Kathlaniidae (Ascaridomorpha: Cosmocercoidea) represents a diverse family of intestinal nematodes that are parasitic in all classes of vertebrates worldwide, except Aves. However, our knowledge on the systematic and molecular phylogeny of this family is unclear and complicated. The phylogenetic relationships between its subfamilies Kathlaniinae, Oxyascaridinae and Cruziinae are still under debate. Moreover, the systematic position of the genus Cruzia (Cruziinae) within Kathlaniidae remains unclear. This work aimed to characterize, both morphologically and genetically, specimens of Cruzia sp. and evaluate the phylogenetic position of this genus within the Kathlaniidae, the phylogenetic relationships of this family with other taxa of Cosmocercoidea, and the status of Cruziinae as a subfamily. During a parasitological survey carried out in December 2024, specimens of Cruzia sp. were collected from the intestine of Salvator merianae (Squamata: Teiidae) from Corrientes (Argentina) and characterized using morphological (light and scanning electron microscopy) and molecular (sequencing of partial fragments of 18S rDNA, and COI mtDNA) methods. Phylogenies were reconstructed based on Bayesian inference. The morphological analysis indicated the presence of 15–16 teeth per row in the pharynx, equatorial vulva in females, and 11 pairs of cloacal papillae in males, arranged as follows: 3 precloacal, 3 paracloacal, 5 postcloacal, and a minute precloacal unpaired, and spicule length less than 1mm. Such a combination of morphological features seems to be unique when compared with that of other congeners, suggesting a possible new taxon. In the phylogenetic reconstructions based on 18S rDNA and COI mtDNA, Cruzia sp. formed an independent lineage, sister to a group formed by C. americana and C. tentaculata. Kathlaniidae was paraphyletic, because Cruziinae formed a separate lineage from other kathlaniids and closely related to the cosmocercid Cosmocerca (Cosmocercidae, Cosmococercoidea). Based on these results, we suggest that Cruziinae should be elevated to family.

Introduction
The family Zenarchopteridae, comprising freshwater and brackish water halfbeaks, is restricted to Asia and Oceania and includes five genera: Dermogenys, Hemirhamphodon, Nomorhamphus, Tondanichthys, and Zenarchopterus. Of the 64 valid species, over half were described after 1950, reflecting considerable taxonomic complexity. The genus Dermogenys contains 13 species found in freshwater habitats across South and Southeast Asia. Despite this diversity, molecular studies are limited and indicate the presence of cryptic speciation. This study explores the barcode library for Zenarchopteridae, demonstrates the efficacy of DNA barcoding techniques for differentiating Dermogenys species, and demonstrates the potential thereof in species discovery.

Methods

In this study, mitochondrial Cytochrome Oxidase subunit I (COI) gene sequences obtained from publicly available databases were analysed to evaluate species-level diversity and phylogenetic relationships within Dermogenys. Maximum Likelihood analysis for reconstructing the phylogenetic tree and mean genetic distances were calculated using MEGA X.

Results

The resulting phylogenetic tree uncovered significant incongruence between morphological identification and genetic clustering. A total of 29 distinct clades were recovered, with D. siamensis and D. collettei each displaying six different genetic lineages; D. bispina and D. pusilla showing three; D. sumatrana having two; and nine additional clades identified solely as Dermogenys sp., indicating cryptic speciation and possible misidentifications. A minimum genetic divergence threshold of approximately 2% in COI sequences, commonly used for species delineation in teleost fishes, supports the presence of cryptic taxa within the group.

Conclusion

All Beloniformes families except Scomberesocidae have been recorded from Indian waters. Compared to the well-studied Belonidae and Hemiramphidae, Zenarchopteridae remains understudied, with the genus Dermogenys represented by only one species, D. brachynotopterus. This study reveals that morphological taxonomy alone is insufficient for species delimitation in Dermogenys, highlighting the need for integrative approaches. The findings have important implications for species validation, conservation, and resource management in Southeast Asia.

Over the last decade, environmental DNA (eDNA) has emerged as a non-invasive and effective tool for characterizing species from water, soil, or air samples. The increasing interest in offshore and deep-sea explorations in Colombian oceans has required the implementation of new technology to improve sampling efforts and data quality in these hard-to-access areas.

In this study, we present the promising complementarity of eDNA-metabarcoding in providing accurate taxonomic delimitations fish obtained on board several scientific expeditions along the Colombian Pacific. We filtered 360L of seawater in each of the 34 sampling stations through 0.2µm capsule filters using peristaltic pumps. Seawater was collected during day and night shifts using oceanographic rosettes in vertical transects (200 to 10m depth). eDNA was preserved and analyzed using a 12S-V5 mitochondrial region, followed by high‑throughput sequencing. Molecular operational taxonomic units (MOTUs) were assigned using OBITools, as well as curated reference libraries that included regional voucher sequences.

The results yielded over 20 million DNA sequences, translated into 320 fish ASVs from 71 families, 59 genera and 84 species, most of which were migratory, demersal, meso-, and bathypelagic taxa. Families with the greatest species richness belonged to Teleostei families such as Myctophidae, Nomeidae, Scombridae, Coryphaenidae and Istiophoridae. Regarding Elasmobranchii, the most conspicuous families were Carcharhinidae, Alopiidae, Myliobatidae and Rhincodontidae. It is important to mention that another 100 MOTUS could not be identified to the species level due to lack of genetic reference databases available in the region.

These results were compared to historical data regarding fishing activities in the past 20 years, demonstrating that eDNA could match over 90% of the known fish biodiversity surveys in offshore areas while reducing sampling effort and costs. Further research should focus on improving genetic databases and on the implementation of eDNA tools as an alternative that should be embedded in routine monitoring programs.

The deep-sea squid family Brachioteuthidae is one of the most systematically
unstable cephalopod taxa in need of a global revision. The general lack of adult
specimens in research collections, incomplete and inaccurate species descriptions,
descriptions based on paralarvae or early juveniles only, and sexual dimorphism
have all contributed to the instability of this family. As part of a global revision, a local
review of the New Zealand and Southern Ocean brachioteuthids is being undertaken
using integrative taxonomy. While the family was founded in 1881, Brachioteuthis
was only formally reported from New Zealand waters in 2019. In the meantime, four
genetically distinct species from around New Zealand have been identified, some of
which may represent unnamed/new species. One of these species (‘Brachioteuthis
sp. Ker 2’, sensu Braid & Bolstad 2019) forms a clade with low variation with
individuals from the northern Atlantic, which suggests that some brachioteuthids may
have very wide geographic ranges. The key morphological characters for species
level delimitation include tentacle-club morphology including carpal (fixing) apparatus
[when present], skin sculpture (useful in sexual dimorphism cases), arm
modifications in males, liver morphology, eye photophore morphology and the
general habitus based on shape analysis. This project represents a step forward in
the systematic resolution of this complicated family. However, an integrative
taxonomic approach will be required to resolve the global systematics of
brachioteuthids.

The family Iguanodectidae comprises small characiform fishes widely distributed across the Amazon Basin, yet species boundaries within some taxa remain poorly understood. In this study, we analyzed specimens of Iguanodectes purusi, collected from the Purus River, and I. spilurus, from different localities including the Madeira River (Aveiro). Phylogenetic analyses based on molecular markers recovered I. purusi nested within the I. spilurus (sensu stricto) clade, with extremely low genetic divergence between them (0.005 ± 0.005). Morphological analyses revealed strong similarities between the two taxa, including a complete lateral line with 60–64 perforated scales, eight scales between the lateral line and the dorsal-fin origin, five scales between the lateral line and the pelvic fin, and an anal fin with 32–34 branched rays. General coloration is light, with a silvery stripe along the midline of the body and a dark blotch on the upper caudal-fin lobe. I. spilurus is the only species of the genus recorded in the main channel of the Madeira River, whereas the other congeners were found exclusively in terra firme streams. Despite these similarities, I. purusi exhibits subtle differences, such as a higher number of predorsal scales (≥27 in I. purusi vs. ≤26 in I. spilurus) and more perforated scales on the lateral line (>65 in I. purusi vs. 60–64 in I. spilurus). However, these differences may represent geographic (clinal) variation among populations distributed across the Amazon Basin rather than valid species-level differentiation. Our findings highlight the need for taxonomic revisions integrating molecular, morphological, and ecological data to clarify the status of I. purusi and to better understand diversity patterns within Iguanodectidae.

Hoplias Gill has long been considered taxonomically challenging among Neotropical freshwater fishes, particularly due to the presence of cryptic species within the H. malabaricus complex, which exhibits extensive morphological overlap among lineages of many Neotropical drainages. In this study, an integrative approach combining morphological and molecular data was employed to describe a new taxon from the upper Paraná River basin, Brazil. A total of 22 specimens were analyzed using morphometric and meristic assessments, along with mitochondrial COI gene sequencing. Species delimitation was performed through multiple methods, including genetic distance analysis on the BOLD Systems platform, Automatic Partitioning (ASAP), Generalized Mixed Yule Coalescent (GMYC), and Poisson Tree Processes (PTP). Phylogenetic trees were reconstructed using Bayesian inference. Hoplias sp. n. presents distinct diagnostic characters among congeners: 36–37 perforated lateral-line scales (vs. 37–43), 13–15 predorsal scales (vs. 15–19), 37–38 total vertebrae (vs. 39–45), and a rectilinear arrangement of scales at the base of the caudal fin. Molecularly, it forms a distinct clade with minimum K2P genetic distances of 3.7% from its closest relative (H. auri), exceeding the commonly accepted 2–3% threshold for species delimitation. All applied methods consistently recovered the new taxon as an independent evolutionary unit: ASAP (nine groups; p = 8.79×10⁻³), GMYC (nine entities; p = 0.0007), and PTP (support = 0.999). The convergence of morphological and molecular evidence strongly supports the recognition of Hoplias sp. n. as a valid new species for the upper Paraná River basin. These findings enhance our understanding of the genus diversity and underscore the power of integrative taxonomy in resolving cryptic species complexes among Neotropical fishes, thereby helping to reduce the Linnean shortfall.

The Navajini, a clade of Neotropical electric fishes within the family Apteronotidae, exhibit exceptional craniofacial diversity that reflects a dynamic interplay of evolutionary forces. This study examines the morphological, ecological, and developmental drivers of phenotypic diversification in this group, which includes some of the most specialized skull morphologies among South American freshwater fishes. We integrate 3D geometric morphometrics, high-resolution micro-computed tomography (micro-CT), and multivariate statistical analyses within a robust phylogenetic comparative framework to assess patterns of skull shape evolution across the clade. Ancestral state reconstruction and tests for phylogenetic signal reveal that key cranial traits such as lower jaw elongation, opercle morphology, and maxilla orientation are not randomly distributed but instead show significant phylogenetic structure and ecological relevance. Morphological disparity is strongly influenced by sexual dimorphism in certain lineages, particularly those exhibiting hypertrophied male traits, while other groups display more conservative, modular cranial architectures. We find that access to novel regions of morphospace has been facilitated by shifts in feeding ecology and developmental modularity, enabling trophic specialization and repeated convergent evolution among ecologically similar taxa. These findings support a model in which cranial evolution is shaped by both adaptive responses to ecological opportunity and intrinsic developmental constraints. Overall, this work sheds light on the mechanisms generating phenotypic diversity in Apteronotidae and contributes to a broader understanding of how ecological and evolutionary processes interact to shape morphological evolution in Neotropical freshwater fishes.

Astyanax Baird & Girard, 1854 is the most widely distributed genus of Acestrorhamphidae, occurring from the West Texas Gulf to Central Argentina. Out of the 120 valid species currently recognized, around 15 occur in the Amazon basin. A possible new species was registered in streams of the Aripuanã River basin (= Madeira River basin) and Juruena River basin (= Tapajós River basin). For the new taxon, morphological, meristic, and coloration characters of 42 specimens were analyzed. Astyanax sp. n. differs from all its congeners by the following combination of characters: two humeral spots, the first vertically elongated and the second approximately rounded, beginning on the dark longitudinal stripe; maxilla toothless or with 1 tooth; premaxilla with two tooth rows: outer row with 4 or 5, tricuspids, inner row with 4 or 5, heptacuspid; dentary with 4 teeth, penta- to hexacuspid; complete lateral line, extending to the end of the caudal peduncle, with 34 to 37 perforated scales; 12 to 15 circumpeduncular scales; 6 or 7 transverse scale rows above the lateral line; 5 or 6 below; anal fin with 22 to 27 branched rays. Males of the new species show a straight anal fin and a bony hook on the distal segments of the last unbranched ray. The record of the new taxon highlights the importance of sampling headwaters of Amazonian drainages, which harbor significant undescribed species diversity, especially small-sized ones, in areas subject to anthropogenic impacts (e.g., extensive agriculture). The description of this new species expands the known diversity of Astyanax and contributes to reducing the Linnean shortfall of Neotropical ichthyofauna.

The class Calcarea comprises 831 (8.5%) out of the 9,700 described species of the phylum Porifera. Knowledge on the diversity and distribution of calcareous sponges remains limited due to insufficient sampling and taxonomy specialists. This is also evident in the Great Barrier Reef (GBR), which presents only 25 (9%) out of the 280 calcareous sponges reported for Australia. Therefore, this study seeks to describe the species diversity of the subclass Calcinea from Heron Island, GBR, using integrative taxonomy (morphological and molecular analyses). Among the 19 specimens analysed, eleven species were identified, seven of them being new to science: Arturia sp. nov., Clathrina sp. nov., Janusya sp. nov. 1, Janusya sp. nov. 2, Neoernsta sp. nov. 1, Neoernsta sp. nov. 2, and Neoernsta sp. nov. 3. Additionally, four previously known species had their distributions widened within the South Pacific Ocean: Arturia dubia, Clathrina fakaravae, Clathrina procumbens, and Clathrina cf. stipitata. Some of these species show trans-Pacific distributions. Knowledge on the Calcinea diversity in Heron Island rose from 4 to 15 species (275%) and from 15 to 26 (73%) in the GBR. Moreover, the endemism of Calcinea in Heron Island is now 53% (8 species) and 46% in the GBR (12 species). This study also documents the first records of the genera Arturia and Neoernsta in the GBR. These results confirm the underestimation of the diversity of Calcarea in the GBR, evidencing that more studies are needed even in well-studied locations.

Taxonomy studies of extant taxa generally focus on external morphology, often ignoring all intraspecific variation, thus possibly creating morphospecies that do not correspond to valid taxonomic units. Additionally, osteological studies are often neglected, which could provide a lot of new information regarding morphological traits. Hence, studying not only osteology but also intraspecific variation in skeletal structures could be of great value for species description and separation. To better assess the relevance of intraspecific osteological variation for taxonomy, here, we analyze this variation in the skeleton of nine specimens of Iguana iguana. We observed considerable individual variability in skull bones, including differences in shape and proportions; variability in the atlas vertebra, which either presented or lacked a neural spine; and variation in the number of ribs; and, most notably, in caudal vertebrae morphotypes. The caudal vertebrae displayed significant variation among individuals, comprising seven distinct morphotypes that exhibited a consistent sequential pattern while also differing in count and presence. As a result, no specimen shared the same caudal vertebral pattern as another. We conclude that a species may present substantial variation in different osteological complexes. Therefore, evaluating intraspecific variation may help prevent the overestimation of the number of existing species. Moreover, understanding the estimated degree of variation in a determined extant taxon could be extrapolated to its fossil representatives. The present study thus highlights the importance of incorporating osteological individual variation into taxonomic analyses.