Angursa olenevskii, Tchesunov & Fedyaeva, 2024

Tchesunov, Alexei V. & Fedyaeva, Maria A., 2024, A new species of Angursa (Tardigrada, Heterotardigrada) from the White Sea, North Russia, Zootaxa 5486 (1), pp. 121-128 : 123-127

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.

Figures

FIGURE 1. Angursa olenevskii sp. n., heads.A holotype female, dorsal view. B paratype 1, female, ventral view.The continuous punctations of the cuticle is shown just as a band. Scale bars 10 μm.

FIGURE 2. Angursa olenevskii sp. n., details. A paratype 2, female, entire. B paratype 1, female 1, hind body ventrally. C holotype female, left leg IV, dorsal view. The continuous punctations of the cuticle is shown just as a band. Scale bars: A 20 μm, B and C 10 μm.

FIGURE 3. Angursa olenevskii sp. n., SEM. A specimen 1 male, entire, ventral view. B specimen 2 female, entire, lateroventral view. C specimen 3, entire, lateral view. D specimen 1, left foot I, ventral view. E specimen I, right foot II, toes with claws withdrawn in hoods. F specimen 4, left foot IV, toes with claws protruded. G specimen 3, primary clava and cirrus A. H specimen 1, male gonopore and anus. Scale bars: A 10 μm, B and C 20 μm, D–F, H 2 μm, G 5 μm.