Description of Macrobiotus scoticus sp. nov. (Tardigrada : Macrobiotidae : hufelandi group) from Scotland by means of integrative taxonomy

A new species of the Macrobiotus hufelandi group is described from Scotland. Both light and scanning electron microscopy were used for collecting morphological and morphometric data whereas genotyping allowed sequences for three nuclear (18S rRNA, 28S rRNA and ITS-2) and one mitochondrial (COI) DNA fragment to be obtained. By undertaking in vitro culturing, we were able to obtain a number of eggs and provide a detailed description. Macrobiotus scoticus sp. nov. exhibits a reduced oral cavity armature, with only the ridges of the third band of teeth visible under light microscopy, therefore the animals of the new species are most similar to individuals of M. almadai Fontoura et al., 2008; M. diversus Biserov, 1990; M. madegassus Maucci, 1993; M. martini Bartels et al., 2009; M. modestus Pilato and Lisi, 2009; and M. paulinae Stec et al., 2015. However, M. scoticus sp. nov. lays eggs with strongly modified processes, which makes this species unique not only among the species listed above but from all hufelandi group taxa. In contrast to mushroom-shaped egg processes found in the majority of the hufelandi complex species, processes in M. scoticus sp. nov. are in the shape of spatulas, with longitudinally flattened terminal portions. Superficially, the eggs of the new species resemble those of M. kristenseni Guidetti et al., 2013, which exhibits elongated, spike- or filament-like processes. Nonetheless, the eggs of M. kristenseni have a smooth inter-process surface whereas in the new species the surface is covered with a very dense reticulum. Moreover, M. kristenseni has a better developed oral cavity armature, with all three bands of teeth detectable under light microscopy.