Richtersius ingemari, Vecchi & Godziek & Kristensen & Piemontese & Calhim & Stec, 2025

Vecchi, Matteo, Godziek, Jakub, Kristensen, Reinhardt M., Piemontese, Lucia, Calhim, Sara & Stec, Daniel, 2025, Taxonomic reanalysis of the genus Richtersius (Tardigrada; Eutardigrada), with description of two new species from Italy and Sweden, European Journal of Taxonomy 981, pp. 155-188 : 170-181

Richtersius ingemari sp. nov.

urn:lsid:zoobank.org:act:8D3E6F1C-BCFA-46A6-9F5C-173C0EB70EF2

Figs 8–13 ; Tables 6–8

Adorybiotus coronifer – Westh & Ramløv 1991. — Ramløv & Westh 1992. — Westh & Kristensen 1992.

Adorybiotus (Richtersius) coronifer – Ramløv & Westh 2001.

Richtersius coronifer – Jönsson & Guidetti 2001. — Jönsson & Rebecchi 2002. — Ivarsson & Jönsson 2004. — Jönsson et al. 2005. — Jönsson 2007. — Jönsson & Schill 2007. — Dunn et al. 2008. — Faurby et al. 2008. — Hindborg Mortensen et al. 2010. — Nilsson et al. 2010. — Persson et al. 2011. — Halberg et al. 2012; 2013. — Czernekova & Jönsson 2016. — Czerneková et al. 2017; 2018. — Vecchi et al. 2018. — Guidetti et al. 2019. — Kamilari et al. 2019. — Pedersen et al. 2020; 2021.

Richtersius coronifer P3 – Rebecchi et al. 2003.

Richtersius coronifer P4 – Rebecchi et al. 2003.

Richtersius Sweden – Guidetti et al. 2016: figs 1–2.

Richtersius Northern Italy 2 – Guidetti et al. 2016.

Richtersius sp. 4 – Stec et al. 2020b.

Richtersius cf. coronifer – Hagelbäck & Jönsson 2023.

Etymology

This species is named after Prof. Ingemar Jönsson of Kristianstad University, Sweden, in recognition of his efforts in studying the physiological adaptations of tardigrades to extreme conditions, utilizing this species as a model organism.

Type material

Holotype

SWEDEN • Öland Island ; 56°32′18.2″ N, 16°27′45.3″ E; 46 m a.s.l.; Oct. 2006; R.M. Kristensen leg.; moss on rock; ISEA-PAS, slide SE.002.5.

Paratypes

SWEDEN • 69 specs; same data as for holotype; ISEA PAS, slides SE.002.1 to SE.002.7, SEM stubs TAR.2.01, TAR.2.02 • 44 eggs; same data as for holotype; ISEA PAS, slides SE.002.13, SE.002.14, SEM stubs TAR.2.01, TAR.2.02 • 22 specs; same data as for holotype; MUC, slides NHMD-1732287, NHMD-1732288 • 41 eggs; same data as for holotype; MUC , slides NHMD-1732289 to NHMD-1732291 .

Description

Animals (measurements in Tables 6–7; Supp. files 3, 4)

Body is bright yellow; all specimens became transparent after the fixation in Hoyer’s medium ( Fig. 8 ). Eyes were visible in all of the animals (excluding hatchlings) mounted in Hoyer’s medium. Body and leg cuticle is without granulation in all life stages and with pores present only in hatchlings ( Figs 8B , 9 ). Hatchlings are similar in appearance to adults, except for a smaller body size and roundish pores (1.5–3.1 µm in diameter) with usually jagged edges, visible under PCM, scattered randomly throughout the body cuticle, with a mean pore density of 5 (range 4–7) per 2500 µm 2 of the dorsal cuticle ( Fig. 9 ).

Claws are slender, primary branches with distinct accessory points ( Fig.10 ) and an internal system of septa as described for Richtersius coronifer s. lat. by Lisi et al. (2020). The claw common tract index has an average value between 57% and 61% across all four leg pairs, meaning that the basal portion of the claw is usually longer than half the total length of the primary branch. Lunulae are large, with a crown of long, numerous and densely arranged spikes ( Fig. 10 ). All the lunulae are trapezoidal ( Fig. 10 ). Double muscle attachments in legs I–III and horseshoe structures in legs IV are visible in PCM, whereas cuticular bars are absent ( Fig. 10 ).

Mouth is antero-ventral. The buccal apparatus is of the Richtersius type ( Fig. 11 ). The oral cavity is followed by a system of large apophyses that form a buccal crown ( Fig. 11A–B ). Anteriorly, the system consists of dorso-lateral and ventro-lateral triangular apophyses ( Fig. 11A ). The dorsal and ventral apophyses are composed of anteriorly positioned large cuticular hooks, followed by longitudinal crests ( Fig. 11B ). The hook in the ventral apophyses is smaller than the dorsal hook ( Fig. 11B ). The wall of the buccal tube exhibits a variable thickness ( Fig. 11A ), but the internal diameter of the buccal tube is almost uniformly narrow ( Fig. 11A ). From the mouth opening to the stylet support insertion point, the thickness of the buccal tube wall increases only slightly, while below this point the evident posterior thickness is clearly visible ( Fig. 11A ). The pharynx is spherical, with bilobed apophyses, three anterior cuticular spikes (typically only two are visible in any given plane, Fig. 11A ) and two granular macroplacoids (2<1). The first and second macroplacoids have a faint constriction positioned centrally and subterminally, respectively ( Fig. 11C ). The oral cavity armature is faintly visible under PCM, with only the second band of teeth visible mainly in the larger specimens ( Fig. 11B ). Under PCM, the second band of teeth is visible as several irregular rows of densely packed and faint dark dots ( Fig. 11B ). The discontinuous third band of teeth is situated between the second band of teeth and the opening of the buccal tube and is divided into a dorsal and a ventral portion, both in the form of a single large tooth resembling a beak.

Eggs (measurements in Table 8 ; Supp. file 3)

Large, roundish, yellow, laid freely. The surface between processes is smooth but with refracting dots faintly visible only under PCM, but difficult to observe because of the amount of debris that is typically attached to the egg surface ( Figs 12–13 ). Processes in the shape of elongated, thin, cones with a ragged surface caused by small granules visible both in LM and SEM ( Figs 12 , 13B ). The processes are sometimes bifurcated ( Figs 12E–F , 13B ). A ring of small pores visible only with SEM is present around each process ( Fig. 13C ). The processes are hollow inside ( Fig. 13D ). Terminal discs or other structures absent.

Reproduction

Thelytokous parthenogenesis, chromosome number 2n = 12 ( Rebecchi et al. 2003; Stec et al. 2020b). Automictic parthenogenesis has been suggested for this species by Rebecchi et al. (2003) based on the presence of chiasmata in the oocytes.

DNA sequences

– 18S: AY582121, KT778706 -7 ( Guidetti et al. 2016), MH681761 -2 ( Stec et al. 2020b)

– 28S: GQ849048 , KT778697 -8 ( Guidetti et al. 2016), MH681758 -9 ( Stec et al. 2020b)

– COI: EU251385 , EU244606 , EU251383 -4, MH676054 -5 ( Stec et al. 2020b), PP986907-8 (this study)

– ITS2: MH681764 -5 ( Stec et al. 2020b)

Distribution

Locus typicus: Möckelmossen, Öland Island, Sweden (56°32′18.2″ N, 16°27′45.3″ E). Moss on tock (sample SE.002 in this study).

Möckelmossen, Öland Island, Sweden (56°31.732′ N, 16°29.474′ E). Moss on rock(sample C 2353 in Guidetti et al. 2016; sample P 4 in Rebecchi et al. 2003; sample C3585-S 6 in Vecchi et al. 2018). This population has been extensively used in studies on cytology, physiology, and ecology under the name of Richtersius coronifer .

Lago di Teleccio, Torino, Italy (45°28′55″ N, 7°22′22″ E; 1830 m a.s.l.). Moss (sample IT. 120 in Stec et al. 2020b).

Sasso del Corvo, Modena, Italy (44°12.774′ N, 10°31.974′ E, 1280 m a.s.l.). Moss on rock (sample C 3226 in Guidetti et al. 2016; sample P 3 in Rebecchi et al. 2003).

Kościeliska Valley, Tatrzański National Park, Poland (49°14′22″ N, 19°51′46″ E; 1083 m a.s.l.). Moss (sample PL. 246 in Stec et al. 2020b).

Differential diagnosis

Richtersius ingemari sp. nov. differs from:

Richtersius coronifer by having smaller eggs (bare diameter 114–137 µm in R. ingemari sp. nov. vs 173– 233 µm in R. coronifer ) and by having a lower pore density in the newborns (PD 4–7 in R. ingemari vs 60–88 in R. coronifer ).

Richtersius ziemowiti by having a lower pore density in the newborns (PD 4–7 in R. ingemari sp. nov. vs 20–24 in R. ziemowiti ).

Richtersius mazepi by having bigger eggs (bare diameter 114–137 µm in R. ingemari sp. nov. vs 77– 91 µm in R. mazepi ), by the absence of a crown of thickenings distributed around the bases of the egg processes (present in R. mazepi ), by the different shape of the egg processes (conical spikes in R. ingemari vs wide dome-shaped proximal portion and an elongated slender distal portion in R. mazepi ), by having a lower pore density in the newborns (PD 4–7 in R. ingemari vs 26–36 in R. mazepi ), and by having a higher claw IV anterior cct (51–69 % in R ingemari vs 32–44 % in R. mazepi ).

Richtersius tertius by having a smaller first macroplacoid (pt 9–13 in R. ingemari sp. nov. vs 14–20 in R. tertius ).

Richtersius nicolai sp. nov. by having a higher pore density in the newborns (PD 4–7 in R. ingemari sp. nov. vs 9–11 in R. nicolai ), and by the reproductive mode (parthenogenesis in R. ingemari vs gonochorism in R. nicolai ).

Figures

Fig. 8. Richtersius ingemari sp. nov. from sample SE.002 (holotype and paratype ISEA-PAS), habitus. A. Adult holotype habitus (PCM). B. Newborn paratype habitus (SEM). Scale bars = 100 µm.

Fig. 9. Newborn Richtersius ingemari sp. nov. from sample SE.002 (paratypes ISEA-PAS), cuticular pores in newborns.A. Dorso-caudal cuticle with pores (PCM).C. Dorso-caudal cuticle with pores (PCM). B, D. Pores (SEM). Arrowheads indicate pores on the cuticle. Scale bars: A, C = 20 µm; B, D = 2 µm.

Fig. 10. Adult Richtersius ingemari sp. nov. from sample SE.002 (paratypes ISEA-PAS), claws and associated structures.A. Claws I (PCM).B. Claws IV (PCM).). Arrowhead indicates muscle attachments. Indented arrowhead indicates horseshoe structure under claws IV. Scale bars = 20 µm.

Fig. 11.AdultRichtersius ingemari sp. nov.from sample SE.002(paratypes ISEA-PAS), buccal apparatus. A. Entire buccal apparatus (PCM).B. Lateral view of the buccal crown (PCM).C. Macroplacoids (PCM). Filled arrow indicates dorsal hook of the AISM. Empty arrow indicates ventral hook of AISM. Empty indented arrowheads indicate triangular apophyses of the buccal crown. Empty arrowheads indicate anterior cuticular spike. Filled arrowhead indicates the third OCA ring. Filled indented arrowheads indicate placoids constrictions. Scale bars: A–B = 20 µm; C = 10 µm.

Fig. 12. Eggs ofRichtersius ingemari sp. nov. from sample SE.002 (paratypes ISEA-PAS).A–B. Chorion surface and processes (PCM). C–F. Egg processes (PCM). Arrowheads indicate bifurcated processes. Scale bars: A–B = 20 µm: C–F = 2 µm.

Fig. 13. Eggs of Richtersius ingemari sp. nov. from sample SE.002 (paratypes ISEA-PAS). A. Egg in toto (SEM). B. Egg processes (SEM). C–D. Egg processes sections (SEM). Scale bars: A = 50 µm; B = 10 µm; C = 5 µm; D = 1 µm.