Milnesium tumanovi, Pilato, Giovanni, Sabella, Giorgio & Lisi, Oscar, 2016

Pilato, Giovanni, Sabella, Giorgio & Lisi, Oscar, 2016, Two new species of Milnesium (Tardigrada: Milnesiidae), Zootaxa 4132 (4), pp. 575-587 : 579-584

Milnesium tumanovi sp. nov.

Fig. 4

Type locality. Yalta (Crimea): 44°30'0''N, 34°9'41''E, 40 m a.s.l.. Material examined. Yalta, holotype (slide no. 3904) and one paratype (slide no. 3916) from a moss sample on stone collected by Dr. Piero Verzì (Catania) in May 1990.

Type repository. Holotype and paratype are deposited in the collection of Binda & Pilato, Museum of the Department of Biological, Ecological and Environmental Sciences, Section of Animal Biology “Marcello La Greca”, University of Catania, Italy.

Specific diagnosis. Colourless, eye spots present, cuticle smooth; six peribuccal and two lateral papillae present; mouth with six triangular peribuccal lamellae with basal stripes. Buccal tube wide; stylet supports inserted on the buccal tube at about 52% of its length; claws of the Milnesium type with configuration [3-3]-[3-3]; main branches with thin accessory points; secondary branches with rounded basal thickenings; a long cuticular bar present under the claws I–III.

Description of the holotype. Body uncoloured, 744 µm long; eye spots present; cuticle smooth without granulation or reticular design, and without pseudopores; six peribuccal and two lateral papillae present. Buccopharyngeal apparatus of the Milnesium type (rigid buccal tube without ventral lamina; apophyses for the insertion of the stylet muscles in the shape of very short and flat ridges symmetrical with respect to the frontal plane and without caudal processes; pharyngeal bulb elongated and without apophyses, placoids or septulum); six triangular peribuccal lamellae, with basal stripes, present. Stylet furcae wide and triangular in shape ( Fig. 4A ). The buccal tube is very wide, cylindrical in shape, not funnel-shaped ( Fig. 4A ); it is 48.8 µm long (measured according to Tumanov 2006, i.e. the caudal flexible portion included); its external width at the level of the stylet insertion point is 26.9 µm (pt = 55.1). Stylet supports short, inserted on the buccal tube at 52.3% of its length (pt = 52.3). The claws are of the Milnesium type ( Fig. 4B,C ). All claws have three points: configuration [3-3]-[3-3] according to the code suggested by Michalczyk et al. (2012). External main branch of legs I, 21 µm long (pt = 43.0) ( Table 2 ); base+secondary branch of leg I, 15.9 µm long (pt = 32.6); the base+secondary branch length is 75.7% of the main claw branch length. On legs III the external main branch is 21.2 µm long (pt = 43.4) and the base+secondary branch, 16.1 µm (pt = 33.0); the base+secondary branch length is 75.9% of the claw main branch length. Posterior main branch IV, 27.0 µm long (pt = 55.3), the base+secondary branch, 20.6 µm (pt = 42.2): the posterior base+secondary branch length is 76.3% of the main branch length.

M. tumanovi sp. nov. M. longiungue M. brachyungue No. slide 3904 holotype 5103 paratype 3940 holotype Main branches with thin accessory points ( Fig. 4B , arrow a); claw bases with rounded basal thickenings ( Fig. 4B , arrow b); a long cuticular bar present under the claws I–III ( Fig. 4B , arrow c).

Eggs not found.

Remarks. The paratype is similar to the holotype in both qualitative and quantitative characters.

Etymology. The specific name tumanovi is in honour of Dr. Denis Tumanov (St. Petersburg, Russia) who recently described several species of the genus.

Differential diagnosis. Sixteen living species of Milnesium having six peribuccal lamellae and claw configuration [3-3]-[3-3] are known, but only eleven of them have smooth cuticle: M. antarcticum Tumanov, 2006 , M. asiaticum Tumanov, 2006 , M. brachyungue Binda & Pilato, 1990 , M. eurystomum Maucci, 1991 , M. longiungue Tumanov, 2006 , M. bohleberi Bartels, Nelson, Kaczmarek & Michalczyk, 2014 , M. zsalakoae Meyer & Hinton, 2010 , M. barbadosense Meyer & Hinton 2012 , M. shilohae Meyer, 2015 , M. vorax Pilato & Lisi, 2016 , and M. sandrae Pilato & Lisi, 2016 .

Milnesium tumanovi sp. nov. differs from all these species in having a lower value of the pt index relative to the stylet support insertion point on the buccal tube (about 52–54 in the new species, at least 58.0, often 60.0 or more, in all the other species); and in having a higher pt index value relative to the buccal tube width, of all but M. eurystomum and M. bohleberi . However, the buccal tube is cylindrical in M. tumanovi sp. nov. whereas in M. eurystomum and M. bohleberi it is clearly funnel shaped.

In addition, the new species differs from M. zsalakoe and M. longiungue in having the accessory points, lower values of the pt index relative to the claw main branches and higher values of the percent ratio between the base+secondary branches length and the main claw branches length (as regards the comparison with M. longiungue see Table 2 and Figs. 4 B,C and 5 B,C ).

Milnesium tumanovi sp. nov. differs from M. brachyungue by having: higher values of the pt index relative to the claw length (both to main and base+secondary claw branches) ( Table 2 ); main and base+secondary claw branches more different in length and, as a consequence, lower values of the percent ratio between the base+secondary branches length and the main claw branches length ( Table 2 ; Figs. 4B,C and 6 B,C).

Milnesium tumanovi sp. nov. differs from M. asiaticum by a higher values of the percent ratio between the base+secondary branches length and the main claw branches length ( Tables 2 and 3 ; Figs. 4 B,C and 7B,C ). These values are particularly different in the hind claws ( Tables 2 and 3 ; Figs. 4C and 7C ).

The new species differs from M. antarcticum ( Tables 2 and 3 ; Figs. 4A and 8A ) by having a shorter buccal tube in proportion to the body length; and a higher difference in length between main and base+secondary claw branches in the hind legs. ( Tables 2 and 3 ; Figs. 4C and 8C ).

Milnesium tumanovi sp. nov. differs from M. barbadosense by having eye spots, higher values of the pt index relative to the claw secondary branches length and, as a consequence, higher values of the percent ratio between the base+secondary branches length and the main claw branches length ( Tables 2 and 3 : Figs. 4B,C and Fig. 2 of Meyer & Hinton, 2012).

The new species differs from Milnesium shilohae by having more slender primary branches (particularly those of the claws I–III).

It differs from Milnesium minutum by having larger body size and higher percent ratio between base+secondary branches length and the main claw branches length in the claws IV.

Milnesium tumanovi differs from Milnesium sandrae by having the percent ratio between the base+secondary branches length and the main claw branches length slightly smaller in the claws I-III and higher in the claws IV; the values of those percent ratios are homogeneous (about 76) in all the claws of the new species, whereas in Milnesium sandrae a clear difference can be noticed between the claws I-III (78.6-85.5) and the claws IV (70.4–71.4).

Figures

FIGURE 6. Milnesium brachyungue (paratype, slide no. 3944). A, Buccal tube. B, Claws of legs I. C, Claws of the hind legs. Scale bar = 10 µm.

FIGURE 4. A – C, Milnesium tumanovi sp. nov. (holotype). A, Buccal tube. B, Claws of legs I (arrow ‘ a’ indicates the accessory points; arrow ‘ b’ a lunule, arrow ‘ c’ indicates the long cuticular thickening). C, Claws of the hind legs. Scale bar = 10 µm.

FIGURE 5. A – C, Milnesium longiungue (paratype, slide no. 5103). A, Buccal tube. B, Claws of legs I. C, Claws of the hind legs. Scale bar = 10 µm.

FIGURE 7. A – C, Milnesium asiaticum (paratype, slide no. 5105). A, Buccal tube. B, Claws of legs III. C, Claws of the hind legs. Scale bar = 10 µm.

FIGURE 8. A – C, Milnesium antarcticum (slide no. 4035). A, Buccal tube. B, Claws of legs II. C, Claws of the hind legs. Scale bar = 10 µm.

FIGURE 2. A – C, Milnesium tardigradum (paratype, slide no. 5489). A, Buccal tube (the arrow indicates a thickening of the buccal tube wall). B, Claws of legs II. C, Claws of the hind legs. Scale bar = 10 µm.

Tables

TABLE 2. Measurements in µm, pt index values relative to some structures, and percent ratio between the base + secondary and the main claw branches of Milnesium tumanovi sp. nov..

µm	pt	µm	pt	µm	pt
Body length 744		747		801
Buccal tube length 48.8		46.6		59.8
Buccal tube width 26.9	55.1	22.1	47.4	23.7	39.6
Stylet supports insertion point	52.3		62.3		69.8
Ext. main branch I 21.0	43.0	22.5	48.3	13.9	23.2
Base+sec. branch I 15.9	32.6	14.2	30.5	12.4	20.7
% Base+sec/main branch I 75.7		63.1		89.2
Ext. main branch II 21.2	43.4	25.4	55.5	15.4	25.8
Base+sec. branch II?	?	15.2	32.6	13.3	22.2
% Base+sec/main branch II?		59.8		86.4
Ext. main branch III 21.2	43.4	27.2	57.7	16.5	27.6
Base+sec.branch III 16.1	33.0	16.4	35.2	14.2	23.8
% Base+sec/main branch III 75.9		60.3		86.1
Posterior main branch IV 27.0	55.3	36.5	78.3	18.9	31,6
Posterior base+sec.branch IV 20.6	42.2	21.5	46.2	15.4	25.8
% Base+sec/main branch IV 76.3		58.9		81.5