The first three mitochondrial (mt) genomes of endosymbiotic turbellarian flatworms are characterised for the rhabdocoels Graffilla buccinicola, Syndesmis echinorum and S. kurakaikina. Interspecific comparison of the three newly obtained sequences and the only previously characterised rhabdocoel, the free-living species Bothromesostoma personatum, reveals high mt genomic variability, including numerous rearrangements. The first intrageneric comparison within rhabdocoels shows that gene order is not fully conserved even at species levels. Atp8, until recently assumed absent in flatworms, was putatively annotated in two sequences. Selection pressure was tested in a phylogenetic framework and is shown to be significantly relaxed in this and another protein-coding gene: cox1. If present, atp8 appears highly derived in platyhelminths and its functionality needs to be addressed in future research. Our findings for the first time allude to a large degree of undiscovered (mt) genomic plasticity in rhabdocoels. It merits further attention whether this variation is correlated with a symbiotic lifestyle. Our results illustrate that this phenomenon is widespread in flatworms as a whole and not exclusive to the better-studied neodermatans.
Many nominal species of microscopic animals traditionally fitting the ‘everything is everywhere’ paradigm have been revealed to be complexes of cryptic species. Here, we explore species diversity within the micrometazoan flatworm Gyratrix hermaphroditus—unique among meiofauna because of its global occurrence in a wide variety of brackish, freshwater and marine environments. With maximum likelihood and Bayesian approaches, we analysed 18S, 28S, 5.8S and ITS2 rDNA sequences from 401 specimens across the global distribution of G. hermaphroditus. Generalized Mixed Yule Coalescent (GMYC) and Automatic Barcode Gap Discovery (ABGD) methods delineated 78 and 62 putative species, respectively. This renders G. hermaphroditus one of the most species‐rich complexes known to date. Based on shape variations of the male copulatory organ, 14 morphotypes corresponding with molecular clades were identified within the species complex. Within morphotypes, morphometric measurements were able to further discriminate between GMYC species using discriminant analyses. While most putative species occur on local or regional scales, over 10% are distributed over vast distances (>500 km apart) and two GMYC and six ABGD species have colonised multiple continents. This suggests that the cosmopolitanism of the G. hermaphroditus species complex is not just caused by mixing cryptic species with a more limited geographic distribution, but is due to the presence of previously unrecognised cosmopolitan taxa. The wide variation in distribution patterns between putative species indicates that meiofaunal biogeography should not be simplified into ‘everything is everywhere’, but rather entails every ecological state, extending from local endemism to true cosmopolitanism.
Four new species of limnoterrestrial rhabdocoels (‘Typhloplanidae’ Graff, 1905) are described. One of these – Faunulus nielsi Houben, Proesmans & Artois gen. et sp. nov. – could not be unambiguously placed within an existing genus. Faunulus nielsi most closely resembles species of the genus Adenocerca Reisinger, 1924 but can be clearly distinguished by the position of the testes. The three other new species described are Bryoplana belgica Houben, Proesmans & Artois sp. nov., Hoplopera isis Houben, Proesmans & Artois sp. nov., and Protoplanella leiae Houben, Proesmans & Artois sp. nov. All three belong to the subfamily ‘Protoplanellinae’ Reisinger, 1924 and are distinguished based on a detailed description of the reproductive system. Finally, new data are provided for nine other, known typhloplanids: Adenocerca minima Kolasa, 1981; Chorizogynopora italica Kolasa, 1981; Hoplopera opaca Reisinger, 1924; K. subterranea Reisinger, 1933; Krumbachia virginiana (Kepner & Carter, 1931) Ruebush, 1938; Olisthanellinella rotundula Reisinger, 1924; Prorhynchella minuta Ruebush, 1939; Protoplanella simplex Reisinger, 1924; and Ventrociliella romanae Kolasa, 1977. A detailed comparison of our material of V. romanae to what is described for Bockia deses Reisinger, 1924, leads us to consider the latter a nomen dubium.
A comprehensive morphological and taxonomic account of the members of the genus Cheliplana de Beauchamp, 1927 is presented. Six new species are described: Cheliplana asinaraensis n. sp., C. cubana n. sp., C. curacaoensis n. sp., C. hawaiiensis n. sp., C. longissima n. sp. and C. mauii n. sp. The new species are mainly distinguished from each other and from other representatives of Cheliplana by the organisation of the reproductive system and the structure of the cirrus. Furthermore, C. triductibus Van Steenkiste, Volonterio, Schockaert & Artois, 2008 is considered a junior synonym of Cheliplana deverticula Ax, 2008. The two subspecies of Cheliplana asica Marcus, 1952, C. asica asica and C. asica terminalis Brunet, 1968, are considered separate species. The systematic position of the genus Dactyloplana Armonies, 2018 is discussed, and its synonymy with Cheliplana is retained. As such, this brings the total number of species of Cheliplana to 49. Finally, we provide an identification key to the members of the genus, based on characters that enable identification to species level in the field.
We describe a new genus of dalytyphloplanid rhabdocoels, with seven new species. Orostylis gen. nov. has a unique combination of characters including the presence of a sclerotised stylet, an anteriorly positioned male copulatory organ with the male genital pore in the buccal cavity, and the absence of an oviduct. The ovary empties directly into the intestinal lumen. Orostylis dohae sp. nov., Orostylis asinaraensis sp. nov., Orostylis caecus sp. nov., Orostylis distortus sp. nov., Orostylis donanae sp. nov., Orostylis gallicus sp. nov., and Orostylis timucuorum sp. nov. are distinguished from each other by the structure of the sclerotised parts of the male copulatory organ. Molecular and morphological evidence place the new genus in Neodalyellida Willems et al. 2006, and similarities with other taxa are discussed.
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