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.\ud 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\ud 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,\ud 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\ud the need to continue the exploration in the Canary Islands

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.