Mixibius parvus Lisi, Sabella & Pilato, 2014, sp. nov.
Creators: name: Lisi, Oscar
name: Sabella, Giorgio
name: Pilato, Giovanni
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Tardigrada
Eutardigrada
Parachela
Hypsibiidae
Mixibius
Mixibius parvus

description: Mixibius parvus sp. nov.
(Figs. 1, 2)
Type locality. Sicily, Madonie Mountains: neighbourhood of Gangi (37° 49′N, 14° 09′E; 1011 m a.s.l.).
Material examined. Madonie Mountains: neighbourhood of Gangi: holotype (slide No. 5536) and one paratype (slide No. 5537) from a moss sample collected by Pilato, August 2002.
Type repository. Holotype and paratype are deposited in the collection of Binda & Pilato, Museum of the Department of Animal Biology “Marcello La Greca”, University of Catania, Italy.
Specific diagnosis. Colourless; cuticle slightly wrinkled; eye spots present; bucco-pharyngeal apparatus of Mixibius type: buccal tube rigid, without ventral lamina; apophyses for the insertion of the stylet muscles in shape of hooks slightly asymmetrical with respect to the frontal plane, and a longitudinal thickening present caudally to both those apophyses; pharyngeal bulb with three macroplacoids and a microplacoid. External claws of the Isohypsibius type, internal claws of modified Isohypsibius type; accessory points present on main branches; small lunules present; no cuticular bar present on the legs.
Description of the holotype. Body length 180 µm; colourless, eye spots present; cuticle slightly wrinkled (Fig. 1A). Bucco-pharyngeal apparatus of Mixibiu s type (Fig 1C, D), i.e. with rigid buccal tube, without ventral lamina and with dorsal and ventral apophyses for the insertion of the stylet muscles in the shape of hooks slightly asymmetrical with the respect to the frontal plane; a longitudinal thickening present caudally to both apophyses (Fig. 1C, D, arrows) (N.B. Fig. 1 views B, C and D are of the same specimen in different orientations as this newly mounted animal was moved to provide the appropriate images). Mouth without peribuccal lamellae or teeth. Buccal tube, measured from the anterior margin of the stylet sheaths to the base of the pharyngeal apophyses, 18.2 µm long and external width 2.2 µm (pt = 12.1); stylet supports inserted on the buccal tube at 65 % of its length (pt = 65.0). Pharyngeal bulb (14.2 µm x 10.4 µm) with very large apophyses (Fig. 1B, arrow), three macroplacoids and a small microplacoid (Fig. 1B). First macroplacoid 2.1 µm long (pt = 11.5), second 2.0 µm (pt = 11.0), third 2.2 µm (pt = 12.1), microplacoid 1 µm long (pt = 5.5); entire placoid row length 7.6 µm (pt = 41.7), macroplacoid row length 6.6 µm (pt = 36.3).
External claws of the Isohypsibius type (Fig. 2A, B), internal claws of a modified Isohypsibius type (Fig. 2A, B, C), which is a characteristic of the genus. Leg II, external claws 9.8 µm long (pt = 53.8), internal claws 6.5 µm long (pt = 35.7); leg IV anterior claws 6.6 µm long (pt = 36.3), posterior claws 10.6 µm long (pt = 58.2).
Small accessory points on main branches (Fig. 2C, arrow); small lunules present on all pairs of legs (Fig. 2D, arrow); no other cuticular thickening present on the legs.
Eggs not found.
Remarks. The paratype is in simplex stage but the characters of the cuticle and claws show that it belongs to the same species as the holotype.
Etymology. The name parvus refers to the small body size (parvus = small).
Differential diagnosis. Excluding Mixibius tibetanus Li & Li, 2008, all the other known species of the genus Mixibius (M. saracenus, M. fueginus,, M. ninguidus Biserov, 1999, M. ornatus, M. sutirae, M. schnurae and M. pilatoi Wang, 2009) have only two macroplacoids and lack the microplacoid. Mixibius parvus sp. nov. also differs from M. saracenus in having a wrinkled cuticle and by the presence of eye spots and lunules; from M. fueginus in having a wrinkled cuticle and by the presence of lunules; from M. ninguidus by the presence of lunules, from M. ornatus and M. sutirae and M. pilatoi in having a wrinkled cuticle without true small tubercles, stylet supports inserted on the buccal tube in a more cephalic position (pt = 65 in M. parvus sp. nov., 69–70.5 in M. ornatus, about 71 in M. sutirae, 67.9 or more in M. pilatoi). The new species also differs from M. schnurae in the type of the cuticular ornamentation and in having a greater difference in length between the external and internal claws of each leg.
As mentioned above, M. tibetanus is the only other known species of Mixibius with three macroplacoids and a microplacoid; the new species differs in having a wrinkled cuticle without true small tubercles, a shorter microplacoid, lower claw pt index values (Table 1), and in lacking a cuticular bar on the first three pairs of the legs. It is possible to hypothesize that in the past, before the description of the genus Mixibius (Pilato, 1992—using the distinctive claw shape character), species would have been ascribed to the genus Isohypsibius. To avoid misunderstandings we compared Mixibius parvus sp. nov. with Isohypsibius species possessing three macroplacoids and a microplacoid. We ascertained that in all cases the new species differs by having a different cuticular ornamentation, or by lacking a cuticular thickening on the first three pairs of legs. Based on these differences, we find it superfluous to indicate additional metric character differences.
description: Published as part of Lisi, Oscar, Sabella, Giorgio & Pilato, Giovanni, 2014, Mixibius parvus sp. nov. and Diphascon (Diphascon) ziliense sp. nov., two new species of Eutardigrada from Sicily, pp. 459-468 in Zootaxa 3802 (4) on pages 460-461, DOI: 10.11646/zootaxa.3802.4.3, http://zenodo.org/record/226826