Macrobiotus insularis, Pilato, Giovanni, 2006

Pilato, Giovanni, 2006, Remarks on the Macrobiotus polyopus group, with the description of two new species (Eutardigrada, Macrobiotidae), Zootaxa 1298, pp. 37-47 : 40-43

Macrobiotus insularis sp. n. ( Fig. 2 A–D)

Type locality. The Andaman Islands, Cinque Island.

Material examined. Holotype (slide no. 3414), one paratype and two eggs.

Species diagnosis. Cuticle smooth with circular and elliptical pores; eye spots present; buccal armature with an almost invisible posterior band of teeth and three dorsal and three ventral transversal ridges; pharyngeal bulb with apophyses, two macroplacoids and a small microplacoid; claws of hufelandi type, short, with a common tract slightly longer than the secondary branch; main branch with accessory points; smooth lunules present, eggs freely laid with conical processes (13–14 around the circumference, about 35 in the hemisphere) with slightly visible annulations; egg shell dotted and with a reticular design with hexagonal meshes.

Description of the holotype. Body length 280 µm, colourless, eye spots present, cuticle smooth and, diversely from the statement of Maucci & Durante Pasa (1980), with circular and elliptic pores present on both dorsal and ventral body surface and on the legs; circular pores diameter up 0.9 µm, elliptical pores dimensions up to 1.8 µm x 1.2 µm. Dots on the legs seem to be absent. Mouth terminal with ten peribuccal lamellae; an almost invisible band of very small teeth is present in the posterior portion of the buccal cavity where also three dorsal and three ventral thin transversal ridges are present. Buccal tube 38.8 µm long ( Fig. 2 A) and 5.2 µm wide (pt = 13.4); ventral lamina longer than double the length of the stylet sheaths (24.0 µm, pt = 61.9). Stylet supports inserted on the buccal tube wall at 73.4 % of its length (pt = 73.4). Pharyngeal bulb ( Fig. 2 A) with apophyses, two rod­shaped macroplacoids and a small microplacoid. First macroplacoid, with a central narrowing, 8.1µm long (pt = 20.9), second 5.3 µm (pt = 13.7), microplacoid 1.8 µm (pt = 4.6); entire placoid row 16.3µm long (pt = 42.0), macroplacoid row 14.3 µm (pt = 38.9).

Claws, of hufelandi type, short but not weak ( Fig. 2 A, B), with the common tract slightly longer than the secondary branch; internal and external claws of the second and third pairs of legs 8.7 µm (pt = 22.4) and 9.1µm (pt = 23.4) long respectively; anterior and posterior claws of the hind legs 9.7 µm (pt = 25.0) and 10.9 µm (pt = 28.1) long respectively. Main branches with accessory point not particularly small; small, complete, smooth lunules present. Two cuticular thickenings are present near the lunules on the first three pairs of legs ( Fig. 2 A,B).

The paratypes is similar to the holotype both in qualitative and metric characters.

Eggs, freely laid, spherical, with conical processes ( Fig. 2 C, D). Diameter 78.7 µm excluding the processes, 94.0 µm including these structures; 13–14 processes are present around the circumference, 35 in the hemisphere. Processes conical with slightly visible annulations, 7.3–8.8 µm high; basal diameter 10.9–13.2 µm; egg shell dotted and with stripes joined to form hexagonal polygons round the processes ( Fig. 2 D).

Etymology. The name insularis refers to the fact that the type locality is an archipelago.

Remarks. Macrobiotus insularis sp. n. differs from M. mandalaae in the following features: cuticular dots on the legs not visible (in M. mandalaae they are present on the legs IV); slightly wider buccal tube ( Table 1 ); longer buccal tube ( Table 1 ) (due to this character, some structures, e.g. placoids and claws that are slightly longer, have slightly lower values of the pt index); and in many characters of the eggs ( Fig. 2 C, D and 1D–F; Table 2): markedly larger dimensions; larger processes; processes less numerous (13–14 around the circumference and 35 in the hemisphere in M. insularis sp. n., 24–26 around the circumference and 70–75 in the hemisphere of M. mandalaae ); basal diameter longer than the height of egg processes in M. insularis , about the same length in M. mandalaae ; egg shell with well visible dots.

polyopus mandalaae insularis ocotensis

Diameter without processes? 45.0 78.7 63.0

Diameter with processes 65.0 55.0 94.0 79.9

Processes around the circumference 18 * 24–26 13–14 25

Processes in the hemisphere 39 * 70–75 35 100

Processes height? 3.4–4.7 7.3–8.8 4.7–6.0

Basal diameter of the processes? 3.2–4.5 10.9–13.2 4.9–6.0

Meshes of the egg shell? smooth dotted smooth

*from the drawing of Marcus (1928).

The presence of cuticular pores in M. mandalaae , neglected in the description of the species ( Pilato, 1974), was pointed out in a following paper ( Pilato, 1984); they are circular and elliptical, present on both dorsal and ventral body surface and on the legs; circular pores diameter up to 1.0 µm, elliptical pores dimensions up to 1.7 m x 0.9 µm.

The new species differs from M. polyopus in the following features: ventral lamina longer; microplacoid present; claws not so weak, with a common portion longer than the secondary branch; and some characters of the eggs ( Table 2): larger diameter (94 µm including processes in M. insularis sp. n., 65 µm in M. polyopus ); processes without longitudinal ribs, with slightly visible annulations; egg shell dotted ( Marcus, 1928, did not specify whether dots are present or not in M. polyopus ; in the drawing they are absent).

Macrobiotus insularis sp. n. is reported only from the Andaman Islands.

Figures

FIGURE 2. Macrobiotus insularis sp. n. A, bucco­pharyngeal apparatus (holotype). B, claws of the second and third pairs of legs (holotype). C, egg. D, detail of the egg. Scale bar = 10 µm.

Tables

TABLE 1. Dimensions (in µm) and pt (in %) of some structures of specimens of M. mandalaae, M. insularis sp. n. and M. ocotensis sp. n. of similar body length.

M. mandalaae	M. insularis sp. n.	M. ocotensis sp.n.
dimensions pt	dimensions pt	dimensions pt
Body length 310	280	261
Buccal tube length 30.7	38.8	29.3
Buccal tube width 3.8 12.4	5.2 13.4	3.1 10.6
Stylet supports 71.1	73.4	72.4
Ventral lamina 18.7 60.9	24.0 61.9	17.7 60.4
Placoid row 13.9 45.3	16.3 42.0	11.5 39.2
Macroplacoid row 12.1 39.4	14.3 38.9	10.7 36.5
First macroplacoid 7.3 23.8	8.1 20.9	5.5 18.8
Second macroplacoid 4.4 14.3	5.3 13.7	4.4 15.0
Microplacoid 1.3 4.2	1.8 4.6	1.2 4.1
External claws II,III 9.1 29.6	9.1 23.4	7.7 26.3
Internal claws II,III 8.9 29.0	8.7 22.4	7.4 25.3
Anterior claws IV 10.3 33.6	9.7 25.0	7.9 27.0
Posterior claws IV 10.4 33.9	10.9 28.1	8.5 29.0