloud forest communities (Ornelas et al. 2013). Regional dispersal of the ancestral Zapotecanillus stock even-tually resulted in allopatric, presumably Quaternary, speciation in the genus, thereby shaping the modern distribution of the genus (Fig. 94).