Milnesium antarcticum, Tumanov, Denis V., 2006

Tumanov, Denis V., 2006, Five new species of the genus Milnesium (Tardigrada, Eutardigrada, Milnesiidae), Zootaxa 1122, pp. 1-23 : 2-5

Milnesium antarcticum sp. nov. ( Figs. 4, 5 , 15–19 , Table 2 )

Type material. Holotype: sex indeterminate, slide number 89(22). Collected by Dr. P. I. Krylov (Zoological Institute of the Russian Academy of Sciences, St. Petersburg) 15.12.1985, King George Island, Antarctica. Paratypes: slide’s numbers 89(1, 5, 17, 18, 19, 23) from the same locality. Type locality: Antarctica, King George Island, vicinity of Henryka Arctowskiego Polish polar station, moss in a little stream from under snowfield. 27 adult and juvenile specimens and 1 exuvium with three eggs were found.

Etymology. This species is named after the region of its type locality, Antarctica.

Description. Large animals, exact body length could not be measured, because of the strong constriction during fixation (even in constricted condition it exceed 800 µm), colour of the fixed specimens reddish­brown; cuticle smooth; eyes present. Six peribuccal and two lateral papillae present. Mouth with 6 peribuccal lamellae longitudinally striped in their basal portion. Buccal tube wide and long.

Claws large, massive. Main branch of each claw with two well developed accessory points. Complex basal claw+secondary branch with well developed rounded basal thickening. First three pairs of legs with elongated cuticular thickening near the claw bases. All dimensions are given in Table 2 .

Smooth eggs (white in incident light, colourless in preparation) deposited within exuviae.

No mature males were found.

Differential Diagnosis. Milnesium antarcticum sp. nov. differs from Milnesium reticulatum by having smooth cuticle without gibbosities, more caudal position of the insertion point of the stylet supports (pt value 70.0– 73.7 in M. antarcticum sp. nov. and 68.5–69.8 in M. reticulatum ), claws with developed basal spurs on the outer claws and larger pt ratio of the length of main branches of the claws of the IV pair of legs (49.8–55.9 in M. antarcticum sp. nov. and 41.7–44.3 in M. reticulatum ).

Milnesium antarcticum sp. nov. differs from M. katarzynae by having smooth cuticle, slightly more cephalic position of the insertion point of the stylet supports (pt value 70.0– 73.7 in M. antarcticum sp. nov. and 73.3–78.3 in M. katarzynae ), claws with developed basal spurs on all claws and larger pt ratio of the length of main branches of the claws of the IV pair of legs (49.8–55.9 in M. antarcticum sp. nov. and 43.8– 43.5 in M. katarzynae ).

Milnesium antarcticum sp. nov. differs from Milnesium dujiangensis by having main claw branches on all legs.

Milnesium antarcticum sp. nov. differs from M. tardigradum by larger buccal tube and claws’ dimensions and more caudal position of the insertion point of the stylet supports (for comparison see Tables 1 and 2 ).

Milnesium antarcticum sp. nov. differs from M. tetralamellatum by having 6 peribuccal lamellae, lesser pt ratio of the length of the complex basal claw+secondary branch of the IV pair of legs (28.0– 34.3 in M. antarcticum sp. nov. and 46.2 in M. tetralamellatum ), larger buccal tube dimensions, more caudal position of the insertion point of the stylet supports (pt value 70.0– 73.7 in M. antarcticum sp. nov. and 63.9 in M. tetralamellatum ) and claws with developed basal spurs on the outer claws.

Milnesium antarcticum sp. nov. differs from M. brachyungue by having larger pt ratio of the length of the claws of the IV pair of legs (pt value of the length of main branches of the claws of the IV pair of legs is 49.8–55.9 in M. antarcticum sp. nov. and 33.1 in M. brachyungue ), more caudal position of the insertion point of the stylet supports (pt value 70.0– 73.7 in M. antarcticum sp. nov. and 69.4 in M. brachyungue ) and longer claws. Milnesium antarcticum sp. nov. differs from M. eurystomum by having typical configuration of buccal apparatus.

Figures

FIGURES 2 – 9. Milnesium tardigradum 2 — claws of the III pair of legs, 3 — claws of the IV pair of legs. Milnesium antarcticum sp. nov. 4 — claws of the III pair of legs, 5 — claws of the IV pair of legs. Milnesium reductum sp. nov. 6 — claws of the I pair of legs, 7 — claws of the IV pair of legs. Milnesium almatyense sp. nov. 8 — claws of the II pair of legs, 9 — claws of the IV pair of legs (9 — holotype; 4 ­ 8 — paratypes.

FIGURES 15 – 19. Milnesium antarcticum sp. nov. 15 — habitus, 16 — bucco­pharyngeal apparatus, 17 — claws of the III pair of legs, 18 — claws of the IV pair of legs (arrow points to the accessory points), 19 — gut content of the adult specimen (phase contrast; 15 ­ 19 — paratypes).

Tables

TABLE 2. Summary of morphometric data for Milnesium antarcticum sp. nov. (n = 15).

Character	Holotype	Mean (Range)	Standard error
buccal tube length (µm)	74.7	71.4 (67.0–74.7)	0.72
ss (µm)	53.3	51 (47.4–54.0)	0.55
pt ss	71.3	71.5 (70.0–73.7)	0.30
outer buccal tube width (µm)	27.4	28.1 (25.9–31.8)	0.41
pt of outer buccal tube width	36.6	39.2 (35.4–43.9)	0.63
claw main branch length, leg I (µm)	26.3	26.5 (23.7–30.3)	0.46
pt of claw main branch length, leg I	35.1	37.2 (34.0–43.2)	0.64
claw base+sec. branch length, leg I (µm)	17.8	18.1 (16.3–20.0)	0.30
pt of claw base+sec. branch length, leg I	23.8	25.4 (22.9–28.4)	0.50
claw basal branch length, leg I (µm)	8.9	8.1 (7.4–8.9)	0.11
bb, leg I	2.0	2.2 (2.0–2.5)	0.05
claw main branch length, leg III (µm)	?	30.0 (25.9–31.8)	0.46
pt of claw main branch length, leg III	?	42.3 (38.5–45.7)	0.65
claw base+sec. branch length, leg III (µm)	18.9	19.8 (18.9–21.1)	0.25
pt of claw base+sec. branch length, leg III	25.2	27.6 (25.2–30.0)	0.46
claw basal branch length, leg III (µm)	8.9	9.2 (8.1–11.1)	0.30
bb, leg III	2.1	2.1 (1.8–2.4)	0.05
claw main branch length, leg IV (µm)	39.2	37.2 (34.0–39.2)	0.36
pt of claw main branch length, leg IV	52.5	52.1 (49.8–55.9)	0.42
claw base+sec. branch length, leg IV (µm)	23.7	22.2 (19.6–25.2)	0.39
pt of claw base+sec. branch length, leg IV	31.7	31.2 (28.0–34.3)	0.49
claw basal branch length, leg IV (µm)	11.8	11.5 (9.3–14.1)	0.30
bb, leg IV	2.0	1.9 (1.6–2.5)	0.06

TABLE 1. Summary of morphometric data for Milnesium tardigradum (European populations) (n = 6).

Character body length (µm) buccal tube length (µm)	Smallest specimen 598.5 48.8	Largest specimen 704.9 46.6	Mean (Range) Standard error 652.8 (598.5–704.9) 18.68 49.4 (46.6–53.3) 1.22
ss (µm) pt ss (%)	32.6 66.7	30.3 65.1	31.9 (30.3–33.3) 0.54 64.6 (62.5–66.7) 0.67
outer buccal tube width (µm) pt of outer buccal tube width claw main branch length, leg I (µm)	18.5 37.9?	20.7 44.4 17.0	19.7 (13.3–22.2) 1.40 39.9 (28.6–46.2) 2.56 16.1 (14.8–17.0) 0.46
pt of claw main branch length, leg I claw base+sec. branch length, leg I (µm)	? 12.6	36.5 14.1	32.6 (28.7–36.5) 1.64 13.1 (11.8–14.4) 0.40
pt of claw base+sec. branch length, leg I claw basal branch length, leg I (µm) bb, leg I	25.8 5.2 2.4	30.2 6.7 2.1	26.6 (24.6–30.2) 0.83 6.1 (4.4–7.4) 0.47 2.2 (1.8–2.7) 0.12
claw main branch length, leg III (µm) pt of claw main branch length, leg III	16.3 33.3	19.6 42.1	17 (14.8–19.6) 0.72 34.6 (30.1–42.1) 2.04
claw base+sec. branch length, leg III (µm) pt of claw base+sec. branch length, leg III claw basal branch length, leg III (µm)	12.6 25.8 5.2	14.1 30.2 5.6	13.4 (12.6–14.1) 0.23 27.3 (25–30.2) 0.78 5.3 (5.0–5.6) 0.09
bb, leg III claw main branch length, leg IV (µm)	2.4 21.5	2.5 25.2	2.5 (2.4–2.6) 0.04 22.7 (21.5–25.2) 0.59
pt of claw main branch length, leg IV claw base+sec. branch length, leg IV (µm) pt of claw base+sec. branch length, leg IV	43.9 15.5 31.8	54.0 17.0 36.5	46.2 (41.7–54.0) 2.06 16.2 (15.5–17.0) 0.23 32.8 (30.6–36.5) 0.98
claw basal branch length, leg IV (µm) bb, leg IV	7.0 2.4	8.1 2.5	7.6 (6.7–8.1) 0.27 2.1 (2.0­2.4) 0.07