Pseudobiotus hirsutellus, Pilato & Lisi & Binda, 2010

Pilato, Giovanni, Lisi, Oscar & Binda, Maria Grazia, 2010, Tardigrades of Israel with description of four new species, Zootaxa 2665, pp. 1-28 : 16-21

Pseudobiotus hirsutellus sp. nov.

( Figs. 8, 9)

Material examined. Localities: Nos. 3, 6, 9, 11, 12, 13, 14, 17, 22, 23 and 24.

Locus typicus. (No. 13: canal near Hula, Agmon): holotype (a female on the slide No. 5400) and over 117 paratypes (slides Nos. 3852-75; 5390-5400), including many females with exuvium and eggs, and five males.

Type repository. Holotype and paratypes are deposited in the collection of Binda & Pilato, Museum of the Department of Animal Biology “Marcello La Greca”, University of Catania .

Specific diagnosis. Sparse, conical and spine-shaped cuticular processes present. Eye spots present. Oval papilla on legs absent. Stylet supports inserted on the buccal tube at c. 68 % of its length. Pharyngeal bulb with two placoids; microplacoid absent. Claws long and slender, without accessory points; lunules and other cuticular thickenings on the legs, absent. Smooth eggs laid into the exuviae.

Description of the holotype. Body length 466 µm; colourless, eye spots present. Caudal portion of the body elongate ( Fig. 8A). Small conical cuticular processes are present on both dorsal and ventral surfaces; they are of diverse size ( Fig 8B, C, arrows), and form transversal bands (the largest processes 2.8 µm long with basal diameter>1.6 µm long). Legs without cuticular pores or granulation. Six peribuccal lobes present. Buccal tube rigid ( Fig. 9A,C). Mouth with many small peribuccal lamellae ( Fig. 9B, arrow a); buccal armature with a dorsal and ventral band of teeth; the lateral teeth of both the dorsal and ventral bands are equally developed; caudal system of transverse ridges absent. Buccal tube, 50.9 µm long and 6.7 µm wide (pt = 13.2) ( Fig. 9A); stylet supports inserted on the buccal tube at 68.8% of its length (pt = 68.8). The apophyses for the insertion of the stylet muscles have the characteristic shape ( Fig. 9C, arrow a) that has already been described for other species in the genus by Bertolani (1976, 1982). Pharyngeal bulb (60 µm x 50 µm) with apophyses and two rod-shaped macroplacoids; microplacoid absent. Second macroplacoid bent ( Fig. 9A, arrow). The margins of both first and second macroplacoids are not smooth but with some small prominences particularly visible at the extremities ( Fig. 9C, arrows b, c). Entire macroplacoid row 27.5 µm long (pt = 54.0), first macroplacoid 10.7 µm long (pt = 21.0), second macroplacoid 15.9 µm (pt = 31.2).

Claws of ‘ Isohypsibius type’ very long, with a long and slender basal portion ( Fig. 9D, E) and slender branches (particularly the main branches). A perfect measurement of both the holotype and paratypes claws is impossible due to their flexibility. They are invariably bent and therefore the dimensions indicated here have to be considered approximate. External claws of the second and third pairs of legs 43.5 µm long (pt = 85.5); posterior claws on the hind legs 45.8 µm long (pt = 90.0). Due to the difficulty in measuring the claws, authors describing species of the genus Pseudobiotus measured separately the main branches, the secondary branches and the basal sections. We used the same method ( Table 7) but the correct measurements of these structures are difficult and have to be considered approximate. The bases of the claws, particularly the external, are slightly enlarged and thickened ( Fig.9D, E) but true lunules are absent. Freely protruding accessory points absent; but their proximal portions, completely adhering to the main branches of the claws, are present ( Fig. 9D, E). Paratype females with eggs in their ovary, and trailing exuvium with eggs, were observed and, as described by Bertolani (1982) for P. kathmanae and P. megalonyx , have modified hind claws with shorter and stouter secondary branches ( Fig. 9F, arrow). Paratype males were smaller and more slender than mature females. As described for P. megalonyx , the secondary branch of the internal claws on the first pair of legs is clearly modified into a stout, curved claw, with small subapical spur and an obvious basal spur ( Fig. 9G, arrow). Oval papilla and cuticular bar on the first three pairs of legs, absent. As reported by Bertolani (1982) for P. megalonyx , some newly hatched juveniles seem to have three placoids. Smooth eggs are laid into the exuviae.

The paratypes are similar to the holotype in both qualitative and metric characters. Measurements of structures of the holotype and of the smallest and largest specimens are indicated in Table 6. Due to the difficulty of measuring the claws and in order to make comparisons with other species possible, we have also measured the main branch, secondary branch and basal portion of the claws separately (see: Table 7).

*) From Chang et. al., 2007; **) Chang et al. (2007) did not distinguish anterior and posterior claws IV; our measurements refer to the posterior claws.

Etymology. The specific name hirsutellus , diminutive of hirsutus (= shaggy) refers to the small length and to the low number of the spine-like cuticular processes.

Differential diagnosis. There are only five valid species currently described in the genus Pseudobiotus : P. megalonyx ( Thulin, 1928) , P. matici ( Pilato,1971) , P. kathmanae , P. vladimiri Biserov, Dudichev & Biserova, 2001 and P. spinifer Chang, Kaczmarek, Lee & Michalczk, 2007 .

Another species, Pseudobiotus longiunguis ( Iharos 1968) , was cautiously placed in this genus by Kristensen (1987) who had reviewed the type material of ‘ Echinursellus longiunguis Iharos 1968 ’, and recognised the specimen was in fact the cyst stage of an eutardigrade ( Iharos (1968) had described Echinursellus longiunguis n. gen. n. sp. as a member of the Arthrotardigrada). Kristensen (1987) noted the cyst had claws similar to those of the known species of the genus Pseudobiotus , and therefore considered the genus Echinursellus as “a junior synonym of Pseudobiotus ” and established the new combination Pseudobiotus longiunguis ( Iharos, 1968) . Unfortunately, neither Iharos, nor Ramazzotti (1972), who had also examined the specimen of Echinursellus longiunguis , described characters useful to compare the species to other genera. Although Kristensen (1987) noted the presence of eye spots and three macroplacoids, he was unable to add any other details (e.g. cuticle ornamentation, macroplacoids length, details of the claw shape, presence or absence of accessory points, and of cuticular bars on legs) as it is difficult to assess such characters within a cyst. However, Kristensen (1987) did specify that peribuccal lamellae are absent, while the species of Pseudobiotus should have about 30 small lamellae. In conclusion, the lack of detail from a single cyst makes Pseudobiotus longiunguis , in our opinion, a species dubia. Despite this, P. hirsutellus sp. nov. has two macroplacoids, which would distinguish it from P. longiunguis (species dubia), which has three macroplacoids.

Comparing P. hirsutellus sp. nov with the truly valid species of the genus, it has to be stressed that P. matici and P.kathmanae have three macroplacoids. The other three valid species have two macroplacoids, but P. megalonyx is distinguished by a smooth cuticle and an oval papilla on the first three pairs of legs.

Pseudobiotus hirsutellus sp. nov is similar to P. vladimiri and P. spinifer , which also have spine-shaped cuticular processes and two macroplacoids. The new species differs from P. vladimiri in the following features: eye spots present; cuticular spine-shaped processes present also in the central portion of the body, not just the anterior and posterior portions; wider buccal tube, longer placoids and longer claws ( Table 7); freely protruding accessory points absent; oval papillae on the first three pairs of legs absent.

The new species differs from P. spinifer in having less numerous and smaller spine-shaped cuticular processes (>2.8 µm long on a 450 µm long specimen,>5 µm long on a specimen of P. spinifer of the same body length); wider buccal tube, longer placoids ( Table 7); oval papilla on the first three pairs of legs absent.