Ichthydium squamigerum Balsamo & Fregni, 1995

Kånneby, Tobias, Todaro, Antonio & Jondelius, Ulf, 2009, One new species and records of Ichthydium Ehrenberg, 1830 (Gastrotricha: Chaetonotida) from Sweden with a key to the genus, Zootaxa 2278, pp. 26-46 : 31-32

Ichthydium squamigerum Balsamo & Fregni, 1995

( Figures 8E–G ; Table 3 )

Localities: Trösvattnet, Västmanland, Sweden (59º33.211’N; 14º29.232’E); Lake Siljan, Dalarna, Sweden (60º53.039’N; 15º06.467’E); Stora Skuggan, Norra Djurgården, Stockholm, Sweden (59º22.068’N; 18º04.152’E).

Material: 7 specimens, 3 measured.

Character Specimen

1 Balsamo & Todaro (1995) Total body L 125 111–143 Head W 30 33–34 Neck W 25 Na

Body W 35 Na

Furca base W ~15 Na

Furca L 18–19 15–22 Adhesive tube L 10 Na

Pharynx L 32 17–33 Mouth ø Na Na

Furca spine L ~10 8.9–13.5 Anterior sensory bristle L ~20 Na

Posterior sensory bristle L ~22 Na

Remarks: The specimens of I. squamigerum agree well with the morphometric data provided by Balsamo & Fregni (1995). The distribution and shape of the rounded keeled scales at the base of the furca as well as the subrectangular ventral terminal scales also agree with the original description. A peculiar difference between the Swedish and the Italian specimens is that the former lack the bi-keeled scales anchoring the posterior sensory bristles. The bristles originate from papillae instead of scales. Fregni et al. (1998) found I. squamigerum exclusively in freshwater sand. Six of the Swedish specimens were found at a sandy beach at lake Siljan and one specimen in a very small sandy patch at lake Trösvattnet. The findings of I. squamigerum in Sweden are the first records outside Italy where the species was described. PhIJ at U28; ASB at U23; PSB at U78.

Associated gastrotrich fauna: Chaetonotus benacensis Balsamo & Fregni, 1995 , C. hystrix Metschnikoff, 1865 , C. mutinensis Balsamo, 1978 , Lepidodermella squamata and Polymerurus rhomboides ( Stokes, 1887) .

Character Specimen

Figures

FIGURE 8. A – H) Incertae sedis continued. A) Ichthydium diacanthum dorsal and B) ventral view. C) I. plicatum dorsal and D) ventral view. E) I. squamigerum dorsal view and F) bi-keeled scales anchoring posterior sensory bristles. G) I. squamigerum ventral view. H) I. tergestinum dorsal view. A, B, original; C, D, modified from Balsamo & Fregni (1995); F, after Balsamo & Fregni (1995); E, G, original; H, modified from Grünspan (1908). Scale bars: 20 µm.