MACROBIOTIDAE Thulin, 1928

Pilato, Giovanni & Binda, Maria Grazia, 2010, Definition of families, subfamilies, genera and subgenera of the Eutardigrada, and keys to their identification, Zootaxa 2404, pp. 1-54 : 36-37

MACROBIOTIDAE Thulin, 1928

Eutardigrades without cephalic papillae. Epicuticular layer compact, without pillar-like structures. The two diploclaws on each leg, similar in shape and size to one another, are symmetrically arranged with respect to the median plane of the leg (conventionally described as: 2112) ( Fig. 1 F). The diploclaws have the two branches fused into a basal section of variable length (diploclaws Y-shaped). In all the known genera the buccal tube is asymmetrical with respect to the frontal plane due to the presence of a ventral lamina ( Fig 2 ). The anterior portion of the ventral lamina has two caudal processes pointing backwards and sideways. Peribuccal lobes are present at least in some genera. Other peribuccal structures (ten lamellae or ten papulae or a velum) present with the sagittal plane passing through the medio-dorsal and the medio-ventral peribuccal structures ( Fig. 2 ).

Types of claws. Various types of claws can be recognized within the family.

1) The Calcarobiotus type ( Fig. 20 A)

The basal section of each diploclaw, with or without basal spurs, is subdivided into a thin flexible stem and a wide distal section in the shape of an upside-down triangle distally delimited by a septum. Primary and secondary branches are similar in shape and size.

2) The Macrobiotus type (= hufelandi type) ( Fig. 1 F, 20C)

The basal section of each diploclaw, without basal spurs in the known species, is subdivided into a thin flexible stem and a distal section poorly sclerified and distally delimited by a septum ( Bertolani & Pilato, 1988; Guidetti et al., 2000); the primary and the secondary branches are rigidly joined to each other for a variable but long common tract and form an acute angle (Y-shaped claws).

In some species (tenuis group) the common portion is very long. In the genus Insuetifurca the basal portion is subdivided into a very short stem and a wide distal portion ( Fig. 20 D).

3) The Xerobiotus type ( Fig. 20 E,F)

The whole diploclaw is equally sclerified; the basal section is not subdivided into a basal stem and a distinct distal portion ( Bertolani & Biserov, 1996) and there are no separating septa. The primary and secondary branches are rigidly joined to each other and form an acute angle (Y-shaped claws).

Figures

FIGURE 1. Some types of claws of the Eutardigrada. A, Milnesiidae; B, Hexapodibius (Calohypsibiidae); C, Microhypsibiidae; D, Eohypsibiidae; E, Hypsibiu s (Hypsibiidae); F, Macrobiotus (Macrobiotidae). ap = accessory points; bs = basal section; bth = basal thickening; ds = distal section; lu = lunula; pb = primary brach; s = stem; sb = secondary branch; sp = spur. (B, from Binda & Pilato, 1969; C, from Pilato, 1998).

FIGURE 2. Scheme of bucco-pharyngeal apparatus of Macrobiotus (Macrobiotidae). cp = caudal processes; pha = pharyngal apophyses; pl = peribuccal lamellae; pla = placoids; sp = sagittal plane; st = stylet; stf = stylet furcae; sts = stylet support; stsh = stylet sheaths; vl = ventral lamina.

FIGURE 20. Claws of Macrobiotidae. A, B: Calcarobiotus type (A, of Calcarobiotu s; B, of Schusterius); C, D, Macrobiotus (or hufelandi) type (C, of Macrobiotus; D, of Insuetifurca); E, Xerobiotus type (E, of Xerobiotus; F, of Biserovus). (B, from Kaczmarek & Michalczyk, 2006; C, from Binda & Rebecchi, 1992; E, from Binda & Pilato, 1971; F, from Guidetti & Pilato, 2003).