Macrobiotus surmaczi Stec, 2026, sp. nov.
Authors: Stec, Daniel
Type: Taxonomic treatment
Published: 2026-05-18
Keywords: Biodiversity, Taxonomy, Animalia, Tardigrada, Eutardigrada, Parachela, Macrobiotidae, Macrobiotus, Macrobiotus surmaczi

<p><b><i>Macrobiotus surmaczi</i> sp. nov.</b></p><p>urn:lsid:zoobank.org:act: 3F006251-3C6E-4D97-802E-99253C71C909</p><p>Figs 16–21; Tables 6–7</p><p><b>Etymology</b></p><p>The species name <i>surmaczi</i> is a patronym honouring Bartłomiej Surmacz, a close colleague and collaborator of the author, in recognition of his contributions to tardigrade research and his involvement in joint studies on tardigrade diversity and ecology. The species epithet <i>surmaczi</i> is a noun in the genitive case.</p><p><b>Material examined</b></p><p>68 animals, 28 eggs mounted on microscope slides in Hoyer’s medium, 6 animals and 4 eggs examined under SEM and two animals processed for DNA sequencing.</p><p><b>Type material</b></p><p><b>Holotype</b></p><p>VIETNAM • Central Lâm Đồng Province, Đà Lạt, city park area (“VƯờn Hoa”); 11°57′05″ N, 108°27′02″ E; 1491 m a.s.l.; Aug. 2018; D. Stec and K. Miler leg.; lichen collected from tree bark in urban environment; ISEA PAS, slide VN.003.07.</p><p><b>Paratypes</b></p><p>VIETNAM • 67 specs; same data as for holotype; ISEA PAS, slides VN.003.07 to VN.003.16 • 28 eggs; same data as for holotype; ISEA PAS, slides VN.003.01 to VN.003.06.</p><p><b>Description</b></p><p><b>Animals</b></p><p>Body transparent in juveniles and yellowish in adults; after fixation in Hoyer’s medium, the body becomes transparent (Fig. 16). Eyes present in alive and Hoyer-fixed specimens. Cuticular pores are scattered randomly over the entire body surface (Figs 16–17), being more sparsely distributed on the ventral side. Pores are circular and uniform in size and shape (0.7–0.9 μm in diameter). Body and leg granulation are absent. On the internal surface of legs I–III, a pulvinus-shaped cuticular bulge is centrally located, and a faint cuticular fold occurs in the distal portion of the legs just above the claws (Figs 16– 17). Both structures are visible only when the legs are fully extended and properly oriented on the slide.</p><p>Claws small and slender, of the <i>hufelandi</i> type (Fig. 18). Primary branches bear distinct accessory points, a common tract, and a well-developed stalk connecting the claw to the lunula (Fig. 18). Lunulae on legs I–IV are smooth (Fig. 18). A divided cuticular bar and double muscle attachments occur above claws I–III but are very poorly visible (Figs 16–18).</p><p>Mouth antero-ventral. Bucco-pharyngeal apparatus of the <i>Macrobiotus</i> type (Fig. 19), with a ventral lamina and ten small peribuccal lamellae followed by six buccal sensory lobes. Under PCM, the OCA is of the <i>maculatus</i> type, with the first and second bands of teeth not visible (Fig. 19); however, all three bands are clearly discernible under SEM (Fig. 19). The first band of teeth consists of numerous extremely small cones arranged in a single row, located anteriorly in the oral cavity on the bases of the peribuccal lamellae and immediately posterior to them (Fig. 19). The second band of teeth is situated between the ring fold and the third band and is composed of several rows of small cones, larger than those of the first band (Fig. 19). The third band of teeth is located in the posterior portion of the oral cavity, between the second band and the opening of the buccal tube (Fig. 19); it is discontinuous and divided into dorsal and ventral portions. Under PCM, the dorsal and ventral teeth appear as a single transverse ridge, with the ventral portion bearing two dark thickenings (Fig. 19). Under SEM, the dorsal and ventral portions are clearly distinguishable and form continuous ridges, each bearing two peaks, with the ventral peaks being larger and more distinct than the dorsal ones (Fig. 19). The pharyngeal bulb is spherical, with triangular apophyses, two rod-shaped macroplacoids, and a small triangular microplacoid (Fig. 19). The macroplacoid length sequence is 2 <1, with the first and second macroplacoids constricted centrally and subterminally, respectively (Fig. 19). Measurements and morphometric statistics are provided in Table 6.</p><p><b>Eggs</b></p><p>Eggs laid freely, yellowish, spherical, and ornamented (Figs 20–21). The surface between egg processes is of the <i>persimilis</i> type, with the eggshell between processes continuous, i.e. smooth or wrinkled but never forming pores or a reticulum (Figs 20–21). Under PCM, the egg surface appears generally smooth but covered with fine, scattered dark dots (Fig. 20). Observations under SEM confirm the continuous nature of the eggshell surface and the absence of reticulation; however, the surface is clearly wrinkled, forming a delicate sculpturing composed of fine grooves and folds (Fig. 21). These surface irregularities most probably correspond to the dark dots observed under PCM. Dark thickenings can be distinguished under PCM around the bases of the egg processes, which under SEM correspond to the thickened portions linking the egg surface with the walls of the egg processes (Figs 20–21). Egg processes are conical, with a wide proximal portion near the egg surface and a distinctly narrower distal portion (Figs 20–21). The walls of the proximal portion are smooth, whereas the distal portion is rough and flattened apically, being covered by granules that are clearly visible under SEM and occasionally very faintly visible under PCM (Figs 20–21). The apical flattening is usually poorly visible under PCM and can be observed only when the egg process is oriented with the flattened surface facing the observer. The wider proximal portion of the egg processes is usually shorter than the narrower distal portion (Figs 20–21). Measurements and morphometric statistics of the eggs are provided in Table 7.</p><p><b>Reproduction</b></p><p>The type population of <i>M. surmaczi</i> sp. nov. is dioecious. Both males with testes filled with sperm and females with ovaries containing oocytes were observed in specimens freshly mounted in Hoyer’s medium.</p><p><b>Differential diagnosis</b></p><p>By having (i) a smooth, continuous body cuticle lacking dorsal gibbosities and (ii) eggs with conical, elongated processes bearing flattened apices and a smooth, continuous eggshell surface between processes, the new species is most similar to only one species of <i>Macrobiotus</i>: <i>Macrobiotus kristenseni</i> Guidetti, Peluffo, Rocha, Cesari & Moly de Peluffo, 2013, known so far only from Argentina (Guidetti <i>et al.</i> 2013).</p><p>However, the new species differs from <i>M. kristenseni</i> in several diagnostic characters: (i) the absence of granulation on both the body and leg cuticle (typical granulation present on the distal portions of all legs in <i>M. kristenseni</i>); (ii) the morphology of the third band of teeth in the OCA, in which the dorsal and ventral portions appear as single, continuous transverse ridges in the new species, whereas in <i>M. kristenseni</i> both portions consist of three separate ridges; (iii) the presence of smooth lunulae on the hind legs (lunulae dentate in <i>M. kristenseni</i>); (iv) the morphology of the egg processes, which in the new species are conical with a wider proximal portion and a distinctly narrower distal portion that is flattened apically and covered with granules, whereas in <i>M. kristenseni</i> the processes are conical, rather spiky in shape, with a flattened distal portion lacking granulation; (v) the morphology of the egg surface between processes, which in the new species appears smooth and covered with fine, scattered dark dots under PCM and, under SEM, is confirmed to be continuous but distinctly wrinkled, forming a delicate sculpturing of fine grooves and folds, whereas in <i>M. kristenseni</i> the egg surface between processes shows light-refracting dots under PCM and is confirmed under SEM to be solid and smooth, without distinct sculpturing; and (vi) smaller eggs (bare diameter 52.3–66.5 μm and full diameter 71.0–95.3 μm in the new species vs 73.0–96.3 μm and 94.0–125.0 μm in <i>M. kristenseni</i>, respectively).</p>