Milnesium sandrae, Pilato, Giovanni & Lisi, Oscar, 2016

Pilato, Giovanni & Lisi, Oscar, 2016, Milnesiumminutum and Milnesiumsandrae, two new species of Milnesiidae (Tardigrada, Eutardigrada, Apochela), ZooKeys 580, pp. 1-12 : 7-11

Taxon classification Animalia Apochela Milnesiidae

Milnesium sandrae sp. n. Fig. 3, Table 3

Locus typicus.

Hawaiian Archipelago: Hawai’i Island.

Material examined.

Hawaiian Archipelago: Hawai’i Island (holotype, slide 4290) and 16 paratypes (slides Nos. 4268, 4288-4290; 4293) collected in 1994 by Dr. D.S. Horning (Sydney).

The precise geographic coordinates relative to the type locality in which the specimens were found in 1994 are not available. The specimens were erroneously considered as Milnesium tardigradum by Binda and Pilato (1994).

Type repository.

Holotype and paratypes are deposited in the Binda and Pilato Collection, Museum of the Department of Biological, Geological and Environmental Sciences, University of Catania, Sicily.

Specific diagnosis.

Colourless; cuticle smooth; eye spots present; six peribuccal and two lateral papillae present; bucco-pharyngeal apparatus of the Milnesium type. Buccal tube wide; mouth terminal with six peribuccal lamellae. Stylet supports inserted on the buccal tube at 58.0-60.5 % of its length. Claws of the Milnesium type with [3-3]-[3-3] configuration; primary claws with thin accessory points; secondary claws each with a rounded basal thickening (lunule); a long cuticular bar present under the claws I–III.

Description of the holotype.

Body 567 µm long, colourless, cuticle smooth without pseudopores, reticulum, tubercles or gibbosities; eye spots present. Six peribuccal and two lateral papillae present. Bucco-pharyngeal apparatus of the Milnesium type (Fig. 3A) (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, pear-shaped, without apophyses, placoids or septulum); mouth terminal with six triangular peribuccal lamellae with basal stripes. Stylet furcae triangular in shape (Fig. 3A). Buccal tube cylindrical, 35.0 µm long; the external width at the level of the stylet supports insertion point is 15.7 µm (pt = 44.9). Stylet supports inserted on the buccal tube at 58.0% of its length.

Claws of the Milnesium type (Fig. 3 B–D), secondary claws with three points: configuration [3-3]-[3-3]. Primary claws on legs I, 14.5 µm long (pt = 41.4), and secondary claw, 12.4 µm (pt = 35.4); primary claws on legs II, 15.2 µm long (pt = 43.4) and secondary claw, 12.4 µm (pt = 35.4); primary claws on legs III, 15.2 µm long (pt = 43.4) and secondary claw, 12.2 µm (pt =34.9); primary claws on legs IV, 19.2 µm long (pt = 54.9) and secondary claw, 13.7 µm (pt = 39.1). The secondary claw length is 85.5% of the primary claw length on legs I, 81.6% on legs II, 80.3% on legs III and 71.4% on legs IV.

Thin accessory points present on the primary claws (Fig. 3C, D); secondary claws each with rounded basal thickening (lunule) (Fig. 3C); a long cuticular bar is present under the claws I–III (Fig. 3B).

Remarks.

The paratypes are similar to the holotype in both qualitative and quantitative characters (Table 3).

Etymology.

The specific name sandrae is in honour of Dr. Sandra J. McInnes (Cambridge, United Kingdom), who kindly improved the English of many of our papers.

Differential diagnosis.

Milnesium sandrae sp. n. is compared with other species of the genus having six peribuccal lamellae, smooth cuticle (without pseudopores, reticulum, tubercles or gibbosities), and the [3-3]-[3-3] claw configuration. The new species differs from all these species, except Milnesium eurystomum , by having a different value of the pt index of the stylet supports insertion point (58.0-60.5 in the new species, over 62 in the remaining taxa) and other characters, which are indicated in detail in the following comparisons.

Milnesium sandrae sp. n. differs from Milnesium eurystomum and Milnesium bohleberi by having a cylindrical instead of a funnel-shaped buccal tube.

Milnesium sandrae sp. n. differs from Milnesium brachyungue by a higher buccal tube width pt index; a higher pt of both the primary and secondary claw lengths, and lower percent ratio values between the secondary claw and primary claw lengths (Tables 3 and 2, and Figs 3BC and 2B); this ratio difference is particularly marked for legs IV where the ratio values of 70.4-71.4 for Milnesium sandrae sp. n. compare with 81 in Milnesium brachyungue (Tables 2 and 3).

The new species differs from Milnesium asiaticum by having a higher pt of the buccal tube width; a higher pt of the secondary claw lengths (particularly on the legs I–III), and a higher percent ratio between the secondary claw and primary claw lengths on all legs (Tables 2 and 3).

Milnesium sandrae sp. n. differs from Milnesium antarcticum by having a shorter buccal tube with respect to the body length; a higher pt index of the buccal tube width; higher pt of the insertion point of the stylet supports on the buccal tube (58.0-60.5 in Milnesium sandrae sp. n., 70.0-73.7 in Milnesium antarcticum according to Tumanov 2006); higher pt indices of the secondary claws, and higher values of the percent ratio between the secondary claw and primary claw lengths (Tables 3 and 4, Figs 3B, C and 2D).

The new species differs from Milnesium longiungue by having accessory points; by having lower pt values of the primary claw, and by a higher percent ratio between the secondary claw and primary claw lengths on all legs (Tables 3 and 4).

The new species differs from Milnesium zsalakoae in having accessory points and a higher percent ratio between the secondary claw and primary claw lengths on all legs. The difference is particularly marked in claws IV where the pt ratios are 70.4-71.4 in Milnesium sandrae sp. n. and 47.2-48.6 in Milnesium zsalakoae (see: Meyer and Hinton 2010).

Milnesium sandrae sp. n. differs from Milnesium barbadosense by higher pt of the secondary claw lengths and by higher values of the percent ratio between the secondary claw and the primary claw lengths on legs I–III (Tables 3 and 4).

Milnesium sandrae sp. n. differs from Milnesium minutum by having a larger body size; shorter buccal tube with respect to the body length; a higher pt of the secondary claw lengths and higher values of the percent ratio between the secondary claw and primary claw lengths. This difference is less marked in legs IV (Tables 1 and 3; Figs 1 and 3).