Hypsibius pallidoides Pilato, Kiosya, Lisi, Inshina & Biserov, 2011, sp. nov.

Hypsibius pallidoides sp. nov.

(Fig. 7)

Material examined. Kherson Oblast, Ivano-Rybalchansky district of Chernomorsky biosphere reserve (46°27ʹ25ʺN, 32°8ʹ56ʺE), collector D.A. Korolesova, moss on wood, June 2008: holotype, seven paratypes and additional 27 specimens and nine exuvia.

Type repository. Holotype, seven paratypes and three exuvia (slide No.5430) are deposited in the collection of Binda & Pilato (Museum of the Department of Animal Biology “Marcello La Greca”, University of Catania, Italy). Other specimens are deposited in the Kiosya's collection (School of Biology, V.N. Karazin Kharkiv National University, Ukraine).

Specific diagnosis. Eye spots present; cuticle smooth; buccal armature without teeth; buccal tube very narrow; pharyngeal bulb with two macroplacoids and a very small, dot-shaped, septulum; claws similar to Hypsibius pallidus (i.e. the main branches of the external claws were inserted on the secondary branches well above the claw base); accessory points present; lunules absent; no cuticular bar on the first three pairs of legs; the cuticular bar between the claws on the hind legs seemed to be absent, but this character needs to be confirmed. Smooth eggs laid in the exuvia.

Description of the holotype. Body length 252 µm; colorless, cuticle smooth without cuticular pores or dots. Eye spots present. Bucco-pharyngeal apparatus of Hypsibius type (Fig. 7A, B). Mouth subterminal without peribuccal lamellae; small buccal cavity without rings of teeth. Narrow, rigid buccal tube, without ventral lamina, 22.3 µm long and 1.5 µm wide externally (pt = 6.7); stylet supports inserted on the buccal tube at 55.5 % of its length (pt = 55.5). Pharyngeal bulb (20.0 µm × 18.2 µm) with apophyses, two macroplacoids and a very small, dotshaped septulum (Fig. 7A, B, arrow). First macroplacoid 3.8 µm long (pt =17.0), second 2.6 µm (pt = 11.7); macroplacoid row length 6.9 µm (pt = 30.9).

Claws of the Hypsibius type, well developed; the main branches of the external claws were inserted on the secondary branches well above the claw base (Fig. 7C, D) as in Hypsibius pallidus. Main brancheses of all claws with very thin accessory points. External and internal claws on the second and third pairs of legs 12.7 µm (pt = 57.0) and 7.6 µm long (pt = 34.1) respectively; claw orientation on the hind legs did not allow correct measurements, but in Table 4 the measurements of two paratypes are shown. Lunules absent; a cuticular bar between the claws of the hind legs seemed to be absent, but this character needs to be confirmed; no cuticular bar on the first three pairs of legs.

Decription of the eggs. Smooth eggs laid in the exuvia.

Remarks. The paratypes were similar to the holotype in qualitative and metric characters. The measurements of three specimens are reported in Table 4.

Etymology. The specific name pallidoides indicates that this new species closely resembles Hypsibius pallidus.

Differential diagnosis. Hypsibius pallidoides sp. nov. was very similar to H. pallidus, which lacks any microplacoid or septulum, and had higher values of pt index for the macroplacoids (Table 4; Figs. 7A–B and 7 E). Five species of Hypsibius were known to have smooth cuticle, two macroplacoids and septulum: H. dujardini, H. iskandarovi, H. septulatus, H. heardensis Miller, McInnes & Bergstrom, 2005, and H. seychellensis. H. pallidoides sp. nov. differed from all in having external claws of Hypsibius pallidus - type and in having smaller, dot-shaped, septulum. Other differences include:

the lack of eye spots and presence of a pseudoseptulum in H. iskandarovi (Figs. 7 A, B and 8 A); the stylet supports inserted on the buccal tube in a more cephalic position (pt = 54.2–55.5 in H. pallidoides sp. nov., more than 58 in H. iskandarovi); shorter claws (pt index relative to the posterior claws of the hind legs: 68.6–72.1 in Hypsibius pallidoides sp. nov., 75.4–95.3 in H. iskandarovi according to Tumanov, 1997); presence of lunules (Figs. 7C, D and 8B) and cuticular bar on the first three pairs of legs for H. iskandarovi, all absent from the new species.

Cuticular undulations in H. septulatus were lacking in H. pallidoides sp. nov, the buccal tube was slightly narrower and the stylet supports inserted on the buccal tube in a more cephalic position (pt = 54.2–55.5 in H. pallidoides sp. nov, 64.5 in H. septulatus) (Table 4; Figs. 7A, B and 8 C); septulum much smaller, claws were slightly shorter (Table 4) and absence of cuticular bar on the legs (Figs 7C, D and 8 D).

H. heardensis lacked eye spots, present in the new species, and possessed cuticular bar on the legs, which were absent from H. pallidoides sp. nov.

The stylet supports of H. pallidoides sp. nov. were inserted on the buccal tube in a more cephalic position than for H. seychellensis (pt = 54.2–55.5 in H. pallidoides sp. nov., 62.3–63.7 in H. seychellensis) and the placoids were slightly shorter.

The buccal tube of H. dujardini gradually increased in width towards the posterior end, while the buccal tube of H. pallidoides sp. nov had a uniform width (Figs. 7A and 9A); the stylet supports were inserted on the buccal tube in a more cephalic position (pt = 54.2–55.5 in H. pallidoides sp. nov, about 64 in H. dujardini); and the cuticular bar between the claws on the hind legs was present in H. dujardini, but apparently absent in the new species.

Hypsibius allisoni had a very small microplacoid (Fig. 9 C), not the septulum present in H. pallidoides sp. nov., though it can be difficult to distinguish the difference between a microplacoid and a septulum. We therefore stress that the claw shape of Hypsibius pallidoides sp. nov. was very different from H. allisoni, as the main branch was inserted on the secondary branch in a more distal position (Figs. 7C, D and 9 D).