Macrobiotus modestus, Pilato, Giovanni & Lisi, Oscar, 2009

Pilato, Giovanni & Lisi, Oscar, 2009, Description of three new species of Tardigrada from the Seychelles, Zootaxa 2005, pp. 24-34 : 27-30

Macrobiotus modestus sp. nov.

Figs. 2 , 3

Material examined: Praslin, Mt. Cabris: holotype, 11 paratypes and 5 eggs some of which contained fully developed embryo, from a moss sample on soil (collected 18.03.2002) sent by Justin Gerlach.

Type repository: The holotype (slide N. 5250) and paratypes are deposited in the collection of Binda & Pilato (Museo del Dipartimento di Biologia Animale “Marcello La Greca”, Università di Catania).

Species diagnosis: Cuticle smooth with round and elliptical pores; eye spots present; buccal armature simple without bands of teeth and with only thin posterior transverse ridges; dorsal ridges joined together to form a thin transverse arc. Buccal tube long and narrow; stylet supports inserted on the buccal tube at 67–70% of its length. Two macroplacoids and a microplacoid present. Claws of hufelandi type, well developed; small lunules present.

Eggs of the hufelandi type with indented terminal disc and egg shell with small pores forming an irregular reticular design with very small meshes.

Description of the holotype: Body length about 180 μm ( Fig. 2 A); colorless, small eye spots present; cuticle smooth with round and elliptical pores, not visible on legs. Mouth opening terminal with 10 small peribuccal lamellae; there is no visible band of teeth; the dorsal transverse ridges are joined to form a thin transverse arc; three thin ventral ridges are visible. Buccal tube long and narrow ( Figs. 2 B–C); it is 28.4 μm long and 2.1 μm wide externally (pt = 7.4); the length is 15.8% of the body length. Stylet supports inserted on the buccal tube at pt = 69.8.

Pharyngeal bulb ( Fig. 2 B) (22 μm x 16 μm) with apophyses, two rod-shaped macroplacoids and a small microplacoid. First macroplacoid, with a slight central constriction, 4.9 μm long (pt = 17.3); second one 3.6 μm long (pt = 12.7); microplacoid 1.5 μm long (pt = 5.3). Entire placoid row 10.5 μm long (pt =37.0); macroplacoid row 8.9 μm long (pt = 31.3).

Claws of hufelandi type, well developed ( Fig. 2 A, D); the orientation of the holotype only permits the measurement of the posterior claw of the hind legs, which is 9.7 μm long (pt = 34.2). Main branches of all claws with well-developed accessory points. Lunules present on all legs, smooth on the first three pairs of legs, slightly indented on the hind legs. A faint cuticular thickening is present below the lunules on the first three pairs of legs.

The paratypes are similar to the holotype in both qualitative and metric characters ( Table 2 ).

The eggs, laid freely, are spherical, with trunco-conical processes with an indented terminal disc ( Fig. 3 ). In a measured egg the diameter is 56.1 μm without processes, 71.7 μm including the processes. In this same egg 32–33 processes are present around the circumference, about 140 in the hemisphere. The processes are 4.6–5.1 μm high with a basal diameter of 4.2–4.9 μm; the indented terminal disc has a diameter of 2.8–3.6 μm.

The surfaces of the processes are smooth; the egg shell has many small pores forming an irregular reticular design with very small meshes ( Fig. 3 ).

Etymology: The name modestus (= modest) refers to the non-gaudy aspect of the narrow buccal tube.

Remarks: Ten species of Macrobiotus are already known having the dorsal transverse ridges of the buccal armature fused to form an unique arc: M. echinogenitus , M. sapiens , M. diversus Biserov, 1990 , M. iharosi , M. madegassus , M. seychellensis , M. biserovi Bertolani, Guidi & Rebecchi,1996, M. humilis , M. semmelweisi and M. drakensbergi .

Macrobiotus modestus sp. n. differs from all these species by having narrower buccal tube, stylet supports inserted on the buccal tube in a more cephalic position, and in characters of the eggs. In further detail, the lack of teeth in the buccal cavity of the new species differentiates it from M. echinogenitus , M. sapiens , M. iharosi , M. seychellensis , M. biserovi ; the lacking of dorsal gibbosities from M. semmelweisi ; the smooth margin of the lunules from M. drakensbergi and M. biserovi ; the presence of eye spots and a shorter first macroplacoid from M. madegassus ; and a smaller first macroplacoid, smaller microplacoid, and more slender claws from M. humilis .

Figures

FIGURE 2. Macrobiotus modestus sp. n. A, habitus of the holotype (scale bar = 20 µm). B, bucco-pharyngeal apparatus of a paratype. C, bucco-pharyngeal apparatus of the holotype; the insertion point of the stylet supports and the macroplacoids are in focus. D, claws of the second and third pairs of legs of a paratype. (B – D: scale bar = 10 µm).

FIGURE 3. Macrobiotus modestus sp. n. A and B, showing details of the eggs. (Scale bar = 10 µm).

Tables

TABLE 2. Measurements (in μm) of some structures, and values of the pt index, of four measured specimens of Macrobiotus modestus sp. n. and two specimens each (one of which is a paratype) of Macrobiotus madegassus and of Macrobiotus humilis.

M. modestus sp. n. Body length 180 180*?	?	M. madegassus 340 370	M. humilis 310 360
Buccal tube length 27.7 28.4 29.2 Buccal tube external width 1.9 2.1 2.3	32.2 2.4	31.7 34.8 3.3 4.1	32.1 34.6 3.6 4.1
pt 7.9 7.4 7.9	7.5	10.4 11.8	11.3 11.8
Stylet supports pt 67.3 69.8 68.8 Placoid row 10.3 10.5 11.0	69.7 12.4	70.6 71.3 14.5 16.8	71.1 71.3 13.8 17.2
pt 37.2 37.0 37.7	38.5	45.7 48.3	43.0 49.7
Macroplacoid row 8.8 8.9 9.7 pt 31.8 31.3 33.2	10.6 32.9	12.3 14.6 38.8 42.0	11.4 14.0 35.5 40.5
First macroplacoid 5.1 4.9 6.0	6.6	7.8 8.9	7.1 8.1
pt 18.4 17.3 20.5 Second macroplacoid 3.7 3.6 3.8	20.5 4.1	24.6 25.6 4.0 5.0	22.1 23.4 4.0 5.0
pt 13.4 12.7 13.0	12.7	12.6 14.4	12.5 14.4
Microplacoid 1.5 1.5 1.5 pt 5.4 5.3 5.1	1.4 4.4	2.1 1.8 6.6 5.2	2.4 2.5 7.5 7.2
Internal claws II,III? 7.6 7.8	8.6	? 9.6	??
pt? 26.8 26.7 External claws II, III???	26.7 9.2	? 27.6 9.6 10.2	?? 9.2 9.5
pt???	28.6	30.3 29.3	28.7 27.5
Anterior claws IV??? pt???	??	? 10.9? 31.3	????
Posterior claws IV? 9.7 9.5	?	10.9 11.1	10.7 11.4
pt? 34.2 32.5	?	34.4 31.9	33.3 32.9
* Holotype.