TANARCTIDAE Renaud-Mornant, 1980

Fontoura, Paulo, Bartels, Paul J., Jørgensen, Aslak, Kristensen, Reinhardt Møbjerg & Hansen, Jesper Guldberg, 2017, A dichotomous key to the genera of the Marine Heterotardigrades (Tardigrada), Zootaxa 4294 (1), pp. 1-45 : 37-38

1.9 TANARCTIDAE Renaud-Mornant, 1980 (emended by Fujimoto et al. 2016)

Considered as subfamily Tanarctinae assigned to the family Halechiniscidae by Renaud-Mornant (1980). Elevated to family level by Fujimoto et al. (2016).

Arthrotardigrada without sclerotized cuticular plates. Cephalic appendages usually consist of unpaired median cirrus, three pairs of cirri, pair of long primary clavae and pair of secondary clavae, which may be indistinguishable. Sensory organs on leg IV long and often bifurcated. Legs long and telescopic, each with lancelike tibia and conical tarsus. Adults with four clawed digits. Internal digits inserted on pretarsi and longer than external digits. Claws with strong calcar. Placoids with subterminal bulbous branch. Rosette-like female gonopore and spindle-shaped seminal receptacles.

1.9.1 Actinarctus Schulz, 1935 (following Boesgaard & Kristensen 2001; Figs 6 D, 11D)

Tanarctidae with epicuticular alae (wings) internally supported by long pillars, increasing in length from body center to periphery. Body with an external thin gelatinous membrane, in which are immersed dorsal and lateral tubular processes (modified pillars). Digits with simple external claws without spurs, internal claws with spurs46.

44. In the terminology of this key internal claws have one primary point and two secondary points while external claws have one primary point and one secondary point.

45. In the terminology of this key “main hook” = primary point, “basal accessory hook” = secondary point, “terminal accessory spur” = accessory point.

All claws with strong calcar. Very thin peduncles may be present on all toes. Internal buccal cirri long and connected at base by membrane from epicuticle; median cirrus always present. Primary clavae long, buccal clavae club-shaped or flat H-shaped structure surrounding the mouth cone47.

Type species: Actinarctus doryphorus Schulz, 1935

1.9.2 Tanarctus Renaud-Debyser, 1959 (emended by Lindgren 1971, Renaud-Mornant 1975b and following Jørgensen & Kristensen 2001; Figs. 6 E, 11D)

Tanarctidae without long rod-shaped dorso-lateral pillars in the epicuticle. The four digits with simple external claws without dorsal spurs25, internal claws with microscopic spurs or without spurs46. The internal digits may be fused proximally and form a pretarsus. The external digits have a basal cuticular fold. The primary clava, when present, is very long and similar to the leg IV appendages, or the leg IV appendages are strongly modified with long spines, leaf-like appendages or balloon-like ampullae. Buccal clavae may consist of fused secondary and tertiary clavae and then appear H-shaped around the mouth, or they can be located rostrally as club-shaped clavae (secondary clavae?). The buccal clavae may be absent or indistinct as a dome or lens-shaped structure.

Type species: Tanarctus tauricus Renaud-Debyser, 1959

Selected literature for further information: See Fujimoto et al. (2013) for a key to this genus. One additional species has been described since this key (see Jørgensen et al. 2014).

1.9.3 Zioella Renaud-Mornant, 1987 (translated from French; Figs. 6 F, 11D)

Tanarctidae with the cephalic cirri aligned on the frontal margin of the head. Secondary clavae reduced to a thin outline in front of the mouth opening. Epicuticle smooth, pillars not observable by light microscopy. Sense organs on legs IV strongly modified originating, after two dichotomies, eight very long membranous leaf-like appendages. Each dichotomy is displayed at the same level.

Type species: Zioella pavonina Renaud-Mornant, 1987

Selected literature for further information: Renaud-Mornant (1987a).

Figures

FIGURE 6. Habitus drawings of marine heterotardigrades. A Florarctus, redrawn from Renaud-Mornant (1989 a). B Ligiarctus, redrawn from Renaud-Mornant (1982 b). C Wingstrandarctus, redrawn from Kristensen (1984). D Actinarctus, redrawn from Renaud-Mornant (1979 a). E Tanarctus, redrawn from Renaud-Mornant (1975 b). F Zioella, redrawn from Renaud-Mornant (1987 a).