Infestation of Setaphyes kielensis

In the material collected in May 1998, 27 out of 69 specimens of Setyphyes kielensis (= 39 %) were infested by 106 specimens of Trematosoma husselae sp. nov. (Table 2). A kinorhynch hosted 1– 15 specimens of suctorian ciliates, on average 4 specimens (Table 2). The vast majority occurred on the ventral side of the basibionts (80 %): the rate attached to the ventral side of basibionts was particularly high on segment 1 (19 % of all attached T. husselae sp. nov.), segment 3 (12 %), and on segments 8 and 9 (8–9 %). Neither Cothurnia buetschlii nor filamentous bacteria were found on the kinorhynchs collected in 1998.

In the material collected in June 2016, 202 specimens of Trematosoma husselae sp. nov. were found on 20 out of 23 S. kielensis mounted for light microscopy and 397 ciliates on 21 specimens mounted for SEM, in total 599 specimens (Tables 3, 4). It should be kept in mind that the kinorhynchs were mounted with one side (usually the lateral side) on the SEM stub, so potential epibionts on this side could not be observed, and the number of epibionts might be slightly higher (Table 3). One kinorhynch revealed no epibionts (ZMB 12455, SEM). It was extremely dirty and may have been dead at the time of collecting, therefore, it was excluded from the further analysis.

A kinorhynch collected in June 2016 hosted 1– 43 specimens of Trematosoma husselae sp. nov., on average 15 specimens (Tables 3, 4). Most epibionts concentrated on the ventral side of their basibionts (82 %) and here especially on segment 1 (17 % of basibionts) and on segments 8–10 (11–13 %; Tables 3, 4). Only 5 % of T. husselae sp. nov. occurred on segment 2, whereas the remaining segments revealed a balanced distribution of 7–9 %. A single suctorian epibiont was found on segment 11 of a single kinorhynch.

Nine specimens of Cothurnia buetschlii were found on five S. kielensis out of 24 specimens mounted for light microscopy and five specimens on two kinorhynchs out of 21 specimens mounted for SEM (ZMB 12486–12489, 12468, 12499; Figs 7–9; Tables 3, 4).

Filamentous prokaryote epibionts occurred in 18 out of 42 specimens of S. kielensis, not all of them carrying ciliate epibionts (Tables 3, 4). A species of coccoid prokaryotes arranged in a row was traced only once (ZMB 12486; Fig. 5J; Table 4).