Dipodarctus anaholiensis Pollock, 1995

Bartels, Paul J., Fontoura, Paulo & Nelson, Diane R., 2015, New records of marine tardigrades from Moorea, French Polynesia, with the description of Styraconyx turbinarium sp. nov. (Arthrotardigrada, Halechiniscidae), Zootaxa 3955 (3), pp. 389-402 : 390-391

Dipodarctus anaholiensis Pollock, 1995

Fig. 1 A–C

Material examined. Eighteen specimens (1 two-digit larva 75 µm long and 17 adult specimens: 12 females, 3 males and 2 of undetermined gender, body length 82–140 µm), collected in coral sand at Cook’s Bay, 0.5–1.0 m depth.

Remarks. According to the original description ( Pollock 1995), one of the main features of the genus Dipodarctus is the relative size of the digits. Pollock (1995) says that at least three of the four digits are short and of equal length on legs I–III. According to the Pollock (1995) terminology (in which digit 1 is the outermost digit) we noted that the adult specimens collected in Moorea have digit 4 (innermost) slightly but consistently shorter (Kruskal-Wallis test H (3 d.f.; n=111)=39.621; p <0.001) (values, in µm, as follows: digit 1: mean=10.8, min– max=8.9–12.6, n=27; digit 2: mean=10.8, min–max=8.9–12.8, n=27; digit 3: mean=10.6, min–max=8.8–12.6, n=28; and digit 4: mean=9.0, min–max=7.0–11.1, n=29). This character has been confirmed by the measurements provided by Pollock (1995) in the original description and also by the examination of type material ( Fig. 1 A). Another interesting character neglected by Pollock (1995) in the original description is the presence of proximal cuticular folds on external digits, particularly evident on legs IV ( Fig. 1 B).

Five species are currently known in this genus, with two recently described species ( Dipodarctus australiensis Jørgensen et al., 2014 and Dipodarctus susannae Jørgensen et al., 2014 ) from Australian marine caves (Jørgensen et al. 2014). Our specimens of D. anaholiensis differ from all other species most notably by the lack of an elongate toe on legs I–III ( Fig. 1 C). Our specimens are most easily distinguished from the new Australian species by the lack of three parallel folds on the digits. In addition, they differ from D. australiensis by the lack of lateral processes between legs III and IV; lack of peduncles on legs IV; and lack of cephalic processes and facial plate. Our specimens also differ from D. susannae by the lack of a cirrophore on sensory organ IV and fine details of the cephalic cirri. For a more thorough discussion of the taxonomy of this genus, including the junior synonym Hemitanarctus chimaera de Zio Grimaldi et al., 1995 /96, see Jørgensen et al. 2014.

Dipodarctus anaholiensis , primarily a shallow subtidal species, has been found in the Indian Ocean, the Mediterranean (Adriatic Sea, Ionian Sea, Tyrrhenian Sea, Strait of Sicily), and the Pacific Ocean ( Pollock 1995; de Zio Grimaldi & D’Addabbo Gallo 2001; de Zio Grimaldi et al. 2003; Gallo et al. 2007). This is the first record for French Polynesia.

Figures

FIGURE 1. Dipodarctus anaholiensis. A. Holotype from Hawaii, USA with arrow showing the smaller digit 4 on leg I. Scale bar = 50 µm. B. Specimen from Moorea, French Polynesia. Leg IV with arrow showing the cuticular folds on external digits. Scale bar = 10 µm. C. Specimen from Moorea, French Polynesia. Habitus. Scale bar = 100 µm.