Aspidiophorus tetrachaetus Kisielewski, 1986

(Figure 5)

Localities. Lake Ånnsjön, Jämtland (N 63º 15’ 35’’; E 12º 26’ 51’’); Small rockpool, Fiskebäckskil, Bohuslän (N 58º 14’ 39’’; E 11º 27’ 16’’).

Material. 4 specimens. TL, 128–140 µm; FL, 16–17 µm; AL, 10–11 µm; PhL, 27–29 µm; MD, 5 µm; DC, 14– 18; DR, 32–38; VC, ~8; VTS, 8– 9 x 4 µm; PL, 0.5–1 µm.

A small sized species with weakly five-lobed head. Two pairs of sensory bristles; anterior pair anchored by papillae and posterior pair by double keeled scales. Dorsal scales are rhomboidal in shape with weakly rounded edges. Two pairs of characteristic simple spines are present in the posterior trunk region. Each spine of the longer anterior pair is 10–12 µm in length and anchored by a scale with keels on either side of the spine base. The shorter posterior pair reaches 5–6 µm in length and is anchored by smaller scales just at the base of the furca. Interciliary field with approximately 8 columns of keels which can be followed up at least halfway the length of the pharynx. Paired ventral terminal keeled scales that widens toward the distal end. Ventral ciliation in two longitudinal bands not merging on the head. Pharynx, broad with large terminal swellings, posterior swelling larger than anterior.

Previously reported from Poland (Kisielewski 1998), Russia (Tretjakova 1989) and Sweden (Kånneby et al. 2009).