Mesobiotus efa 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 : 25-33

Mesobiotus efa sp. nov.

urn:lsid:zoobank.org:act:EA291ABA-E1E5-4571-90AE-53D6A0DF530C

Figs 1–6 ; Tables 2–3

Etymology

Named after the children’s teaching laboratory in St Petersburg “Efa”. The studied material was collected during the field tip on the occasion of its anniversary.

Material examined

Holotype

RUSSIA • ♀; Leningrad Oblast, Vsevolozhsky District; a hill near the Lembolovo railway station, approx. 60.41612° N, 30.34266° E; 10 Sep. 2020; E. Androsova leg.; association of moss and lichen on soil; SPbU 275(72) .

Paratypes

RUSSIA • 30 ♀♀, 14 eggs; same data as for holotype; SPbU 275(39, 47, 65–66, 68–72, 74–75, 77–80, 85–88, 104–106, 133–134, 136, 143, 147, 155, 182, 197, 207–208, 210–213) • 1 adult, 2 eggs; same data as for holotype; SEM stub SPbU Tar_33 • 2 adults; same data as for holotype; ZM FEFU (slides 275(73), 275(76)) • 2 eggs; same data as for holotype; ZM FEFU (slides 275(67) and 275(180)) .

Morphological description

Adult animals

Body elongated ( Fig. 1 ) (morphometrics in Table 2 , raw morphometric data are provided in the Supp. file 4). Fresh specimens uncolored or whitish with slightly greenish gut content, transparent after fixation in Hoyer’s medium. Black eyes present ( Figs 1A , 3A , black arrowheads), 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. 2A ). All legs with granulated areas consisted of small granules, poorly discernible or, sometimes, completely invisible in LM. Legs I–III with small granulated areas on the external surfaces, near the claw bases ( Fig. 2B–C ), the internal leg surfaces without granulation, with distinct pulvinus. Legs IV with better-developed granulation mainly dorsally to the claws ( Fig. 2D ) and around the claw bases ( Fig. 4C–D , white arrowhead).

Buccal-pharyngeal apparatus of Macrobiotus type ( Fig. 3A ) with the ventral lamina and ten peribuccal lamellae. 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 ( Fig. 3D, F–G ). Second band consists of a row of longitudinally elongated triangular teeth ( Fig. 3D–G ). Third band comprises three dorsal and three ventral transverse ridges ( Fig. 3D–G ). Medio-ventral ridge usually never divided into separate parts, only single specimen was found with detached lateral part of the medio-ventral ridge. Ventrally OCA with numerous additional teeth between the second and the third teeth bands ( Fig. 3F–G ). Pharyngeal bulb with apophyses, three macroplacoids and a large microplacoid ( Fig. 3B–C ). Macroplacoid length sequence is 2<3 ≤1. First macroplacoid is anteriorly narrowed, third macroplacoid with distinct subterminal constriction ( Fig. 3B–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. 4A–C, E ). Primary and secondary branches diverge below the half of the claw height, main branches with well-developed accessory points ( Fig. 4A, C–D ). Claws of fourth pair of legs slightly longer than claws of first three pairs of legs ( Fig. 4C ). All claws with smooth lunules ( Fig. 4 ). Anterior (internal) and posterior (external) claws of the legs IV are similar in shape ( Fig. 4D ). Lunules on posterior claws distinctly larger than on anterior claws ( Fig.4C–D ). Single continuous cuticular bars are present below claw bases of the first three pairs of legs ( Fig. 4A–B , black arrowhead) with poorly developed muscle attachment points below ( Fig. 4B ). Claws of the legs IV are connected with a wide but poorly sclerified horseshoe-like structure, visible in PhC only ( Fig. 4E , black arrowhead).

Eggs

One adult female with mature oocites was islolated and cultivated for three days until the eggs were layed. After that the female was taken for the DNA extraction and gene sequencing (voucher slide SPbU 275(211)) while the layed eggs were taken for the morphological analysis using LM.

Eggs spherical, white, ornamented and laid freely ( Figs 5A–C , 6A ; morphometrics in Table 3 ). Chorion with conical processes that can be attributed to the “cones with long slender endings and filaments” and “reticular design with “bubbles” morphotypes” (according to Kaczmarek et al. 2020). Egg processes with wide bases and thinned and flexible apices usually well differentiated ( Figs 5 , 6A–B, D ). Processes (with the exception of the thinned 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. 5 ). Apical parts of the processes with bubble-like internal structure ( Fig. 5 ), rarely bifurcating ( Fig. 5A, F–G , black arrowheads), usually with a tuft of very short (0.5–2,75 µm) apical and subapical filaments ( Figs 5E, G–H , 6D , white arrowheads). Large pores (ca 1 µm in diameter), mostly indiscernible in LM and well-visible in SEM, are present on the basal part of all processes, forming a single row ( Figs 5I , black arrowhead, 6B–D, black arrowheads). Process bases with well-developed crone of dark thickenings, visible in LM ( Fig. 5A–D, H ). Egg surface between the processes without areolation or pores but with a system of irregularly distributed wrinkles poorly discernible in LM as irregularly distributed granules and well-visible in SEM ( Figs 5D , 6A–C ).

Reproduction

No males were found.

DNA sequences

Sequences for 18S rRNA marker were obtained from four specimens (accession numbers: OR804457– OR804460; voucher slides: SpbU 275(077, 104–106)). Sequences for 28S rRNA and COI markers were obtained from five specimens (accession numbers: OR805135–OR805139 and OR803035–OR803039 respectively; voucher slides SpbU 275(077, 104–106, 211). Sequences for ITS-2 marker were obtained from three specimens (accession numbers: OR805169–OR805171; voucher slides SpbU 275(077, 104, 211). Presence of two COI haplotypes was revealed.

Figures

Fig. 1. Mesobiotus efa sp. nov., total view. A. Holotype, ♀ (SPbU 275(72)). Dorso-ventral view, black arrowheads indicate eyes, PhC. B. Paratype (SPbU Tar_33). Ventral view in SEM. Scale bars = 50 µm.

Fig. 2. Mesobiotus efa sp. nov., cuticular sculpture. A–B, D. Paratype (SPbU Tar_33). C. Paratype (SPbU 275(197)). 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. Dot-like sculpture on the external surface of leg III, PhC, black arrowhead indicates dots. D. Dot-like sculpture on the dorsal side of hind legs, SEM. Scale bars: A–B, D = 2 µm; C = 5 µm.

Fig. 3. Mesobiotus efa sp. nov.,bucco-pharyngeal apparatus.A. Holotype (SPbU 275(72)).B–G. Paratype (SPbU 275(197)). A. Total dorso-ventral view of the bucco-pharyngeal apparatus, black arrowheads indicate eyes, PhC. B–C. Placoids, PhC (B) and DIC (C). D–G. Oral cavity armature (D–E = dorsal view, F–G = ventral view), PhC (D, F), DIC (E, G). Scale bars: A = 10 µm; B–G = 5 µm.

Fig. 4. Mesobiotus efa sp. nov., claws.A–B, E. Holotype (SPbU 275(72)).C. Paratype (SPbU 275(197)). D. Paratype (SPbU Tar_33). A. Claws of leg I, black arrowhead indicates bar-like cuticular thickening, PhC. B. Claws of leg II, black arrowhead indicates bar-like cuticular thickening, PhC. C. Claws of leg IV, white arrowhead indicates cuticular sculpture around the claw base, PhC. D. Claws of leg IV, white arrowhead indicates cuticular sculpture around the claw base, SEM. E. Claws of leg IV, black arrowhead indicates horseshoe-like structure, PhC. Scale bars: A–C, E = 10 µm; D = 5 µm.

Fig. 5. Mesobiotus efa sp. nov., eggs. A–E, H–I. Paratype (SPbU 275(210)). F–G. Paratype (SPbU 275(180)). A. Total view of the optical section of the embryonated egg, PhC. B. Total view of the egg surface, PhC. C. Total view of the egg surface, DIC. D. Details of the egg surface, PhC. E–H. Egg processes, PhC. I. Optical section of the egg process, DIC. Black arrowheads indicate bifurcated tips, white arrowheads indicate terminal and subterminal filaments, black arrow indicates a pore. Scale bars: A–C = 20 µm; D–I = 10 µm.

Fig. 6. Mesobiotus efa sp. nov., paratype (SPbU Tar_33), eggs. A. Total view of the egg, SEM. B–C. Details of the egg surface, black arrowheads indicate pores on the egg processes, black arrow indicates wrinkles on the egg surface, SEM. D. Egg process, black arrowheads indicate pores, white arrowhead indicates terminal filaments, SEM. Scale bars: A = 20 µm; B = 5 µm; C–D = 2 µm.