Mesobiotus vulpinus sp. nov., 2024

Tumanov, Denis V., Androsova, Evgenia D., Gavrilenko, Marina D. & Kalimullin, Aidar A., 2024, Integrative description of two new species of the genus Mesobiotus (Eutardigrada, Macrobiotoidea) from Russia, with an updated phylogeny of the genus, European Journal of Taxonomy 947 (1), pp. 20-52 : 33-41

Mesobiotus vulpinus sp. nov.

urn:lsid:zoobank.org:act:CC615859-F0A0-49F4-A035-28889F370283

Figs 7–13 ; Tables 4–5

Etymology

Named after the latin name ( Vulpes vulpes ) of the most famous animal inhabiting Russkij Island – the common fox.

Material examined

Holotype

RUSSIA • ♀; Primorsky Krai, Vladivostok, Russkij Island , road to the Kruglaja Bay; 43.01386° N, 131.78838° E; 3 Feb. 2023; A. Kalimullin leg.; moss on tree trunk; SPbU 320(10) .

Paratypes

RUSSIA • 8 ♀♀, 4 eggs; same data as for holotype; SPbU 320(2–9, 11, 13–15) • 2 adult, 2 eggs; same data as for holotype; SEM stub SPbU Tar_65 • 1 adult; same data as for holotype; ZM FEFU (slide 320(1)) • 1 egg; same data as for holotype; ZM FEFU (slide 320(12)) .

Morphological description

Adult animals

Body elongated ( Fig. 7 ) (morphometrics in Table 4, raw morphometric data are provided in the Supp. file 5). Fresh specimens uncolored or whitish with slightly greenish gut content, transparent after fixation in Hoyer’s medium. Black eyes present, often dissolving after slide mounting. Cuticle smooth in LM, with fine uniform sculpture consisting of minute conical granules with pointed apices visible under SEM only ( Fig. 8A ). All legs with granulated areas consisted of small granules, usually well visible in LM. Legs I–III with small granulated areas on the external surfaces, near the claw bases ( Fig. 8B– C , black arrowhead), the internal leg surfaces without granulation, with indistinctly demarcated large pulvinus, visible in SEM only ( Fig. 10A , white arrowhead). Legs IV with better-developed granulation mainly dorsally to the claws ( Fig. 8D–E , white arrowhead) and around the claw bases ( Fig. 10E, H , black arrowheads).

Buccal-pharyngeal apparatus of Macrobiotus type ( Fig. 9A ) with the ventral lamina and ten peribuccal lamellae ( Fig. 8F ). Oral cavity armature ( OCA) of harmsworthi type (according to Kaczmarek et al. 2020) with three bands of teeth visible in LM. Evident first (anterior) band consists of a wide band of numerous minute teeth visible as dots in LM ( Figs 8F , white arrow, 9E, G). Second band consists of a row of longitudinally elongated triangular teeth ( Fig. 9D–H ). Third band comprises three dorsal and three ventral transverse ridges ( Figs 8F white arrowhead, 9D–H). Medio-ventral ridge often divided in two or three separate teeth ( Fig. 9H ). Latero-ventral ridges often with strong indentations ( Fig. 9G ), sometimes almost fragmented to separate teeth. Rare additional teeth are present ventrally, between the second and the third teeth bands ( Fig. 9F–H ). Pharyngeal bulb with apophyses, three macroplacoids and a large microplacoid ( Fig. 9B–C ). Macroplacoid length sequence is 2<3 ≤1. First macroplacoid is anteriorly narrowed, third macroplacoid with poorly developed subterminal constriction ( Fig. 9B–C ).

Claws of Mesobiotus type with minute stalk, distinct distal part of the basal portion, short common tract and developed internal septum, defining a distal part ( Fig. 10B, D–E ). Primary and secondary branches diverge below the half of the claw height, main branches with well-developed accessory points ( Fig. 10B–F ). Claws of fourth pair of legs slightly longer than claws of first three pairs of legs ( Fig. 10E ). All claws with smooth lunules ( Fig. 10B–C, E, G ). Anterior (internal) and posterior (external) claws of the legs IV are similar in shape ( Fig. 10E ). Single continuous cuticular bars of characteristic shape (two wide short bars connected by thin angular strip) are present below claw bases of the first three pairs of legs ( Fig. 10B, D , black arrowhead) with poorly developed muscle attachment points below ( Fig. 10B, D ). Claws of the legs IV are connected with a poorly sclerified horseshoe-like structure, visible in PhC only ( Fig. 10H , white arrowhead).

Eggs

No eggs with developed embryos were found, but taking into account that M. vulpinus sp. nov. was the only tardigrade species present in the sample we believe that the adult specimens and the eggs belong to the same species.

Eggs spherical, white, ornamented and laid freely ( Figs 11A , 12A, C ; morphometrics in Table 5 ). Chorion with conical processes that can be attributed to the “sharp narrow cones” and “reticular design with “bubbles” morphotypes” (according to Kaczmarek et al. 2020). Egg processes in form of elongated cones with poorly differentiated basal and apical parts ( Figs 11B, E–F , 12–13 ). Processes (with the exception of the elongated apical parts) with bilayered walls, with a net of trabecular structures between the internal and external layers, forming irregular rounded meshes of different size, so the processes seem to be reticulated in LM ( Fig. 11 ). Apical parts of the processes with bubble-like internal structure ( Fig. 11F ), rarely bifurcating ( Figs 11E , 13A ). Processes surface bears annulations, visible in SEM only ( Figs 12B, D , 13 ). Rare large pores (1.4–2.3 µm in diameter), poorly discernible in LM and well-visible in SEM, are present on the basal part of all processes, below the half of the process height, forming a single row ( Figs 11H , white arrowheads, 12, 13, white arrowheads), Second row of distinctly smaller and more numerous pores is located in the most basal part of each process ( Fig. 13 , black arrowheads). Process bases with poorly developed, sometimes almost invisible crone of dark thickenings ( Fig. 11C, E–F ). Egg surface between the processes with distinct polygonal relief consisted of ridges forming hexagonal (rarely pentagonal) cells around each process ( Figs 11C–D , 12 ). Points of ridges intersection bears small bulbous processes ( Figs 11B , 12B, D , 13B ). Both ridges and bulbous processes with internal trabecular structures, similar to the main processes walls. Egg surface between the processes bases and the ridges of polygonal relief with a system of smaller radial ridges and pores discernible both in LM and SEM ( Figs 11C–D , 12B, D , 13 ).

Reproduction

No males were found.

DNA sequences

Sequences for all four molecular markers were obtained from two specimens (18S rRNA – OR804461, OR804462, 28S rRNA – OR805140, OR805141, ITS-2 – OR805172, OR805173, COI – OR803040, OR803041; voucher slides SpbU 320(08) and 320(15))

Figures

Fig. 7. Mesobiotus vulpinus sp. nov., total view. A. Paratype, ♀ (SPbU 420(1)). Dorso-ventral view, PhC. B. Paratype (SPbU Tar_65). Ventro-lateral view in SEM. Scale bars = 50 µm.

Fig. 8. Mesobiotus vulpinus sp. nov., cuticular sculpture and oral cavity armature (OCA). A–B, E–F. Paratype (SPbU Tar_33). C–D. Holotype (SPbU 320(10)). A. High magnification of the sculpture of the dorsal body surface, SEM. B. Dot-like sculpture on the external surface of leg III, SEM. C. Dotlike sculpture on the external surface of leg III, PhC, black arrowhead inticates the zone of sculpture. D. Dot-like sculpture on the dorsal side of hind leg, PhC. E. Dot-like sculpture on the dorsal side of hind leg, SEM, white arrowhead indicates the zone of sculpture. F. Mouth opening with dorsal OCA visible, SEM, white arrow indicates the first band of teeth, white arrowhead indicates the dorsal crests of the third band of teeth. Scale bars A–B, F = 2 µm; C–E = 5 µm.

Fig. 9. Mesobiotus vulpinus sp. nov., bucco-pharyngeal apparatus. A–G. Holotype (SPbU 320(10)). H. Paratype (SPbU 320(1)). A. Total dorso-ventral view of the bucco-pharyngeal apparatus, PhC. B–C. Placoids, black arrowheads indicate the preterminal constriction of the third macroplacoid, PhC (B), DIC (C). D–G. Oral cavity armature (D–E = dorsal view, F–G = ventral view), PhC (D, F), DIC (E, G). H. Oral cavity armature with fragmented medio-ventral ridge, PhC. Scale bars: A = 20 µm; B–H = 10 µm.

Fig. 10. Mesobiotus vulpinus sp. nov., claws. A, C, F–G. Paratype (SPbU Tar_33). B. Paratype (SPbU 320(1)). D, H. Holotype (SPbU 320(10)). E. Paratype (SPbU 320(5)). A. Inner surface of leg III, white arrowhead indicates indistinctly marked pulvinus, SEM. B. Claws of leg II, black arrowhead indicates bar-like cuticular thickening, PhC. C. Claws of leg III, SEM. D. Claws of leg I, focused on bar-like cuticular thickening, black arrowhead, white arrowhead indicates the zone of dot-like sculpture, PhC. E. Claws of leg IV, black arrowheads indicate cuticular sculpture around the claw bases, PhC. F. Claws of leg IV, SEM. G. Lunules of claws of leg IV, SEM. H. Leg IV, focused on horseshoe-like structure, white arrowhead, black arrowhead indicates cuticular sculpture around the claw base, PhC. Scale bars: A–B, D–E, H = 10 µm; C, F–G = 5 µm.

Fig. 11. Mesobiotus vulpinus sp. nov., paratype (SPbU 320(6)), egg. A. Total view of the egg, PhC. B. Egg processes with small bulbous process between them, black arrowhead, DIC. C–D. Details of the egg surface, black arrowheads indicate small bulbous processes, PhC (C), DIC (D). E. Bifurcated egg process, PhC. F. Egg process with “bubble”, black arrowhead, PhC. G–H. Optical sections of the egg process basal part, white arrowheads indicate a pore, DIC. Scale bars: A = 20 µm; B–H = 10 µm.

Fig. 12. Mesobiotus vulpinus sp. nov., egg. A–D. Paratypes (SPbU Tar_65). A, C. Total view of the eggs, SEM. B, D. Details of the egg surface, SEM. Note the difference in the degree of development of small tubercles and numerous small pores on the egg surface. Scale bars: A–B = 20 µm; C–D = 5 µm.

Fig. 13. Mesobiotus vulpinus sp. nov., paratype (SPbU Tar_65), egg. A–B. Details of the egg processes, whire arrowheads indicate large pores, black arrowheads indicate small pores, SEM. Scale bars = 5 µm.