Milnesium vorax, 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 : 576-579

Milnesium vorax sp. nov.

Fig. 1

Type locality. Sicily, neighbourhood of Ramacca (Catania), 37°23′00″N, 14°42′00″E, 270 m a.s.l. (holotype and one paratype, slide no. 2775).

Material examined. Type material from a moss on soil sample collected by our colleague Vera D’Urso (University of Catania) in April 1998.

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

Specific diagnosis. Colourless; cuticle smooth; eye spots present; six peribuccal and two lateral papillae present; mouth terminal with six triangular peribuccal lamellae with basal stripes; buccal tube wide; stylet supports inserted on the buccal tube at nearly 62 % of its length; claws of the Milnesium type with configuration [2-3]-[3-2]; 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 585 µm long; cuticle smooth without granulation or reticular design, and without pseudopores; eye spots present. 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, piriform and without apophyses, placoids or septulum); six triangular peribuccal lamellae present with basal stripes. Stylet furcae wide and triangular in shape. The buccal tube ( Fig.1A ) is cylindrical, 35.0 µm long (measured according to Tumanov, 2006, i.e. including the caudal flexible portion); the external width at the level of the stylet insertion point is 21.1 µm (pt = 60.3). Stylet supports short, inserted on the buccal tube at 62.2% of its length (pt = 62.2). Claws of the Milnesium type ( Fig.1B–D ). The external claws of the first three pairs of legs have two points, the internal claws three points, on leg pair four the anterior claws with two points and posterior claws with three points, (configuration [2-3]-[3-2] according to the code suggested by Michalczyk et al. 2012). External main branch of legs I, 16.3 µm long (pt = 46.6); base+secondary branch of leg I, 12.5 µm long (pt = 35.7); the base+secondary branch length is 76.7% of the main branch length. External main branch on legs II 17.4 µm (pt. = 19.7). External main branches on legs III, 18.1 µm long (pt = 51.7) and the base+secondary branch, 13.5 µm (pt = 38.6); the base+secondary branch length is 74.6% of the main branch length. Posterior main branch on legs IV, 20.8 µm long (pt = 59.4), posterior base+secondary branch, 14.9 µm (pt = 42.6); the base+secondary branch length is 71.6% of the main branch length. Main branches with thin accessory points; claw bases with rounded basal thickenings ( Fig. 1B . arrow a, and Fig. 1D ); a long cuticular bar present under the claws I–III ( Fig.1B , arrow b, and Fig. 1C ).

Eggs not found.

Remarks. The paratype is similar to the holotype in both qualitative and quantitative characters ( Table 1 ).

Etymology. The specific name vorax ( vorax = voracious) refers to the remarkable width of the buccal tube.

Differential diagnosis. Three species are known having smooth cuticle, six peribuccal lamellae and claws configuration [2-3]-[3-2]: M. reductum , M. tardigradum , and, according to Meyer & Hinton (2012), some specimens of M. barbadosense Meyer & Hinton, 2012 .

Milnesium vorax sp. nov. differs from M. tardigradum by the shape of the buccal tube, which is clearly wider and without a thickened wall posterior to the stylet supports (see Table 1 and Figs. 1A and 2A , arrow). In addition, in M. vorax sp. nov. the percent ratio between the base+secondary and the main claw branches is slightly higher ( Table 1 ).

The new species differs from M. reductum by the shape of the buccal tube, which is clearly wider and without a thickened wall posterior to the stylet supports (see Table 1 and Figs. 1A and 3A : arrow); by having the stylet supports inserted on the buccal tube in a more cephalic position (pt = 62–62.2 in M. vorax sp. nov., 65.5 – 69.3 in M. reductum according to Tumanov 2006) ( Table 1 ); by having claw main branches with accessory points, higher values of the pt index relative to the base+secondary claws and, as a consequence, a higher percent ratio between the base+secondary and the main claw branches ( Table 1 ).

In M. barbadosense the claw configuration is [3-3]-[3-3], but Meyer & Hinton (2012) also attributed to the same species a few specimens, most less than 300 µm long and some larger, with claw configuration [2-3]-[3-2]. M. vorax sp. nov. differs from these specimens by having: eye spots present; higher pt index value of the buccal tube width (about 60 in M. vorax sp. nov., about 50 in larger specimens of M. barbadosense according to Meyer & Hinton, 2012); stylet supports inserted on the buccal tube in a more cephalic position (pt = 62 in M. vorax sp. nov., at least 66 in M. barbadosense (according to Meyer & Hinton 2012); higher values of the pt index relative to the base+secondary claws and, as a consequence, higher percent ratio between the base+secondary and the main claw branches (the difference is clearer in the claws I–III, and very small in the claw IV).

Figures

FIGURE 1. A – D, Milnesium vorax sp. nov. (holotype). A, Buccal tube. B, Claws of legs I (arrow ‘ a’ indicates a lunule; arrow ‘ b’ indicates the long cuticular thickening). C, Claws of legs III (the arrow indicates the long cuticular thickening). D, Claws of the hind legs (the arrow indicates a lunule). 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.

FIGURE 3. A – C, Milnesium reductum (paratype, slide no. 5102). A, Buccal tube (the arrow indicates a thickening of the buccal tube wall). B, Claws of legs III. C, Claws of the hind legs. Scale bar = 10 µm.

Tables

TABLE 1. Measurements in µm, pt index values relative to some structures, and percent ratio between the base + secondary and the main claw branches of Milnesium vorax sp. nov..

No. slide	M. vorax sp. nov. 2775 Ramacca paratype	2775 Ramacca holotype	M. tardigradum 3436 Tunisia	M. reductum 5102 paratype
Body length Buccal tube length Buccal tube width	µm pt 578 35.8 21.3 59.5	µm pt 585 35.0 21.1 60.3	µm pt 492 40.4 19.6 48.5	µm pt 594 46.0 13.3 28.9
Stylet supports insertion point Ext. main branch I	62.0 16.1 45.0	62.2 16.3 46.6	60.7 16.5 40.8	65.5 18.2 39.6
Base+sec. branch I % Base+sec/main branch I Ext. main branch II Base+sec. branch II	12.5 34.9 77.6 17.2 48.0 13.4 37.4	12.5 35.7 76.7 17.4 49.7??	12.2 30.2 73.9 18.1 44.8 13.1 32.4	12.5 27.1 68.7 20.9 45.4 13.5 29.3
% Base+sec/main branch II Ext. main branch III	77.9 18.1 50.6	? 18.1 51.7	72.4 17.9 44.3	64.6 22.4 48.7
Base+sec. branch III % Base+sec/main branch III Posterior main branch IV	13.2 36.9 72.9 21.2 59.2	13.5 38.6 74.6 20.8 59.4	12.8 31.7 71.5 21.8 54.0	14.4 31.3 64.3 27.0 58.7
Posterior base+sec. branch IV % Base+sec/main branch IV	14.9 41.6 70.3	14.9 42.6 71.6	14.0 34.7 64.2	15.5 33.7 57.4