Milnesium swansoni, Young, Alexander, Chappell, Benjamin, Miller, William & Lowman, Margaret, 2016

Young, Alexander, Chappell, Benjamin, Miller, William & Lowman, Margaret, 2016, Tardigrades of the Tree Canopy: Milnesium swansoni sp. nov. (Eutardigrada: Apochela: Milnesiidae) a new species from Kansas, U. S. A., Zootaxa 4072 (5), pp. 559-568 : 561-566

Milnesium swansoni sp. nov.

Figure 1 , Tables 2–4

Diagnosis. Milnesium without eyes, with a smooth cuticle, with short, narrow buccal tube, and four peribuccal lamellae. Main branch of claw long, without accessory points. Basal thickening wide, basal spurs small but present with a secondary branch configuration of [3-3]-[3-3].

Description of the holotype. Female Milnesium swansoni , body transparent, length 330 µm (BL pt = 1,430%), eye spots not found. Cuticle smooth without ornamentation, pores, reticulations, or gibbosities. Mouth with six peribuccal papillae, four peribuccal lamellae and two lateral papillae. Buccal tube short, narrow, and cylindrical; length 23.1 µm, width 9.2 µm (BTW pt = 39.7). Stylet support attachment at 15.5 µm (SSA pt = 67). Pharyngeal bulb elongated, pear-shaped, without apophyses, placoids, or septula. Claws of Milnesium type, main branch separated from secondary branch without accessory points. Secondary branch with base and primary, secondary, and basal spurs [3-3]-[3-3]. Basal thickening wide. Length of primary branches, secondary branches, basal spurs and the width of basal thickenings are given in Table 2, with all measurements and ranges for paratypes. Individual measurements for all type material is provided in the Supplementary Data.

Type location. Collected from between 9 and 12 meters high on 20th June 2014, by Alexander Young: lichen on bark of a Virginia creeper ( Parthenocissus quinquefolia ) in the Baker University Wetlands (38.91426N, - 95.22858W) Douglas County, Kansas, U.S.A.

Etymology. The new species is named in honour of Kent Swanson Jr. whose family established the Swanson Family Scholarship, for which author AY was a recipient.

Holotype. Deposited at the California Academy of Science, San Francisco, California, U.S.A. Slide Collection number: CASIZ-198191.

Paratypes. Four female and five male for a total of nine paratypes deposited at the California Academy of Science, San Francisco, California, U.S.A. Slide Collection numbers: CASIZ-198192, CASIZ-198193, CASIZ- 198194, CASIZ-198195, CASIZ-198196, CASIZ-198197, CASIZ-198198, CASIZ-198199, CASIZ-198200 (details in Supplementary Data).

Sexual dimorphism. Species exhibits qualitative sexual dimorphism in the structure of claw I. Males exhibit wide, thick secondary claws lacking sub-branches ( Table 3 and Supplementary Data).

A question mark indicates a value that could not be accurately measured. An em-dash indicates a value that is not mathematically applicable.

Eggs. Oval, smooth, deposited in exuvium.

Habitat. The new species was found at all nine of the collection sites indicating wide distribution within the region ( Table 1 ). One-hundred specimens were extracted from lichen habitat and 15 specimens from moss habitat on 38 of the 135 trees climbed, representing 15 of the17 tree species sampled. The new species did not show selection of substrate (tree species) or habitat (moss or lichen).

The new species was collected from ground level up to 20 m with 18, 27, 39, and 31 specimens found at levels 1, 2, 3, and 4 respectively. Milnesium swansoni sp. nov. was found to occur significantly more often at the three upper levels than was expected for its occurrence to be considered uniform with the base level 1 (X2 = 4.5, 24.5, 9.4 respectively). Thus a preference for upper canopy habitat is suggested.

Differential diagnosis. The new species is in the tardigradum group with a smooth cuticle but differs from all species in the group except M. tetralamellatum by having only four peribuccal lamellae. It differs from M. tetralamellatum by its [3-3]-[3-3] vs [2-3]-[3-2] claw configuration. The new species also differs from M. tetralamellatum by not having eyes or claw accessory points, and by having a narrower buccal tube (BTW pt = 40.2 vs BTW pt = 49), and a more posterior stylet support attachment point (SSA pt = 68 vs SSA pt = 64). Additionally, it is distinct among the other Milnesium with four peribuccal lamellae for its combination of BTW and SSA ranges ( Figure 2 ). The new species is easily distinguished from the other species described from North America with four peribuccal lamellae, M. lagniappe , by the smooth cuticle, the claw configuration, the narrower buccal tube and a more anterior attachment point for the stylet support bar ( Table 4 ).

Key: pt = trait / buccal tube length *100, BL = Body Length, BTW—Buccal Tube Width, SSA = Stylet Support Attachment.

Figures

FIGURE 1. Milnesium swansoni sp. nov. A. Body of holotype showing smooth cuticle, B. Mouth showing holotype with narrow buccal tube and four peribuccal lamellae, C. showing secondary characteristic of male paratype, D. Claw I of paratype showing [3 - 3] claw formation, E. showing claw IV with [3 - 3] claw.

FIGURE 2. Tardigrade species with four peribuccal lamellae group, comparison of pt values for Buccal Tube Width (BTW) vs Stylet Support Attachment (SSA) point. pt = trait / Buccal Tube Length. Error bars = trait range (BTW / SSA). The numbers in the graph indicate the stylet support attachment and buccal tube width pt values of the holotype specimen of each species.

Tables

TABLE 3. Male morphometric data for Milnesium swansoni sp. nov.

Male Character	N	RANGE		MEAN	SD	a*
		µm	pt	µm pt	µm pt	µm
Body length	5	381–448	1165–1493	417 1376	25 133	-
Peribuccal papillae length	3	3.9–4.5	14.1–15.7	4.2 14.7	0.3 0.8	4.2
Buccal Tube
Length	5	25.8–36.1	-	30.6 -	4.1 -	30.7
Stylet Support	5	17.8–24.2	67.0–71.5	21.1 69.0	2.5 1.9	21.2
Anterior width	5	9.3–12.5	33.3–36.8	10.6 34.7	1.3 1.3	10.7
Standard width	5	9.1–12.4	33.4–36.3	10.6 34.6	1.4 1.2	10.6
Posterior width	5	9.5–12.9	34.8–36.7	10.9 35.7	1.5 0.9	10.9
Standard width/length ratio	5	33%–36%	-	35% -	-	34%
Posterior/anterior width ratio	5	100%–100%	-	103% -	-	103%
Claw 1
External primary branch	4	14.2–17.4	51.5–55.4	15.8 54.1	1.4 2.0	15.8
External base + secondary branch	5	10.1–14.3	38.2–42.4	12.2 39.8	1.5 1.6	12.3
External spur	0	?–?	?–?	??	??	?
Internal primary branch	5	14.3–18.6	51.2–56.4	16.4 53.8	1.7 2.4	16.5
Internal base + secondary branch	4	10.5–14.2	39.2–41.4	12.7 40.8	1.6.9	12.8
Internal spur	3	2.5–4.3	9.1–11.8	3.5 10.8	0.9 1.5	3.9
Basal thickening width	4	4.5–4.8	13.0–16.6	4.7 14.8	0.1 1.5	4.7
Claw 2
External primary branch	4	14.9–19.6	54.1–58.6	16.9 56.2	2.0 2.3	17.1
External base + secondary branch	5	10.7–14.1	39.1–43.3	12.7 41.6	1.5 1.7	12.7
External spur	2	3.4–3.7	10.7–13.4	3.5 12.1	0.2 2.0	3.6
Internal primary branch	5	15.0–19.5	54.1–59.7	17.1 56.2	1.7 2.5	17.3
Internal base + secondary branch	5	10.1–14.0	38.7–42.7	12.3 40.1	1.8 1.7	12.2
Internal spur	2	3.4–3.5	9.7–10.7	3.4 10.2	0.1 0.7	3.5
Basal thickening width	4	3.6–4.3	12.0–13.9	3.8 13.2	0.3 0.8	3.8
Claw 3
External primary branch	5	15.8–21.3	58.4–62.4	18.5 60.5	2.3 1.8	18.5
External base + secondary branch	5	11.0–13.8	38.2–42.5	12.3 40.5	1.2 1.8	12.4
External spur	2	3.0–3.6	8.4–11.5	3.3 9.9	0.4 2.2	3.0
Internal primary branch	4	14.8–20.2	54.2–57.4	16.9 56.1	2.4 1.4	17.0
Internal base + secondary branch	5	10.1–14.1	36.8–39.9	11.7 38.2	1.6 1.3	11.7
Internal spur	4	2.7–3.6	9.7–12.6	3.2 10.6	0.4 1.3	3.3
Basal thickening width	5	2.7–4.1	9.8–12.9	3.4 11.0	0.6 1.5	3.3
Claw 4
Anterior primary branch	5	15.9–22.5	61.6–65.5	19.4 63.5	2.6 1.5	19.5
Anterior base + secondary branch	4	11.8–15.5	42.2–45.9	13.7 43.5	1.5 1.6	13.8
Anterior spur	2	1.6–1.6	5.9–6.4	1.6 6.1	0.0 0.3	1.6
Posterior primary branch	5	17.3–23.2	64.3–67.6	20.2 66.2	2.4 1.3	20.3
Posterior base + secondary branch	5	11.0–14.4	39.8–44.7	13.0 42.6	1.4 1.9	13.1
Posterior spur	2	1.0–2.5	3.6–6.8	1.7 5.2	1.0 2.3	2.0
Basal thickening width	5	2.8–5.0	10.2–15.4	4.1 13.3	0.9 2.0	4.4

TABLE 4. Comparison of diagnostic characters of Milnesium species within the tetralamellatum group.

Species	Cuticle surface	Peribuccal lamellae	Eyes	Accessory points	Claw configuration	pt BL	pt BTW	pt SSA
M. reticulatum	gibbosities	4	yes	present	[2-3]-[3-2]	1058	37.4	68.5
M. lagniappe	sculptured	4	no	present	[2-3]-[3-2]	1430	64.5	70.2
M. tetralamellatum	smooth	4	yes	present	[2-3]-[3-2]	1418	49.1	63.9
M. swansoni sp. nov.	smooth	4	no	absent	[3-3]-[3-3]	1597	40.2	67.5