Anisonychidae MOBJERG, JORGENSEN & KRISTENSEN 2020, FAM. NOV.

FAMILY ANISONYCHIDAE MØBJERG, JØRGENSEN & KRISTENSEN FAM. NOV.

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Diagnosis: Unplated, interstitial, marine heterotardigrades. Four claws inserteddirectly on eachof the first three leg pairs, and three claws inserted directly on the fourth pair of legs (in adults). Paired basal hooks on all claws, with the two hooks oriented at right angles to one another. Median cephalic cirrus is always present, butcan bereduced. Cephalicappendagesincludeinternal and external cirri, lateral cirri (cirri A) and generally also primary clava and flat, often indistinct, secondary clava. Cirri Eis always present. Papillae on leg IV are often present, and sensory structures on legs I–III may also be present (presently seen in only one species, Anisonyches mauritianus Grimaldi de Zio, D’Addabbo Gallo, Morone De Lucia & D’Addabbo, 1987). Black eyes are present. Stylets are long, with stylet sheaths; stylet supports are lacking. The three placoids are CaCO 3 incrusted. Paired seminal receptacles are present in females. The coiled receptacles open relatively distant from the six-lobed female gonopore. The anal system consists of two lateral lobes connected by a median zig-zag structure, with the anus formed by a small terminal pore.

Type genus: Anisonyches Pollock, 1975.

Generic diagnosis (amended): The same diagnosis as for the family.

Type species: Anisonyches diakidius Pollock, 1975.

Other species in the genus: Anisonyches mauritianus Grimaldi de Zio, D’Addabbo Gallo, Morone De Lucia & D’Addabbo, 1987; Anisonyches deliquus Chang & Rho, 1998; and Anisonyches eleutherensis Bartels, Fontoura & Nelson, 2018.

Discussion: For the present study, we have examined three specimens of the type species, A. diakidius (Fig. 1A–E). These specimens (ZMUC-TAR 1200– 1202) were collected by J. Renaud-Mornant in 1979 from Guadeloupe (French Antilles) and sent to our museum along with a drawing of one of the specimens (Fig. 1F). Furthermore, we have examined a specimen of A. eleutherensis from the Bahamas, present in our collection(ZMUC-TAR1204),withadistinct Anisonyches claw configuration as described by Bartels et al. (2018). From our recent investigations, and that of colleagues (Bartels et al., 2018), it is apparent that Anisonyches, with its seminal receptacles (Fig. 1B), median cirrus (Fig. 1C) and unique claw configuration (Fig. 1D), does not belong among the echiniscoidids. Consequently, based on the presence of a median cephalic cirrus and seminal receptacles, we place Anisonyches in its own family, Anisonychidae, in the order Arthrotardigrada, but at the same time strongly emphasize that Arthrotardigrada is paraphyletic and thus in need of taxonomic revision. We note that the claw configuration of Anisonyches bears some resemblance to the limnic Carphanidae Binda & Kristensen, 1986 currently retained in Echiniscoidea. Within Echiniscoidea, the family Oreellidae has retained seminal receptacles as in Anisonyches, but the claw configuration in Oreella is different from Anisonyches and Carphania with regard to the position of the basal hooks, putative indications of toes and four claws on all legs (Binda & Kristensen, 1986). Here, we emphasize the fact that both caphanids and oreellids lack a median cirrus. Grimaldi de Zio et al. (1987) suggested that Anisonyches is more closely related to the arthrotardigrade taxa Coronarctidae or Stygarctidae thanto Echiniscoididae. Wenote that claws inserted directly on the leg is a characteristic of both Coronarctidae and Stygarctidae, clearly underlining the need for thorough future investigations into limnic and marine heterotardigrades.