Isohypsibius improvisus Dastych 1984

“Isohypsibius improvisus sp. nov. (fig. 18, phot. 31)

Length 360-520 μm. The body is white of white-green, most specimens with lumps of brownish pigment. The eyes are large or very large (their diameter up to 10 μm). The cuticle is relatively thick and covered with numberous small “cavities”, up to several dozen per individual (fig. 18c), which are sparsely and irregularly distributed and most often poorly visible. Their shape is a little similar to cavities found in Macrobiotus pustulatus RAMAZZOTTI, 1959 (comp. l.c., 1972). The “cavities” are usually oval, 2-7 μm in size (mostly 4-5 μm) and occurred on the whole body though on the ventral side they are less numerous. In the area between the “cavities” the cuticle is smooth. Mouth opening situated ventrally. Buccal cavity short (fig. 18b); its anterior part with well visible roundish thickenings (lamellae?), occurring however in a few speciments only. Buccal tube bent towards the ventral side, its outer diameter is 5 μm, inner one 3 μm (-dimension in a specimen 480 μm long), its length is 54 μm. There are large apophyses. Pharynx usually spherical (39 X 38 μm), sometimes short-oval (fig. 18b, d), with two macroplacoids. No microplacoid. Macroplacoids are roundish, short and wide; the first one strongly constricted in the middle (fig. 18b, d, phot. 31), the second one with delicate incision on the outer side of its posterior part (immersion—fig. 18b, d). The first macroplacoid is 6 μm long, second one 4.5 μm; their width is 2.5 μm. Claws are relatively large (fig. 18e-g, phot. 31), their branches are strongly bent and have small accessory spines. The bases of main branches with large, bubble-like thickening which refracts light in a different way than the rest of claw. All claws bases with lunules which are most strongly turned up and poorly visible (fig. 18e, g). The lunules of outer claws are bigger than inner ones. Claws of I-IIIrd pair with the smooth lunules; on the IVth pair there are either curled or with a few distinct teeth. The legs of I-IIIrd pair without cuticular thickenings (bars) at the bases of inner claws. On the fourth pair the claws are 36 μm long.

The eggs are oval, chorion is smooth and they are layed into exuvium, 2-8 eggs in each one. A few eggs with well developed embryos showing distinct buccal apparatus and claws. Dimension of eggs 105-80 μm XX 78-60 μm.

Isohypsibius improvisus sp. nov. is most similar to I. marcellinoi BINDA and PILATO, 1971. However, the new species distinctly differs by the lack of cuticular bars at the inner claws of I-IIIrd pair of legs, by the occurrence of “cavities” in cuticle, comparatively shorter placoids, longer claws and greater dimensions of the body.

Localities: Enderby Land- 2(3, including holotype), 3(46); King George Island-6(1).

Type repositories. Holotype and 29 paratypes in the collection of DAM, 13 paratypes in NMNH, 6 paratypes in BAS, 1 paratype in NMNZ.”

(Dastych, 1984: 406-407)

Dastychius improvisus, unique représentant du genre Dastychius, est une espèce de tardigrades de la famille des Isohypsibiidae.