Minibiotus sidereus, Pilato, Giovanni, Binda, Maria Grazia & Lisi, Oscar, 2003

Pilato, Giovanni, Binda, Maria Grazia & Lisi, Oscar, 2003, Remarks on some species of tardigrades from South America with the description of Minibiotus sidereus n. sp., Zootaxa 195, pp. 1-8: 2-7

publication ID 10.5281/zenodo.156839

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Minibiotus sidereus

sp. n.

Minibiotus sidereus   sp. n.

Material examined: Ecuador: Papallacta Pass: holotype (slide N. 4925), 27 paratypes and 6 eggs, 1 of which with fully developed embryo, in a moss sample ( Leptodontium viticulosoides   ); Cosanga (1 specimen in a moss sample: Entodon abbreviatus   ).

Description of the holotype. Body length 249 m, colorless, eyes present. Cuticle with pearls of three types also on the ventral body surface: small circular (diameter 0.7 m ­ 1.2 m), slightly larger elliptical and larger star­shaped pearls (fig. 1 A, B). Circular and elliptical pearls uniformly distributed also in the intersegmental folds; the star­shaped pearls are less numerous, scattered, with 3­8 arms (those with 4­5 arms are more numerous); they are absent on the intersegmental folds and therefore they form transversal bands. The largest star­shaped pearls are visible on the head and on the legs; a very large star­shaped pearl, with many arms, present on each leg of the fourth pair; this large star­shaped pearl on the hind legs is present in all specimens and it has to be considered as a specific character. Diameter of the largest star­shaped pearls up to 3.3 m (in a paratype up to 3.9 m). Besides the pearls, very fine granulation is present on the extremities of the hind legs.

Bucco­pharyngeal apparatus of Minibiotus   type (fig. 2 A, B): rigid buccal tube with ventral lamina, mouth without peribuccal lamellae but with peribuccal papulae. Buccal tube 26.4 m long and 1.7 m wide (pt = 6.4) with two bends. Lateral walls of the buccal tube thickened caudally to the stylet supports; this thickening rises and decreases gradually and it is more evident when examined on dorsal or ventral view (fig. 2 B).

Buccal armature very simple: only two very thin dorso­lateral and two ventro­lateral transversal ridges are present.

Stylet supports inserted on the buccal tube at 58.9 % of its length.

Oval pharyngeal bulb, 21.2 m x 18.2 m, with large apophyses partially overlapping the first macroplacoid, three short macroplacoids and a small, granular, microplacoid; first macroplacoid 3.1 m long (pt = 11.7), second 2.4 m (pt = 9.1), third 2.6 m (pt = 9.8); microplacoid 1.3 m long (pt = 4.9); placoid row length 9.6 m (pt = 36.4) including the microplacoid, 7.9 m (pt = 29.9) excluding it.

Claws, of hufelandi type (fig. 1 A, 2 C,D), well developed in relation to the small body size, with large accessory points on the main branches. The unfavorable orientation does not allow the measurement of the length of all the claws. The internal and external claws of the third pair of legs are 8.0 m (pt = 30.3) and 8.1 m (pt = 30.7) long respectively.

Small, smooth lunules present on all legs. A narrow cuticular bar, difficult to see, present near the lunulae on the first three pairs of legs (fig. 1 A).

Eggs, free laid, spherical (fig. 2 E) with many conical processes (about 30 in the optical section). Diameter of the eggs 62­69 m excluding the processes, 73­83.5 m including them; the processes, up to 9.5 m high, are conical, sharpened, with a flexible terminal portion rarely bifurcate; the basal diameter is up to 5.3 m in the largest eggs; few very small processes are also present among the larger ones. Egg processes smooth but with 6­7 annulations; egg shell, among the processes, smooth.

The paratypes are similar to the holotype (in the population we found 58.6 and 61.6 as minimum and maximum value of the pt index relative to the insertion point of the stylet supports). In table 1 the length of some structures of the smallest and of the largest measured specimens are indicated.

Etymology: sidereus   = sidereal; the name refers to the aspect of the cuticular sculpture similar to a starry sky.

Remarks: Minibiotus sidereus   differs from the other species of the genus in the aspect of the cuticular pearls, in characters of the eggs and, in some cases, also in other characters. We compared the new species with those of the genus also having star­shaped pearls: Minibiotus furcatus ( Ehrenberg 1859)   , M. aculeatus (Murray 1910)   , M. stuckenbergi Dastych et al., 1990   , M. vinciguerrae Binda and Pilato 1992   , M. asteris Claxton 1998   , M. ethelae Claxton 1998   ; none of these species has pearls with more than 4 arms, while M. sidereus   has some pearls with up 6, 7 or 8 arms; moreover, the characters of the eggs are clearly different (no of these species has egg processes with annulations) and the stylet supports are inserted on the buccal tube in a more cephalic position (pt = 58.6­61.6 in M. sidereus   , about 64 in M. aculeatus   and M. asteris   , about 65 in M. ethelae   (according to Claxton 1998), about 68.5 in M. furcatus   (according to Binda & Pilato 1992), 66­69 in M.

vinciguerrae   ). Besides, M. sidereus   differs from M. aculeatus   also by lacking conical spines, from M. stuckenbergi   by having cuticular dots only on the hind legs, different buccal armature, and lunules on the hind legs with a smooth margin. It also differs from M. vinciguerrae   by having shorter and less slender claws and narrower buccal tube; from M. ethelae   also by having the caudal cuticle not particularly thickened; from M. furcatus   also by having a narrower buccal tube and fine dots on the hind legs.

Fractonotus caelatus ( Marcus, 1928)  

Material examnined: Ecuador: Loreto (5 specimens in an undetermined moss sample).

Fractonotus caelatus ( Marcus, 1928)   has been described as a subspecies of Calohypsibius ornatus (Richters 1900)   . Pilato, Claxton and Binda (1989) considered it as a bona species named Calohypsibius caelatus ( Marcus, 1928)   ; later Pilato (1998) stated that it has claws of Microhypsibius   type and transferred it to the family Microhypsibiidae Pilato 1998   , and erected for it the new genus Fractonotus   . In that genus the dorsal apophysis for the insertion of the stylet muscles splits into two portions: an anterior ridge and a posterior, longitudinal thickening. In one specimen from Ecuador these two portions seemed to be joined to one another by a very thin lamina. This should be confirmed by studying other specimens.

The species has been found in some European and Australian localities but it is new for South America.

Hypsibius allisoni Horning, Schuster & Grigarick, 1978  

Material examined: Ecuador: Pichincha (6 specimens in a soil sample). The species, described from New Zealand, has also been reported from Patagonia by Maucci (1988).

Diphascon pingue ( Marcus, 1936)  

Material examined: Ecuador: Alto Tambo: (1 specimen in a liverwort sample: Plagiochila punctata   ).

The characters of the specimen correspond to those attributed to the species by Pilato & Binda (1977, 1997/ 1998). A very wide geographical distribution is attributed to the species but many reports must be confirmed.

Milnesium tardigradum Doyère, 1840  














Minibiotus sidereus

Pilato, Giovanni, Binda, Maria Grazia & Lisi, Oscar 2003


Pilato 1998

Hypsibius allisoni

Horning, Schuster & Grigarick 1978

Diphascon pingue (

Marcus 1936

Fractonotus caelatus (

Marcus 1928

Fractonotus caelatus (

Marcus 1928

Calohypsibius caelatus (

Marcus 1928

Calohypsibius ornatus

Richters 1900

Milnesium tardigradum Doyère, 1840

Doyere 1840