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The ant genus Temnothorax is one of the most diverse in the Palearctic region, comprising several species with different life histories and uncertain taxonomic backgrounds. Socially parasitic Temnothorax ant species were typically described decades ago, primarily based on traditional morphological traits. In some aspects, these species have come back into the spotlight in recent years, necessitating a comprehensive taxonomic revision of the species of the genus. In this paper, we present a quantitative morphology-based taxonomic revision of the Temnothorax corsicus species group (formerly called Myrmoxenus genus) based on the analysis of 20 continuous morphometric traits collected from 394 worker and 19 traits from 473 gyne individuals belonging to 240 samples. Based on morphometric analyses, we propose junior synonymy for Temnothorax tamarae (Arnol'di, 1968) under T. ravouxi (André, 1896), and T. microcellatus (Soudek, 1925) is revived and is considered a senior synonym of T. menozzii (Finzi, 1924). Detailed descriptions, measurements, distribution, and host usage of all ten species are given. Dichotomous keys to workers, known gynes, and photographs of all species are presented., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Báthori et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Madagascar is one of the world's greatest biodiversity hotspots, meriting special attention from biodiversity scientists. It is an excellent testing ground for novel techniques in taxonomy that aim to increase classification objectivity and yield greater taxonomic resolving power. Here we reveal the diversity of a unique and largely unexplored fragment of the Malagasy ant fauna using an advanced combination of exploratory analyses on quantitative morphological data allowing for increased objectivity in taxonomic workflow. The diversity of the Nesomyrmex sikorai species-group was assessed via hypothesis-free nest-centroid-clustering combined with recursive partitioning to estimate the number of morphological clusters and determine the most probable boundaries between them. This combination of methods provides a highly automated and objective species delineation protocol based on continuous morphometric data. Delimitations of clusters recognized by these exploratory analyses were tested via confirmatory Linear Discriminant Analysis (LDA) and Multivariate Ratio Analysis (MRA). The final species hypotheses are corroborated by many qualitative characters, and the recognized species exhibit different spatial distributions and occupy different ecological regions. We describe and redescribe eight morphologically distinct species including six new species: Nesomyrmex excelsior sp. n., N. modestus sp. n., N. reticulatus sp. n., N. retusispinosus (Forel, 1892), N. rugosus sp. n., N. sikorai (Emery, 1896), N. striatus sp. n., and N. tamatavensis sp. n. An identification key for their worker castes using morphometric data is provided.

In the current revisionary work, the Temnothorax nylanderi species-group of myrmicine ants is characterized. Eighteen species belonging to this group in the Ponto-Mediterranean region are described or redefined based on an integrative approach that combines exploratory analyses of morphometric data and of a 658bp fragment of the mitochondrial gene for the cytochrome c oxidase subunit I (CO I). The species group is subdivided into five species complexes: T. angustifrons complex, T. lichtensteini complex, T. nylanderi complex, T. parvulus complex, T. sordidulus complex, and two species, T. angulinodis sp. n. and T. flavicornis (Emery, 1870) form their own lineages. We describe seven new species (T. angulinodis sp. n., T. angustifrons sp. n., T. ariadnae sp. n., T. helenae sp. n., T. lucidus sp. n., T. similis sp. n., T. subtilis sp. n.), raise T. tergestinus (FINZI, 1928) stat.n. to species level, and propose a new junior synonymy for T. saxonicus (SEIFERT, 1995) syn.n. (junior synonym of T. tergestinus). We describe the worker caste and provide high quality images and distributional maps for all eighteen species. Furthermore, we provide a decision tree as an alternative identification key that visually gives an overview of this species-group. We make the first application to Formicidae of the Semantic Phenotype approach that has been used in previous taxonomic revisions.