Università degli studi di Modena e Reggio Emilia

Gastrotrichs are highly diverse and abundant in all aquatic ecosystems; however, they are often overlooked. During a biodiversity survey in Sardinia (Italy), a new species of gastrotrich herein described was discovered. Specimens of Urodasys bifidostylis sp. nov. were found in sandy sediments from two submarine caves. Using an integrative approach of traditional light (DIC) and high-resolution (CLSM) microscopies, we herein reveal, for the first time, the fine structure and function of the reproductive organ in an Urodasys representative. This is particularly relevant considering the complex reproductive organs and strategies of this group. Results allow comparisons between the reproductive apparatus and sperm transfer modalities in Urodasys and the closely related genus Macrodasys. One similarity is that both groups transfer male gametes in packets, suggesting the production of spermatophores to be a common phenomenon in Gastrotricha. Unique to Urodasys is the ability of multiple and consecutive copulations and sperm transfers and, differently than Macrodasys, the transfer of sperms unlikely occurs simultaneously between the two hermaphroditic partners. These findings provide new insights into the reproductive strategies of Urodasys and are expected to advance future studies on the evolution of reproductive strategies and the rise of interspecific reproductive barriers in interstitial meiofauna.

I gastrotrichi marini popolano quasi esclusivamente le sabbie costiere, soprattutto dell’infralitorale superiore. Le specie conosciute sono circa 520, delle quali 163 rinvenute anche in Italia. Per la Sicilia sono segnalate una quarantina di specie, molte raccolte negli anni ‘90. Nel settembre 2022 abbiamo intrapreso nuove indagini, focalizzandoci sulla costa del canale di Sicilia e sul golfo di Mondello. Sono state investigate dieci località prelevando in ciascuna 1-2 litri di sedimento. L’analisi tassonomica è stata condotta nel laboratorio da campo creato a Sciacca. Gli animali sono stati estratti mediante narcotizzazione/decantazione e i gastrotrichi rinvenuti montati su vetrino e studiati a fresco utilizzando microscopia Nomarski. Nel complesso sono state rinvenute oltre 40 specie con una media di 11 ± 6,8 specie per località. La gastrotricofauna, divisa più o meno equamente tra l’ordine Macrodasyida e Chaetonotida, è stata documentata con oltre 2500 fotografie. La Località Le Solette (Menfi, AG) è risultata la più ricca con ben 22 specie, seguita da Mondello (PA) con 19. Valori di ricchezza specifica che figurano tra i più elevanti in assoluto, e che sono da mettere in relazione con il tipo di substrato di queste località: sabbia pulita a granulometria media-fine, la più idonea alla vita di questi micrometazoi. Complessivamente, la fauna documentata nel 2022 risulta costituita per la maggior parte da specie già note per la Sicilia, ma non mancano le novità, sia a livello regionale (e.g., Mesodasys littoralis Remane, 1951, Tetranchyroderma antenniphora Hummon & Todaro, 2010, T. polyprobolostomum Hummon, Todaro, Balsamo & Tongiorgi, 1996, Halichaetonotus margaretae Hummon, Balsamo & Todaro, 1992, Heteroxenotrichula subterranea (Remane, 1934), Xenotrichula punctata Wilke, 1954) sia in senso assoluto. Gli esemplari dei generi Dolychodasys Gagne, 1977 e Lepidodasys Remane, 1926 da noi rinvenuti apparterrebbero infatti a specie nuove per la scienza. La conferma verrà dalle analisi molecolari ancora in corso. I risultati ottenuti indicano che le conoscenze sulla fauna a gastrotrichi della Sicilia non sono complete e invogliano a proseguire le indagini lungo altri tratti costieri.

Sampling campaign took place in October 2011 and included 7 locations and 16 stations along the eastern coast of the island of Lanzarote (Spain). Samples yielded 61 species for a total of 96 records. Thirty-six species (27 genera and 11 families) belong to Macrodasyida while 25 species (18 genera, 7 families) to Chaetonotida. Thirty-two are known species while 29 appear to be undescribed taxa or putatively so. The finding at Lanzarote of some of the known species bear particular significance: Oregodasys cirratus and Tetranchyroderma canariense are recorded for the second time ever, while Musellifer delamarei and Urodasys acanthostylis were previously known only from the Mediterranean, and Urodadys mirabilis was acknowledge only for northern Europe. Furthermore, the presence in the island of Chaetonotus apechochaetus, C. apolemmus, C. siciliensis, Heterolepidoderma loricatum, Lepidodasys unicarenatus, Musellifer delamarei, Thaumastoderma mediterraneum, and Urodasys acanthostylis, strongly suggest them to be part of the temperate/warm fauna that invaded the Mediterranean basin after the Missinian crisis during the different climate eras. Of the new species, one is described as its characteristics widen substantially our knowledge on the entire genus. Urodasys completus sp. nov. is unique in that it possesses, among others, two testes and a sclerotic stylet. Results of a phylogenetic analysis indicated that the sequence of the evolutionary transformation that have occurred in the reproductive system of the species of Urodasys are likely dissimilar from the ones proposed thus far. The overall results testify the need to continue the exploration in the Canary Islands.

Macrodasyidan gastrotrichs are hermaphrodites with complex accessory reproductive organs that function in sperm transfer and receipt. Unfortunately, homology among the organs of members of different clades is largely undetermined, troubling a clear understanding of the evolutionary trends in the reproductive biology of these animals. The present study investigates the evolution of reproduction in species of the peculiar genus Urodasys, quite popular among researchers working on meiofauna in virtue of their very long tail. These gastrotrichs are extremely interesting also because they show a wide range of structures, modes, and reproductive strategies. It is likely that a phylogenetic study of these taxa may shed light on the evolutionary trends in the reproductive biology of the genus and possibly of the entire phylum. Urodasys presently consists of 15 species, one of which, U. viviparus, is parthenogenetic and ovoviviparous, while the others are hermaphroditic and oviparous. Four of the latter species show paired ovaries and testes, but no accessory sexual organ, whilst 10 possess two ovaries, a single testis and a sclerotic, copulatory organ called a stylet. Recently, a new species bearing a stylet but two testes was found at Lanzarote (Canary Islands). All this data was opportunely coded and cladistically analyzed. Meanwhile, phylogenetic analyses based on sequences of the 18S rDNA gene obtained from representative species were concurrently carried out. The results of the two analyses are widely overlapping and substantially separate the investigated species into two clades, with the new species that appears as an early divergent line along the evolutionary branch of the stylet-bearing taxa. However, U. viviparus appears to be allied with the stylus-lacking species in the morphological analyses, while the molecular analyses place it amongst the stylet-bearing species. In any case, regardless of the position of U. viviparus, the results indicate that the sequence of evolutionary transformations occurred in the reproductive system of the species of Urodasys is likely dissimilar from those previously proposed by other authors.

Macrodasyidan gastrotrichs are hermaphrodites with complex accessory reproductive organs that function in sperm transfer and receipt. Unfortunately, homology among the organs of members of different clades is largely undetermined, troubling a clear understanding of the evolutionary trends in the reproductive biology of these animals. The present study investigates the evolution of reproduction in species of the peculiar genus Urodasys, quite popular among researchers working on meiofauna in virtue of their very long tail. These gastrotrichs are extremely interesting also because they show a wide range of structures, modes, and reproductive strategies. It is likely that a phylogenetic study of these taxa may shed light on the evolutionary trends in the reproductive biology of the genus and possibly of the entire phylum. Urodasys presently consists of 15 species, one of which, U. viviparus, is parthenogenetic and ovoviviparous, while the others are hermaphroditic and oviparous. Four of the latter species show paired ovaries and testes, but no accessory sexual organ, whilst 10 possess two ovaries, a single testis and a sclerotic, copulatory organ called a stylet. Recently, a new species bearing a stylet but two testes was found at Lanzarote (Canary Islands). All this data was opportunely coded and cladistically analyzed. Meanwhile, phylogenetic analyses based on sequences of the 18S rDNA gene obtained from representative species were concurrently carried out. The results of the two analyses are widely overlapping and substantially separate the investigated species into two clades, with the new species that appears as an early divergent line along the evolutionary branch of the stylet-bearing taxa. However, U. viviparus appears to be allied with the stylus-lacking species in the morphological analyses, while the molecular analyses place it amongst the stylet-bearing species. In any case, regardless of the position of U. viviparus, the results indicate that the sequence of evolutionary transformations occurred in the reproductive system of the species of Urodasys is likely dissimilar from those previously proposed by other authors.