Tardigrada of the Revdalen (Spitsbergen) with the descriptions of two new species: Bryodelphax parvuspolaris (Heterotardigrada) and Isohypsibius coulsoni (Eutardigrada)

Despite a century long history of research, tardigrade fauna of the Svalbard Archipelago remains poorly known. In order to deepen our knowledge of tardigrade biodiversity in the Arctic, we collected forty-one moss and lichen samples from the Revdalen and on the south-east slopes of the Rotjesfjellet (Spitsbergen, Svalbard Archipelago) in June 2010. In these samples, twenty-five tardigrade species were found, including two new for science: Bryodelphax parvuspolaris sp. nov. and Isohypsibius coulsoni sp. nov. B. parvuspolaris sp. nov. belongs to the weglarskae group but differs from all other species of the group by a unique configuration of ventral plates. I. coulsoni sp. nov. differs from the most similar species I. ceciliae Pilato and Binda, 1987 mainly by the absence of ventral sculpture. Two additional species, Milnesium asiaticum Tumanov, 2006 and Diphascon (Adropion) prorsirostre Thulin, 1928, are recorded from the Svalbard Archipelago for the first time.


Introduction
Although the first studies on water bears (Tardigrada) of the Svalbard Archipelago took place as early as in the nineteenth century (Scourfield 1897) and were continued by a number of researchers throughout the twentieth century (e.g. Richters 1903Richters , 1904Richters , 1911Murray 1907;Marcus 1928;Węglarska 1965;Dastych 1985;Pugh and McInnes 1998;Łagisz 1999), our knowledge about the tardigrade fauna of this region is still relatively poor. The most comprehensive work on Spitsbergen tardigrades (Dastych 1985) provided a complete species list, new records and also investigated the ecology of these microscopic invertebrates. A decade later, Pugh and McInnes (1998) analysed the origin of the Arctic Tardigrada. Other papers were published sporadically, and the majority were limited to reports and descriptions of new species from the Svalbard Archipelago (e.g. Binda et al. 1980;Pilato et al. 1982;Dastych 1983;De Smet et al. 1987Pilato and Binda 1987;Van Rompu and De Smet 1988, 1991, 1994De Smet and Van Rompu 1994;Maucci 1996;Tumanov 2007;Smykla et al. 2011). In the region of Hornsund, studies were previously conducted by Węglarska (1965), Dastych (1985), Maucci (1996), Janiec (1996) and Łagisz (1999). Up to now, only 84 species were recorded from the Svalbard Archipelago, but none specifically from the Revdalen (Coulson 2011).
Here, we provide a list of tardigrades species from the Revdalen, including two new records from the Svalbard Archipelago and descriptions of two species new for science, Bryodelphax parvuspolaris sp. nov. and Isohypsibius coulsoni sp. nov. The genus Bryodelphax consists of only 17 species, but its distribution is global-it has been recorded from the polar regions to tropical rain forests (Kaczmarek and Michalczyk 2004;Kaczmarek et al. 2005;Kristensen et al. 2010;Degma et al. 2011). In contrast, the genus Isohypsibius is one of the largest in the phylum Tardigrada, with more than 130 species and subspecies described from all over the world (McInnes 1994;Degma et al. 2011).

Materials and methods
Moss and lichen samples for this study were collected from the Revdalen and the Rotjesfjellet, which are located on the north coast of Hornsund (Spitsbergen, Svalbard Archipelago; Fig. 1). The total of forty-one moss and lichen samples were collected on the 26th June 2010 from the Revdalen and on the 29th June 2010 from the south-east slopes of the Rotjesfjellet (see Table 1). Twenty-nine (over 70%) of the samples provided a total of 461 specimens and 83 eggs.
All specimens and eggs were mounted on microscopic slides in Hoyer's medium and then examined and photographed with a Phase Contrast Microscope (PCM). Species were identified using the key to the World Tardigrada (Ramazzotti and Maucci 1983) and original descriptions from the literature.
All measurements are given in micrometres (lm). Structures were measured only if their orientations were suitable. Body length was measured from the anterior to the posterior end of the body, excluding the hind legs. Measurements of the species used in differential diagnoses are given or calculated according to the original descriptions (i.e. Pilato 1972Pilato , 1974Bertolani et al. 1995;Kristensen et al. 2010). Claws of Isohypsibius coulsoni sp. nov. were measured according to Beasley et al. (2008).
In eutardigrades, the pt ratio is the ratio of the length of a given structure to the length of the buccal tube, expressed as a percentage (Pilato 1981). Similarly, to provide relative measurements in echiniscids, the sc ratio of the length of a given structure to the length of the scapular plate is used (e.g. Fontoura and Morais 2011). Both values are always provided in italics, in order to differentiate them from other measurements and ratios. The configuration of ventral plates in the genus Bryodelphax is described using an analogous system to that used for the description of cuticular gibbosities in some eutardigrades , i.e. a Roman number with a colon at the beginning of the sequence indicates the total number of rows of ventral plates and following Arabic numbers separated by dashes refer to the numbers of plates in each row, starting from the most anterior row.
All the investigated material is preserved in the collection of the first author, at the Department of Animal Taxonomy and Ecology, A. Mickiewicz University, Poznań, Poland.

Results
Taxonomic accounts of the new species found in the study  Table 2) Body (Figs. 2-4) transparent to slightly rose, eyes absent or not visible after the preparation. Apart from the head appendages (cirrus internus and externus and drop-shaped cephalic papillae (secondary clava)), only lateral cirrus A (with clava near the base (primary clava) present).

Description (measurements in
Dorsal plates covered with fine, but distinct dark dots that appear as granulation under PCM, but are in fact cuticular pillars within cuticle Kaczmarek 2006, 2007). ''Granulation'' distinctly larger on the scapular and the terminal plate. In addition to the ''granulation'', slightly larger and irregularly distributed pores are visible mainly on the margins of all dorsal plates (Fig. 5). Scapular plate facetted with a median longitudinal fold and a few smaller transverse folds. Paired plates divided into two unequal anterior and posterior parts by a transverse stripe without ''granulation''. Median plates 1 and 2 divided, and median plate 3 undivided. Twelve supplementary plates poorly visible near median plates 1-3. The terminal plate facetted with two longitudinal folds.
Ventral plates arranged in eight rows: 1 plate in row I (between legs I), 1 plate in row II (between legs I and II), 2 plates in row III (between legs I and II), 2 plates in row IV (between legs II), 2 plates in row V (between legs II and III), 2 plates in row VI (between legs III), 2 plates in row Spine on legs I and papilla on legs IV absent or not visible under PCM. Collar on legs IV with poorly developed and irregular teeth. External claws of all legs smooth, internal claws with very small spurs directed downwards (Fig. 7).
Eggs unknown.
Remarks In some specimens, ventral plates are indistinct; thus, an examination of at least several specimens to ensure correct identification is strongly recommended.
Etymology The name 'parvuspolaris', meaning 'a small dweller from the polar regions', was chosen by the participants of the XXXIII Polar Expedition of the Polish Academy of Sciences, who provided us with logistical support and helped collecting samples from Spitsbergen.     Table 3) Body transparent/white, eyes present (in live and mounted animals) in 83% of the examined specimens (Fig. 9). Dorso-lateral cuticle without gibbosities but covered with a reticular pattern (polygons diameter 0.9-3.2) (Fig. 10). Ventral cuticle smooth.
Claws of the Isohypsibius type, similar in size and shape on all legs (Figs. 12,13). All main branches with welldeveloped accessory points. Smooth lunules present on all claws, slightly larger on claws IV. Cuticular bars present under internal claws I-III.
Etymology The new species is named in honour of Dr. Differential diagnosis Isohypsibius coulsoni sp. nov. differs from all other known Isohypsibius species with sculptured dorsal cuticle and three macroplacoids in the pharynx by a unique combination of the following characters: the presence of a microplacoid, the absence of cuticular gibbosities and the presence of accessory points on primary branches of all claws. The new species differs from the most similar: • Isohypsibius glazovi Biserov, 1999 (known only from Novaya Zemlya) by the absence of the cuticular gibbosities. • Isohypsibius ceciliae Pilato and Binda, 1987 (which is also known from Spitsbergen) by: the absence of the reticular sculpture on the ventral side of the body, a distinctly smaller diameter of the reticular mesh on the dorsal cuticle (0.9-3.2 in the new species and about 5.0-6.0 in I. ceciliae) and the absence of the oral cavity armature. • Isohypsibius lineatus (Mihelčič, 1969) (known only from Austria) by: a different shape and composition of the reticular sculpture (reticular mesh in the new species and irregular undulating lines in I. lineatus), different macroplacoid length sequence (2-1-3 in the new species and equal lengths in I. lineatus), the presence of accessory points on the primary branches of external claws and the presence of smooth lunules on all claws.
Other tardigrade species recorded from the Revdalen In total, we found 25 species, including two new to science (described above) and two recorded from the Svalbard Figs. 9210 Isohypsibius coulsoni sp. nov. Fig. 9. habitus (ventral view, holotype). Fig. 10. sculpture on the dorsal cuticle (paratype). Scale in lm Figs. 11-13 Isohypsibius coulsoni sp. nov. Fig. 11. buccal apparatus (ventral view, holotype). Fig. 12. claws III (paratype). Fig. 13. claws IV (paratype). Scale in lm, on 12-13 same as on 11 N number of specimens or structures measured, Range the smallest and the largest structure found among all specimens measured, SD standard deviation, pt ratio of the length of a given structure to the length of the buccal tube, expressed as a percentage, ? structure oriented unsuitably for measurement Polar Biol (2012) 35:1013-1026 1021 Table 4 A list of all species found in the present study with information on previous records from Svalbard and zoogeographic and taxonomic remarks

Species Previous records in Svalbard
Current study (localities: number of specimens ? eggs found)

Previous records in Svalbard
Current study (localities: number of specimens ? eggs found)