Considerations on the claws of the Apochela and a novel detail of the bucco-pharyngeal apparatus of the genus Milnesium (Tardigrada: Apochela: Milnesiidae)

Figures & data

Table I. Examined species of Milnesium deposited in the Pilato and Binda collection, with type specimens, if any, indicated (if none, the geographic provenance is given), slide numbers and number of specimens analysed. If not specified, specimens were of undetermined age and sex (likely females)

Species	Type specimens	Slide numbers	Number of specimens examined
M. cf. almatyense	No (from Sicily)	1031, 2775	3
M. almatyense	Paratype	5106	1
M. alpigenum	Specimens of the neotype series	5814–5819	6
M. antarcticum	Paratype	5104	1
M. asiaticum	Paratype	5105	1
M. beasleyi	Paratype	5518	1
M. brachyungue	Holotype and paratypes	3940–3949	10
M. eurystomum	No (from Greenland)	1815	1
M. inceptum	Paratypes	5820–5822	9
M. longiungue	Paratype	5103	1
M. minutum	Holotype and paratypes	3238, 4127	3
M. reductum	Paratype	5102	1
M. reticulatum	Holotype and paratypes	4851–4862, 5237, 5275–5277, 5697–5699, 5702, 5277	44 (25 adult females, 3 adult males and 16 young specimens)
M. sandrae	Holotype and paratypes	4268, 4288–4290, 4293	17
M. sandrae	No (from southern Italy)	5788	1
M. tardigradum	Specimens of the neotype series	5489	16
M. tardigradum	No (from Sicily)	2775	2
M. tetralamellatum	Holotype and paratypes	3704	7 adults (6 females and 1 male)
M. tumanovi	Holotype	3904	1
M. validum	Holotype and paratypes	4035–4039	6
M. vorax	Holotype and paratype	2775	2
M. sp. 1	No (from Israel)	Not deposited	1
M. sp. 2	No (from Tanzania)	3746	1
M. sp. 3	No (from Tanzania)	3746	1
M. sp. 4	No (from Sicily)	5703	1

Table II. Species of Milnesium by valvular system type, with indication of examined specimens and/or figures (from the literature or the present paper) on which the system attribution is based. Types means holotype and paratypes; slide numbers are as indicated in Table I

Table

Table III. Species of the genus Milnesium of which young and adult specimens, and/or males and females, have been observed (in the present study or the literature, as indicated). Types means holotype and paratypes; slide numbers are as indicated in Table I

Species	Data source	Young + adult specimens	Males + females
Valvular system type 1, literature with photographs:
M. almatyense	Morek et al. (2020c) (redescription)	+	-
M. pacificum	Sugiura et al. (2020)	+	-
“M. eurystomum” according to Morek et al. (2020a) (GB.005 strain from Scotland)	Morek et al. (2020a)	+	+
M. tardigradum	Sugiura et al. (2020) (OTM strain)	+	-
	Sugiura et al. (2020) (KNY strain)	+	-
M. variefidum	Morek et al. (2016)	+	-
Valvular system type 1, literature with only text/tables (no photographs):
M. alabamae	Wallendorf and Miller (2009)	+	-
M. alpigenum	Morek et al. (2019) (redescription)	+	-
M. beasleyi	Kaczmarek et al. (2012) (male paratype)	-	+
M. berladnicorum	Ciobanu et al. (2014)	+	-
M. dornensis	Ciobanu et al. (2015)	+	+
M. inceptum	Morek et al. (2019)	+	-
M. pentapapillatum	Morek et al. (2020b)	+	-
M. pseudotardigradum	Surmacz et al. (2019)	+	-
M. reductum	Morek et al. (2020c) (redescription)	+	-
Valvular system type 2, literature with photographs:
M. fridae	Moreno-Talamantes et al. (2020)	+	+
Valvular system type 2, slides examined in the present study:
M. reticulatum	44 types examined (3 adult males, 25 adult females, 16 young specimens)	+	+
M. tetralamellatum	7 types examined (1 adult male, 6 adult females)	-	+
Valvular system type 2, literature with only text/tables (no photographs):
M. barbadosense	Meyer and Hinton (2012)	+	-
M. burgessi	Schlabach et al. (2018)	+	-
Dubious valvular system type:
M. cassandrae (with photos)	Moreno-Talamantes et al. (2019)	+	-
M. argentinum (text/tables)	Roszkowska et al. (2015)	+	-
M. matheusi (text/tables)	Kaczmarek et al. (2019)	-	+
M. swansoni (text/tables)	Young et al. (2016)	-	+

Table IV. Species with type 1 valvular system, correlated to body size, pt (= “percentual tube”, i.e. percentual ratio of the given structure with the buccal tube length (Pilato 1981)) of buccal tube standard width, and mounting medium. Data source indicates the literature sources and/or material examined by us (as indicated in Table I) to determine the valvular system type and obtain other data (body size, pt of buccal tube standard width, and mounting medium); the provided references are species’ original descriptions, or redescriptions (as specified), or refer to cultured strains (as specified). Body and buccal tube measurements, unless otherwise indicated, are from the corresponding cited literature source and refer to the specimen(s) with photograph(s) published in the same paper, in order to match the precise specimen with determined valvular system type, with its measurements; “our measurement(s)” refers to measurements taken by us on the previously indicated slide(s). Mounting media: AAF = fixed in acetic acid end mounted in Faure medium; Hoyer’s = Hoyer’s medium; PVA = polyvinyl alcohol; PVLF = polyvinyl lactophenol

Species	Data source	Body size of specimens examined or photographed (from the literature) (in µm)	Pt of buccal tube standard width of specimens examined or photographed (from the literature)	Mounting medium
M. alabamae	Wallendorf and Miller (2009)	-	-	PVA
M. almatyense	Tumanov (2006); 1 examined paratype	-	-	AAF
	Morek et al. (2020c) (redescription)	-	-	Hoyer’s
M. cf. almatyense	3 specimens examined from Sicily	-	-	PVLF
M. alpigenum	Morek et al. (2019) (redescription); 6 specimens from neotype series	751 neotype; Our measurements: 426–731	34.7 neotype	Hoyer’s
M. beasleyi	Kaczmarek et al. (2012)	481 male paratype	25.8 male paratype	Hoyer’s
M. beatae	Roszkowska et al. (2015)	-	-	Hoyer’s
M. berladnicorum	Ciobanu et al. (2014)	-	-	Hoyer’s
M. dornensis	Ciobanu et al. (2015)	-	-	Hoyer’s
M. inceptum	Morek et al. (2019); 9 paratypes examined	743 holotype; Our measurements: 500–789	37.8 holotype	Hoyer’s
M. katarzynae	Kaczmarek et al. (2004)	-	-	Hoyer’s
M. kogui	Londoño et al. (2015)	-	-	Hoyer’s
M. longiungue	Tumanov (2006); 1 examined paratype	Our measurements: 747–898	Our measurements: 40.3–47.4	AAF
M. pacificum	Sugiura et al. (2020)	593 holotype ca. 350 hatchling	33.0 holotype ca. 30.1–35.8 hatchling	Hoyer’s
M. pentapapillatum	Morek et al. (2020b)	-	-	Hoyer’s
M. pseudotardigradum	Surmacz et al. (2019)	-	-	Hoyer’s
M. reductum	Tumanov (2006)	665 holotype	37.1 holotype	AAF
	Morek et al. (2020c) (redescription)	-	-	Hoyer’s
M. tardigradum	Michalczyk et al. (2012) (redescription); 16 specimens of the neotype series examined	334 neotype Our measurements: 307–549	34.8 neotype	Hoyer’s
	Sugiura et al. (2020) (OTM strain)	ca. 700 adult ca. 320 hatchling	ca. 31.6–38.6 adult ca. 27.9–32.4 hatchling	Hoyer’s
	Sugiura et al. (2020) (KNY strain)	ca. 600 adult ca. 350 hatchling	ca. 34.4–48.3 adult ca. 25.5–37.5 hatchling	Hoyer’s
	1 specimen from Sicily	-	-	PVLF
M. variefidum	Morek et al. (2016)	-	-	Hoyer’s
M. wrightae	Kaczmarek et al. (2019)	-	-	Hoyer’s
Uncertain/questionable diagnosis:
“M. eurystomum” according to Morek et al. (2020a) (GB.005 strain from Scotland)	Morek et al. (2020a)	-	-	Hoyer’s
M. sp. 1	1 specimen from Israel			PVLF
M. sp. 2	1 specimen from Tanzania			PVLF

Table V. Species with type 2 valvular system, correlated to body size, pt of buccal tube standard width, and mounting medium. Data source indicates literature sources and/or material examined by us (as indicated in Table I; types mean holotype and paratypes) to determine the valvular system type and obtain other data (body size, pt of buccal tube standard width, and mounting medium); the provided references are species’ original descriptions, or redescriptions (as specified). Body and buccal tube measurements, unless otherwise indicated, are from the corresponding cited literature source and refer to the specimen(s) with photograph(s) published in the same paper, in order to match the precise specimen with determined valvular system type, with its measurements; “our measurement(s)” refers to measurements taken by us on the previously indicated slide(s). Mounting media: AAF = fixed in acetic acid end mounted in Faure medium; Hoyer’s = Hoyer’s medium; PVA = polyvinyl alcohol; PVLF = polyvinyl lactophenol; “Polivinil” is what Ramazzotti, in 1962, wrote on his slides containing the type material of M. granulatum (the exact medium is unknown)

Species	Data source	Body size of specimens examined, or photographed (from the literature) (in µm)	Pt of buccal tube standard width of specimens examined, or photographed (from the literature)	Mounting medium
M. antarcticum	Tumanov (2006)	All types larger than 800	36.6 holotype	?
M. barbadosense	Meyer and Hinton (2012)	686 holotype	43.9 holotype	PVLF
M. brachyungue	10 types examined	729 holotype	39.6 holotype	PVLF
M. burgessi	Schlabach et al. (2018)	862 holotype	64.1 holotype	PVA
M. eurystomum	Michalczyk et al. (2012) (redescription)	847 holotype from Maucci (1991)	61.8 holotype from Maucci (1991)	?
	1 specimen from Greenland	-	-	?
M. fridae	Moreno-Talamantes et al. (2020)	-	-	PVA
M. granulatum	Michalczyk et al. (2012) (redescription)	-	-	“Polivinil” (by Ramazzotti)
	Bartels et al. (2014)	-	-	Hoyer’s
M. jacobi	Meyer and Hinton (2010)	669 holotype	55.4 holotype	Hoyer’s
M. reticulatum	44 types examined	Our measurements: 245–280 young 387–423 adult females 270–405 adult males	30.4 paratype (young) 37.4 holotype (adult)	PVLF
M. shilohae	Meyer (2015)	-	-	PVLF
M. tetralamellatum	7 types examined	510–770	49.1 holotype	PVLF
M. tumanovi	Pilato et al. (2016); holotype examined	744 holotype	55.1 holotype	PVLF
M. validum	6 types examined	424–482	29.8	PVLF
M. vorax	2 types examined	578–585	60.3 holotype	PVLF
M. zsalakoae	Meyer and Hinton (2010)	477 holotype	41.9 holotype	Hoyer’s
Uncertain diagnosis:
M. sp. 3	1 specimen from Tanzania	-	-	PVLF
M. sp. 4	1 specimen from Sicily	-	-	PVLF

Figure 1. Claws of the hind legs of a Milnesium sp. to demonstrate the new nomenclature. Arrows: primary (or main) claws; arrowheads: secondary claws. Black arrows: posterior primary claws; white arrows: anterior primary claws; black arrowheads: posterior secondary claws; white arrowheads: anterior secondary claws. For legs I–III, “external” (or “lateral”) and “internal” (or “medial”), instead of “posterior” and “anterior”, will be used to indicate the single claws.

Figure 2. Valvular system of the tardigradum type (type 1); arrows indicate the cuticular folds in the tract connecting buccal tube and pharynx; arrowheads in (b) and (c) indicate the flaps. Scale bars: 20 µm. All slides deposited in the Pilato and Binda collection. (a) Paratype of Milnesium almatyense Tumanov (2006) (Slide No. 5106). The flaps are not well visible while the flexible tract between buccal tube and pharyngeal bulb, with some folds (arrows), is well visible. (b) Valvular system of a specimen of the neotype series of Milnesium tardigradum Doyère (1840) (Slide No. 5489). One flap (arrowhead) and the flexible tract between buccal tube and pharyngeal bulb, with some folds (arrows), are well visible. This flexible tract is caudally dilated the pharyngeal bulb being closer to the buccal tube than in (a). (c) Valvular system of a paratype of Milnesium inceptum Morek et al. (2019) (Slide No. 5821). One flap (arrowhead) and the flexible tract between buccal tube and pharyngeal bulb, with some folds (arrows), are well visible. This flexible tract is caudally dilated, the pharyngeal bulb being closer to the buccal tube than in (a). (d) Valvular system of a specimen of the neotype series of Milnesium tardigradum Doyère (1840) (Slide No. 5489). Two flaps (arrowheads) and the flexible tract between buccal tube and pharyngeal bulb, with some folds (arrows), are well visible. This flexible tract is caudally completely dilated, the pharyngeal bulb being pushed onto the buccal tube.

Figure 3. Valvular system of the shilohae type (type 2). Two flaps (arrowheads) and two conical thickenings (arrows) are visible, while the third ones are not in focus. The drawing (of Milnesium shilohae) is based on Figure 1(b) of Meyer (2015).

Figure 4. (a–c). Valvular system of the shilohae type (type 2); arrows indicate the conical projections; arrowheads indicate the flaps. Scale bars: 20 µm. All slides deposited in the Pilato and Binda collection. (a) Holotype of Milnesium tetralamellatum Pilato and Binda (1991) (Slide No. 3704). Two flaps (arrowheads) and two conical projections (arrows) are visible. The third ones are not in focus. (b) Holotype of Milnesium brachyungue Binda and Pilato (1990) (Slide No. 3940). Two flaps (arrowheads) and two conical projections (arrows) are visible. The third ones are not in focus. (c) Specimen of Milnesium sp. 4 (Slide No. 5703). Two flaps (arrowhead) are clearly visible, and the three flexible conical projections (arrows) are partially visible, despite the partially reduced distance between buccal tube and pharyngeal bulb. (d) Paratype of Milnesium reticulatum Pilato et al. (2002) (Slide No. 4851). Two flaps (arrowhead) are visible, and three flexible conical projections (arrows) are also visible (the third in the middle, barely) despite the reduced distance between buccal tube and pharyngeal bulb.

Table VI. Correlation between valvular system type (type 1 = tardigradum type; type 2 = shilohae type), eventual cuticular sculpture, number/configuration of the peribuccal lamellae, claw configuration, and ecozones in which each species results recorded. ° = species recorded in an ecozone different from that of the locus typicus. The fossil species M. swolenskyi has been excluded because it is not ecologically comparable with the other species’ actual zoogeography

	Type 1	Type 2	Dubious	Cuticle	Peribuccal lamellae	Claw configuration	Ecozone
M. alabamae	+			Reticulated	6 or 4 + 2	[3-3]-[3-3]	Nearctic
M. almatyense	+			Smooth	4 + 2	[2-3]-[2-2]	Eastern Palearctic
M. alpigenum	+			Pseudoporous	4 + 2	[3-3]-[3-3]	Western Palearctic
M. beasleyi	+			Pseudoporous	6 or 4 + 2	[2-3]-[3-2]	Western Palearctic
M. beatae	+			Pseudoporous	6 or 4 + 2	[3-3]-[3.3]	Neotropical
M. berladnicorum	+			Pseudoporous	4 + 2	[2-3]-[3-2]	Western Palearctic, Afrotropical°
M. dornensis	+			Pseudoporous	(2 + 2) + 2	[3-3]-[3-3]	Western Palearctic
M. inceptum	+			Smooth or pseudoporous	4 + 2	[3-3]-[3-3]	Western Palearctic, Eastern Palearctic°, Nearctic°, Afrotropical°, Australasian°
M. katarzynae	+			Reticulated	?	[2-2]-[2-2]	Eastern Palearctic, Neotropical°
M. kogui	+			Smooth	6 or 4 + 2	[2-2]-[2-2]	Neotropical
M. longiungue	+			Smooth	6 or 4 + 2	[3-3]-[3-3]	Indomalayan
M. pacificum	+			Reticulated	4 + 2	[2.2]-[2-2] hatchlings; [2-3]-[3-2] adults	Eastern Palearctic
M. pentapapillatum	+			Smooth	4 + 2	[3-3]-[3-3]	Eastern Palearctic
M. pseudotardigradum	+			Smooth	4 + 2	[3-3]-[3-3] hatchlings; [2-3]-[3-2] adults	Western Palearctic, Eastern Palearctic°
M. reductum	+			Smooth	4 + 2	[2-3]-[3-2]	Eastern Palearctic
M. tardigradum	+			Pseudoporous	4 + 2	[2-3]-[3-2]	Western Palearctic, Eastern Palearctic°, Afrotropical°
M. variefidum	+			Pseudoporous	4 + 2	[2-2]-[2-2] juveniles; [2-3]-[2-2] adults	Western Palearctic
M. wrightae	+			Pseudoporous	6	[3-3]-[4-4]	Afrotropical
M. antarcticum		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Antarctic
M. barbadosense		+		Smooth	6	[3-3]-[3-3]	Neotropical
M. brachyungue		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Nearctic
M. burgessi		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Nearctic
M. eurystomum		+		Smooth	6	[3-3]-[3-3]	Nearctic, Neotropical°, Western Palearctic°
M. fridae		+		Pseudoporous	6 or 4 + 2	[3-3]-[3-3]	Neotropical
M. granulatum		+		Reticulated	6 or 4 + 2	[3-3]-[3-3]	Neotropical
M. jacobi		+		Smooth	6 or 4 + 2	[2-3]-[3-3]	Nearctic
M. reticulatum		+		Reticulated	4	[2–3] -[3-2]	Afrotropical
M. shilohae		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Oceanian
M. tetralamellatum		+		Smooth	4	[2-3]-[3-2]	Afrotropical
M. tumanovi		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Western Palearctic
M. validum		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Antarctic
M. vorax		+		Smooth	6 or 4 + 2	[2-3]-[3-2]	Western Palearctic
M. zsalakoae		+		Smooth	6 or 4 + 2	[3-3]-[3-3]	Nearctic
M. argentinum			+	Pseudoporous	6 or 4 + 2	[3-3]-[3-3]	Neotropical
M. asiaticum			+	Smooth	6 or 4 + 2	[3-3]-[3-3]	Western Palearctic
M. bohleberi			+	Smooth	6	[3-3]-[3-3]	Nearctic
M. cassandrae			+	Pseudoporous	4 + 2	[2-2]-[2-2] juveniles; [2-3]-[3-2] adults	Neotropical
M. krzysztofi			+	Reticulated	?	[2-3]-[3-2]	Neotropical
M. lagniappe			+	Pseudoporous	4 or 4 + 2	[2-3]-[3-2]	Nearctic
M. matheusi			+	Pseudoporous	6	[3-3]-[3-3]	Afrotropical
M. minutum			+	Smooth	6 or 4 + 2	[3-3]-[3-3]	Western Palearctic
M. quadrifidum			+	?	?	[4-4]-[4-4]	Western Palearctic
M. sandrae			+	Smooth	6 or 4 + 2	[3-3]-[3-3]	Oceanian
M. swansoni			+	Smooth	4	[3-3]-[3-3]	Nearctic
M. swolenskyi †			+	?	?	?	-

Morek W, Surmacz B, Michalczyk Ł. 2020c. Novel integrative data for two Milnesium Doyère, 1840 (Tardigrada: Apochela) species from Central Asia. Journal of Zoological Systematics and Evolutionary Research 96(2):499–514. DOI: 10.3897/zse.96.52049.

 Google Scholar

Sugiura K, Minato H, Matsumoto M, Suzuki AC. 2020. Milnesium (Tardigrada: Apochela) in Japan: The first confirmed record of Milnesium tardigradum s.s. and description of Milnesium pacificum sp. nov. Zoological Science 37(5):476–495. DOI: 10.2108/zs190154.

 Web of Science ®Google Scholar

Morek W, Blagden B, Kristensen RM, Michalczyk Ł. 2020a. The analysis of inter- and intrapopulation variability of Milnesium eurystomum Maucci, 1991 reveals high genetic divergence and a novel type of ontogenetic variation in the order Apochela. Systematics and Biodiversity 18(5):461–479. DOI: 10.1080/14772000.2020.1771469.

 Google Scholar

Morek W, Gąsiorek P, Stec D, Blagden B, Michalczyk Ł. 2016. Experimental taxonomy exposes ontogenetic variability and elucidates the taxonomic value of claw configuration in Milnesium Doyère, 1840 (Tardigrada: Eutardigrada: Apochela). Contribution to Zoology 85(2):173–200. DOI: 10.1163/18759866-08502003.

 Web of Science ®Google Scholar

Wallendorf M, Miller WR. 2009. Tardigrades of North America: Milnesium alabamae nov. sp. (Eutardigrada: Apochela: Milnesiidae) a new species from Alabama. Transactions of the Kansas Academy of Science 112(3–4):181–186. DOI: 10.1660/062.112.0404.

 Google Scholar

Morek W, Suzuki AC, Schill RO, Georgiev D, Yankova M, Marley NJ, Michalczyk Ł. 2019. Redescription of Milnesium alpigenum Ehrenberg, 1853 (Tardigrada: Apochela) and a description of Milnesium inceptum sp. nov., a tardigrade laboratory model. Zootaxa 4586(1):35–64. DOI: 10.11646/zootaxa.4586.1.2.

 Web of Science ®Google Scholar

Kaczmarek Ł, Jakubowska N, Michalczyk Ł. 2012. Current knowledge on Turkish tardigrades with a description of Milnesium beasleyi sp. nov. (Eutardigrada: Apochela: Milnesiidae, the granulatum group). Zootaxa 3589:49–64. DOI: 10.11646/zootaxa.3589.1.3.

 Google Scholar

Ciobanu DA, Zawierucha K, Moglani I, Kaczmarek Ł. 2014. Milnesium berladnicorum sp. n. (Eutardigrada, Apochela, Milnesiidae), a new species of water bear from Romania. Zookeys 429:1–11. DOI: 10.3897/zookeys.429.7755.

 Web of Science ®Google Scholar

Ciobanu D, Roszkowska M, Kaczmarek Ł. 2015. Two new tardigrade species from Romania (Eutardigrada, Milnesiidae, Macrobiotidae) with some remarks on secondary sex characters in Milnesium dornensis sp. nov. Zootaxa 3941(4):542–564. DOI: 10.11646/zootaxa.3941.4.4.

 PubMed Web of Science ®Google Scholar

Morek W, Ciosek CA, Michalczyk Ł. 2020b. Description of Milnesium pentapapillatum sp. nov. from Kazakhstan, with an amendment of the diagnosis of the order Apochela (Tardigrada) and abolition of the class Apotardigrada. Zoologischer Anzeiger 288:107–117. DOI: 10.1016/j.jcz.2020.07.002.

 Web of Science ®Google Scholar

Surmacz B, Morek W, Michalczyk Ł. 2019. What if multiple claw configurations are present in a sample? A case study with the description of Milnesium pseudotardigradum sp. nov. (Tardigrade with unique developmental variability). Zoological Studies 58(32):1–15. DOI: 10.6620/ZS.2019.58-32.

 Google Scholar

Moreno-Talamantes A, León-Espinosa GA, García-Aranda MA, Flores-Maldonado JJ, Kaczmarek Ł. 2020. The genus Milnesium Doyère, 1840 in Mexico with description of a new species. Annales Zoologici (Warszawa) 70(4):467–486. DOI: 10.3161/00034541ANZ2020.70.4.001.

 Google Scholar

Meyer HA, Hinton JG. 2012. Terrestrial Tardigrada of the Island of Barbados in the West Indies, with the description of Milnesium barbadosense sp. n. (Eutardigrada: Apochela: Milnesiidae). Caribbean Journal of Science 46(2–3):194–202. DOI: 10.18475/cjos.v46i2.a8.

 Web of Science ®Google Scholar

Schlabach S, Donaldson E, Hobelman K, Miller WR, Lowman MD. 2018. Tardigrades of the Canopy: Milnesium burgessi nov. sp. (Eutardigrada: Apochela: Milnesiidae) a new species from Kansas. Transactions of the Kansas Academy of Science 121(1–2):39–48. DOI: 10.1660/062.121.0204.

 Google Scholar

Moreno-Talamantes A, Rozkowska M, García-Aranda MA, Flores-Maldonado JJ, Kaczmarek Ł. 2019. Current knowledge on Mexican tardigrades with a description of Milnesium cassandrae sp. nov. (Tardigrada: Milnesiidae) and discussion on the taxonomic value of dorsal pseudoplates in the genus Milnesium. Zootaxa 4601(5):501–524. DOI: 10.11646/zootaxa.4691.5.5.

 Google Scholar

Roszkowska M, Ostrowska M, Kaczmarek Ł. 2015. The genus Milnesium Doyère, 1840 (Tardigrada) in South America with description of two new species from Argentina and discussion of the feeding behaviour in the family Milnesiidae. Zoological Studies 54:1–17. DOI: 10.1186/s40555-014-0082-7.

 Web of Science ®Google Scholar

Kaczmarek Ł, Grobys D, Kulpa A, Bartylak T, Kmita H, Kepel M, Kepel A, Roszkowska M. 2019. Two new species of the genus Milnesium Doyère, 1840 (Tardigrada, Apochela, Milnesiidae) from Madagascar. ZooKeys 884:1–22. DOI: 10.3897/zookeys.884.29469.

 PubMed Web of Science ®Google Scholar

Young A, Chappell B, Miller W, Lowman M. 2016. Tardigrade of the three Canopy: Milnesium swansoni sp. nov. (Eutardigrada: Apochela: Milnesiidae) a new species from Kansas, U.S.A. Zootaxa 4072(5):559–568. DOI: 10.11646/zootaxa.4072.5.3.

 Web of Science ®Google Scholar

Pilato G. 1981. Analisi di nuovi caratteri nello studio degli Eutardigradi. Animalia 8:51–57.

 Google Scholar

Tumanov DV. 2006. Five new species of the genus Milnesium (Tardigrada, Eutardigrada, Milnesiidae). Zootaxa 1122:1–23. DOI: 10.11646/zootaxa.1122.1.1.

 Google Scholar

Kaczmarek Ł, Michalczyk Ł, Beasley CW. 2004. Milnesium katarzynae sp. nov. a new species of eutardigrade (Milnesiidae) from China. Zootaxa 743:1–5. DOI: 10.11646/zootaxa.743.1.1.

 Google Scholar

Londoño R, Daza A, Caicedo M, Quiroga S, Kaczmarek Ł. 2015. The genus Milnesium (Eutardigrada: Minesiidae) in the Sierra Nevada de Santa Marta (Colombia), with the description of Minesium kogui sp. nov. Zootaxa 3955(4):561–568. DOI: 10.11646/zootaxa.3955.4.7.

 PubMed Web of Science ®Google Scholar

Michalczyk Ł, Wełnicz W, Frohme M, Kaczmarek Ł. 2012. Redescriptions of three Milnesium Doyère, 1840 taxa (Tardigrada: Eutardigrada: Milnesiidae), including the nominal species for the genus. Zootaxa 3154:1–20. DOI: 10.11646/zootaxa.3154.1.1.

 Google Scholar

Maucci W. 1991. Tre nuove specie di Eutardigradi della Groenlandia meridionale. Bollettino del Museo Civico di Storia Naturale di Verona 15:279–289.

 Google Scholar

Bartels PJ, Nelson DR, Kaczmarek Ł, Michalczyk Ł. 2014. The genus Milnesium (Tardigrada: Eutardigrada: Milnesiidae) in the great smoky mountains national park (North Carolina and Tennessee, USA) with the description of Milnesium bohleberi sp. nov. Zootaxa 3826(2):356–368. DOI: 10.11646/zootaxa.3826.2.5.

 PubMed Web of Science ®Google Scholar

Meyer HA, Hinton JG. 2010. Milnesium zsalakoae and Milnesium jacobi, two new species of Tardigrada (Eutardigrada: Milnesiidae) from the southwestern USA. Proceedings of the Biological Society of Washington 123(2):113–120. DOI: 10.2988/09-29.1.

 Web of Science ®Google Scholar

Meyer HA. 2015. Water bears (Phylum Tardigrada) of Oceania, with the description of a new species of Milnesium. New Zealand Journal of Zoology 1–14. DOI: 10.1080/03014223.2015.1062402.

 Web of Science ®Google Scholar

Pilato G, Sabella G, Lisi O. 2016. Two new species of Milnesium (Tardigrada: Milnesiidae). Zootaxa 4132(4):575–587. DOI: 10.11646/zootaxa.4132.4.9.

 Web of Science ®Google Scholar

Doyère LMF. 1840. Memoire sur les tardigrades. I. Annales des Sciences Naturelles, Paris S. 2(14):269–362.

 Google Scholar

Pilato G, Binda MG. 1991. Milnesium tetralamellatum, new species of Milnesiidae from Africa (Eutardigrada). Tropical Zoology 4:103–106. DOI: 10.1080/03946975.1991.10539480.

 Google Scholar

Binda MG, Pilato G. 1990. Tardigradi della Terra del Fuoco e Magallanes. Milnesium brachyungue, nuova specie di tardigrado Milnesiidae. Animalia 17:105–110.

 Google Scholar

Pilato G, Binda MG, Lisi O. 2002. Notes on tardigrades of the Seychelles with description of two new species. Bollettino Delle Sedute dell’Accademia Gioenia Di Scienze Naturali, Catania 35(261):503–517.

 Google Scholar