Heterolepidoderma ocellatum ( Metschnikoff, 1865 )

Kånneby, Tobias, 2011, New species and new records of freshwater Chaetonotida (Gastrotricha) from Sweden, Zootaxa 3115, pp. 29-55 : 41-42

Heterolepidoderma ocellatum ( Metschnikoff, 1865)

( Figure 9 )

Localities. Among Sphagnum spp., Saltö, Bohuslän (N 58º 52’ 21’’; E 11º 07’ 34’’); Freshwater Sphagnum spp. rockpool, Kristineberg, Bohuslän (N 58º 14’ 50’’; E 11º 26’ 22’’); Freshwater Sphagnum spp. rockpool, Islandsberg, Bohuslän (N 58º 12’ 38’’; E 11º 25’ 09’’); Small pond, Askö, Södermanland (N 58º 49’ 23’’; E 17º 38’ 32’’).

Material. 14 specimens. TL, 114–127 µm; FL, 14–15 µm; AL, 7–8 µm; PhL, 31–34 µm; MD, 4–5 µm; DC, 14–17; DR, 20–22; TS, 5– 6 x 2–3 µm; VTS, 5– 6 x 2–3.

A relatively small sized species, with five-lobed head and a pair of ocellar granules. Sporadic absence of ocellar granules have been reported in some populations ( Schwank 1990; Fregni et al. 1998). Two pairs of sensory bristles present, each of the posterior pair anchored by a double-keeled scale. Dorsal body surface covered by elongated elliptical keeled scales, smaller in size in head and neck regions. Interciliary area naked except for a pair of keeled terminal scales and 1–2 transverse rows of 3–4 keeled scales. Pharynx with small swellings at both ends.

Two of the Swedish specimens were in post-parthenogenetic phase with X-organ and sperm present ( Figure 9 A). Another peculiarity is that several specimens had more or less well developed short ventrolateral spines. In one specimen, the area between the edges of the posterior lateral parts of the scale appeared to be depressed giving the appearance of a tri-lobed scale. The keels were not modified in this part but instead gave the impression of a short spine. Whether the keel was actually in contact with the depressed area could not be determined.

This species is widely distributed in Europe (see e. g. Greuter 1917; Mola 1932; Remane 1935 –36; Valkanov 1937; Rudescu 1967; Martin 1981; Schwank 1990; Kisielewski 1998) and is also reported from Canada ( Schwank 1990), United States ( Schwank 1990), Japan ( Saito 1937) and Brazil ( Kisielewski 1991).

Figures

FIGURE 9. Heterolepidoderma ocellatum. A) Habitus, arrowheads indicate spermatozoa. B) Dorsal view, showing distribution of scales. Scale bars: 15 µm.