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

Pilato, Giovanni & Lisi, Oscar, 2009, Tardigrades of the Seychelles Islands, with the description of three new species, Zootaxa 2124, pp. 1-20 : 13-18

Macrobiotus diguensis sp. n.

Fig. 6

Material examined: La Digue, Belle Vue, holotype (slide No. 5180), 2 paratypes and 7 eggs, with fully developed embryo, in a moss sample.

Type repository: Holotype and paratypes are deposited in the collection of Binda and Pilato (Museum of the Department of Animal Biology, University of Catania).

Specific diagnosis: Cuticle smooth; eye spots absent; mouth terminal with ten peribucal lamellae, a posterior ring of triangular teeth and three dorsal and three ventral transversal ridges; an anterior band of small teeth not visible. Stylet supports inserted on the buccal tube at about 75% of its length. Pharyngeal bulb with apophyses, three short macroplacoids and a large microplacoid. Claws of hufelandi type; accessory points and lunules present. Eggs laid freely with conical processes with reticular design and each one with 8-10 basal ridges radiating out over the egg surface. Egg shell not areolated.

Description of holotype: Body length about 153 µm; colorless; eye spots absent; cuticule smooth without pores and granulation. Bucco-pharyngeal apparatus of Macrobiotus type ( Fig. 6 A); mouth terminal with ten peribucal lamellae; an anterior band of small teeth is not visible in the paratypes but this may be a consequence of the small dimensions of the specimens; a posterior ring of triangular teeth and three dorsal and three ventral transversal ridges are present. Buccal tube 25.1 µm long and 3.9 µm wide externally (pt = 15.5). Stylet supports inserted on the buccal tube at 75.5% of its length (pt = 75.5).

Pharyngeal bulb (18.3 µm x 16.7 µm) with apophyses, three short macroplacoids and a large microplacoid ( Fig. 6 A). First macroplacoid 2.8 µm long (pt = 11.2), second 2.5 µm (pt = 10.0), third 2.8 µm (pt = 11.2), microplacoid 2.5µm (pt =10.0). Placoid row length including microplacoid 11.1 µm long (pt = 44.2); excluding microplacoid 8.6 µm (pt = 34.3).

Claws of hufelandi type ( Fig. 6 B) with accessory points on the main branches. Internal and external claws of the first pair of legs 5.4 µm (pt = 21.5) and 5.6 µm long (pt = 22.3) respectively; internal and external claws of the second and third pairs of legs 5.7 µm (pt = 22.7) and 6.1 µm long (pt = 24.3) respectively; anterior claws on the fourth pair of legs 5.9 µm (pt = 23.5), posterior claws of the same pair of legs 6.2 µm long (pt = 24.7). Smooth lunules present; a cuticular thickening is present below the lunules on the first three pairs of legs.

Macrobiotus diguensis sp. n.

smallest specimen largest specimen (holotype) Body length? 153 Buccal tube length 23.9 25.1 Buccal tube external width 3.6 3.9 pt 15.1 15.5 Stylet supports pt 74.4 75.5 Placoid row 10.0 11.1 pt 41.8 44.2 Macroplacoid row 7.9 8.6 pt 33.1 34.3 First macroplacoid 2.6 2.8 pt 10.9 11.2 Second macroplacoid 2.6 2.5 pt 10.9 10.0 Third macroplacoid 2.6 2.8 pt 10.9 11.2 Microplacoid 2.4 2.5 pt 10.0 10.0 Internal claws I? 5.4 pt? 21.5 External claws I? 5.6 pt? 22.3 Internal claws II, III? 5.7

? 22.7

External claws II, III? 6.1 pt? 24.3 Anterior claws IV 5.7 5.9 pt 23.8 23.5 Posterior claws IV 5.9 6.2 pt 24.7 24.7

Eggs laid freely, spherical, with conical processes (12–15 in the circumference, 32–38 in the hemisphere). Diameter 67–73 µm excluding the processes, 88–92 including these structures. The processes have 8–10 basal ridges which radiate out over the egg surface ( Fig. 6 C, D, arrows); the distal extremities of these ridges are enlarged and appear dark when examined under phase contrast. The ridges of adjoining processes are not connected, so the egg shell is not areolated. The surface of the processes, basal ridges included, have a reticular design with small, almost isodiametric, meshes. The processes are 9–11 µm height and have basal diameter (ridges excluded) of 13.4–16.2 µm.

Remarks: The paratypes are similar to the holotype in both qualitative and metric characters ( Table 8). Considering the dimensions of the eggs, and of the adults of similar species, the found specimens of M. diguensis sp. n., seem probably to be juveniles; for this reason in the comparisons ( Table 9 ), as well as the dimensions of adults, also the dimensions of juveniles of the similar species are provided.

M. diguensis sp. n. M. erminiae M. snaresensis

(juveniles) adults (juveniles) adults Etymology: The name diguensis refers the name of the isle, La Digue, where the species has been found. Differential diagnosis: Macrobiotus diguensis sp. n. is similar to Macrobiotus snaresensis and Macrobiotus erminiae , particularly in the characters of the eggs. It differs from M. snaresensis in having the stylet supports inserted on the buccal tube in a more cephalic position ( Table 9 ); shorter placoid row; claws more slender ( Figs. 6 B and 7A, B) and for some characters of the eggs: the processes are smaller and are gradually tapering cones while in M. snaresensis they have a large basal portion and a long and thin terminal portion ( Figs. 6 C, D and 7C).

M. diguensis sp. n. differs from M. erminiae in lacking eye spots; in having very slightly shorter placoids ( Table 9 ); claws more slender ( Figs. 6 B and 7D) and for some characters of the egg: the processes are smaller and more numerous ( Table 10 ), and have a reticular design also on the terminal portion which is usually Minibiotus continuus Pilato & Lisi, 2006 b

Material examined: Silhouette, La Passe, 14 specimens and 3 eggs in a sample of moss ( Calymperes nashii Williams ).

This is the second record of the species, for it was recorded only for southern Mexico; it is therefore new for the Seychelles and for the African fauna. In Table 11 the measurements of some structures of specimens of the Seychelles and of the holotype are indicated. In Table 12 some characters of the eggs from the same localities are compared.

Minibiotus continuus

Seychelles Southern Mexico

Figures

FIGURE 6. Macrobiotus diguensis sp. nov. A, bucco-pharyngeal apparatus (holotype); B, claws of the first three pairs of legs (holotype); C, D, details of the eggs, the arrows indicate the basal ridges which radiate out over the egg surface. Scale bar = 10 μm.

Tables

TABLE 9. Measurements (in μm) of some structures of Macrobiotus diguensis sp. n., M. erminiae and M. snaresensis.

Body length 153	190	555	270	488
Buccal tube length 25.1	29.4	66.5	37.9	63.4
Buccal tube external width 3.9	5.1	15.9	6.9	11.9
pt 15.5	17.6	23.9	18.2	18.8
Stylet supports pt 75.5	76.9	77.3	76.9	78.6
Placoid row 11.1	14.6	44.4	20.7	44.8
pt 44.2	49.7	66.8	54.6	70.6
Macroplacoid row 8.6	11.0	34.6	16.3	36.7
pt 34.3	37.4	52.0	43.0	57.8
First macroplacoid 2.8	3.6	11.7	?	11.6
pt 11.1	12.2	17.6	?	18.3
Second macroplacoid 2.5	3.2	9.4	?	8.0
pt 10.0	10.9	14.1	?	12.6
Third macroplacoid 2.8	3.6	10.2	?	10.1
pt 11.1	12.2	15.3	?	15.9
Microplacoid 2.5	3.2	8.1	4.2	7.3
pt 10.0	10.9	12.2	10.7	11.5
Internal claws I 5.4	?	14.5	?	?
pt 21.5	?	21.8	?	?
External claws I 5.6	?	15.6	9.2	14.5
pt 22.3	?	23.4	23.6	22.9
Internal claws II, III 5.7	?	15.0	10.0	?
pt 22.7	?	22.6	26.4	?
External claws II, III 5.9	7.6	17.6	10.3	15.1
pt 23.5	25.9	26.5	27.2	23.8
Anterior claws IV 5.9	?	?	?	?
pt 23.5	?	?	?	?
Posterior claws IV 6.0	?	20.1	9.8	18.2
pt 23.9	?	30.4	25.9	28.7

TABLE 10. Measurements (in µm) of selected morphological structures, and number of processes, of eggs of Macrobiotus diguensis s p. n. and Macrobiotus erminiae.

	M. diguensis sp. n.	M. erminiae
Diameter of egg without processes Diameter of egg with processes	67–73 88–92	52–94 100–116
Processes on the circumference	12–15	8–9
Processes on the hemisphere Processes height	32–38 9–11	18–20 12–24
Basal diameter of processes	13.4–16.2	16–21