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Ctenomys Blainville, 1826 (known as tuco-tucos) is considered one of the most diverse genus within mammals; however, its taxonomy is far from resolved. In recent years, new species have been described, and many other forms have been synonymized, while other lineages remain as candidate species. In this work, based on molecular and morphological evidence, we proposed that C. “rosendopascuali”, a taxon considered as a nomen nudum, is in fact a synonym of C. bergi Thomas, 1902. The molecular phylogeny based on the mitochondrial cytochrome b gene showed that individuals from populations a priori assigned to C. bergi and C. “rosendopascuali” were not reciprocally monophyletic. Additionally, geometric morphometric analyses based on cranial morphology showed significant overlap in the morphospace of these two taxa. Our results also show a high genetic similarity among C. bergi, C. “yolandae”, and C. bonettoi Contreras and Berry, 1982, questioning the taxonomic status of the latter two taxa and highlighting the need for exhaustive comparison with C. bergi. We also identified a second locality for a highly divergent lineage within the Mendocinus group (Quijadas lineage). Our study confirms the divergence of this lineage and highlights the need to further taxonomic studies in order to evaluate whether it represents a possible undescribed Ctenomys species.

We describe a new species of the genus Atlantirivulus from a small first-order stream on the right margin of the Paraná River basin in the Mato Grosso do Sul, Brazil. The region of occurrence of the new species is known to be a hotspot for Melanorivulus species. This area, however, is approximately 700 km away from the record of occurrence of its closest congeners, which are distributed along the Brazilian coast in different hydrographic basins. Atlantirivulus enigmaticus, new species, is distinguished from all congeners by it s unique coloration, which consists of the flank being purplish grey with light green iridescence with brownish red dots scattered along of the body, by the neuromasts of the infraorbital series being aligned around eye, and by the presence of the short ventral process of the posttemporal. The phylogenetic position of the new species within the Atlantirivulus genus was based on molecular phylogenetic analysis using sequences of the mitochondrial gene cytochrome oxidase subunit 1. The results show that the new species is closely related to Atlantirivulus luelingi from the coastal drainages of the Brazilian state Santa Catarina. The phylogenetic position of the new species among congeners endemic to coastal river basins may be related to ancestral connections between coastal drainages and the Paraná River basin. The new species constitutes the westernmost record for the genus, and the first record of Atlantirivulus in the Paraná River basin. Insufficient collection efforts in areas of potential occurrence for the group and extinction processes in the broad region between the locality of the new species and the distribution areas of the remaining species may be a possible explanation for this disjunct distribution.

The representatives of the genus Ablepharus Fitzinger, 1824 have not been studied in detail from a morphological and taxonomic perspective. The morphology of hemipenes of 14 taxa of the fused eyelids species of the genus was studied. Manual eversion and inflation with absolute ethanol was used for preparation of the organs. The results indicate that the Ablepharus hemipenes show little variation in general shape and main structures: all hemipenes are deeply bifurcated, without large external calcified or keratinous spines or similar structures. Based on hemipenial morphology, the studied taxa can be separated into two clades: 1) with long, slender and 2) with short, robust lobes of the hemipenis. The morphology of this structure demonstrates close relationships between the fused eyelids ablepharine skinks, points out unresolved taxonomic problems, and shows general congruence with available molecular phylogenies. Hemipenial characteristics appear to be a useful tool for the identification of the species within the genus. Problems associated with the real taxonomic status of the Ablepharus budaki anatolicus paratypes and the distribution of other taxa are discussed. The morphology of the hemipenis of the family Scincidae and the related, inconsistent use of terminology are also commented on.

The ongoing depletion of the diversity of Pachylinae, the largest subfamily within Gonyleptidae, is progressing. The unranked clade DRMN continues to expand, now incorporating two additional genera – Gyndoides Mello-Leitão, 1927, and Sertaneja Saraiva, Hara & DaSilva, 2021 – previously classified under Pachylinae. Through a cladistic analysis, with an expansion of the morphological dataset used in previous works, our research reveals that both Gyndoides and Sertaneja are separately placed within DRMN. As DRMN is not a formal Linnean taxon, both genera are herein called Gonyleptidae incertae sedis to avoid the establishment of new monogeneric subfamilies. A new species of Gyndoides is described from the state of Paraná, marking the first record for the genus from this state. The other two species, from Santa Catarina state, are herein redescribed, and an emended diagnosis is provided for the genus.

Herein we present a survey on the variation in the morphology of the structures that compose the larval buccopharyngeal cavity of Thoropa miliaris tadpoles based on samples of 18 different stages of development, from embryos (removed from the egg capsules) to stages near or at metamorphosis. Our observations revealed that several structures vary independently along the stages. This variation appears in the number of (sub) unities, shape, and positions. Structures observed acquire a “mature format”, increase and decrease in size, and are reabsorbed during distinct tadpole stages. Our observations suggest that caution should be taken when assigning presence/absence or a specific morphology to characters derived from these structures and that samples of several semaphoronts (from as many different stages as feasible) should be evaluated prior to stating for instance that a structure is absent. We also discuss our findings regarding several interpretations of buccopharyngeal features of tadpoles and compare with the ontogenetic studies regarding this character system found in the literature.

In the course of Digenea evolution the transitions to a passive strategy of infection of the first intermediate host occurred multiple times. In these cases, miracidia – ciliated larvae – relinquished their role as active seekers for a suitable snail host and began relying on the chance of being accidently ingested by it. The structural changes resulting from these transitions are diverse, but the majority of them are reductive. In this study we present our ultrastructural survey on the opisthorchioid Cryptocotyle lingua miracidium. The transition to passivity led to extensive reduction in almost all somatic elements of the larva: only four epithelial plates cover its body; just a single nervous cell, a single protonephridium and a single longitudinally-oriented muscle cell have been found in this miracidium. Several undifferentiated cells comprise the germinal material of the larva. The greatest part of its body is occupied by three glandular elements. The position of these glands is consistent within Opisthorchioidea and strikingly corresponds to that of some of the optically studied miracidia of Plagiorchioidea. This similarity is suspicious, because the C. lingua larva appeared to differ vastly from other ultrastructurally described passive miracidia. Here we create a basis for the future comparison of the miracidia of Opisthorchioidea and Plagiorchioidea, expecting the ultrastructural data on the latter to be published someday.

New material of four Acrobeloides species (Acrobeloides arenicola, Acrobeloides bodenheimeri, Acrobeloides nanus and Acrobeloides tricornis) are redescribed from xeric areas in Spain. This species are morphological (based on light microscopy and scanning electron microscopy study) and morphometrically differentiated in two groups. One of them, including A. arenicola, A. nanus and A. tricornis (belonging to the buetschli-group), are characterised by having smaller body, lip region with labial probolae having rectangular base, pharynx with long isthmus, female genital system scarcely developed with vulva midventral, and usually males absent, these with small spicules. Other species group, including A. bodenheimeri (belonging to the maximus-group), is characterised by having longer body, lip region with triangular base, pharynx with very short isthmus, female genital system well developed with vulva usually located ventrolateral, and males frequent with large and robust spicules. This division is corroborate with molecular analyses based on 18S and 28S rDNA. According to this, the separation of the genus Acrobeloides in two different genera is proposed. As Paracephalobus litoralis is morphologically similar to the species of the maximus-group, the genus Paracephalobus is restored to name the species included in the maximus-group. An updated list of species for the genera Acrobeloides and Paracephalobus is included. In addition, Acrobeloides insignis, A. sexlineatus, A. thornei and A. varius are proposed new junior synonyms of A. tricornis.

Morphological alterations of the gill and digestive gland were studied in Magallana gigas from areas with different degrees of human activity over one year. For that, the height of the plicas and filaments of the gill and the mean epithelial thickness were measured, the ratio of cell type and tissue composition analyzed of the digestive gland as well as alterations in the pattern of structural organization in these organs were assessed. The specimens were collected in November 2021, and February, May and August 2022 from two representative sampling sites of distinct anthropic pressures in the coastal area of Buenos Aires Province: Arroyo Parejas (AP, 38° 55′ S, 62° 04′ W) and Pehuén-Có (PC, 39° 01′ S; 61° 32’ W). The results of the morphological parameters, ratio of cell-type, tissue composition, and histological alterations of M. gigas showed differences between the studied areas and seasons, suggesting a negative relationship between human activity and the health of the gills and digestive gland of the oyster. Understanding the gill and digestive gland morphology of oysters, as well as their response to varying levels of human activity in the study region, could help mitigate the impacts of this non-native species.

The tribe Alticini (Newman, 1834) is a diverse and amply distributed group of beetles, although its internal arrangement is still poorly defined. The taxonomy of the subtribe Oedionychina is especially challenging, due to mimicry. The present study integrates cytogenetic, morphological, and molecular data to describe Alagoasa neoequestris sp. nov. and establishes its phylogenetic position within the group. The morphological characteristics of the new species are consistent with the genus Alagoasa. The comparison of the male genitalia among the species indicates reproductive isolation. The diploid number and the giant and asynaptic sex chromosomes are typical of the oedionychines, although with considerable differentiation in chromosome morphology and the distribution of the heterochromatin. The location of the rDNA 45S and 5S cistrons is conserved as in Coleoptera. The phylogenetic analysis placed A. neoequestris sp. nov. in Alagoasa, in a cluster with Alagoasa plaumanni, clearly separated from all other genera. The karyotype of the new species contradicts that reported for "Alagoasa equestris” (2n = 12), which coincides with that of the morphologically very similar Omophoita communis. It thus seems likely that “A. equestris” is in fact O. communis. The sum of the evidence supports clearly the description of the new Alagoasa species from southern Brazil.

Head shape plays a crucial role in ecological and evolutionary processes in lizards, and scientists have studied head shape using traditional and 3D geometric morphometrics. Lizards are classic subjects for ecological studies because closely related and ecologically similar species coexist. Sympatric species tend to show higher levels of morphological divergence compared to allopatric species.

In this study, we focus on two parthenogenetic Darevskia species (Darevskia dahli and Darevskia armeniaca) that share a maternal species, Darevskia mixta, but have different paternal species (Darevskia portschinskii and Darevskia valentini). We aim to assess the relative importance of morphologically inheritable traits and environmental conditions on head shape in these parthenogenetic species. Specifically, we aim to determine whether local adaptations or intermediate phenotypes between parental species drive head shape variation in parthenogens. To accomplish this, we analyze the head shapes of samples from both parthenogens, their paternal species, and their common maternal species from 3 sites in Georgia. Our study shows that certain aspects of head shape are associated with body size and habitat climate, with high mountain species exhibiting larger and deeper heads with stronger jaws regardless of breeding mode. In addition, both parthenogens exhibit narrower and more elongated jaw areas, flatter mandibles, and thus weaker jaws compared to females of their maternal and paternal species.