Gieysztoria dodgei ( Graff, 1911 ) Ruebush & Hayes, 1939

Steenkiste, Niels Van, Gobert, Stefan, Davison, Paul, Kolasa, Jurek & Artois, Tom, 2011, Freshwater Dalyelliidae from the Nearctic (Platyhelminthes, Rhabdocoela): new taxa and records from Ontario, Canada and Michigan and Alabama, USA, Zootaxa 3091, pp. 1-32 : 19-20

Gieysztoria dodgei ( Graff, 1911) Ruebush & Hayes, 1939

( Figs. 6 D–F)

syn. Dalyellia dodgei Graff, 1911

syn. Microdalyellia (Gieysztoria) dodgei ( Graff, 1911) Ruebush & Hayes, 1939

New locality in the Nearctic. Richland, Kalamazoo County, Michigan, USA (42°24’57”N, 85°26’22”W). Cool, fast groundwater-fed creek entering into Little Long Lake. On private property, with a well-developed riparian zone: organic material in slower pools in the bend of the creek, where coarse sand and decaying hardwoods have accumulated (08/06/2009).

Other localities in the Nearctic. Charlevoix? (Michigan, USA) ( Woodworth 1896; Stringer 1951; see remark Table 1); Rochester (New York, USA) ( Graff 1911); Kapsigdlit ( Greenland) ( Reisinger & Steinböck 1927); upper Mississippi Basin (Wisconsin and possibly other states, USA) ( Higley 1918; Hayes 1942; Watermolen 2005).

Material. One whole mount containing the stylets of two individuals and the bundle of spermatophores of probably one individual. This material was recovered from specimens kindly provided by Christopher Laumer (Harvard University, USA), but animals were unfortunately decaying when received at Hasselt University ( Belgium). It appeared that one stylet belonged to an individual eaten by another, cannibalistic specimen. Other observations were impossible because of the advanced state of decomposition of the animals.

Description and remarks. Although observations on live animals were impossible, the whole mount allows a relatively detailed study of the stylet morphology. The stylet is 135 µm long and consists of a proximal, 20 µmhigh, half open girdle (gi) and a distal, 115 µm-long tube (tu) surrounded by a partly-open, funnel-shaped sheath (sh) and flanked by a number of heteromorphic spines on both sides ( Figs. 6 D–F). The girdle has a concave proximal edge and appears fibrous and reticulate. Proximally, the sheath is relatively broad and contains a large open window. At about halfway along its length, it becomes more narrow and closes around the tube. Distally, the sheath and inner tube tightly fit, but their relative positions become very difficult to discern. At one lateral side of the girdle, a somewhat broadened plate (bp) bearing two smaller, straight spines (20 µm) is present. On the other side, the girdle edge bears a long, somewhat curved spine (50 µm), accompanied by a large, hollow, S-shaped spine (ss) (60 µm) with a very broad, open base. Luther (1955) rightly compares its shape with that of a drinking horn (“Trinkhorn”). In one of the whole mounts, its distal point is somewhat broadened to form a small triangular plate (arrow in Fig. 6 D). In between both lateral spine duos and the central sheathed tube, a long, straight spine (s) (55 µm) flanking the sheath on each side, complete the stylet.

Apart from the stylet, about thirteen, slender spermatophores (up to 300 µm long) could be discerned in the whole mount. They are elongated with one end tapering to a pointed tip and the other end being curled. Luther (1955) even described them as nematode-shaped (“nematodenförmig”). Although some might have changed position when making the whole mount, most of them seem to have been organized in a relatively solid, spirally-curled bundle.

Although reported as very abundant in its type locality by Graff (1911) and considered to be widespread by Higley (1918), Gieysztoria dodgei ( Graff, 1911) Ruebush & Hayes, 1939 is a poorly-known species. All confirmed findings are located around the Great Lakes, except for the locality in Greenland (see above). Based on sketches of the habitus and copulatory organ by Woodworth (1986) and Stringer (1918), Luther (1955) stated that Vortex bilineata Woodworth, 1886 [later renamed Dalyellia bilineata (Woodworth, 1886) Stringer, 1918 ], also from Michigan, might probably also be attributed to G. dodgei .

Luther’s (1955) descripition of the stylet based on the accounts of Graff (1911, 1913), does not completely correspond with our observations. While the conspicuous, horn-shaped spine is identical as in the specimens studied in this paper, all previous authors describe the central tube and its sheath as two extremely long spines flanked by other spines of various sizes. In our opinion, the central tube and its sheath have a similar construction to that of Gieysztoria infundibuliformis ( Fuhrmann, 1894) Ruebush & Hayes, 1939 , i.e. a long, funnel-shaped double-walled tube (“Rinne”) with a very large proximal window (“Fenster”) in the outer wall (sheath). The inner tube (“Rohr”) is probably formed by the fusion of the superimposed sidewalls of the whole structure (for a detailed description, see Luther 1955). Although this sheathed tube is also flanked by long straight spines, G. infundibuliformis lacks a large, horn-shaped spine as in G. dodgei . Instead, multispinous axes (“Endäste”) are present on both outer girdle edges.

The stylet construction of another species, Gieysztoria koiwi ( Eggers, 1925) Luther, 1955 , is very similar, but more simple with two central plates (“Rinne”) proximally, fusing to a tube (“Rohr”) distally. Both G. infundibuliformis and G. k o i w i are confined to the Palearctic. Based on stylet morphology, it seems that G. dodgei , G. infundibuliformis and G. k o i w i are closely related representatives of a Holarctic group.

Figures

FIGURE 6. Gieysztoria rubra (Fuhrmann, 1894) Ruebush & Hayes, 1939 (A) Squeezed live animal, dorsal view. (B) Detail of the genital system in a live animal. (C) Stylet. Gieysztoria dodgei (Graff, 1911) Ruebush & Hayes, 1939 (D – F) Stylets.