Anisonyches diakidius Pollock, 1975

Bartels, Paul J., Fontoura, Paulo & Nelson, Diane R., 2018, Marine tardigrades of the Bahamas with the description of two new species and updated keys to the species of Anisonyches and Archechiniscus, Zootaxa 4420 (1), pp. 43-70: 58-60

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Anisonyches diakidius Pollock, 1975


Anisonyches diakidius Pollock, 1975  .

Table 3, Figure 8 View Figure

Material examined: Holotype from the U.S. National Museum of Natural History, Smithsonian Institute ( USMN #50901)  . East Plana Cay, Bahamas. Preserved in 70% ETOH, mounted in glycerine. Collector: L.W. Pollock. 1968. Additional specimens from Bimini, Bahamas from the Muséum National d'Histoire Naturelle in Paris ( MNHN# 169View Materials Ma, one slide with four females and one male, col. J. Renaud-Debyser) and from Guadeloupe ( USNMAbout USNM # W62023, one specimen, col. Renaud-Mornant, 1979). 

Specific diagnosis (emended): Anisonyches  with primary clavae present and papillae on base of fourth pair of legs only, claws on legs I–III progressively longer from innermost to outermost, all claws of legs IV similar in length, basal spurs widely divergent from each other and horizontally directed. Accessory points on medial claws I–III and inner two claws on legs IV. Claws slightly curved apically.

Re-description of holotype: Female with characteristic worm-like body 175.1 µm long and 53.4 µm wide (at level of third pair of legs) ( Fig. 8A View Figure ). Conical head with terminal mouth. Cephalic cirri with a swollen transparent pedunculate base (scapus) and a short flagellum. Median cephalic cirrus is present but very short and difficult to see (2.5 µm). Primary clavae ovoid (3.6 µm) with thickened cuticle; van der Land’s body and pore not visible but they are confirmed in the A. diakidius  specimens from MNHNAbout MNHN. Thin, short lateral cirri A (4.2 µm), slightly anterior to primary clavae; accordion-like pleats not visible on slightly swollen base. Slight bulges seem to appear on either side of the head that are likely to be secondary clavae, but air spaces along the leading edge of the head make measurements and description impossible ( Fig. 8A and C View Figure ). Internal cephalic cirri (3.0 µm overall, 1.2 and 1.8 µm for the basal peduncle and the flagellum, respectively) dorsal to external cephalic cirri (3 µm overall, 1.4 and 1.6 µm for the basal peduncle and the flagellum, respectively). Black ovoid eyes antero-lateral to lateral cirri.

Pharyngeal bulb small and somewhat flattened posteriorly (13.4 µm diameter). Buccal tube thin (24.0 µm length, 0.6 µm width); apophyses not visible. Thin stylets (31.6 µm length); furcae not visible. Stylets enter buccal canal through prominent sheaths (21.1 µm length). Stylet supports absent. Three placoids approximately 6 µm in length, but anterior fusion point not visible.

Cuticle smooth without thickened plates, ornamentation or evident punctations. Cirri E (5.5 µm) located dorsoanterior to legs IV. Accordion-like pleats not visible on slightly swollen base. Slight lateral constriction in body just anterior to eyes, otherwise body has smooth contour without additional projections. Rosette-like gonopore, surrounded by six small membranes, 11.2 µm distant from the anus. Seminal receptacles not visible. Anus a fissure surrounded by irregular folds between legs IV.

Stubby legs of approximately equal length with claws attached to leg with basal membrane. Four claws on legs I to III and three claws on legs IV. Claws progressively longer from innermost to outermost. Claws on leg II 5.2 µm, 6.2 µm, 6.8 µm, 7.1 µm, from inner to outer, respectively ( Fig. 8B View Figure ); on leg III 5.6 µm, 6.5 µm, 6.8 µm, 7.0 µm, from inner to outer, respectively. On other legs, including IV, all claws are not measurable, however leg IV claws appear to be approximately equal in length (around 8 µm). The claws are slightly curved apically and paired basal spurs exit at right angles to one another, projecting away from the main claw branch almost horizontally giving the appearance of spread bird wings (see leftmost medial claws in Fig. 8B View Figure ). Accessory points occur on the two medial claws only in legs I–III ( Fig. 8B View Figure ); leg IV inner two claws appear to have accessory points and outer claw does not, but these characters are poorly visible on claw IV. These accessory points are visible on the specimens from MNHNAbout MNHN. Papillae (3.7 µm) present dorsally near base of legs IV, van der Land’s body not present and pore poorly visible, but they are clearly visible on the MNHNAbout MNHN specimens. Spines not present on legs IV. Papillae and spines absent from legs I–III.

Remarks: Our measurements differ from Pollock’s original descriptions, and in the case of cirri E rather dramatically. This could be due to greater accuracy based on current digital technology, changes in the specimen over time, or other causes. Our measurements and Pollock’s original measurements are included in Table 3. As speculated by both Grimaldi de Zio et al. (1987) and Chang & Rho (1998b), the holotype of A. diakidius  does have a small median cirrus ( Fig. 8C View Figure ). Pollock overlooked this small, difficult-to-see structure. Accessory points were not discussed in the original paper. The archived specimens we examined from Bimini and Guadeloupe have claws with widely divergent basal spurs, claws I–III progressively longer from innermost to outermost (the diakidius  - type claws of Chang & Rho 1998b) and with accessory points on medial claws; claws IV similar in length and the two innermost claws with accessory points. They match the holotype in claw structure and for all other observable characters. We confirm that these are A. diakidius  . This verifies that the previous record of Anisonyches  from the East Plana Cay ( Pollock 1975) is a different species than the new one described here. The specimen from Bimini is undated, and inexplicably it was not reported in Renaud-Debyser (1959, 1963).


Smithsonian Institution, National Museum of Natural History


Museum National d'Histoire Naturelle