<i>Thaidasys tongiorgii</i> gen. et sp. nov. Scanning electron microscope photomicrographs.

<p>A, habitus, mostly dorsal view, but with a twisted posterior end; B, anterior end, showing the head and the mouth; C, close-up of the head leaf-like sensorial organ; D, close up pharyngeal region, showing the dorsal tubes and the opening of the epidermal glands (arrows); E, close up of the caudum, ventral view, showing the arrangement of the posterior adhesive tubes. Scale bars: A = 100 μm, B = 20 μm, C = 2 μm, D, E = 10 μm.</p

<i>Thaidasys tongiorgii</i> gen. et sp. nov. Schematic drawings of the muscular system.

<p>A, Anterior region, ventral view. B, Anterior region, lateral view. C, Posterior region, ventral view. hm, helicoidal muscles; scm, somatic circular muscles; svlm, somatic ventrolateral muscles; vcm, visceral circular muscles; vdm, visceral dorsal longitudinal muscles; vvm, visceral ventral longitudinal muscles. Scale bars 100 μm (A, B same scale).</p

<i>Thaidasys tongiorgii</i> gen. et sp. nov. Differential interference contrast photomicrographs.

<p>A, close-up of the anterior region, ventral view, showing the locomotor ciliation and the anterior adhesive tubes (arrow); B, close-up of the internal view of the anterior region of a different specimen, showing the pharynx, pharyngeal pores (arrows) and pharyngo-intestinal junction (arrowhead). C, D, Posterior region of the trunk of two subadult specimens, showing the caudal organ (arrows) at different development stages. E, a juvenile. Scale bars A, B, E = 100 μm, C, D = 50 μm.</p

Phylogenetic relationships of <i>Thaidasys tongiorgii</i> gen. et sp. nov. inferred from Maximum likelihood analysis of 18S rRNA.

<p>The analysis includes 45 Gastrotricha Macrodasyida and the outgroup is represented by <i>Xenotrichula intermedia</i> (Chaetonotida, Xenotrichulidae). The tree with the highest log likelihood (-19946.9339) is shown. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Number at nodes represents bootstrap values (1000 replicates).</p

Line art illustrations of <i>Thaidasys tongiorgii</i> gen. et sp. nov.

<p>A, habitus as seen from the dorsal side; B, same as the previous but at a different focal plane, showing the internal anatomy with the maturing oocytes and the putative caudal organ; C, anterior region seen from the ventral side, showing the arrangement of the anterior adhesive tubes. An, anus; CO, caudal organ; DSH, dorsal sensory hair; Eg, egg; EpG, epidermal gland; In, intestine; HCF, head ciliary fringe; LSH, lateral sensory hair; LSO, leaf-like sensorial organ; Ph, pharynx; PhIJ, pharyngo-intestinal junction; PhP, pharyngeal pore; TbA, anterior adhesive tube; TbD, dorsal adhesive tube; TbP, posterior adhesive tube; TbVL, ventrolateral adhesive tube. Drawings are made mostly from the specimen shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130278#pone.0130278.g002" target="_blank">Fig 2</a>. Scale bars = 100 μm.</p

<i>Thaidasys tongiorgii</i> gen. et sp. nov. Serotonergic nervous system and nuclear staining visualised with CLSM.

<p>A, whole organism. B, serotonergic cerebral ganglion. C, cerebral ganglion stained with DAPI and antiserotonin. af, anterior neurites extended from the dorsal commissure to the ventral somata in the cerebral ganglion; br, cerebral ganglion; dc, dorsal commissure; dcn, dorsal cerebral neurons; lo, leaf-like organ; pl, posterior loop; vlc, ventrolateral cord; vnc, ventral cerebral neurons. Scale bars A = 100 μm, B, C = 10 μm.</p

<i>Thaidasys tongiorgii</i> gen. et sp. nov. FMRFamide immunoreactive nervous system visualised with CLSM.

<p>A, whole organism. B, anterior region, showing the FMRF-IR (green) cerebral ganglion and the anti-tubulin staining (red) in the sensory structures; arrows indicate anterior ventral neurites. C, close up of the cerebral ganglion. acv, anterior commissure of the ventrolateral cords; af, anterior fibres extended from the dorsal commissure to the ventral somata in the cerebral ganglion; avmn, anterior ventromedial neurite; br, cerebral ganglion; dac, cerebral dorsal anterior commissure; dcc, cerebral dorsal central commissure; dcn, cerebral dorsal neurons; dpc, cerebral dorsal posterior commissure; lo, leaf-like organ; ph, pharynx; pbc, ventral commissure at the level of the pharyngo-intestinal junction; pl, posterior loop; post, posterior region; pvmn, posterior ventromedial neurite; van, cerebral ventral anterior neurons; vcc, cerebral ventral commissure; vlc, ventrolateral cord; vpn, cerebral ventral posterior neurons. Scale bars A = 100 μm, B, C = 50 μm.</p

Phylogenetic relationships of <i>Thaidasys tongiorgii</i> gen. et sp. nov. inferred from Bayesian analysis of 18S rRNA.

<p>The analysis includes 45 Gastrotricha Macrodasyida and the outgroup is represented by <i>Xenotrichula intermedia</i> (Chaetonotida, Xenotrichulidae). Number at nodes represents posterior probabilities.</p

<i>Thaidasys tongiorgii</i> gen. et sp. nov. Schematic drawings of the nervous system.

<p>The serotoninergic component is emphasised in red. The other components of the nervous system not reactive to serotonin antibodies (e.g., anti-FRMFamide and anti-tubulin) are shown in blue. The anterior neurites connecting the brain to the anterior sensorial cilia are drawn mainly by inference from data on other Macrodasyida. A, anterior region, dorsal view. B, anterior region, lateral view. C, posterior region, dorsal view. af, anterior neurites extended from the dorsal commissure to the ventral somata in the cerebral ganglion; dc, dorsal commissure; dcn, dorsal cerebral neurons; vlc, ventrolateral cord; vcn, ventral cerebral neurons. Scale bars = 100 μm (A, B same scale).</p

<i>Thaidasys tongiorgii</i> gen. et sp. nov. Muscular system visualised with CLSM.

<p>A, whole organism. B, close up of the pharynx, showing circular, helicoidal and longitudinal muscles. C, musculature supplying the caudal organ. D, posterior end. E, F, three-dimensional reconstructions of the musculature of the complete (E) and internal (F) view of the caudal organ. com, musculature supplying the caudal organ; hm, helicoidal muscles; ppm, muscular ring supplying the pharyngeal pore; scm, somatic circular muscles; svlm, somatic ventrolateral muscles; vcm, visceral circular muscles; vdm, visceral dorsal longitudinal muscles; vvm, visceral ventral longitudinal muscles. Scale bars A-D = 50 μm, E, F = 25 μm.</p