Angursa olenevskii Tchesunov & Fedyaeva, 2024, sp. nov.
Creators: name: Tchesunov, Alexei V.
name: Fedyaeva, Maria A.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Tardigrada
Heterotardigrada
Arthrotardigrada
Halechiniscidae
Angursa
Angursa olenevskii

description: Angursa olenevskii sp. nov.
Figs 1–3, Table 1
Diagnosis
Angursa with ballon-shaped primary clava inserted on pedestal together with cirrus A; cirrus A two to three times longer than primary clava; secondary and tertiary clavae not evident; cirrus E simple, tapered to the end; legs I–III with equal setose sensory organs on coxae; external digits with fine peduncle along their length and attached to the claw.
Etymology
The species name refers to the Olenevski Island where the new tardigrade was found.
Type material
Holotype (female) and three paratypes in permanent glycerine slide each are deposited in collection M. V. Lomonosov Moscow State University Zoological Museum, Moscow, Russia under inventory numbers: Holotype, female— 1 ZMMU R-2, Paratype 1, female—2 ZMMU R-3, Paratype 2, gender unknown—2 ZMMU R-4, Paratype 3, female—4 ZMMU R-5.
Type locality
White Sea, Kandalaksha Bay, Karelian coast, Olenevski Island, 66°52’N and 33°11’E, intertidal sandy littoral, medium sand, 10–15 cm sediment depth. August 2021.
Description
Body elongate, cylindrical, its length to width ratio 3.6–4.5. Body cuticle smooth, without sculpture and surface differentiations, but looking indistinctly punctated because of dense intracuticular pillars.
Cephalic region provided with complete set of appendages. All the appendages, except cA and primary clavae consist of two parts with indistinct borders, a high slim basal truncate cone (scapus) and a distal acute cirrus. The basal cones and pedestals rise up smoothly from the body surface. Internal cirri situated a bit dorsally and a bit more close to one another than the external cirri. Cirrus A and primary clava inserted together on the stout truncate conical pedestal, the clava just posterior and ventral to the cirrus A. The primary clava generally balloon-shaped. Cirrus A exceeds the clava two to three times in length (fig. 1 A, B; 3 G). Secondary and tertiary clavae not visible in light nor in scanning electron microscope. There is a pair of small, slightly pigmented bodies (ocelli) situated interiorly just posterior to the cirrus A+clava pedestals (fig. 1 A); the ocelli distinctly visible but in only holotype female. Cirri E situated dorso-laterally close to posterior margin of the body and consist also of basal truncate conical pedestal and long pointed flagellar cirrus without annulation (fig. 2 A, C).
Each limb bears a sensory organ located dorsally on coxa (basal part) of the leg. Sensory organs of the legs I–III appear as simple spines equal in shape and size (fig. 2 A, 3 C). Leg IV sensory organ shaped as short ovoid to hemispherical papilla with a minute apical spine and without a cuticular sheath (fig. 2 A).
Limbs conical, with barely discernible coxa and femur, and retractable distal part, tibia and tarsus with four digits terminating with claws. Digits unequal in length, laterally flattened and transparent. Internal digits slightly to significantly longer (1.3–1.5 times) than the external digits. External digits have a long peduncle extended along the ventral edge to the claw while internal digits do not have peduncle. Internal digits proximally differentiated in proximal pads while the external digits are not (fig. 2 C, 3 D). Claws minute, equal in shape and size, crescent-like in overall appearance. Primary point and secondary point broadly collocated; accessory point present on all claws but clearly discernible in only scanning electron and not in optical microscope (fig. 3 F). Claws may be projected or withdrawn into a fine transparent hood-like claw sheath. External and internal claws of all leg pairs equal in size.
Mouth opening subterminal. Stylets short and straight. Muscular bulb ovoid, its length to width ratio 1.14–1.25. Stylets short and straight, 10–16 μm long. Midgut pale brownish. No anal papillae.
Female gonopore a small six-lobed rosette at a short distance anterior to the longitudinal anal slit (fig. 2 B). Spermathecas and ducts poorly discernible. Male gonopore an arcuate transversal slit at anterior edge of a round areole just anterior to the longitudinal anal slit (fig. 3 H).
Differential diagnosis
Comparison of Angursa species is given on the Table 2. A. olenevskii is easily distinguished from other congeneric species by having well-developed sensory organs on all the legs. Most Angursa species have no sensory organs on legs II and III except A. clavifera where those organs are quite tiny and barely visible. Another feature differing A. olenevskii from all other Angursa species is evident claw and toe structures. Peduncles of A. olenevskii are extended along the ventral edge of digits from the base to the claw while the peduncles of all other congeneric species present a short curved bar at the base of the external digit stretched or even not stretched to basal third of the digits. Finally, A. olenevskii differs from almost all species of Angursa (with possible exception of A. bicuspis) by lack of even any traces of secondary and tertiary clavae which could not be observed neither with light microscope nor with SEM.
description: Published as part of Tchesunov, Alexei V. & Fedyaeva, Maria A., 2024, A new species of Angursa (Tardigrada, Heterotardigrada) from the White Sea, North Russia, pp. 121-128 in Zootaxa 5486 (1) on pages 123-127, DOI: 10.11646/zootaxa.5486.1.5, http://zenodo.org/record/13209805