Tenuibiotus yeliseii, Tsvetkova & Tumanov, 2024

Tenuibiotus yeliseii sp.nov.

( Figs 1–5)

Holotype. Sex not determined; Norway, Svalbard , West Spitsbergen, nr. Longyearbyen settlm., 78°13′13.8″N 15°38′10″E; moss, leaf litter and soil, 15 Sept. 2019, Yelisei Mesentsev leg., SPbU 295(11). GoogleMaps

Paratypes. Sex not determined; 8 adults and 20 eggs, same data as for holotype, SPbU 295(1, 2, 9–18, 27, 28, 32) GoogleMaps ; 3 adults and 4 eggs, same data as for holotype, SEM stub, SPbU_Tar48 GoogleMaps .

The type specimens are kept at SPbU.

Morphological description. (Measurements and statistics in Table 1; see also Addenda: Electronic supplementary material 5). Body whitish, after mounting in Hoyer’s medium transparent ( Fig. 1a), with relatively short legs. Body surface with numerous well-developed cribrose areas functioning as muscle attachment points ( Fig. 1b). Eyes present in most of living specimens, visible after mounting. Body cuticle without pores; body surface with fine uniform sculpture consisting of minute granules visible under SEM only ( Fig. 2a). Patches of dense granulation composed of cushions with aggregated granules present on all legs ( Fig. 2b). Patches of granulation clearly visible under LM and SEM present on legs I–III on their outer surfaces and above claws ( Fig. 4a, c). Inner surfaces of legs I–III lacking granulation ( Fig. 4b); pulvinus absent. Patch of dense granulation present on legs IV, covering leg surface around claws ( Fig. 4d, f, g).

Bucco-pharyngeal apparatus of Macrobiotustype ( Fig. 3a, i–k). Mouth anteroventral, surrounded by ten peribuccal lamellae. Oral cavity armature comprising three bands of teeth ( Fig. 3b–h). Under LM, only second and third bands of teeth visible (second looking extremely faint) ( Fig. 3e). However, under SEM all three bands of teeth visible, with first band appearing as a narrow zone of very small teeth situated at bases of peribuccal lamellae ( Fig. 3c). Second band of teeth situated posterior to ring fold of buccal cavity and represented by a wider zone of larger granular or cone-shaped teeth ( Fig. 3d, e). Third band of teeth divided into three dorsal and three ventral transverse ridges. Dorsomedial ridge slightly caudally curved ( Fig. 3d, f); ventromedial ridge apparently consisting of closely spaced and partially fused large teeth ( Fig. 3g). (Granular structures posterior to third band of teeth visible in LM images identified as food particles in buccal cavity.)

Stylet furcae with well-developed sphaerical condyles ( Fig. 3i). Ventral lamina relatively long, constituting more than half of length of buccal tube ( Fig. 3i). Buccal tube terminating in well-developed apophyses ( Fig. 3j, k). Pharyngeal bulb containing two elongate macroplacoids and a drop-like microplacoid. Macroplacoid length sequence 2 <1. First macroplacoid with central constriction whereas second macroplacoid constricted subterminally ( Fig. 3j, k).

Claws of tenuis - type, large, primary branches with distinct accessory points ( Fig. 4a, c, d, g). Lunulae large on all legs, especially on legs IV. Lunulae I–III smooth ( Fig. 4a, c), lunulae IV with clear dentation ( Fig. 4d, f, g). Legs I–III only with double muscle attachments under claws, without cuticular bars ( Fig. 4e). Lunulae on legs IV connected by a horseshoe structure visible under LM ( Fig. 4f). Each hind leg with a pair of gibbosities on dorsal surface, right above claws ( Fig. 4d, f, g).

Eggs (measurements and statistics in Table 2; see also Addenda: Electronic supplementary material 5). Laid freely, yellow whitish, sphaerical, with relatively small conical processes ( Fig. 5a–d). Apices of processes often furcated, sometimes bent towards egg surface ( Fig. 5f). Several rows of roundish pores visible only under SEM on basal surface of processes ( Fig. 5f), with pores not fully perforating the process wall and instead appearing as individual round recesses ( Fig. 5g). Apical surface without pores. Surface between processes lacking areolation or reticulation but bearing minute sparsely spaced pores and system of well-developed radial ridges, visible under SEM ( Fig. 5e, f: incut). Layered egg chorion with pillars ( Fig. 5g) appearing as dots on egg surface under LM ( Fig. 5e).

A.Yu. Tsvetkova & D.V. Tumanov. Tenuibiotus yeliseii sp. nov., a new species of Macrobiotidae

Of all the eggs discovered, several contained fully formed embryos. The claw shape and placoid configuration of the embryos matched those in adult specimens. Moreover, all other species found in the same sample belong to the superfamily Hypsibioidea ; they are characterised by laying their eggs into exuviae after molting. Therefore, we can conclude that all discovered eggs belong to the new species.

Phenotypic comparison. Tenuibiotus yeliseii sp.nov. is most similar to T. voronkovi also known from Svalbard ( Tumanov, 2007; not T. voronkovi sensu Zawierucha et al., 2016 ; see also Stec et al., 2020), but is easily distinguished from it by the structure of egg processes (by the presence of rows of pores at the bases of processes), and by the absence of granulation on the dorsal and lateral body cuticle visible under LM.

Compared to the other Tenuibiotus species, T. yeliseii sp. nov. differs from T. bondavallii [described from Canada by Manicardi (1989) and later reported from Russia, namely, from Dikson Island, the Taimyr Peninsula ( Biserov, 1996) and the Kuril Islands ( Dudichev & Biserov, 2000), but the records from Russia need verification] in the absence of granulation on the dorsal body cuticle in the posterior region visible under LM [vs. body surface sculpture visible under LM (Fig. 8a)] and in much smaller egg processes (process base diameter ranging 7.7–13.4 µm in T. yeliseii sp. nov., while process base diameter in T. bondavallii is measured to be 16–18 µm);

A.Yu. Tsvetkova & D.V. Tumanov. Tenuibiotus yeliseii sp. nov., a new species of Macrobiotidae from T. bozhkae [described from the Crimean Peninsula by Pilato et al. (2011)], in the larger eggs (87 µm bare diameter / 123 µm diameter with processes in T. bozhkae vs. 116/138 µm on average in the new species) and in wider process bases (6.1–6.3 µm in T. bozhkae , with the processes therefore appearing more narrow and elongate, vs. 7.7–13.4 µm in the new species);

from T. ciprianoi [described from Spain by Guil et al. (2007)], in the presence of well-developed accessory points on the main claw branch, in narrower and more elongate macroplacoids, and in wider egg processes (process height / base width ratio ranging 120–286% in T. ciprianoi vs. 50– 110% in the new species);

from T. danilovi [known from Kyrgyzstan ( Tumanov, 2007; Stec et al., 2021)], in the shape of mediodorsal ridge of buccal armature (paired granules in T. danilovi and arch-shaped ridge in the new species) and in larger egg processes (30 on the egg circumference in T. danilovi vs. only 20–23 in the new species);

from T. higginsi [described from Wyoming, USA, by Maucci (1987)], in the significantly shorter claws, especially on legs IV (length of claws on hind legs up to 28 µm in T. higginsi vs. 9.2–16.8 µm in the new species; with pt index for claws on hind legs 41.2 in the holotype of T. higginsi * vs. pt range 24.2–31.4 in the new species) and in narrower and taller egg processes (process height / base width ratio is 40% in T. higginsi vs. 50–110% in the new species);

from T. hystricogenitus View in CoL [described from Turkey ( Maucci, 1978), later recorded from Germany and Greece ( McInnes, 1994); the record from Alaska ( Johansson et al., 2013) needs verification ( Kaczmarek et al., 2016)], in the shape of egg processes (filiform and flexible in T. hystricogenitus View in CoL vs. conical in the new species);

from T. kozharai View in CoL [described from Turkmenistan by Biserov (1999)], in the well-pronounced accessory points and in a longer ventral lamina (less than half of the buccal tube length in T. kozharai View in CoL vs. 52.0–59.4% of its length in the new species);

from T. mongolicus [described from Mongolia by Maucci (1988)], in the narrower buccal tube (mean pt index for internal width is 11.05 ± 1.37 in T. mongolicus vs. 6.8 ± 1.1 in the new species);

Notes. Measurements are given in µm. N – number of eggs/structures measured, range refers to the smallest and the largest structure among all measured specimens; SD – standard deviation.

from T. tenuiformis [described from Kyrgyzstan ( Tumanov, 2007; Stec et al., 2021) and also report- ed from China ( Beasley & Miller, 2012)], in the absence of a large mediodorsal tooth in the buccal armature, in the shape of egg processes (truncat- ed cones in T. tenuiformis vs. elongate cones in the new species);

from T. tenuis View in CoL [described from Italy by Binda & Pilato (1972); Canadian record needs verification ( Kaczmarek et al., 2016)], in the shape of egg processes (truncated cones in T. tenuis View in CoL vs. elongate cones in the new species);

from T. willardi View in CoL [described from Canada ( Pilato, 1977), also reported from USA, Greenland, Poland and numerous locations in Russia ( McInnes, 1994; Kaczmarek et al., 2016)], in the presence of well-pronounced teeth on leg 4 lunules and in the size of the eggs (bare diameter ranging 74–82 µm in T. willardi View in CoL vs. 104.4–126.1 µm in the new species);

from T. zandrae View in CoL [described from Greenland ( Stec, Tumanov et Kristensen, 2020)], in the absence of granulation on the dorsal body cuticle visible under LM, in the absence of granulation on the inner surfaces of legs I–III, in well-developed medioventral ridge with less pronounced fragmentation, the presence of rows of roundish pores at the base of egg processes (such pores completely absent in T. zandrae View in CoL ), in a larger number of these processes (13–15 processes on the egg circumference in T. zandrae View in CoL vs. 20–24 in the new species) and in smaller size of the processes (process base width ranging 13.6–29.6 µm in T. zandrae View in CoL vs. 7.7– 13.4 µm in the new species).

DNA sequences. Sequences of good quality for the four molecular markers mentioned above were obtained from three paratypes [two hologenophores available: voucher specimens 295(1) and 295(2)], except for the ITS-2 marker, which was obtained from two specimens only. Each gene was represented by a single haplotype. All obtained sequences were deposited in GenBank.

18S rRNA sequence (GenBank: OR142418– OR142420), 1011, 1033 and 1008 bp long.

28S rRNA sequence (GenBank: OR142426 – OR142428), 729, 736 and 732 bp long.

ITS-2 sequence (GenBank: OR142424 and OR142425), 370 and 422 bp long.

COI sequence (GenBank: OR145334– OR145336), 681, 699 and 696 bp long.

Molecular comparison. The ranges of uncorrected genetic p -distances between the studied population of Tenuibiotus yeliseii sp. nov. and the other species of the genus Tenuibiotus , for which sequences were available from GenBank (see Addenda: Electronic supplementary material 2) are as follows:

18S rRNA: our analysis shows that all examined species of Tenuibiotus do not differ by the 18S rRNA fragment chosen for calculating p -distances, therefore appearing to share the same haplotype.

28S rRNA: 0.28%–4.18% (mean 1.76%), with the most similar being T. zandrae ( Stec et al., 2020) from Greenland ( MN443035 View Materials : Stec et al., 2020), and the least similar being T. tenuiformis from Kyrgyzstan ( MN888363 View Materials : Stec et al., 2021).

ITS-2: 0.54%–12.30% (mean 4.50%), with the most similar being T. aff. voronkovi * from Nordaustlandet ( KX810046 View Materials – KX810048 View Materials : Zawierucha et al., 2016), and the least similar being T. tenuiformis ( MN888350 View Materials : Stec et al., 2021).

COI: 12.43%–24.75% (mean 17.95%), with the most similar being T. aff. voronkovi from Nordaustlandet ( KX810043 View Materials : Zawierucha et al., 2016), and the least similar being T. tenuiformis ( MN888330 View Materials : Stec et al., 2021).

* The sequences of T. aff. voronkovi used in the analysis were presented in a study of Zawierucha et al. (2016). The authors provided a redescription of T. voronkovi , adding the molecular data to the existing morphological description. However, Stec et al. (2020) reexamined the material used by Zawierucha et al. and concluded that it significantly differs morphologically from the type material collected by Tumanov (2007). Therefore T. aff. voronkovi is most likely a yet undescribed Tenuibiotus species, which closely resembles T. zandrae (see discussion in Stec et al., 2020).

Full matrices with p -distances are provided in Electronic supplementary material 6.

Etymology. We dedicate the new species to Yelisei Mesentsev, who kindly collected the samples on the Svalbard Archipelago during an expedition in 2019.