Echiniscidae Thulin 1928

Family: Echiniscidae Thulin, 1928

Genus: Pseudechiniscus Thulin, 1911

Pseudechiniscus saltensis sp. nov.

(Figures 1–4; Table 1, 2)

Material examined: holotype (adult female), 16 adult paratypes: 15 females and 1 male, and three exuvia in polyvinyl lactophenol mounting media. All specimens were found in samples of lichens, on sidewalk tree trunks.

Type locality: Salta city (24°27´– 25°47´S, 64°55´– 65°40´W), 1150 m asl, Salta province, Republic of Argentina.

Type repositories: the holotype (MCNS Tar.000019-2) and one paratype (MCNS Tar.000019-1) are deposited in the Museum of Natural Sciences, National University of Salta, Argentina; four paratypes (slide number: 5860) are deposited in the Pilato and Binda collection, Museum of Animal Biology, University of Catania, Italy. 11 paratypes and three exuvia are housed in Rocha and Doma collection in the Department of Natural Sciences at the National University of La Pampa, Argentina (slide numbers: UNLPam 148-2-3, UNLPam 146-1-2-3, UNLPam 126, UNLPam 171-1-2, UNLPam 119-2, UNLPam 172-3, UNLPam 124- 1 Paratypes: 11; exuviae: UNLPam 170-1-2, UNLPam 168).

Description of the species: Size range: 164–204 µm body length. Colour green in vivo and beige after mounting on slides. Black large, oval eyespots present. Cephalic appendages and cirri A present (Fig. 2 C). Cirri A short (20–25 µm); well-developed cephalic papillae, free, prominent and directed forward; clavae present. No trunk appendages or lateral papillae. Dorsal cuticle with evident cuticular plates (Fig. 1 A–D). Cephalic plate with a Wshaped fold as typical for most Pseudechiniscus species. Neck plate present, but sometimes can be hidden under the anterior margin of the scapular plate. Scapular plate divided into an anterior and a posterior portion by a transverse fold (Fig. 1 A, B), with the anterior portion longer than the posterior (proportion about 2:1); sometimes the posterior portion divided by three longitudinal folds, lateral folds absent. Median plate II divided into two portions by a transverse fold (anterior part wider and shorter than the posterior) (Fig. 1 C); median plate I and III undivided. Two lateral intersegmental plates on each side of median plates I and II present, divided by transversal fold (Fig. 1 A, B, arrows). Pseudosegmental plate divided by a longitudinal fold, and with posterior margin showing two small triangular pointed projections, orientated backwards (Figs. 1 D, arrow). Caudal plate not faceted but with two raised folds without forming a Y-shaped bifurcation (Fig. 1 D).

Ornamentation of the dorsal plates formed by uniformly spaced “dots” (i.e. endocuticular pillars) joined by delicate striae forming a usually hexagonal net design. The distance between the pillars is shorter than their diameter, which is about 0.5–2.4 μm. With respect to the pillar size, they are usually distributed rather uniformly (with a degree of individual variability); only the most lateral pillars of each plate tend to be smaller. The lateral intersegmental plates have less evident ornamentation, with pillars that are also smaller. Additionally, each leg shows a lateral patch of pillars similar in size of those of the dorsal plates, also joined by striae (Fig. 2 A, arrows). Ventral cuticle with small “granulation” forming a unique pattern (Fig. 2 B, C; Fig. 3), with patch configuration (PG): I-II- III-IV-V-VI-VII-VIII g, with also very tiny “granules” (= pillars) between the bands.

Internal claws with spurs oriented towards the claw base, no difference in shape between spurs on legs I–III and legs IV (Fig. 2 D, arrow). Absence of lateral spine of legs I, while a straight, cylindrical, slightly elongated papilla (no banana-like appearance) is present on the external side of the fourth pair of legs near their bases (Fig. 2 A, arrowhead). Dentate collar on hind legs absent. The differences between female and male are indicated below.

Female: probably larger body size and stouter in shape (finding only one male prevents certainty); rosetteshaped gonopore. Strangely, in most females with visible gonopore this appears surrounded by five, instead of six “petals” (which is the rule in Heterotardigrada), see following sections for more detailed discussion (Fig. 4 A, B, arrows); only one female with visible gonopore was observed with the typical six-petal structure. Interesting perianal structures are visible (Fig. 4 A, B, arrowheads) but this would require more thorough morphological investigations (e.g. using SEM). PG II with triangular shape, network meshes are smaller and mostly isodiametric (Fig. 3). 2–4 spherical eggs were found in exuviae.

The measurements of selected morphological structures, with relative indices, of the holotype and ranges within the female population, are given in Table 1.

Male: probably smaller body and more slender in shape than females; rounded gonopore without the six-petal rosette structure. Patches of “granulation” more pronounced than in females, PG II with oval shape and network meshes wider and more elongated (Fig. 3).

and body length (BO), of the holotype and female paratypes of Pseudechiniscus saltensis sp. nov. SD = standard devia-

tion.

The measurements of selected morphological structures, with relative indices, of the only male found, are given in Table 2.

Etymology: The specific epithet refers to the to the locus typicus, Salta city: saltensis = inhabiting Salta.

Taxonomic remarks: The holotype and the female paratypes are very similar, with just the usual moderate variability in morphometric characters (Tab. 1), though this may arise, at least partially, from the difficulty in measuring structures and from different preparation results. As already mentioned, most adult females with visible gonopore showed a five-petal rosette-shaped structure (instead of six-petals, i.e. the rule in Heterotardigrada); one of the five “petals” appears larger (Fig. 4 A, B, arrows), thus letting us suspect that actually two of the six petals are fused into a single one. Also perianal morphology of females (Fig. 4 A, B, arrowheads) might prove to be interesting once investigated in detail (which was not possible in the present study with the methodology used and the available material).

Differential diagnosis: P. saltensis sp. nov., due to the presence of free, elongated cephalic papillae, should fall within the P. novaezeelandiae group; this was instituted by Cesari et al. (2020), although those authors were able to place into this group only P. novaezeelandiae (Richters, 1908) and P. titianae Vecchi, Cesari, Bertolani, Jönsson, Rebecchi & Guidetti, 2016, provisionally leaving many other species unplaced. For this reason, we here compare P. saltensis sp. nov. with those two species (and the taxa derived from the various “forms” of P. novaezeelandiae), and, in addition, with other eight species having the following characters in common with P. saltensis sp. nov.: absence of spines of legs I, scapular plate with a transversal fold, presence of projections at the posterior margin of the pseudosegmental plate, caudal plate not faceted, and cuticular ornamentation appearing as “dots” joined by striae. These taxa are: P. bartkei Węglarska, 1962, P. quadrilobatus Iharos, 1969, P. brevimontanus Kendall-Fite & Nelson, 1996, P. spinerectus Pilato, Binda, Napolitano & Moncada, 2001, P gullii Pilato & Lisi, 2006, P. pilatoi Li, 2007, P. yunnanensis Wang, 2009 and P. santomensis Fontoura, Pilato & Lisi, 2010.

P. saltensis sp. nov. differs from P. novaezeelandiae novaezeelandiae (Richters, 1908), known from New Zealand, in having endocuticular pillars of the cephalic plate medial “facet” not smaller than on the other “facets” (smaller in P. novaezeelandiae novaezeelandiae according to Pilato et al. 2005), pseudosegmental plate longitudinally divided (undivided in P. novaezeelandiae novaezeelandiae) and with two small triangular pointed projections (usually well developed as spines in P. novaezeelandiae novaezeelandiae); internal claws with spurs in the new species (absent in P. novaezeelandiae novaezeelandiae).

According to the current checklist of Tardigrada species (Degma et al. 2020), three other subspecies of P. novaezeelandiae are recognisable: P. novaezeelandiae aspinosa Iharos, 1963, P. novaezeelandiae laterospinosa Iharos, 1963 and P. novaezeelandiae marinae Bartoš, 1934; however, Tumanov (2020) pointed out that the two former “should be considered as nomina dubia until the investigation of the type material of these forms is performed” while the latter “should be re-evaluated as a bona species Pseudechiniscus marinae Bartoš, 1934 ”. Here, we indicate the only differences between P. saltensis sp. nov. and the two subspecies (if valid) P. novaezeelandiae aspinosa Iharos, 1963 and P. novaezeelandiae laterospinosa Iharos, 1963, which can be obtained from Tumanov (2020), considering that other differences obtainable form older literature could be unreliable; instead, we treat P. marinae as a separate species as suggested by Tumanov (2020). Therefore, P. saltensis sp. nov. differs from:

• P. novaezeelandiae aspinosa and P. novaezeelandiae laterospinosa, both known from southern Argentina, in having pseudosegmental plate with two small triangular pointed projections (only blunt lobes in those subspecies of P. novaezeelandiae), and internal claws with spurs in the new species (presumably absent in P. novaezeelandiae aspinosa).

• P. marinae, originally known from Czech Republic, in having no lateral papillae (present in P. marinae), no spines on legs I (present in P. marinae), pseudosegmental plate longitudinally divided (undivided in P. marinae), and with two small triangular pointed projections (two blunt lobes in P. marinae); moreover, the new species lacks the peculiar characters which P. marinae exhibits: an extremely developed relief on the caudal plate and lateral teeth of the pseudosegmental plate.

• P. titianae, known from Antarctica, in having: green colour (orange-red in P. titianae), scapular plate divided only by one transverse fold (additionally to that a fold, the scapular plate has anterior portion divided by a longitudinal fold in P. titianae), median plate I undivided (divided in P. titianae), larger dorsal cuticular pillars (0.5–2.4 µm vs about 0.5 µm in P. titianae), far shorter cirri A (20–25 µm vs 64-74 µm in P. titianae). Vecchi et al. (2016) did not describe the venter in P. titianae, but a ventral pattern seems to be visible in figure 6 C therein, therefore this character cannot be compared between the two species.

• P. bartkei, known from Vietnam, in having: green colour (orange in P. bartkei), median plate II divided (undivided in P. bartkei), distance between the dorsal cuticular pillars not longer than the pillar diameter (distance clearly longer than the diameter in P. bartkei). The ventral ornamentation of P. saltensis sp. nov. is well developed while in P. bartkei it has a simplified ventral pattern, with less bands, lower variety of pillar size and in particular, without the smallest pillars between the bands, present in P. saltensis sp. nov.

• The original description of P. quadrilobatus (known from Vietnam) is rather poor, therefore it is difficult to perform a thorough comparison based on data all resulting absolutely sure and reliable; however, referring to the data available from the literature and to our observations on material attributed to this species (see Material and methods section), P. saltensis sp. nov. differs from P. quadrilobatus in having: green colour (orange-reddish in P. quadrilobatus); all plates without uplifted lobes (present in some plates in P. quadrilobatus); pseudosegmental plate divided and with two triangular pointed projections (undivided and without those projections in P. quadrilobatus), median plate II divided (undivided in P. quadrilobatus), external cirri longer (about 8% of the body length in the new species vs about 3% in P. quadrilobatus), shorter cirri A (about 12.5% of the body length in the new species vs about 23% in P. quadrilobatus), internal claws with spurs (absent in P. quadrilobatus).

• P. brevimontanus, known from the USA, in having: median plate I undivided (divided in P. brevimontanus), pillars of paired and pseudosegmental plates more uniform in size on each plate (more variable in P. brevimontanus), shorter internal cirri (9.0– 10.9 µm vs about 15 µm in P. brevimontanus in spite of its smaller body size), shorter cirri A (about 12.5% of the body length in the new species vs about 17% in P. brevimontanus).

• P. spinerectus, known from Ecuador, in having: green colour (reddish in P. spinerectus), scapular and paired plates without longitudinal folds (present in median plate II and paired plates II–III of P. spinerectus), pseudosegmental plate with two small triangular projections pointing posteriorly (two well developed spines directed upwards in P. spinerectus), rather similar size of the pillars on all plates (terminal plate with larger pillars, head plate with smaller ones, intermediate size on the other plates, in P. spinerectus), shorter cirri A (about 12.5% of the body length in the new species vs about 20% in P. spinerectus), shorter internal cirri (about 5.4% of the body length in the new species vs about 8.2% in P. spinerectus).

• P. gullii, known from Mexico, in having: green colour (reddish in P. gullii), cephalic plate with an evident W-shaped fold (not visible in P. gullii), no median concavity on scapular plate (present in P. gullii), median plate I undivided and median plate II divided (median plate I divided and II undivided in P. gullii), pseudosegmental plate divided and with two small triangular pointed projections (pseudosegmental plate undivided and with one evident triangular lobe raised dorsally in P. gullii), dorsal pillars not more distant from one another than their diameter (more distant than their diameter in P. gullii), ventral pillars (absent in P. gullii), shorter cirri A (about 12.5% of the body length in the new species vs about 17% in P. gullii), spurs on internal claws (absent in P. gullii).

• P. pilatoi, known from China, in having: green colour (red in P. pilatoi), eye spots present (absent in P. pilatoi), median plate I of ordinary shape (crescent-shaped, in P. pilatoi), rhomboidal, divided median plate II (triangular, undivided in P. pilatoi), pseudosegmental plate with two small triangular pointed projections (only one median triangular lobe in P. pilatoi), non-uplifted joints of paired plates near the dorsal line (uplifted in P. pilatoi), terminal plate with two raised folds (without them in P. pilatoi), internal claws with spurs (without spurs in P. pilatoi), cirri A and clavae smaller (cirri A about 12.5% in the new species vs about 17.4% in P. pilatoi).

• P. yunnanensis, known from China, in having: green colour (red in P. yunnanensis), larger body size (164- 204 µm vs about 116-163 µm in P. yunnanensis), median II and pseudosegmental plate divided (undivided in in P. yunnanensis), paired plates without lobes (with a median lobe on the posterior margin of the paired plates in P. yunnanensis), less developed spines of the posterior margin of the pseudosegmental plate (compare Fig. 1 D arrow with figure 1A in the original description of P. yunnanensis in Wang 2009), shorter cirri A (about 12.5% of the body length in the new species vs about 20% in P. yunnanensis), two raised folds of the terminal plate present (absent in P. yunnanensis), ventral pillars (absent in P. yunnanensis), internal claws with spurs (no spurs in P. yunnanensis).

• P. santomensis, known from Democratic Republic of Sao Tomé and Principe, in having: green colour (reddish in P. santomensis), eyes present (absent in P. santomensis), median plate I undivided (divided in P. santomensis), pseudosegmental plate divided (undivided in P. santomensis).